Symposium BM7 : Functional Nanostructured Polymers for Emerging Energy Technologies

Charged polymer membranes are widely used for water purification applications involving control of water and ion transport, such as reverse osmosis and electrodialysis. Efforts are also underway worldwide to harness separation properties of such materials for energy generation in related applications such as reverse electrodialysis and pressure retarded osmosis. Additional applications, such as energy recovery ventilation and membrane-assisted capacitive deionization, rely on polymer membranes to control transport rates of water, ions, or both. Improving membranes for such processes would benefit from more complete fundamental understanding of the relation between membrane structure and ion sorption, diffusion and transport properties in both cation and anion exchange membrane materials. Ion-exchange membranes often contain strongly acidic or basic functional groups that render the materials hydrophilic, but the presence of such charged groups also has a substantial impact on ion (and water) transport properties through the polymer.

We are exploring the influence of polymer backbone structure, charge density, and water content on ion transport properties. Results from some of these studies will be presented, focusing on transport of salt, primarily NaCl, through various neutral, positively charged and negatively charged membranes via concentration gradient driven transport (i.e., ion permeability) and electric field driven transport (i.e., ionic conductivity). One long-term goal is to develop and validate a common framework to interpret data from both electrically driven and concentration gradient driven mass transport in such polymers and to use it to establish structure/property relations leading to rational design of membranes with improved performance.

Ion sorption and permeability data were used to extract salt diffusion coefficients in charged membranes. Concentrations of both counter-ions and co-ions in the polymers were measured via desorption followed by ion chromatography or flame atomic absorption spectroscopy. Salt permeability, sorption and electrical conductivity data were combined to determine individual ion diffusion coefficients in neutral, cation exchange and anion exchange materials. Manning’s counter-ion condensation models and the Mackie/Meares model were used to correlate and, in some cases, predict the experimental data.

Anion-exchange membranes (AEMs) for alkaline fuel cells have triggered great interest in the energy field because of their distinct advantages in terms of enabling the use of non-precious metal catalysts, better oxygen reduction kinetics and fuel flexibility. However, the current AEMs often suffer from low OH⁻ conductivity and poor chemical stability. Among the various strategies to improve the hydroxide ion conductivity, construction of a microphase separated morphology composed of hydrophilic ion nanochannel and a hydrophobic phase has been demonstrated as the most important strategy. Although several trials to construct microphase separated membranes using block copolymers, comb-shaped polymers, and graft polymers have been reported, achieving membranes with highly ordered and well-defined ionic nano-channels is still challenging.
The uses of molecular self-assembly to create nanostructured liquid-crystalline (LC) materials with highly ordered and well-defined ionic channels has been shown to be good candidates for efficient ion transportation. In particular, bicontinuous cubic liquid crystals are of considerable interest because of their 3D interconnected and well-defined periodical channel networks. The fixation of LC nanostructures within a polymeric film provides a considerate solution to achieve simultaneous enhancement of many required AEM properties. In this talk, our recent studies will be presented regarding the facile construction of AEMs with LC nanostructures via the self-assemble of polymerizable ionic liquids. Hexagonal, lamellar and bicontinuous cubic LC samples were prepared by the self-organization of polymerizable amphiphilic imidazolium-based ionic liquids. And for the first time, AEMs with hexagonal, lamellar and bicontinuous cubic nanostructures were fabricated through in-phase photopolymerization of liquid crystals. The AEMs performance in terms of ionic conductivity, hydration behavior, and chemical stability were characterized, which turned out to be closely related with the LC nanostructures retained after photopolymerization.

Methacrylate monomer having an inverse phosphorylcholine at the side chain (MiPC) was synthesized by N,N-dimethylaminoethyl methacrylate, 2-chloro-2-oxa-1,3,2-dioxaphospholane, and isopropanol with 25% yield. Surface-initiated atom transfer radical polymerization of MiPC was carried out in methanol at 50 °C for 2 h to give poly(MiPC) brush with a 110 nm thick (dry state) on silicon wafer. The resulting poly(MiPC) was water soluble, however, the surface free energy was estimated to be 40.8 mN m^-1 by Owens-Wendt method based on a water contact angle of 71 degree. When the poly(MiPC) brush was immersed in water, the thickness of brush increased from 110 to 171 nm due to the swelling of brush and hydrophilicity of poly(MiPC). Adhesion force of poly(MiPC) brush in water was also measured to be 30 nN by force curve measurement using a propylsilane-modified silica probe (d = 20 mm), indicating that poly(MiPC) brush has a relatively large hydrophobic interaction in spite of its hydrophilicity.

The response of ionomer thin films and bulk membranes to humidity is distinctly different. Hydration of fuel cell ionomers in supported thin films leads to complex multimodal interactions among water, polymer chains and substrate and these interactions may lead to interesting mechanical and transport properties. However, the properties of ionomers in thin film format are still not well understood. This understanding is crucial to explore the properties of the ionomer-catalyst interface of fuel cell electrodes. In this work, thin films of sulfonated aromatic ionomer, S-Radel were investigated to know how thickness and hydration lead to changes in density, water-polymer distribution and mechanical properties. A fluorescent rotor probe was incorporated into the polymer films (~25-250 nm thick) to predict the stiffness of the films using time resolved fluorescence. The density values obtained from quartz crystal microbalance and spectroscopic ellipsometry showed a similar trend with thickness to those obtained from neutron reflectometry. A ~25 nm thick film had lower density as compared to a ~250 nm thick film which corroborated with greater mobility and lower stiffness of thinner film observed at dry state. When the same sample was hydrated, film density and interfacial water volume fraction significantly increased. A very thin pure water layer was found at the substrate interface of the ~25 nm thick sample from neutron reflectometry. On the other hand, thicker films were less water-rich at the interface as compared to thinner samples. The water distribution near substrate interface in the aromatic s-Radel films was distinctly different from that in fluorocarbon based Nafion films seen in previous work. Antiplasticization, or stiffening of the films upon hydration, was observed at different extents from fluorescence lifetime of rotor probes. The plasticization properties appeared to be controlled by film thickness, film density, and water mobility.

Salty waters (e.g., seawater) are important sources for drinkable water production through various desalination technologies, such as reverse osmosis and distillation. Meanwhile, salinity gradients between two solutions of different concentrations offer great potential for renewable energy production, which has been demonstrated by pressure retarded osmosis (PRO) as well as other processes. However, challenges exist for both desalination and osmotic energy production, such as insufficient energy efficiency, serious fouling and relatively high costs, etc.

Alternative routes to achieve desalination or energy production from salty waters remain interesting to the community; one possible approach is by mechanical stress. Hydrogels are a group of materials that might respond differently to the changes in salt concentration or mechanical stress. For example, charged hydrogels absorb both ions and water when immersed in salt solutions and may release solutions with lower concentration upon application of mechanical stress, thereby achieving desalination; they also change their volume towards different salt concentration, which can be utilized to produce energy if mechanical stress is applied. In this study, we chose zwitterionic hydrogels because of their hydrophilic, super water-absorbing properties and their outstanding anti-fouling capability. Fundamental understanding on the structure-swelling-mechanical strength behaviors will be provided, and the potential of such hydrogels for desalination and energy production will be explored and discussed.

In 2010, Kraton Polymers started producing a grade line of ion containing, styrenic block copolymers under the tradename of Nexar(R) Polymers. The polymers are made by a 3 step process. In the first step, a 5 block copolymer is prepared by a living anionic polymerization technology - sequential addition of 1) t-butylstyrene, 2) isoprene, 3) styrene, 4) isoprene, and finally, 5) t-butylstyrene; the living anionic polymerization method affords polymer segments that are nearly monodispersed in molecular weight. In the second step of the synthesis, the isoprene segments are selectively hydrogenated to remove the C=C unsaturation. In the final step, the pentablock copolymer is selectively sulfonated in the polystyrene segment (center block).
The sulfonated polystyrene segment in these polymers gives the material unique structure and unusual performance features. Solutions of these polymers tend to be structured. In non-polar solvents, spherical micelles are formed with the ion microphase in the core of the structure. In polar solvents, spherical micelles are also formed but have the ion microphase on the outside of the micelle. Under some conditions with mixtures of polar and non-polar solvent blends, a different species is formed that has been hypothesized to be of a vesicle nature. Due to the structured nature of these polymer solutions, they have interesting rheological features.
The Nexar Polymer solutions have been cast into membranes which have found utility in energy recovery ventilation applications. By running fresh air over one side of the membrane and spent air over the other side of the membrane, water vapor can be transferred from on air stream to the other. In this way, humidity can be regulated in the incoming air stream with the result that the air can be conditioned at a substantially reduced cost. Regulation of humidity in the conditioned air can improve comfort, as well.
The Nexar Polymer solutions have also been printed onto fabrics and the resulting coated fabrics made into garments that provide an improved micro-climate for the wearer. This technology provides a mechanism for cooling the person wearing the garment when working in a hot climate.
At present, we are developing methods for spray coating these polymers onto porous and irregularly spaced surfaces - microporous membranes and various carbon powder coated structures.
Ongoing research is addressing opportunities for these polymers in water transport and water treatment applications. Various energy storage and energy generation applications are being examined, as well.
This presentation will focus on the science that supports these technologies.

We introduce a new self-cleaning, photoresponsive membrane that can remove pre-deposited foulant layers upon exposure to UV light, exhibit UV-triggered surface morphology changes, and sustain stable pore size and permeance throughout. We first synthesized novel comb-shaped graft copolymers at two side-chain lengths with polyacrylonitrile (PAN) backbones and photoreactive side-chains using atom transfer radical polymerization (ATRP). The side-chains undergo a light-induced transition between a hydrophobic spiropyran (SP) state and a zwitterionic, hydrophilic merocyanine (MC) state, allowing photo-regulated control over membrane features. We used these comb-shaped copolymers to produce thin film composite (TFC) membranes by coating a commercial PVDF membrane with a thin layer of the copolymer solution. Changes in fingerprint IR peaks pertinent to SP and MC forms upon light treatment confirm the structural difference between the two forms at a molecular level. Prior to any photo-treatment, as-coated membrane surface consists mainly of hydrophobic SP groups, which promote the adsorption of hydrophobic solutes on pore channel walls, reducing flow rate. Upon reversing the photochemical response by irradiation with UV light, the SP groups are converted to hydrophilic MC groups that release the adsorbed molecules and permit water passage once again. This “self-cleaning” behavior is shown by measuring pre- and post-UV water permeability after fouling with model protein bovine serum albumin (BSA). We found that flux decline through a BSA-fouled membrane can be fully recovered back to its original value by a simple, non-mechanical intervention of exposure to UV light. In addition, despite the as-coated membrane, the UV-induced MC form membrane surface is fouling resistant, indicated by zero flux decline after two hours of protein filtration. To better understand how polymer self-organization controls the responsive behavior, the light-induced changes in surface topography and hydrophilicity are analyzed.

Membrane has been used from time immemorial to purify water. Advances made in membrane technology for more than a century have to do with either enhancing separation efficiency of the membrane or improving the permeation flux. Enhancing the separation efficiency, however, inevitably led to reducing the permeation flux, and improving the permeation flux resulted in a loss in the separation efficiency. This inherently built-in dilemma has to be dislodged for the filtration membrane to fully reach its potential. In this presentation, we suggest multiscale porous membranes that allow for high permeation flux without sacrificing separation efficiency. In order to create the multiscale architectured membranes, primary structure is first prepared by assembling closely packed colloidal particles, filling the gaps with a suitable material, and dissolving out the particles to form inverse opal structure. Then, secondary nanostructures are incorporated inside the structured template to elaborately tune the pore size, tortuosity, and interfacial properties. Embedded nanostructures can be created by layer-by-layer assembly of polyelectrolyte multilayers, microphase separation of block copolymers, or self-assembly of another colloidal particles, etc. Finally, the constructed multiscale architectures are utilized for water-treatment applications, such as ultrafiltration of nanoparticles or nanofiltration of metallic ions. Due to the perfectly ordered characteristics of the multiscale architecture, it offers advantages of reduced tortuosity as well as pore size uniformity, resulting in high permeability and selectivity simultaneously.

References
1) D. K. Rhee, B. Jung, Y. H. Kim, P. J. Yoo, ACS Appl. Mater. Interfaces 6, 9950-9954 (2014).
2) Y. M. Lee, B. Jung, Y. H. Kim, W.-S. Choe, P. J. Yoo, Adv. Mater. 26, 3899-3904 (2014).
3) Y. H. Kim, H. Kang, S. Park, D. Y. Ryu, P. J. Yoo, Adv. Mater. 26, 7998-8003 (2014).
4) G. H. Choi, F. Caruso, P. J. Yoo, ACS Appl. Mater. Interfaces 8, 3250-3258 (2016).

Access to clean water and separation of oil/water mixtures have become urgent global issues due to the increased incidents of oil spills, water contamination, and water shortage. Separation oil/water via membranes with selective oil/water absorption is a relatively recent development. While simple oil/water mixtures can be separated by gravity, separation of surfactant stabilized oil/water emulsions is especially challenging. Meanwhile, to enhance selectivity of the membrane, smaller nanopores are preferred; while to achieve high permeation flux, micropores are preferred. Therefore, it is highly desirable to create a membrane with precisely controlled, hierarchical pores over a large area in a simple yet efficient way. Here, we utilize photofluidization of electrospun fiber network from azopolymer (polydisperse orange 3, PDO3), to fine-tune the pore size ranging from nano- to micron-scale. It is well known that azopolymers can undergo trans- to cis- isomerization under irradiation by visible light; even below the glass transition temperature (T_g), the polymer chains can move around, leading to photofluidization. This nature of azopolymers is caused by the repeated photo-isomerization of azobenzene molecules attached to the main chain of the polymer and their resulting anisotropic alignment in the direction perpendicular to the light polarization. First, we fabricate the microporous membranes by electrospinning of the azopolymers. Subsequently, we partially melt the fiber scaffold to shrink the pore size far below micron level by controlling the laser (l = 532 nm) irradiation time. Lastly, we demonstrate that the fabricated membranes can be utilized to separate submicron-sized water-in-oil emulsions with high separation efficiency (> 99.95 %).

Over the recent years, nanoparticle filled polymeric systems have attracted significant interest due to the fact that addition of such particles can drastically change the properties of the polymers, along with imparting its own functionality. In this regard, nanoparticle filled polymer blend thin film is getting greater attention as it has tremendous potential when implemented using functional polymer in the field of bulk heterojunction solar cells (BHJ). Unlike a homopolymer thin film, a polymer – polymer blend thin film on spin coating forms a laterally phase segregated morphology instead of smooth flat film. The effect of addition of nanoparticles on the phase-segregated morphology and on the stability of such systems is highly complex compared to its homopolymer counterparts and involves a richer physics as it deals with additional polymer–polymer interfaces. Hence, we present here a fundamental study on influence of addition of nanoparticle in the two-phase region of a polymer blend thin film.
With this work, we investigate the influence of organic nanoparticles on a phase-segregated morphology of a spin casted immiscible polymer blend on a flat substrate. For this fundamental study, poly(styrene) (PS) - poly(methylmethaacrylate) (PMMA) were chosen as immiscible polymers and fullerene (C₆₀) as the organic nanoparticle (NPs). PS and PMMA being UCST blends, phase segregates at room temperature. Atomic Force Microscope images of ascast PS-PMMA blend reveals that on addition of nanoparticles, the lateral phase segregation of the domains reduces. From our initial experiments it was observed that on increasing the concentration of NP, lateral phase segregated domains reduces gradually. Moreover, beyond a critical concentration (C_n-NP*), the phase segregation was completely arrested leading to a flat film. By ellipsometric studies, thickness of the polymer blend with nanoparticle before and after selective phase removal hinted vertical phase separation instead of a typical lateral phase separation. Hence, from the results we qualitatively understand that the nanoparticles while spin coating, migrates towards the polymer–polymer interfaces and impart stability to the interface, thereby arresting the lateral phase segregation process during the latter stages of spin coating. This interfacial stability led to a vertical phase segregation of the PS and PMMA forming a polymer–polymer bilayer. This study can help us build a technique that is fast, simple yet novel to obtain coatings of multifunctional polymers.
Keywords: Polymer Blend, Thin Film, Phase Segregation, Nanoparticles, Fullerene, Thin Film Coatings, Interfacial Stability.

Zwitterionic groups, defined as functional groups with equal numbers of positive and negative electrostatic charges, strongly resist biomacromolecular adsorption due to their high degree of hydration. This has led to their incorporation into membranes to prevent fouling by various methods, especially by grafting from and surface functionalization of existing porous membranes. In addition, however, zwitterionic groups have interesting self-assembly capabilities due to their high dipole moments and strong intra- and inter-molecular interactions. Our group aims to better understand how zwitterion-containing amphiphilic copolymers self-assemble, and utilize their behavior to develop membranes with improved capabilities: controlled, monodisperse pore size, controlled selectivity, high flux, fouling resistance, and scalable manufacture. We have prepared high flux, fouling resistant, size-selective membranes whose selective layers are made of random copolymers of zwitterionic and hydrophobic monomers. We have shown that within certain composition ranges, these copolymers self-assemble to form bicontinuous networks of nanochannels that allow water passage, and filter out solutes larger than the channel size. Membranes made by coating a thin layer of these copolymers onto a porous support exhibit fluxes as high as 21 L/m².h.bar, which can be further be improved by better coating methods. Based on the rejection of anionic and neutral dyes of varying sizes, they show size-based selectivity with a cut-off around 1 nm. This pore size closely matches the size of the zwitterionic nanochannels, measured to be ~1.3 nm in diameter by transmission electron microscopy (TEM). These membranes also exhibit exceptional fouling resistance, showing little to no flux decline and essentially complete flux recovery with a water rinse upon the filtration of foulants such as protein solutions and oil suspensions. Well-designed membranes show no flux decline even in week-long fouling experiments with oil suspensions. This resistance arises from the presence of chemically dissimilar domains (hydrophobic and zwitterionic) of ~1 nm size, which frustrates the adsorption of foulants such as proteins. Furthermore, molecular imprinting approaches can be used to control and alter the selectivity of these membranes, further expanding their potential applications. These are the first examples of membranes that gain their selectivity from the self-assembled nanostructure of zwitterionic groups, in addition to exploiting this functionality for fouling resistance. These membranes are highly promising for a wide range of applications, including energy-efficient separations in the chemical and biochemical industries and industrial wastewater treatment.

Polymers of intrinsic microporosity (PIMs) are glassy polymers which possess high free volume and high internal surface area as a consequence of their relatively rigid, contorted macromolecular backbones. They comprise fused ring sequences interrupted by spiro-centres or other sites of contortion. PIMs have a high affinity for gases such as carbon dioxide, and for small organic species. The first commercial application of a PIM is in a sensor developed by 3M that acts as an end-of-life indicator for vapour-adsorbing cartridges. PIMs are being investigated as adsorbents and membrane materials for a variety of industrial separation processes, including gas separations (e.g., carbon dioxide capture) and organophilic liquid separations (e.g., bioalcohol recovery). For membrane gas separation, PIMs contributed to the revision of the upper bounds of performance by Robeson in 2008. For the practical application of high free volume polymers such as PIMs in membrane processes, the most significant issue to address is that of physical ageing, which leads to a reduction in permeability over time.

In recent years there has been significant research on PIMs aimed at tailoring selectivity, enhancing permeability and improving the ageing behaviour. This includes (1) new polymer synthesis, (2) chemical post-modification of precursor polymers, (3) thermal or ultraviolet treatment of membranes, (4) formation of polymer blends and (5) the addition of inorganic materials, carbons (activated carbons, nanotubes, graphene), metal-organic frameworks or purely organic materials, to form mixed matrix membranes.

Surface roughness of membranes is often perceived by many as a factor that promotes fouling during filtration, and thus is undesirable. Almost all liquid-based separation membranes have surfaces that are flat on the macroscale with local intrinsic surface roughness that is associated with the membrane manufacturing process. In this presentation, we show that surface patterns, i.e. engineered roughness, on membrane surfaces can improve their fouling resistance during microfiltration (MF), ultrafiltation (UF), nanofiltration (NF) and reverse osmosis (RO) processes. We will describe the underlying mechanisms and the corresponding processing-structure-performance relationships for surface patterning of different types of membranes. Comprehensive experimental studies reveal that the presence of the surface patterns significantly improved the overall filtration productivity and regeneration characteristics of the patterned membranes, in comparison to that of non-patterned controls, during separation of model suspensions of colloids and protein as well as salt solutions. Based on fluid mechanics modeling studies, the enhancement in performance was attributed to pattern-enhanced fluid shear.

Carbon capture and sequestration (CCS) could be an important approach to mitigate CO₂ emissions to the atmosphere. Membrane technology has been widely explored for CO₂ capture from coal power plant derived flue gas, due to its low cost and high energy-efficiency. The key to the success of this technology is membranes with high CO₂ permeability and high CO₂/N₂ selectivity. The current leading materials for membrane CO₂/N₂ separation are poly(ether oxide) (PEO) containing polymers, because ether oxygens can interact favorably with CO_2, leading to high CO₂ sorption and permeability. Given the enormous flow rate of the flue gas, any improvement in CO₂/N₂ separation properties can significantly decrease the cost of CO₂ capture. The goal of this work is to design and synthesize a series of new polymers containing higher content of ether oxygens than PEO to improve CO₂ permeability and CO₂/N₂ selectivity. More specifically, we have synthesized poly (1, 3 dioxolane) (PDXL) with different molecular weights of 510 g/mol and 1005 g/mol with a ratio of oxygen to carbon of 0.67, which is higher than that in PEO (0.5). These PDXL oligomers were also functionalized with acrylate groups and were thoroughly characterized using NMR, MS and FTIR. These oligomers were then polymerized by photo-polymerization and the resulting polymers were characterized for gas sorption and permeation. These new polyethers have demonstrated their promise for membrane CO₂/N₂ separation. For example, PDXL (n=5) derived polymer exhibits CO₂/N₂ selectivity of 82 with CO₂ permeability of 100 Barrers at 35^oC. The CO₂/N₂ selectivity is much higher than that of crosslinked PEO analogues (with CO₂/N₂ selectivity of 52). This presentation will also report fundamental solubility and diffusivity of other gases such as ethylene and ethane in these polymers.

Solid sorbents for carbon dioxide capture have many benefits, including high diffusion rates and surface areas, but also suffer from low capture capacities and selectivity for carbon dioxide. One popular method to overcome this challenge is to load amines onto the solids, through physical impregnation or covalent attachment to surface groups. While these materials can show high capacities with enough amine content, there is a tradeoff that exists between the kinetics of capture and amine loading, because the pores where amine is impregnated into the support are often the only channel available for gas diffusion. To overcome this challenge we have begun investigating sorbents that contain multiple pore channels which can be preferentially loaded with amines via size selection, allowing for a material which contains high contents of amine groups but still retains fast diffusion speed. One material, known as 3-Dimensional Disordered Silica, is composed of agglomerated spheres of zeolite beta that when loaded with polyethylenimine show fast capture kinetics and high capacities. We have shown that this material can be preferentially loaded in either the micropores present within spheres, or mesopores between spheres, allowing for an increased control of the pore-amine interaction and resulting capture performance.

Covalent organic frameworks (COFs) represent an emerging class of crystalline, porous materials exhibiting unique structural and functional diversity. By combining multidentate building blocks via covalent bonds, two- or three-dimensional frameworks with defined pore size and high specific surface area can be constructed.^[1] Crystallinity and porosity are of central importance for many properties of COFs, including electronic transport.^[2] Here, we present a new method for strongly enhancing both aspects through the introduction of a modulating agent in the synthesis. The competition between the bridging COF building block and the terminating modulation agent influences the dynamic equilibrium during framework formation, slowing down the COF growth and supporting the self-healing of crystal defects. Under optimized conditions, the crystal domains of COF-5 reach several hundreds of nanometers. The obtained materials feature fully accessible pores with an internal surface area of over 2000 m² g^-1.
Compositional analysis via NMR spectroscopy revealed that the COF-5 structure can form over a wide range of boronic acid to catechol ratios, spanning from highly boronic acid-deficient frameworks to networks with catechol voids.
Using functionalized modulators, this synthetic approach also provides a new and facile method for an external surface functionalization of COF domains, providing accessible sites for post-synthetic modification reactions.^[3]
We anticipate that the realization of highly crystalline COFs with the option of additional surface functionality will render the modulation concept beneficial for a range of applications such as gas separation, catalysis, and optoelectronics.

[1] A. P. Côte, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J. Matzger, O. M. Yaghi, Science 2005, 310, 1166-1170.
[2] M. Calik, F. Auras, L. M. Salonen, K. Bader, I. Grill, M. Handloser, D. D. Medina, M. Dogru, F. Löbermann, D. Trauner, A. Hartschuh, T. Bein, Journal of the American Chemical Society 2014, 136, 17802-17807.
[3] M. Calik, T. Sick, M. Dogru, M. Döblinger, S. Datz, H. Budde, A. Hartschuh, F. Auras, T. Bein, Journal of the American Chemical Society 2016, 138, 1234-1239.

Mixed-matrix membranes composed of highly CO₂-permeable montmorillonite aligned layers interspersed with polyvinylamineacid was bonded onto porous polysulfone membrane substrates. High-speed gas transport channels are formed by aligned interlayer gaps of the modified montmorillonite, through which CO₂ transport primarily occurs. A high CO₂ permeance is achieved combined with high mixed CO₂-gas pair selectivity that is stable over time, independent of water content in the feed.

Carbon capture and storage (CCS) technology has been gaining more attention due to considerable correlation between atmospheric carbon dioxide concentration and global climate changes.^1,2 Among many potential methods and materials for CO₂ Capture, alkaline earth-based oxide materials such as calcium oxides and magnesium oxides have emerged as one of the promising solid sorbent materials owing to their advantages such as wide availability of precursors in nature, low cost and low toxicity.^3,4

CO₂ capture by metal oxides follows the exothermic reaction: MO(s)+CO₂(g)↔MCO₃(s), where M can be alkaline metals including Mg, Ca, Sr and Ba. Specifically, magnesium oxides have been widely studied mainly because of their lower energy requirement for regeneration compared to calcium oxides.³

However, owing to the mediocre CO₂ adsorption capacities and the large capacity decrease at high temperatures caused by the formation of a nonreactive surface layer of carbonate which affects all metal oxides, there must be actions taken to enhance the efficiency of MgO absorbents. Currently, there are two methodologies for MgO performance enhancements: one of them is the impregnation and wet mixing of K₂CO₃ and other alkaline metals with MgO which resulting in better CO₂ adsorption capacity and remarkable regeneration⁵; another method is synthesis of porous MgO as a more desirable sorbent due to its high surface area and narrow pore size distribution.⁶

In this work, we focus on the synthesis and CO₂ adsorption performances of mesoporous magnesium oxide nanoparticles synthesized via thermal decomposition of metal organic frameworks (MOFs). For instance, a Mg(BDC) MOF is hydrothermally synthesized and used as a precursor to create MgO nanoparticles via calcination. Characterization techniques such as X-ray diffraction, SEM, TEM, IR and BET surface area analysis were employed to access the structural information of MgO nanoparticles, while their CO₂ adsorption characteristics were analyzed using TGA at different adsorption and desorption temperatures. More details about the roles which different calcination temperatures and heating rates play in terms of CO₂ capacities and regenerability, as well as the possible explanations for good regenerability will be discussed.



References:

[1] C. F. Cogswell, H. Jiang, J. Ramberger, D. Accetta, R. J. Willey, and S. Choi, Langmuir, 2015, 31, 4534−4541.

[2] D. Andirova, C. F. Cogswell, Y. Lei, S. Choi, Micropor. Mesopor. Mat., 2016, 219, 276–305.

[3] S. Choi, J. H. Drese and C. W. Jones, ChemSusChem, 2009, 2, 796–854.

[4] S. Lee and S. Park, J. Ind. Eng. Chem., 2015, 23, 1–11

[5] S. C. Lee, B. Y. Choi, C. K. Ryu, Y. S. Ahn, T. J. Lee, J. C. Kim, Environ. Sci. Technol., 2008, 42, 2736–2741.

[6] S. Bian, J. Baltrusaitis, P. Galhotra and V. H. Grassian, J. Mater. Chem., 2010, 20, 8705–8710.

Engineering and scaling-up new material for better water desalination is imperative to find alternative fresh water sources to meet future demands. Here, the fabrication of polyetherimide (PEI) composite nanofiber membranes doped with novel periodic mesoporous organosilica (PMO) nanoparticles comprising ethylene-pentafluorophenylene bridges is reported. The results showed an increase in hydrophobicity that is propertional to the percent of PMOs in the composite membranes. Direct Contact Membrane Distillation (DCMD) experiments were carried out for a comercial polytetrafluoroethylene membrane, PEI, and PEI-PMO doped nanofiber membranes. PEI nanofiber membranes showed more than 100% flux improvement compared to the comercial membrane. PMO doping of only 5%, showed a further increase of flux by ~140% compared to commercial membrane. Quantitative studies showed that bacterial adhesion on the engineered PEI-PMO nanofiber membrane has reduced by 40% due to the low surface energy of the embeded hybrid nanoparticles and the surface roughness of the composite nanofibers . The high porosity of PMO nanoparticles was further utilized to load an antimicrobial agent, namely Eugenol, showing a dramatic enhancement in the anti-biofouling properties of the electrospun nanofiber membrane where ~70% reduction of the bacterial attachment was noted after 24 hours .

Residential and commercial buildings consume a large amount of energy in cooling. About 45% of energy consumption is related to building temperature regulation through air conditioning (AC) and the demand for AC load is estimated to be increased by 6.2% annually. Therefore, it is appealing to develop alternative cooling technologies to assist or even substitute the conventional vapor compression (VC) cooling systems, especially for hot and humid climate with high latent heat load. Solid desiccant cooling (SDC) is one of the promising technologies because it can separately treat latent and sensible heat loads by pre-dehumidifying the moist air with desiccants, leading to high coefficient of performance (COP). Moreover, SDC systems are environmental friendly as it does not use chlorofluorocarbon refrigerants and is compatible with low-grade thermal energy, e.g., from solar or waste heat, for desiccant regeneration. The performance of SDC systems is hinged on the characteristics of the desiccants, most notably the adsorption capacity and the regeneration temperature. Typical desiccants exhibit either high adsorption capacities (e.g. ~2 g/g for polymeric desiccants with regeneration temperature of 80-100 ^oC ) or low regeneration temperatures (e.g. 40-57 ^oC for natural rock-based composite desiccants with adsorption capacities of ~ 0.2 g/g ), but it has been difficult to simultaneously achieve high absorption capacity with relatively low regeneration temperature. Here, we synthesized a novel desiccant, which shows both high adsorption capacity (~2 g/g) and low regeneration temperature (~ 40-50 ^oC) for the first time, by impregnating hygroscopic salts into a polymer matrix. Our thermodynamic modelling and experimental work further showed that the COP of SDC systems based on this novel desiccant can be enhanced by 3-fold, which is promising for energy saving and greenhouse gas emission reduction from building cooling.

Polymers are an important class of materials because of their desirable and tunable properties, abundance and low-cost. The properties of individual polymer nanofibers can be significantly different from those of the corresponding bulk, especially when the orientation and crystallinity of the molecular chains in the nanofibers are carefully tuned. For example, it has been shown that polyethylene (PE) nanofibers can possess thermal conductivities that are orders of magnitude higher than the bulk value. As such, it is important to characterize the microstructure and physical properties of polymer nanofibers to establish structure-property relations, which may help identify the key factors that dominate the properties and provide guidance when engineering the properties of a polymer for a specific application.

We have measured the thermal conductivities and Young’s moduli of three kinds of vinyl polymer nanofibers, i.e., polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA) and polyvinyl chloride (PVC), fabricated by electrospinning. These fibers have the same backbone, composed of carbon-carbon bonds, with only one or two atom differences in each monomer. The molecular orientation and crystallinity of individual nanofibers was carefully characterized using polarized micro-Raman spectroscopy. To characterize the physical properties of individual nanofibers, we used a thermal bridge method with suspended microheaters/thermometers to extract the thermal conductivities and the well-established three-point bending method to characterize the Young’s modulus with an atomic force microscope.

Our results show that in addition to the molecular chain orientation, the molecular composition and structure can also have important effects on the thermal transport properties. Among the measured fibers, PVA has the highest thermal conductivity and PVC has the lowest thermal conductivity with PVDF in the middle. It is also worth noting that all these fibers have a thermal conductivity much lower than that of electrospun PE fibers. We attribute the difference in the measured thermal conductivities to the composition and structure of the monomers, the basic building block of polymers. Lighter atoms on the side chains do not significantly alter the carbon atom vibrational modes and allow phonons to propagate without much disturbance, leading to high thermal conductivity. On the other hand, heavy atoms on the side chains may significantly change the vibrational modes to reduce the thermal transport capability. Similarly, the observed Young’s modulus of PVA nanofibers is higher than that of PVDF nanofibers, which correlates with the measured thermal conductivity trend.

We perform molecular dynamics (MD) simulations to understand thermally triggered shape memory behavior with an enhanced coarse-grained (CG) model of a thermoplastic polyurethane (TPU) elastomer. Hard and soft phases of shape memory polymers (SMPs) are known as fixed and reversible phase, respectively. Fixity depends on the content of hard segments due to their restricted mobility. On the contrary, recovery depends on the dynamic motion of the soft segments as well the degree of cross-linking, which is also affected by the quantity of hard segment. Several CG models of the TPU are constructed varying the weight percentage of soft segments to observe their effects on shape recovery and fixity. All of the models are equilibrated at 300K (above glass transition, Tg: 200-250 K) and deformed under uniaxial loading with NPT (isothermal-isobaric) ensembles. The deformed state is cooled to 100K (below Tg) and further equilibrated to estimate the shape fixity. Shape recovery is predicted by heating and equilibrating the structures back to 300K. By the end of this study, we may answer how much the shape fixity and recovery are changed for varying concentration of soft segments from thermomechanical cycles with CGMD simulations.

Molecular dynamics simulations are used to investigate the self assembly of a mixture of bare and polymer grafted nanoparticles in a polymer melt. The nanoparticles are modeled as spherical beads, polymers and grafted chains as bead-spring chains. Addition of grafted particles to polymer/(bare) particle blends results in the self assemble of bare particles into different anisotropic structures ranging from spherical to cylinders to branched cylinders. In all systems, the grafted nanoparticles attach to the surfaces of bare particle clusters due to depletion attraction. The rate of addition of bare nanoparticles to the cluster is higher than the rate of grafted particles. Finally, the minimization of the system energy results in the formation of different nanoparticle morphologies. At intermediate graft densities, the effective graft density of each individual bare nanoparticle cluster increases, as a result steric repulsions between the clusters increases, which leads to the formation of more number of small spherical clusters. For higher graft densities, the grafted particles are dispersed and separated from the bare cluster, which leads to the formation spherical clusters by the bare particles. These systems undergo structural transitions due to the interplay of grafted chain length, graft density and concentration of grafted particles. The structural map obtained by this study provide insights into how the geometric characteristics of the cluster can be tuned to achieve experimentally desired structural behavior. Our results indicate a possibility of formation of anisotropic structures with bare nanoparticles in polymer nanocomposites and offer flexibility in the design of new smart materials like chemical sensors, light emitting devices and photonics.

Thermally stable and periodically ordered mesoporous ceramic and ceramic–carbon composite materials are appealing for use in various high temperature catalysis, separation, and energy related applications. We describe a one-pot synthesis approach to generate ordered mesoporous crystalline γ-alumina–carbon composites and ordered mesoporous crystalline γ-alumina materials via the combination of soft and hard templating chemistries using block copolymers as soft structure-directing agents. Periodically ordered alumina hybrid mesostructures were generated by self-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) terpolymer, butanol and aluminum tri-sec-butoxide derived sols in organic solvents. The triblock terpolymer was converted into a rigid carbon framework during thermal annealing under nitrogen to support and preserve the ordered mesoporous crystalline γ-alumina–carbon composite structures up to 1200 °C. Subsequently the carbon matrix was removed in a second heat treatment in air to obtain ordered mesoporous crystalline γ-alumina structures.

Polymer self-assembly is a promising tool for scalable manufacture of membranes while maintaining high permeability and controlled pore size. Tuning copolymer composition (monomers, additives) and processing methods can change copolymer behavior which can dramatically affect the self-assembly and hence the membrane performance (permeability, selectivity, fouling resistance). Studies based on block copolymers demonstrate the influence of additives (solvent, homopolymer etc.) on the copolymer self-assembly and membrane performance. But studies on additives in casting solutions of random copolymers and how they affect membrane performance have not been reported to our knowledge. Recently, we have introduced a new class of membranes with ~ 1 nm effective pore size whose selective layers are made of self-assembling zwitterionic amphiphilic random copolymers. These membranes derive not only their excellent fouling resistance but also their permeability and selectivity from this self-assembled nanostructure. These membranes have numerous applications in the biochemical and pharmaceutical industries, as well as wastewater treatment processes. These membranes are prepared simply by coating random copolymers of hydrophobic and zwitterionic monomers onto a porous support membrane. In this study, we have used ionic liquids and other additives in the coating solutions to boost and alter the performance of these membranes. Membranes prepared by coating copolymer solutions with sufficient amounts of selected additives on commercial ultrafiltration membrane supports exhibit permeances as high as 50 L/m².hr.bar, up to 10 times higher than membranes formed without additives. These membranes also exhibit a narrow pore size distribution, retaining the same size-based selectivity with a ~1 nm size cut-off demonstrated by filtering negatively charged dyes. Performance of these membranes depends on the amount of additive as well as the membrane manufacturing method (non-solvent, drying time etc.). This is attributed to phase separation and solvent diffusion kinetics that are in play during membrane formation. These new membranes with high fluxes and sharp selectivity are promising for various applications such as textile wastewater treatment, pharmaceutical purification and bioseparation applications.

A highly innovative Shear Thickening Fluid (STF) was developed based on nano-silica particles. These particles have the ability to form a highly viscous gel at high shear/high temperature conditions. The inspiration of this innovation was taken from the medical industry mimicking the dynamic of biopolymers in a blood clotting cascade. The concept of the new STF is based on the introduction of short and long polymers grafted randomly onto silica particles. By inserting a hydrophobic functional group in a short polymer chain with hydrophilic macromolecules (silica with a long polymer chain) that will aggregate in water when the fluid experiences high shear rates (such as when passing through a drill bit). The remarkably strong hydrogen bonding resulting from high shear and high temperature provides a significant increase in fluid viscosity.
The gelling behavior of the material under shear and temperature should offer significant advantages in different application in Oil and Gas operation such as: drilling, well control and EOR. At the low shear rates encountered, the fluid is a low-viscosity, pumpable liquid. Yet as it passes through well, the resulting high shear rates cause the fluid to thicken either reversibly or permanently into a high-strength viscous fluid depending on the application.

Dynamic self-assembly is one of the most important tools to give living cells the biological functions such as sensing of external environment, cellular movement, and division. In contrast to static self-assembly, dynamic self-assembly could be deformed or reformed by kinetic control, which indicates it has a tremendous potential to be utilized for novel energy-function converting materials and complicated modulation of the material functionalities. However, there have been few reports on the functional materials that utilized the dynamic self-assembling system.
Currently, we are focusing on designing thermoplastic elastomers that can change their self-assembled structure and physical properties in responsive to the applied mechanical stimuli utilizing polyrotaxane. Polyrotaxane is a family of supramolecules with a topological characteristic, in which many cyclic molecules are threaded onto a single polymer chain capped at both chain ends with bulky end-groups. It is easily imagined that the cyclic compoinds can be freely sliding when the mechanical stimuli are applied.
The polyrotaxane was newly synthesized from poly(ethylene glycol) (PEG) and α-cyclodextrines (CDs) functionalized with trimethylsilyl groups. It was found that the CDs stacked parallel to the elongated direction of the polyrotaxane film with a d-spacing of 1.3 nm. The cylindrical rigid rod structure formed by stacked CDs was determined to form a hexagonally packed cylindrical structure with a d-spacing of 1.7 nm using wide-angle X-ray diffraction analyses. Furthermore, the cylindrical structures found to form a periodic domain with a d-spacing of 40 nm by applied mechanical stimuli, which was determined by small angle X-ray scattering analyses. It can be considered that the ring components slid along the PEG axis polymer chain to form a periodic rigid rod hard domains with the mechanical force is applied. This drastic morphological change was coupled to the physical properties revealed by dynamic viscoelasticity measurements.
We promise the new thermoplastic elastomer designed based on novel concept open a much wider window for materials of which functionalities can be precisely modulated by external mechanical stimuli.

At present, metallocene catalysts have attracted worldwide attention for the polymerization of ethylene because of their excellent catalytic performance ^[1~4]. In the case of polymerization in slurry, the metallocenes can be supported on some mesoporous silicate materials^[5]. The investigation revealed that the external morphology of mesoporous materials was the major factors to influence their practical applications ^[6–8]. Therefore, the kind of mesoporous material contained montmorillonite with sphere-like morphologies was successfully prepared via spray-drying method for the first time. Such mesoporous material was applied as the support to immobilize metallocene for the homopolymerization of ethylene and copolymerlzation of ethylene/1-hexene.
The kind of sphere-like shape catalyst was synthesized according to analogous procedures reported ^[9~12]. Such mesoporous material was applied as a support to immobilize metallocene ((n-BuCp)₂ ZrCl₂ and MAO) with the Al content of 24 % (wt) and Zr content of 0.6% (wt) (from (XPS)). The texture, structure and morphology of material were characterized by power XRD, SEM, TEM, and N₂ adsorption. XRD and TEM result showed that the catalyst remained mesoporous structure. SEM results indicate that the sphere-like shape morphology of mesoporous materials remained even after metallocene loading. The mean partical diameter of the material was analyzed by laser particle size analyzer. The catalytic performance of supported catalysts was studied systemically for polymerization of ethylene. The results revealed that the supported catalyst could remain the initial morphology and microstructure of mesoporous support materials, and presented uniform pore size distribution.
In summary, the kind of sphere-like shape mesoporous material contained montmorillonite supported by metallocene has been synthesized from a spray-drying synthesis approach successfully. And the catalyst showed superior catalytic properties for homopolymedzation and copolymenzation of ethylene/1-hexene to the commercial catalysts using silica gel.

Reference
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Poly(vinylidene fluoride) (PVDF) is one of representative fluoropolymers, and their unique piezo-, pyro-, and ferroelectric properties are utilized for versatile applications such as sensors, memories, actuators, power storage. PVDF primarily forms three types of chain conformation in the crystalline state: α-phase with a trans-gauche⁺-trans-gauche^– (tg⁺tg^–) conformation, β-phase with an all-trans conformation, and γ-phase with an intermediate state of α- and β-phases (tttg⁺tttg^–). Among these, β-phase PVDF exhibits ferroelectric properties due to its unidirectional polarization. However, the most thermodynamically stable conformation is α-phase. Therefore, methodology for the β phase transformation is a key issue for utilizing PVDF as ferroelectric materials.
Recently, fluoropolymer nanoparticles (NPs) are produced and utilized for enhancing the electronic properties of materials. For example, by an addition of polarized fluoropolymer NPs into the active layer of π-conjugated polymer photovoltaics, the charge separation is accelerated while the charge recombination is efficiently suppressed.
In our research, we focus our attention on PVDF NPs, and attempt a construction of colloidal crystals from the PVDF NPs. Colloidal crystals have attracted a lot of interests because of their simple fabrication process to construct 3D periodic structures. Most polymeric colloidal crystals studied thus far consist of optically and electrically inert polymers such as polystyrene (PS) and poly(methylmethacrylate) (PMMA). If colloidal crystals are constructed from ferroelectric polymers, novel photonic properties can be expected such as confinement of higher-order harmonics into colloidal crystals.
The obtained PVDF NPs with an average diameter of 230 nm mostly form α-phase, which is consisted of 46% α-phase and 54% amorphous PVDF. Firstly, the PVDF NPs were assembled on a quartz substrate by means of vertical deposition method from a tetrahydrofuran (THF) dispersion of PVDF NPs with a few volume percentage of n-alkane that is higher b.p. than THF. The resultant colloidal thin films displayed a pale-greenish structural color with the selective reflection at around 550 nm wavelength due to closely packed PVDF NPs. Furthermore, The fabricated PVDF colloidal thin films has particular angular dependence of selective reflectance to colloidal crystals. The fabricated colloidal thin films were then immersed into an acetonitrile solution containing 2 wt% ionic liquid, subsequently air-dried, and thermally annealed at 140 °C, just below the melting point of the PVDF-IL blends. After annealing, the PVDF NPs partially transformed into its β phase with the volume percentages of α-, β- and amorphous phases of 22, 32, and 46%, respectively. The post-annealed colloidal films still maintained the periodic fcc assembling structure of PVDF NPs, thus displaying the greenish structural color and selective reflection.

The possibility of stretchable gas barrier nanocoating was studied with an all-polymer multilayer using layer-by-layer assembly. Electrostatically-bound polyethyleninmine (PEI)/polyacrylic acid (PAA) and hydrogen bonding-based polyethylene oxide (PEO)/PAA layers were incorporated into four interbonding layers in which PAA serves as a bridging molecule. Assembly pH had a direct effect on the film’s growth and structure. With all layers deposited from pH 3 aqueous solutions, a densely packed multilayer thin film was formed with relatively high gas barrier, achieving an oxygen transmission rate (OTR) 15 times lower than the 1 mm thick polyurethane (PU) rubber substrate. At 10% strain, the film becomes more oriented and densified (reducing free volume), resulting in a significant improvement in OTR (28 times lower than uncoated PU rubber). When stretched between 10 and 50%, an OTR that is 7 to 8 times lower than the substrate was maintained. This unique, stretchable coating, along with its excellent gas barrier properties, would make possible to expand the horizon of applications for elastomeric objects and electronic packaging applications, many of which are used in energy generation and medical devices.

Along with the continuous deepening research on nanofibers, the applications of fibers are no longer limited to the textile industry, and also show a wide range of application prospects in civil, medical, military, and other fields. Although there are many kinds of methods to prepare nanofibers, the electrospinning is one of the most popular and convenient method. Compared with other methods, the fibers made by electrospinning have large specific surface area, controllable diameter, strong structural stability, and other properties. In this work, polyethylene glycol/polyvinyl alcohol (PVA/PEG) phase change composite nanofibers were prepared by using a self-designed electrospinning device at ambient temperature. The diameter, morphology, composition, thermal and mechanical properties of PVA/PEG nanofibers were studied by scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR), differential scanning calorimetry (DSC), atomic force microscopy (AFM). The SEM results showed that the electrospinning effect became worse with the increase of the content of PEG. DSC studies shows that PVA increased the thermal structural stability of PEG. According to AFM measurement, it was proved that additive PEG reduced the Young's Modulus of the composite fibers compared with the pure PVA fibers.

A triboelectric nanogenerator (TENG), a renewable energy technology to efficiently harvest mechanical energy into electrical energy, has elicited worldwide attention because of its cost-effectiveness and sustainability. This device utilizes contact electrification which is induced by friction between two dielectrics with triboelectric polarity to produce electricity from wasted mechanical energy. Recently, the TENG was developed using water-solid contact electrification, which used water as dielectric itself and significantly reduced the friction damage between two materials. In this study, we developed a cylindrical water triboelectric nanogenerator which controls the water flow by fabricating patterned hydrophobic/-philic surface with polytetrafluoroethylene (PTFE) nanolayer. As a first report, this study demonstrates new design of fully packaged water-solid contact TENG, called cylindrical water triboelectric nanogenerator (CW-TENG), which has a complete packaged design to generate multiple output in single rotation through patterned surface. CW-TENG can be integrated with multiple generating hydrophobic/-philic generating units in single TENG device without occupying extra space for installation. Furthermore, this study is the first to demonstrate possibility of using hydrophilic surface as additional energy harvesting device as well as water reservoir in a packaged design. Until now, hydrophilic surface was only considered as incompatible element for TENG because water volume on the hydrophilic surface remains after the first contact. The rotating design pushes water on the hydrophilic surface constantly to force the water volume change to induce electrical potential difference between two surfaces. In addition, this study demonstrates analysis of the electrical energy generation by water volume change on the hydrophilic surface with computational dynamic simulation. The electrical potential difference between water and the electrode is shown to increase as the water volume change is increased. Utilizing this new result and analysis, various TENG design using hydrophilic surface can be developed for practical use. In this design, the super-hydrophobic surface TENG generates open-circuit voltage (V_OC) of 7 V and closed circuit current (I_CC) of 50 nA, and hydrophilic surface TENG can produce V_OC of 2 V and I_CC of 60 nA. With more super-hydrophobic and hydrophilic patterned electrode inside this device, the total power generated by the device is estimated to be multiplied. Thus, with this research will provide a potential solution of energy harvesting using water flow and self-powered system.

Organic microporous polymers are at the front line in the field of advanced material science due to their interesting chemical, physical, and optical properties arising from tremendous monomers and various synthesizing routes. Among diverse synthesizing strategies, we prefer to choose two methods to carry out our experimental. First is Sonogashira coupling reaction. Second is Schiff base reaction. Sonogashira coupling reaction is relatively matured method to couple two molecules by eliminating halogen (I or Br) and proton bonded to alkyne from two different monomers. After careful polymerization, we could obtain high surface area (1000 m²/g) conjugated or tetrahedral structured polymers depending on monomer’s structures with protected alkyne group. As it known to all, polymers with alkyne allow us to post-treat it using click chemistry to obtain tri-azole which could lead to transition metal chelates. Even though Sonogashira coupling reaction has many advantages in synthesizing polymer it still faces an issue, homo-polymerization of alkyne monomer. In order to solve this problem we select Pd/TBAF catalysts instead of commonly used Pd/CuI. By adopting Pd/TBAF catalyst, we obtained ideally ordered polymer. In the case of the Schiff base, synthesized polymers containing amide group show high crystallinity and high surface area but are weak under aqueous condition including acidic and basic. In order to solve this problem, we will use electron donating-withdrawing properties of functional group to fortify the stability of the polymer under the aqueous conditions. We select the methoxy group as an electron donating group to abate the repulsive forces arising from the unequally distributed electron cloud densities commonly resulting in the unstable structure of the polymers. By using as synthesized polymers in our team, we tested its potential in the field supercapacitor, catalytic reactions, and so on.

This study was supported by the National Research Foundation of Korea (grant no.: 2015R1A4A1042434).

Block copolymers (BCPs) composed of two or more chemically distinct polymer chains linked by covalent bonding can self-assemble into a variety of nanometer-scale domains including sphere, cylinder, and lamellae, which can become versatile platforms to fabricate well-defined nanostructures for potential applications. However, the self-assembly of block copolymers on flat surface inevitably meets imperfection like dislocation, and grain boundaries in ordering of the domains. These defects are currently regarded as major drawbacks that should be overcome to realize ultra-high density array of ordered nano-features in large area. Directed self-assembly (DSA) of block copolymers has often been used to generate long-rage ordering of BCP domains in thin films. But, conventional methods for DSA in BCP thin films are still limited due to several disadvantages that require complicated multi-step process, high cost templates and so on. In this study, we introduce an intuitive and effective method to achieve highly ordered nanostructures of block copolymers in thin films by using solvent-annealing process on polymer nano-stripes. The extremely aligned nano-stripes of poly(tetrafluoro ethylene) (PTFE) which has low friction coefficient and high wear rate were directly produced on various substrates (Si wafer, glass, and polymer films) by mechanically rubbing a PTFE bar. Then polystyrene-block-poly(2-vinylpyridine) copolymers (PS-b-P2VP) were subsequently spin-coated on the nano-stripes of PTFE and annealed in vapor of organic solvents to induce self-assembly of block copolymers. By adjusting solvent-annealing conditions, highly ordered BCP nanostructures which were oriented either vertically or horizontally to the surface were revealed in large area because of the guidance of underlying PTFE patterns. These well-ordered BCP nanostructures were utilized as either templates to synthesize inorganic nanodots or nanowires or etching masks for wet etching process.

There is a growing demand for renewable energy technologies due to the shortage of fossil energy resources and environmental concerns. Nanogenerators (NGs) that can harvest energy from ambient sources (e.g., mechanical vibration, heat, acoustic waves, and human activities) have attracted significant attention during the past decade. Piezoelectric materials, capable of generating electrical power from accessible and ubiquitous mechanical energy sources are the most promising candidates for developing NGs. Nevertheless, several factors including high cost of raw materials (e.g., ZnO nanowire or BaTiO₃), and/or complicated fabrication procedures have limited their mechanical flexibility as well as their production scalability and ultimately, their potential applications. Thus, there is an ongoing pursuit for novel and cost-effective flexible piezoelectric materials that can be fabricated via simple and scalable processes while providing high output power and device flexibility.
Considering cellulose nanofibrils (CNF)’s excellent mechanical properties, chemical stability and relatively high piezoelectric coefficient (26–60 pC/N), flexible CNF-based aerogels hold great promise in the development of self-powered electronic systems including piezoelectric NGs. We recently develop a novel, simple, cost-effective, and scalable technique to fabricate high-performance flexible piezoelectric nanogenerators (NGs) using porous CNF/poly(dimethylsiloxane) (PDMS) aerogel film. The porous CNF/PDMS aerogel film was prepared by coating a layer of PDMS on the porous surface of a compressed CNF aerogel film produced via an environmentally friendly freeze-drying process. The porous CNF/PDMS aerogel film was then sandwiched between two thin PDMS films, followed by two aluminum foils, to form the flexible NGs. Under periodic external mechanical deformation by an oscillator, the resulting flexible porous CNF/PDMS aerogel film-based NGs exhibited very stable and high output piezoelectric signals; namely, an open-circuit voltage (V_oc) of 60.2 V, a short-circuit current (I_sc) of 10.1 μA, and a corresponding power density of 6.3 mW/cm³. The electric power generated by these NGs was able to directly turn on 19 blue light-emitting diodes (LEDs) and charge a capacitor up to 3.7 V. Furthermore, these NGs also demonstrated excellent stability, integratability and durability. Considering their excellent piezoelectric performance, ease of large-scale manufacturing, and environmental friendliness, this technology provides a promising solution for developing practical, flexible, and self-powered electronic devices.

Three-dimensional porous polymer structure was fabricated by interference lithography. The direct carbonization of 3D nanostructure has attracted interest for obtaining 3D carbon materials. The polymer flow and subsequent change occur during high temperature treatment. Liquid immersion thermal treatment was applied to enhance the thermal resistance and maintain the structural integrity during high temperature treatment. The thermal crosslinking reaction of structured polymer pattern was characterized. The 3D polymer pattern successfully converted to 3D carbon pattern via liquid immersion thermal treatment. Structured carbon pattern was applied to the supercapacitor after nitrogen doping for pseudocapacitance. The liquid immersion heat treatment can be extended to the carbonisation of various polymer or photoresist 3D patterns and also provide a facile way to control the surface energy of polymer 3D patterns for various purposes, for example, to block copolymer or surfactant self-assemblies.

Organophosphorus hydrolase (OPH) can efficaciously degrade harmful organophosphates (OPs), a class of acutely toxic neuro-inhibitory chemicals extensively employed as pesticides and chemical warfare agents. However, OPH tends to aggregate in aqueous solution, resulting in a significant decrease of its native activity within hours. Furthermore, there has been limited success in incorporating OPH into synthetic materials to fabricate smart fabrics or devices because most materials processing techniques require organic solvents, which denature the protein. Several groups have demonstrated that OPH can retain activity when exposed to organic solvents, but the techniques employed thus far have had limited success in generating effective OPH-based functional materials.
Inspired by natural chaperons, we have created a random heteropolymer comprising different chemical moieties with complimentary interactions to OPH – hydrophobic, hydrophilic, and negatively charged – to encapsulate and stabilize OPH in both aqueous and organic media. When complexed with the designed polymer, OPH demonstrates a drastic increase in biological activity in buffered aqueous solution – approximately 15 times greater than the native biological activity of pure OPH in the same environment. Additionally, the heteropolymer-OPH complex is soluble and remains active when stored in organic media (while pure OPH is insoluble in the same media). This allowed us to fabricate OPH-loaded electrospun nanofibers from a toluene/chloroform mixture using a wide range of polymers. Our OPH-loaded fibers displayed substantial biological activity in aqueous media as well as in organic solvents, providing a route for functional materials toward efficient large-scale degradation of these harmful OP chemicals.

A bottom-up approach towards protein-based nanoassemblies has the potential to change the current paradigm of materials science. Synergistic integration of protein and synthetic block copolymer is of particular interest. A protein library rich in functionality coupled with a block copolymer’s ability to direct the assembly of nanoparticles into well-defined nanoscale structures has the potential to improve a variety of technological sectors. This includes biosynthetic catalysis, energy conversion, and molecular sensing. However, it still remains a challenge to preserve protein structure and function while making them readily processable. Proteins primarily reside in aqueous media and are typically not amenable for usage beyond biomedical applications. Conversely, amongst the numerous processing conditions required to fabricate materials, organic solvent-use generally remains a common necessity. A protein’s insolubility and inability to remain functional in non-aqueous solutions are significant hurdles that need to be addressed. Here, we show that through the development of rationally designed statistically random copolymers, it has become possible to stabilize proteins and process them in organic media. The chemical complexity offered by statistically random copolymers allows us to manipulate the interactions between protein, solvent, and block copolymer. Their amphiphilic nature and ability to multivalently hybridize with a protein’s surface enables protein-use far beyond the current scope of aqueous-based device fabrication and chemistry. After encapsulation in statistically random copolymer-based complexes, proteins are readily available for co-assembly with block copolymers. Proteins remain functional throughout the entire process, block copolymer microphase separation remains unhindered, and proteins are nanoscopically arranged in controllable hierarchical structures.

Chirality is universally present in nature and imparts specific functionality to organic and inorganic compounds. Introducing a chiral side-chain to donor-acceptor conjugated polymers results in self-assembly of helical aggregate nanostructures. The asymmetry of the side-chain influences the packing structure of the polymer chains in the aggregate and in the solid state. Adding a chiral side chain to a benzotriazole-thiophene copolymer results in self-assembly into a chiral aggregate. Circular dichroism (CD) spectroscopy reveals the expected bisignate Cotton effects in solution with solvents ranging from toluene to dichlorobenzene. CD response is obtained even at low solution concentrations (0.0025mg/mL) and when 90% of the material in solution contains racemic side chains and only 10% contains chiral side chains. The magnitude of the CD response is about one-tenth that of the purely chiral solution. The chiral organization translates from solution to the solid state. The difference in secondary structure with the substitution of chiral for racemic side chains provides a method for controlling the geometry of the aggregates. This control over aggregate geometry could prove beneficial in a variety of optoelectronic applications such as organic thin film transistors and sensors.

The development of conjugated microporous polymers (CMPs) showed a unique possibility for high energy storage electrochemical supercapacitor. CMPs are classified as of microporous organic polymers (MOPs). CMPs have been extensively investigated for gas storage, controlled drug release, catalysis, and energy storage devices because of their low densities, chemical and thermal stability, permanent porosity, high specific surface area, pore volume, and regular pore size distribution. Specially, in supercapacitor system for high energy storage and fast charge-discharge performance based on its reaction mechanism, the material having high and regular pore structure have been needed. Recently, the activated carbon used at commercial supercapacitor market have been struggled to make a high energy storage device due to its irregular and isolated pore structure.
Herein, we demonstrate a facile strategy for the design and synthesis of triazine based microporous carbon nanoparticles (T-MCNs) having regular micro-pore structure as a high performance supercapacitor electrode. T-MCNs were fabricated using novel organic polymer synthesized simple Friedel-Craft method which was for the first time synthesized by cyanuric chloride and 1,3,5-triphenylbenzene in dichloromethane (DCM) under solvothermal condition at 70 ^oC using anhydrous aluminium chloride as a catalyst. After synthesis, the attained sample was carbonized in tubular furnace at 700, 800, and 900 ^oC with nitrogen and carbon dioxide atmosphere, respectively. T-MCNs carbonized at 800 ^oC (T-MCNs 800) as a supercapcitor electrode showed unique capacity behavior (418 F/g at 1 A/g) and excellent cycling stability (98 % retention after 1000 cycles at 1 A/g) in 6 M KOH aqueous electrolyte. Therefore, well designed T-MCNs through triazine based microporous polymer supplied promising prospect as new supercapacitor electrode material for substituting activated carbon.
Acknowledgement
This study was supported by the National Research Foundation of Korea (grant no.: 2015R1A4A1042434).

Recently, in the electrical and electric devices, such as motors in hybrid car, or PC and mobile phones with high performance and small sizes, the increase of the heat generated inside them has become severe problems. As insulating materials, epoxy polymer is typically used in these kind of devices, but the thermal conductivity of the epoxy polymer is small (around 0.2 Wm^-1K^-1), 1 to 3 orders smaller than those of metal or ceramics in general. The addition of filler increases of the thermal conductivity of epoxy polymer, but the viscosity also increases at the same time. Thus, the high thermal conductivity of the polymer itself is required
The liquid crystalline epoxy polymer which include twin mesogens, the twin-mesogen epoxy polymer has shown recently to have a relatively large thermal conductivity, five times larger than those of conventional epoxy polymers and such a large thermal conductivity of the liquid crystalline epoxy polymer has been explained qualitatively to come from its higher orderliness of liquid crystalline structure.
We also synthesized and analysed thermo-plastic liquid crystal polymers and found the methacryl polymers with biphenyl type mesogen show twice larger thermal conductivities than that of conventional methacryl polymer (PMMA).
In this work, we synthesized side chain type liquid crystalline methacryl polymers with spacer carbon numbers of 3,5 of which mesogen end group was methyl group and investigated the effects of high-order structure changes due to the difference of spacer carbon numbers and alkyl carbon numbers of the mesogen end group on the thermal conductivities. We will discuss the effects of even and odd spacer carbons and the alkyl chain length of end group of mesogen on the higher-order structure and the thermal conductivities of side chain type liquid crystal polymers.

Amorphous polymers (APs) generally act as thermal insulators, as their thermal conductivities (κ) are low, falling primarily within a narrow range of 0.1-0.5 Wm^-1K^-1 (compared to ~100s Wm^-1K^-1 for metals). Low-cost and scalable methods to increase thermal conductivity in APs would have significant impact in numerous industries, as applications range from electronics packaging to vehicle structures. Most previous efforts, however, have either limited practical scope (e.g., mechanical stretching) or greatly increased material cost (e.g., blending with high-κ fillers such as metal powders).

Here we present a means to tackle this challenge using a scalable and low-cost molecular engineering approach, utilizing charge repulsion forces between ionizable side groups in a polyelectrolyte (polyacrylic acid, PAA) to extend its backbone and hence promote the efficient flow of thermal (vibrational) energy. Using this method, we achieve a factor of six increase in κ for spin-cast thin films. The solution pH is used to control the degree of ionization in PAA (the fraction of carboxylic groups that ionize) and hence the backbone charge density, with which the extent of chain extension and thermal conductivity are positively correlated.

We apply a number of experimental techniques to characterize the physical properties that change upon PAA ionization and lead to the dramatic enhancement observed in thermal conductivity. Fourier transform infrared spectroscopy (FTIR) is used to quantify the degree of ionization (α) in the solid-state PAA films, where the height of the carboxylic group (COOH) peak relative to that of the ionized carboxylic group (COO^-) peak is observed to continuously decrease as pH grows, suggesting a steady increase in α. To quantify backbone chain extension in the aqueous state, the PAA radius of gyration (R_g) is calculated by measuring the viscosity (η) of the PAA solution at various pH values, since R_g is related to η^1/3 (as well as to molecular weight, which is kept constant) by the Flory viscosity constant. As PAA chains swell in solution, their enhanced viscosity translates into thicker films under identical spin-cast conditions, which we confirm by thickness data obtained via ellipsometry. We then use a differential 3ω technique to determine the cross-plane thermal conductivities of thin film samples both with and without an alumina capping layer (to block humidity), measuring similar κ values for both configurations. PAA films spin-cast from pH 1 to pH 10 solutions exhibit a continuously increasing trend in thermal conductivity (0.2 to 1 Wm^-1K^-1). Lastly, the amorphicity of PAA is verified by XRD, where the absence of prominent crystalline peaks excludes contributions to κ enhancement by polymer crystallization. Therefore, we establish the links between pH and chain extension (by FTIR), chain extension in solution and in solid-state (by viscosity and ellipsometry), and chain extension in solid-state and thin film thermal conductivity.

Recently, electrical machineries and apparatuses have become smaller and higher quality, and heat generated inside machineries causes overheating and various malfunction of these. Thus it is a serious problem how the heat is radiated and cooled. Generally, machineries have been cooled by radiator, but cooling efficiency of the insulating part in the machinery is very inefficient as thermal conductivity of polymers that were used to insulting material, is very low. It has been used to solve this problem that the inorganic fillers are added to the matrix conventional polymers of which thermal conductivities are very small. Thus we should add so much fillers that the necessary physical properties like low viscosity of the materials are lost. Therefore increase of the thermal conductivity of polymer itself is required.
The thermo-setting epoxy polymer is used generally for the insulating material. We investigated and found that the epoxy polymer which had twin mesogens showed liquid crystal structures and five times larger thermal conductivity than a conventional one.
Thermo-plastic polymer is better than thermosetting polymer, for example, in forming processability. Thus molded article made by thermoplastic polymer can be produced in large quantities easily. In this work, we synthesized thermoplastic side chain type liquid crystal methacrylate polymers that have spacer length 2 or 6 and end group, alkyl chain length 6 of phenyl benzoate as mesogen and analyzed their high thermal conductivity mechanism, comparing their thermal conductivities to those of side chain type liquid crystal methacrylate polymers with odd number spacer carbons and with methyl group as end group of mesogen. We will discuss the effects of even and odd spacer carbons and the alkyl chain length of end group of mesogen on the higher-order structure and the thermal conductivities of side chain type liquid crystal polymers.

A series of thermoplastic polyurethane (TPU) based on poly(tetramethylene glycol) (PTMG 1000) as a polyol and methylene diphenyl diisocyanate (MDI) as a isocyanate were successfully synthesized on different formulation to evaluate the molecular weight (MW) effect. Graphene oxide (GO) sheets were chemically grafted with allophanate-functionalized TPUs. Mechanical properties and thermal properties of TPU/Graphene oxide (TPU-g-GO) nanocomposites were systematically estimated with adding the stoichiometric GO to TPU with different MW. Transmittance of individual TPU-g-GO were sequentially changed in the range from 79.72 to 90.15 %, with dependence of GO content. Water-barrier properties of TPU-g-GO nanocomposites was measured using water vapor transmission rate test. TPU-g-GO films would be extensively attracted for greatly potential possibility of high-performance films for electrical and electrochemical applications.

Polyether-polydimethylsiloxane (PDMS) polyurethane (PU) are successfully synthesized using three different molecular weights (= 550, 6000, 110,000) of siloxane polyol and one fixed molecular weight of polyethylene glycol (PEG) polyol as a soft segment. Wettability and surface properties of PDMS-PU are evaluated with respect to PDMS molecular weight and PDMS mol %. PDMS enrichment at the air-polymer interface could result from the phase separation effect between PDMS segments and urethane segments. Surface energy of PDMS-PU is decreased with increasing PDMS molecular weight and content. PDMS segments in PCDMS-PU attributes to high- or super-hydrophobic surface and high contact angle with water, which could lead to the potential water-barrier property. The optical transmittance and water vapor transmission rate of PDMS-PU are investigated to use as an encapsulation material for the environmental protection and industrial applications.

We report here an experimental strategy for preparing polyacetyelene, (CH)_x, as an array of stereoregular polyene chains constrained within the channels of a crystalline solid. The method we used to synthesize this composite/hybrid conjugated material is based on the solid-state polymerization of a reactive molecule (1,4-diiodo-1,3-butadiene, DIBD) constrained within a one-dimensional tunnel host (urea, CO(NH₂)₂) structure.

DIBD/urea single-crystals were grown by standard crystallization procedures, from a solution containing DIBD guest molecules, and urea dissolved in methanol (MeOH).[1] Organo-iodine compounds like DIBD, when irradiated with either UV or visible light, undergo a homolytic breakage of the carbon-iodine bond to generate I-CH=CH-CH=CH● radicals and I● atoms; the I atoms, ultimately as I₂, escape the urea matrix after photodissociation as determined by weight measurements. Such radical species are stable in isolation in the urea inclusion complexes. Two adjacent radicals can react to form the stable dimeric species IHC=CH-CH=CH-CH=CH-CH=CHI. Continuation of this process results in the production of tunnel-bound longer diiodopolyene.

Raman spectroscopy was used to probe the resulting conjugated polyene chains and to study the time dependence of the photoinduced polymerization in these crystals. We found that UV or broadband UV/visible radiation results in two strong and sharp resonance-enhanced Raman modes at 1121 and 1509 cm^-1. A weaker non-resonant band at 1293 cm^-1 was also observed; we used this line as an internal standard for “good” samples.[2] The Raman spectra of the confined polyenes are very similar to that of known polyene species and to spectra of trans-(CH)_x prepared by solution methods. A qualitative interpretation of these new Raman features as due to diiodopolyenes products will be discussed.

The kinetic evolution of the product polyene features exhibits three phases. Initially, there is an appearance of a very strong scattering near 1500 cm^-1 and a second one with a relative lower intensity near 1100 cm^-1, associated with C=C and C-C stretching deformations, respectively. This is followed by an increase in the intensity ratio I₁₁₀₀/I₁₅₀₀ with the 1100 cm^-1 feature becoming dominat. Furthermore, during this time interval, the non-resonate polyene band near 1290 cm^-1 is observed as well. The intensity of the 1290 cm^-1 band is constant for most of the photochemical transformation, but eventually disappears at later times. The third phase of the kinetic process shows the progressive loss of Raman intensity for both of the two polyene bands with the 1100 cm^-1 band being the last to disappear. This is the behavior expected as very long conjugated chains are produced.

1. A. E. Lashua, T. M. Smith, H. Hu, L. Wei, D. G. Allis, M. B. Sponsler, and B. S. Hudson, Cryst. Growth Des. 12, 3852 (2013).
2. H. Kuzmany, E. A. Imhoff, D. B. Fitchen, and A. Sarhangi, Phys. Rev. B, 26, 7109 (1982).

Today the incorporation of nano-clay in polymer matrixes greatly enhances the properties of the polymer. However, its application is extensive, such as coatings, auto parts, rubber stamps, and many others. In the present work, the thermal behavior and composition of a copolymer nanocomposite with Montmorillonite clay nanoparticles are discussed. The copolymer composition is composed of butyl acrylate (BA), styrene (STY), and methacrylic acid (MAA), and a Na montmorillonite nano-clay (MMT) was used. The nanoparticles are incorporated during the polymerization process (in-situ process). The state of chemical composition was performed by infrared spectroscopy (IR).The spectra showed that increasing the clay-nanoparticles it was observed an increment of Si-O incorporated in the copolymer matrix. Also, these nanocomposites retain their common optical transparency of an acrylic even increasing the concentration of MMT. In addition, the study of thermal gravimetric analysis (TGA), shows that the nanoparticles have a negative trend in thermal stability disregarding the copolymer matrix concentrations. It was also observed an increment in the glass transition temperature by differential scanning calorimetry.

Due to the thermodynamic incompatibility between different blocks of a block copolymer (BCP), it can self-assemble into highly-ordered microdomains with a wide range of morphologies and sizes that can be subsequently transferred into a functional material layer. This provides an effective pathway for fabrication of useful nanostructures in a rapid and low-cost process. BCPs thus offer a path to meso-scale patterning techniques and are promising candidates for enabling sub-10 nm nanolithography for the semiconductor industry. Poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) is of particular interest due to its relatively large Flory-Huggins segmental interaction parameter ( χ~ 0.27 at room temperature), which leads to a high driving force for microphase separation. BCPs with high χ value demonstrate strong microphase separation, low defectivity, and sharp interfaces between different blocks, resulting in lower line edge roughness. Furthermore, the Si-containing PDMS block is etch-resistant compared to PS when subjected to an oxygen plasma, which is desirable for pattern transfer.

Although BCPs with small period have received much attention, the self-assembly of BCPs with large period (~100nm) is also important for photonic or phononic applications. High molecular weight PS-b-PDMS possesses large segregation strength (χN >>100, with N the degree of polymerization), but the kinetics of the microphase separation are limited due to high chain entanglement and low diffusivity. Here we describe the thin film morphology of a 123 kg/mol PS-b-PDMS BCP processed by solvent vapor annealing at room temperature. The kinetics of thin film morphology evolution was illustrated as a function of as-cast film thickness (50~90 nm), the composition of the binary mixture of solvent vapors (toluene:heptane) and the solvent annealing time (1~24 hr). Thin film structures with long-range (micron scale) ordered PDMS in-plane cylindrical domains with period of 90 nm were achieved after a 12 hr 5:1 toluene:heptane mixture vapor annealing. The conditions of as-cast thickness of 80 nm and swelling ratio of 2.68 enables the commensurability between the swelled film thickness and block copolymer period, leading to a uniform, monolayer cylinders formed over the film without severe terrace and hole formation. The directed self-assembly of the BCP within lithographically patterned trench confinement was demonstrated, showing alignment of the cylinders parallel to the sidewalls. Fabrication of ordered cobalt nanowire arrays by pattern transfer is also demonstrated, and their magnetic properties and domain wall behavior characterized. This study shows how the kinetic limitations inherent to large period BCPs can be overcome, enhancing their utility in energy applications such as photonic crystals and solar cells.

Tuning the shape and size of nanostructure materials with their unique properties is an area of great interest for the development of nanoscience and nanotechnology [1]. Among several approaches to achieve this goal block copolymers (BCPs) have received considerable attention recently, due to the inherent self-assembly property which can lead to various nanoscopic structures, like spheres, cylinders, bicontinuous gyroids, and lamellae, depending on the composition and chain architecture of the BCPs [2]. The well-aligned and periodic nanostructures of BCPs can be used as template of inorganic oxide patterning for microelectronics and optoelectronics applications. In this work we are using cylindrical polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) and spherical micelles structures polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCPs as template for the inorganic oxides deposition. TiO₂ with unique structural and functional properties can be extensively used in photo catalysis, water splitting, solar cells, supercapacitors and lithium-ion batteries [3]. For TiO₂ nanostructures synthesis we are using two methods. In the first method, we are using a unique solution process deposition method to deposit the oxide inside selective blocks of the copolymers. In the second method, we are using pulse laser deposition (PLD) method as the TiO₂ deposition method after selectively etching one copolymer. After removing the polymers using calcination, the inorganic nanostructures can be used for various microelectronic, catalytic and optoelectronic applications.

References:

S. Barth et. al., Progress in Materials Science , 55 (6), 563-627, (2010).
Y. Tseng et. al., Polymers, 2, 470-489, (2010).
M. Ge et. al., Journal of Materials Chemistry A, 4, 6772, (2016).

Patterning micro- and nano-scale features are broadly desired because of their high technological relevance to many applications, including microelectronics, magnetic storage media and a range of devices that impact energy. A general trend in this area is that device structures shrink in size with every new device generation and traditional lithography strategies (i.e., photoresists light exposed through photomasks within projection systems) are continually being challenged to reach targets. In recent years, complementary strategies are gaining more traction in academia and industry. One promising approach involves exploiting block copolymers (BCPs) that naturally self-assemble into domains ~1-100 nm in size. However, a major challenge is that their self-assembled structures must be directed into device relevant arrangements to be useful for manufacturing. I will provide an overview of our efforts in this area and then focus on a specific photochemical process for controlling BCP domain orientation in an area selected manner.

Porous conductive networks are highly desired for energy conversion and storage, catalysis and chemical sensing. PEDOT is a stable (thermally, chemically and electrochemically), biocompatible polymer with a wide range of applications, but it hasn’t been made into regular nanoporous materials. MOFs, on the other hand, have highly regular open framework structures, but are not conductive and generally fragile. Use of metal-organic frameworks (MOFs) as templates for PEDOT nanostructures promises to create novel conductive nanostructured materials, which are flexible, have high surface area, and novel reactivity. Here we present a wet-chemistry approach to achieving sub-millimeter sized materials of nanostructured poly(3,4-ethylenedioxythiophene) (nano-PEDOT) and conductive PEDOT-MOF composites. We perform extensive characterization of the materials both by spectrometry and by microscopy of the micrometer-structures from these materials.
Electrical property measurement via conductive AFM shows insulating behavior for the pure MOF and reveals semiconductor-like current-voltage curves for both the PEDOT-MOF composite and nano-PEDOT. The Young’s modulus obtained by nanoindentation for nano-PEDOT (ca. 0.5 GPa) is lower than the bulk PEDOT (ca. 2 GPa). Currently, open-channel nanostructures are mostly realized by methods such as inverse opals with pore normally larger than 50 nm. Here, we break that limit by using a MOF as the template, with pores/channels smaller than 2 nm in diameter. We believe the work will stimulate fundamental studies of polymer reactions in confinement and the discovery of other MOF-polymer systems where the MOF can act as a (sacrificial) template. Meanwhile, such pores/channels offer potential enhancements in species migration and chemisorption on a large area. These novel structures, combined with the stability and conductivity advantages of PEDOT, will be beneficial for numerous applications related to energy conversion and storage, such as supercapacitors and full cells.

Ferroelectric polymer nanostructures are of great interest due to their potential use in a wide range of applications. With the increasing application of ferroelectric polymer in the area of flexible electronics,^1,2 high-throughput and low-cost fabrication of 2D and 3D ferroelectric polymer nanostructures on flexible substrates can be a significant basis for future research and applications. Here, we report that large arrays of ferroelectric polymer nanostripes and nanopillars can be fabricated directly on soft, flexible substrates by soft-mold reverse nanoimprint lithography (reverse NIL) at 135 °C and at pressures as low as 3 bar.^3,4 The low pressure reverse NIL approach is compatible with flexible substrates with conductive thin film electrodes. More importantly, it leaves little or no residual polymer layer in-between the nanostructures, which obviates the need for additional etching processes that arise with conventional low-contrast nanoimprinting. The ferroelectric polymer nanostructures were highly uniform over large areas of at least 200 × 200 µm and had good crystallinity with nearly optimum (110) orientation. The ferroelectric properties of individual nanostripes or nanopillars were probed by piezoresponse force microscopy, which showed that they exhibited switchable and bi-stable polarization. In addition, the polarization hysteresis loops probed by pyroelectric measurements of the entire array showed that the nanostructure capacitor arrays had good ferroelectric switching characteristics, over areas of at least 1 mm × 1 mm.
Furthermore, our most recent results showed that ferroelectric nanostructures with remarkably smaller size beyond the designed nanoimprinting mold cavities could be prepared due to the unique nanoconfined self-assembly properties of the ferroelectric copolymer during the reverse NIL process. The reverse NIL method described here is a high-yield, low cost, scalable, and highly customizable method that provides a promising alternative to the traditional rigid-mold high pressure direct nanoimprinting processes. This method may facilitate future studies of functional polymer nanostructures for applications in flexible electronics, electro-mechanics, and energy harvesting.

[1] S. K. Hwang, I. Bae, R. H. Kim, and C. Park, Adv Mater 24 (44), 5910 (2012).
[2] L. Persano, C. Dagdeviren, Y. W. Su, Y. H. Zhang, S. Girardo, D. Pisignano, Y. G. Huang,
and J. A. Rogers, Nat Commun 4 (2013).
[3] J. Song, H. Lu, K. Foreman, S. Li, L. Tan, S. Adenwalla, A. Gruverman, and S. Ducharme,
J Mater Chem C (2016).(back cover)
[4] J. Song, H. Lu, S. Li, L. Tan, A. Gruverman, and S. Ducharme, Nanotechnology 27(1),015302 (2016).

The solubility of semiconducting polymers can be “switched off” using addition of a high electron affinity molecular dopant. Spontaneous charge transfer with the dopant generates an organic salt that is completely insoluble in non-polar solutions. Here we demonstrate both chemical and optical mechanisms by which the doping can be reversed and the solubility of the polymer is “switched back on.” Using these techniques, we are able to vertically stack and laterally pattern mutually soluble polymer layers, which are vital processing steps needed to expand the use of organic semiconductors in device applications. Optimization of these techniques has yielded diffraction limited optical film patterning with regular features of 200-300 nm with only solution processing steps and direct write laser patterning. Comparison of patterned and initial samples shows no change in the optical, electrical or chemical properties of the polymer. This means that the film is quantitatively dedoped after the patterning process is complete yielding intrinsic semiconducting polymer that is nano-patterned. Dopant induced solubility control (DISC) patterning offers a new avenue to process semiconducting polymers with applications in all areas of organic electronics and in particular for PV and thermoelectric devices.

Ordered non close packed (NCP) array with colloidal particles are central to various applications such as optics, photonics, sensing, surface patterning etc. We report a simple, facile spincoating based approach for fabricating two dimensional colloidal crystals with hexagonal and non hexagonal close packed (HCP) arrays with organic as well as inorganic colloidal particles on flat and nano patterned substrates, respectively. Appropriate amounts of surfactant molecules are added to the colloidal dispersion ahead of spin coating to ensure the formation of the HCP patterns. The non-HCP arrays are fabricated by spin coating the particles onto soft lithographically. The substrate patterns impose directionality to the particles by confining them within substrate grooves during spin coating, thereby breaking the hexagonal close packed symmetry into structures that are commensurative with the substrate patterns. Parameters like coating speed, dilution of the colloids, amount of surfactant added and volume dispensed provide a control over the formation of HCP as well as the number of layers deposited.
We have also developed a novel technique by which the HCP as well as non-HCP array of the colloidal particles can be transferred to planar as well as non-planar surfaces. For this purpose the colloidal arrays are fabricated on a sacrificial PMMA layer which is subsequently degraded by UV exposure, resulting in transfer of the particles onto any other substrate, including non-planar, curves and rough surfaces. This allows the colloidal structures to be transported across substrates irrespective of their surface energy, wettability or morphology. Since the particle array is transferred onto a substrate, without exposing it to any kind of chemical or thermal environment, it can be utilized for placing particles on top of thin film solar cells for improving their absorption efficiency, without subjecting the completed cell to any further solution processing.

References

1. R. A. Weiss, X. Zhai, and A.V. Dobrynin, Langmuir 24, 5218-5225 (2008).
2. N. V. Dziomkina, and G. J. Vancso, Soft Matter 1, 265-272 (2005).
3. P. Jiang, T. Prasad, M. J. McFarland, and V. L. Colvin, Appl. Phys. Lett. 89, 011908-011916 (2006).

Robust thermal radiation absorber with high absorbance is very attractive for detection applications. Quarter-wavelength coatings can realize high absorption but only for a particular wavelength. Metal-black coating can provide broad band absorption but it is very fragile. Anti-reflective nanostructures can reduce the reflection and improve the absorption of light from wide angles of incidence over a broad wavelength region. Based on the self-assembling of polyimide in oxygen plasma etching, an extremely low cost approach is developed to generate small controllable patterns for anti-reflective structure fabrication. By tuning dry etch recipes, inorganic nanopillar structures with heights of 200~ 700nm, diameters of 300~1000 nm and lateral spatial frequency in the range (1~10um^-1), are fabricated. With the combination of suitable stack layers and thin metal layer coating, perfect broad-band infrared absorber (nearly 100% absorption in certain wavelength regions) has been developed through suppressing the reflection because of the light bend propagation in fabricated subwavelength structure. This strategy can be applied to different materials to form tunable multi-band absorber for targeted applications.

Protein-based materials have the potential to change the current paradigm of material science. However, it still remains a challenge to preserve protein structure and functionality while making them readily processable. Our recent studies show that through the development of rationally designed statistically random copolymers, it is possible to stabilize proteins and process them in organic solvents, a common condition for material fabrication. Using horseradish peroxidase as model system, we have successfully tailored a polymer-based protecting agent that stabilizes enzymes at multiple hierarchical levels and has allowed for the retention of its activity when processed in organic solvents. Furthermore, the modularity of this approach has been confirmed through incorporation of other proteins that differ in size, surface chemistry, and functionality.

Dewetting is a phenomenon where thin film tends to rupture due to destabilizing attractive Van-der Waal’s interaction and formed isolated random droplets [1]. Dewetting study become very fascinating problem to encounter not only for understanding the fundamental physics but for fabrication of nanoscale or mesoscale non lithographic structure of soft materials like homo-polymer, block co-polymer,liquid crystal (LC) etc. Here, we have reported the dewetting and rupture mechanism of liquid crystal (5CB) thin film on patterned substrates (one dimension grating and two dimensions cross pattern) and then tried to co-relate the rupture mechanism with initial film thickness and surface structural effect. It is seen in experiments that rupturing of liquid crystal thin films on topographically patterned substrates is independent of surface heterogeneity which shows different mechanism than homo-polymer dewetting on patterned substrates. Pattern directed dewetting has been observed for homo-polymer like polystyrene on patterned substrates [2]. We have also reported the morphology, macroscopic orientation and phase transition of spin dewetted LC (5CB) meso scale droplets on flat and topographically patterned substrates. Spin dewetting is very unique process where dewetting and rupturing of an ultra thin film occurs during the spin coating process itself with very low concentration of casting material and formed isolated random droplets [3]. This spin dewetted random LC droplets were aligned by coating on different periodic structural surfaces. Complete dewetting and rupturing process of LC thin films as well as morphology and phase transition of spin dewetted LC droplets have been observed under optical polarised microscope and atomic force microscope platform.
References:
[1]. Reiter, G., Phys. Rev. Lett., 1992, 68, 75.
[2]. Roy, S., Mukherjee, R., ACS Appl.Mater. Interfaces., 2012, 4, 5375.
[3]. Bhandaru, N., Das, A., Salunke, N., Mukherjee, R., Nano Lett., 2014, 14(12), 7009.

Ultrathin unstable polymer films exposed to a solvent vapor dewet by the growth of surface instability, the wavelength of which depends on the film thickness. We show that meso patterns present on the surface of a polymer thin film can engender an ordered dewetted morphology under certain specific conditions. The pre-patterned polymer thin film undergoes pattern directed rupture along the thinnest parts of the film when the initial local thickness over these zones (h_rm) is reduced to a limiting thickness (h_lim » 10 nm). In addition, depending on the periodicity of the imprinted patterns, the wavelength of instability corresponding to h_rm must be lower than the width of the patterned grooves (l_s). A morphology phase diagram is constructed which indicates a transition from the surface tension induced flattening to the ordered pattern directed rupture. The versatility of this technique is shown in its ability to form myriad of aligned meso-patterns starting from a simple grating structure on the film surface. The morphology of the evolving patterns is controlled by several parameters including the initial film thickness (h_F), pre-pattern amplitude (h_st), duration of solvent vapor exposure and wettability of the stamp used for pre-patterning the film. The evolution can be interrupted at any intermediate stage by removal of solvent vapor thereby achieving patterns on demand, which are well ordered as well as significantly miniaturized as compared to features obtained from dewetting of a flat film of same initial thickness. This concept is further be extended in multi polymer systems for obtaining ordered structures by dewetting of a thin polymer bilayer with a topographically structured interface.

The self-assembly of solvent-annealed block copolymer thin films susceptible to microphase separate into cylindrical, lamellar and gyroid phases is investigated. Here, we report on untemplated and templated semicrystalline poly(1,1-dimethyl silacyclobutane)-block-polystyrene (PDMSB-b-PS) thin films enabling the production of highly-ordered patterns with sub-10 nm features. These periodic structures, consisting of easily etchable PDMSB cylinders or lamellae with an out out-of-plane orientation separated by PS domains, are suitable for next generation lithography. We also explore the directed self-assembly of sub-100 nm thick PDMSB-b-PS layers into a double gyroid structure with long-range 211 plane ordering achieved by using topographical substrates. Such a morphology consisting of two continuous interpenetrating networks in 3D space makes them a good candidate to fabricate efficient device active layers.

We demonstrate a solvent-free, low temperature (25-170 °C) approach using chemical vapor deposition (CVD) grafting and polymerization processes to passivate the unpaired electrons or “dangling” bonds on the surface of silicon. These bonds behave as charge carrier recombination centers, thereby lowering the overall operating efficiency of silicon devices for applications like photovoltaics. The multifunctional (dielectric and electronically conducting) passivating layers described in this work achieves several orders of magnitude improvement in minority carrier lifetime (> 2 milliseconds) compared to bare silicon (~ 30 microsecond), and remained stable in air for over 200 hrs. These values approach that of silicon nitride (SiNx) films deposited at significantly higher temperatures (> 400 oC).

Two CVD polymerization processes were carried out in sequence, namely initiated (iCVD) and oxidative (oCVD). iCVD covalently grafts the polymer film directly onto the silicon substrate by initiating a chemical reaction between the surface hydride bonds on silicon and the reactive vinyl (C=C) groups on the monomer; thereby satisfying surface dangling bonds and “passivating” electrically active interface states. We explored three iCVD monomers of varying sizes, which polymerize to form dielectric passivation layers. To obtain the conducting passivation layer, oCVD was used to graft poly(3,4-ethylenedioxythiophene) (PEDOT) films to the unreacted vinyl groups of the iCVD grown polymer layer.

The polymer passivation processes can reduce surface recombination rates through a combination of (1) reduction of the surface state density (iCVD) and (2) adjustment of the charge (electron or hole) carrier concentrations at the silicon surface by altering interfacial band bending (oCVD). We demonstrate this results using a combination of quasi-steady state and transient photoconductance measurements; effective charge and band bending calculations; and surface characterization using x-ray photoelectron spectroscopy (XPS). Passivation quality also improved on grafting aliphatic monomers compared to aromatic ones suggesting a reduction in steric effects in the former, helping us posit design rules for polymer based surface passivation of silicon. Additionally, tests using a nanomechanical tester reveal that grafting eliminates cracking and delamination via the strong covalent chemical bonds formed at the substrate-film interface.

The mild CVD processes retain delicate organic functionalities in the monomers, enabling the subsequent growth of both insulating/dielectric and conducting polymer layers on top, potentially serving diverse functionalities. Examples in solar cells include dielectric antireflective coatings and patterned conducting polymer grids to replace the expensive silver metallization. Finally, the ability to use an electrically conducting polymer for passivation creates a direct interface between traditional silicon microelectronics and organic electronics.

Hierarchical porous structured materials are highly desirable for a large plethora of applications, ranging from separation, sensing, energy conversion and storage, to tissue engineering. However synthesis of hierarchical materials with multi-dimensional complexities and novel functional properties remains challenging. Here we describe the controlled generation of hierarchically porous polymer structures and shapes coupling block copolymer-directed self-assembly with spatially localized transient laser irradiation. The combined approach further provides pathways to electrically conducting carbon structures, as well as generation of complex crystalline silicon nanostructures. The method is compatible with standard semiconductor manufacturing processes and suitable to fabricate porous structures with high surface area and connectivity for integrated energy storage and sensing applications.

The vast majority of photocatalysts for overall water splitting are inorganic materials, such as metal oxides. In this talk, I will discuss the use of organic polymers as water splitting catalysts. I will present recent advances in photocatalytic hydrogen evolution using conjugated organic polymers in the presence of a sacrficial hole scavenger [1, 2], focusing on the potential advantages of polymers such as band gap tuning and solution processability. I will then discuss the prospects for using organic polymers as components in materials or devices for overall photochemical water splitting. The talk will also discuss the advantages and disadvantages of organic polymers as photocatalysts with respect to the widely studied class of materials known as graphitic carbon nitrides [3].

1. R. S. Sprick, et al., J. Am. Chem. Soc., 2015, 137, 3265-3270
2. R. S. Sprick, et al., Angew. Chem. Int. Ed., 2016, 55, 1792-1796
3. X. Wang, et al., Nature Mater., 2009, 8, 76-80

Organic framework polymers, including both metal-organic and fully covalent networks, hold promise as materials for gas absorption, membranes, and organic electronics. In all three of these applications, attaining in-plane ordering of backbone conducting channels and porous free volume is the most critical feature from the material structure that impacts the ability to adsorb gas, selectively filter molecules, and conduct charges. In this work, hard and soft x-ray scattering and soft x-ray spectroscopy are of focus to study the pore structure, texture and electronic structure of fully covalent organic framework (COF) thin films. Using GIWAXS and x-ray absorption spectroscopy (XAS), it is shown that thin film formation of an imine-based COF is quite complex, where three different solution growth stages govern the texture and thus pore directionality control. The synergy of GIWAXS and XAS with electronic structure modeling is then highlighted towards doping studies; charge transfer salts as well as ionic liquids are used to electrochemically dope the COF material, following which it is shown there will be a balance between transistor mobility optimization and COF order degradation, which will lead to a deleterious performance effect. Finally, control over pore order in ladder polymers, in which the inefficient packing of rigid conjugated polymer backbones inherently produces porous free volume, is illustrated and monitored by SAXS studies at hard and resonant (carbon K edge) photon energies. We demonstrate that control over pore size and distribution is possible by controlling aggregation of the conjugated polymer in solution, as observed by SAXS, and during film formation by control of the drying rate. In this talk, focus will be placed on state-of-the-art x-ray scattering and spectroscopy, highlighting the importance of chemically sensitive structural information enabled by the combination of spectroscopy and scattering at play with the use of resonant soft x-rays.

Block copolymer-directed assembly is a versatile tool for synthesizing porous functional materials with high surface area that can be tuned for various applications from separation to energy conversion and storage. A process called self-assembly and non-solvent induced phase separation (SNIPS) is used to make graded, hierarchically porous materials which have increased pore accessibility, diffusion, and flux. In the SNIPS process, block copolymer solutions are cast into membranes with an ordered mesoporous surface layer atop a graded asymmetric macroporous support structure. We have developed a one-pot synthesis route to co-assemble block copolymers and organic additives to obtain graded, hierarchically porous all-organic materials. Heat treatment up to 1100°C under an inert environment creates amorphous carbon materials that are potentially useful as electrode materials in energy conversion and storage.

In this presentation, we show self-assembly of highly fluorescent energy-donating and accepting polymers from their mixture in a solution.¹ Recently, we have developed a technique to fabricate well-defined microspheres from π-conjugated polymers.^2–3 We found that these microspheres act as both fluorophore and resonator; the fluorescent microcavities exhibit resonant PL from whispering gallery modes (WGM) upon focused laser excitation.^4–6 The polymers used in the present research, when assembled alone (homotropic assembly), form well-defined spheres with sub- to several-micrometer in diameter that depends on their molecular weight. On the other hand, when assembled from their mixed solution (heterotropic assembly), the polymers with mismatched molecular weights are immiscible with one another, only giving irregular aggregates. However, when molecular weights are identical and the nucleation time and growth rate of the polymers match well under the vapor diffusion condition, well-defined microspheres are formed exclusively. Photoluminescence (PL) experiments clearly show that an efficient FRET occurs inside the microspheres, indicating that these polymers are highly miscible with one another in the microspheres. Upon focused laser excitation, a single microsphere exhibits WGM PL as a result of the confinement of PL inside the microsphere. The PL color shifts systematically, depending on the mixing ratio of the polymers. Furthermore, by connecting the microspheres, long-range PL propagation and subsequent color conversion are achieved. The self-assembly strategy for obtaining highly miscible polymer blends within nano- to microstructures will be advantageous for the use of electronically and optically active polymers to optoelectronics device applications.

References
[1] S. Kushida et al., ACS Nano 10, 5543–5549 (2016).
[2] T. Adachi et al., J. Am. Chem. Soc. 135, 870 (2013).
[3] L. Tong et al., Polym. Chem. 5, 3583 (2014).
[4] K. Tabata et al., Sci. Rep. 4, 5902 (2014).
[5] S. Kushida et al., Macromolecules (2015).
[6] D. Braam et al., Sci. Rep. 6, 19635 (2016).

The self-assembly of block copolymers provides a powerful platform to produce well-defined, periodic nanoscopic patterns useful for nanostructural engineering of energy materials. Nevertheless, its employment in scalable manufacturing methods requires the formation of self-assembled morphologies with long-range order across large substrates in minute time scales. This imperative is especially difficult to fulfill with large molecular weight block copolymers, where ordering is severely kinetically hindered by chain engtanglement and large segregation strength. We show that ternary blends of symmetric polystyrene-block-poly(methyl methacrylate) block copolymers (PS-PMMA) and equal parts of much smaller molecular weight PS and PMMA homopolymers order very rapidly. Thermal annealing of a blend shows a clear increase in the power law exponent for grain coarsening with respect to the neat block copolymer, without dramatically changing the natural period. The blends are also compatible with solvent vapor annealing; a block-copolymer with molecular weight > 500 kg/mol blended with 50% (w/w) homopolymer annealed in tetrahydrofuran vapor can self-assemble with linear grain sizes over 10 times the grain size of the neat block copolymer solvent annealed under the same conditions.

Organic charge-transfer superstructures are a family of crystalline polymeric materials with promising applications in optoelectronics, thermoelectrics and spintronics. Although active research on the design and synthesis of organic charge-transfer complexes has been ongoing for almost two decades, the crystallization mechanism of organic charge-transfer superstructures remain poorly understood. Here we report three dimensional assembly of a spherical organic charge-transfer superstructure through solvent-annealing. A detailed processing condition-dependent study of superstructure formation reveals that the de-wetting and drying-mediated assembly processes are responsible for the spherical crystallite formation. The assembled spherical superstructures are highly tunable, crystalline and chemically stable, exhibiting visible light photoresponsive behavior. This simple, generalizable three-dimensional assembly can be modified for the formation of ordered functional organic superstructures for emerging applications.

The growing interests in wearable electronic devices, roll-up displays, and portable gadgets have propelled the advancement of flexible energy storage electrodes. Single-walled carbon nanotubes (SWCNTs) potentially offer a high percentage of electrolyte infiltration, small ion-transport resistance, short solid-state ion diffusion path length, as well as to dissipate the stress associated with electrode expansion and contraction for energy storage or conversion. MXenes, a new class of two-dimensional (2D) early transition metal carbides and carbonitrides, have also shown promising performance in electrochemical energy storage. In comparison, conducting polymers are flexible and easily processable. Here, I will discuss three polymer hybrid systems as electrodes for flexible energy storage. First, we prepared free-standing, flexible lithium ion battery electrodes via in situ synthesis of hybrid aerogels consisting of interpenetrating single-walled carbon nanotubes and polyaniline (PANI) nanoribbons with high capacity (185 mAh/g) and good cycling performance of nanocomposites (500 times). Assisted by the surfactant assemblies on SWCNTs, ultrathin PANI nanoribbons (thickness of 10–100 nm, width of 50–1000 nm, and length of 10–20 μm) are formed within the SWCNT network. Because of the intrinsic flexibility of nanotubes and nanoribbons and the double interpenetrating network, the nanocomposite film is bendable up to 180°. We then prepared triple networks of macroporous cellulose fibers, SWCNTs, and PANI nanoribbons as foldable supercapacitors. The hybrid material showed good volumetric (40.5 F/cm³) and areal capacitance (0.33 F/cm²), attributed to the synergistic effect between electron transport within the SWCNTs network and fast charge transfer of the PANI nanoribbons. The composite films could be folded back and forth as an origami crane up to 1000 times without mechanical failure or loss of capacitance. Lastly, I will present our recent work of self-assembling MXene/CNT composites on electrospun polycarpolactone (PCL) fibers for flexible, high performance supercapacitor.

Edible electronics are a specialized subset of medical devices with prospective applications in the diagnosis and treatment of many different types of disease states within the gastrointestinal tract. Edible electronics require novel materials for on-board electrochemical storage (e.g. batteries) that balance important figures of merit such as performance and cost-effectiveness with toxicity and intrinsic risk to the patient. Here we will present recent advances on the use of redox active biologically-derived melanin pigments as electrode materials for prospective use in batteries to power ingestible electronic devices. Specifically, melanin pigments are platform materials can be used as either anodes or cathodes in aqueous electrochemical storage systems with various battery chemistries. In addition to technological applications, electrochemical cells with systematic variation of the cation can also probe the enigmatic structural motifs of this class of biopolymers. Finally, recent work on the use of melanin pigments for selective cation separation will be presented. Taken together, these results broadly inform the structure-property-processing relationships in both natural and synthetic eumelanin pigments.

Supramolecular polymeric hydrogels are promising for a range of biomedical and industrial applications on account of their dynamic behavior such as shear thinning and self-healing properties. While noncovalent interactions between polymer chains within the hydrogels have been extensively investigated, the incorporation of nanoscale objects enables unique tuning of hydrogel structure leading to emergent functions. We report a novel means to assemble hierarchical supramolecular polymer-colloidal hydrogels (SPCH).

Functionalized polymer-grafted silica nanoparticles were incorporated into a supramolecular hydrogel of a hydroxyethyl cellulose derivative assembled in water with cucurbit[8]uril. The resulting material (98 wt% water) exhibits extraordinary elasticity and can be drawn into uniform ‘supramolecular fibers’ at room temperature with an aspect ratio > 1 x 10⁵ and an uniform diameter of 6 µm.

The hierarchical nature of the SPCH composite is readily confirmed through high-resolution microscopy; supramolecular fibers result from dehydration of the hydrogel filament, which in turn is comprised of nanoscale fibrils with dispersed silica particles (filler) in a cellulose matrix. The composite is remarkably different to hydrogels assembled from two linear functional polymers, suggesting that the high elasticity of the SPCH emerges the realignment of from nano fibrils during the drawing process.

Moreover, the mechanical properties of these supramolecular fibers were investigated illustrating better tensile properties and superior stiffness compared to conventional regenerated fibers (e.g. cellulose-based viscose, and protein-based artificial silks) and animal hair. Cyclic loading tests suggest that these fibers are efficient at absorbing energy with a very high damping capacity (60-70%), comparable to viscose.

The systematic study of the SPCH provides profound understanding of self-assembled materials demonstrating a novel manufacturing process for fiber materials, leading to the first ‘supramolecular fiber’ prepared from high water content (98%) at room temperature. SPCH represent a new class of hybrid supramolecular composites, opening a new window into fiber technology through low-energy manufacturing from a broad range of sustainable materials.

Advances in modern electronics require the development of polymer-based dielectric materials with high dielectric constant, low dielectric loss, and high thermal stability. Fundamental dielectric theory suggests that weakly-coupled strongly dipolar materials have the potential to reach relatively higher dielectric constant than the widely used non-polar or weakly dipolar polymers. These materials possess a high glass transition temperature (T_g >200°C), hence may lead to high operating temperature (>150°C).
In dipolar polymers, it is well known that above glass transition (T_g), there is a large increase in the dielectric constant, due to the creation of “free volume” around the dipoles. For example, polyvinyl chloride (PVC), an amorphous polymer, has a dielectric constant of ca. 3 and low loss at temperature below T_g, which increases to K>9 above T_g. The penalty is that the dielectric loss is also increased markedly (loss > 5%). The large increase in the dielectric constant observed above T_g in these strongly dipolar polymers is attributed to an increase of the empty spaces surrounding the dipoles termed “free-volume effect”, which makes it easier for dipoles to follow the applied field, and hence reach a higher dielectric constant. However, large-chain-segment motions above T_g, which have long relaxation times also causes high dielectric loss. The challenge is to design a strongly dipolar polymer that can generate the “free volume effect” at temperatures below T_g, thus leading to high K while avoiding large-chain-segment motions causing dielectric loss.
In this study, an approach to enhance the dielectric response of strongly dipolar polymers has been investigated by making blends of strongly dipolar polymers. The polymer blend of aromatic polythiorea (ArPTU) and polyetheretherurea (PEEU) shows exceptionally high dielectric constant while maintaining the low loss, which is the result of increased free volume due to the nano-interfaces between two dissimilar, but not phase separated polymers. The experimental results show that the blending of two dipolar polymers in the glass state introduces nano-structured interfaces which has the potential to create “free volume” for easier reorientation of dipoles to external field and improve the dielectric response while maintaining the low loss. This study uncovers a new path to design polymers with high dielectric constant, without compromising the low loss.

Electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) are the two most powerful approaches for harvesting ambient mechanical energy, but the effectiveness of each depends on the triggering frequency. Here, after systematically comparing the performances of EMGs and TENGs under low-frequency motion (<5 Hz), we demonstrated that the output performance of EMGs is proportional to the square of the frequency, while that of TENGs is approximately in proportion to the frequency. [1] Therefore, the TENG has a much better performance than that of the EMG at low frequency (typically 0.1–3 Hz). Importantly, the extremely small output voltage of the EMG at low frequency makes it almost inapplicable to drive any electronic unit that requires a certain threshold voltage (∼0.2–4 V), so that most of the harvested energy is wasted. In contrast, a TENG has an output voltage that is usually high enough (>10–100 V) and independent of frequency so that most of the generated power can be effectively used to power the devices. Furthermore, a TENG also has advantages of light weight, low cost, and easy scale up through advanced structure designs. All these merits verify the possible killer application of a TENG for harvesting energy at low frequency from motions such as human motions for powering small electronics and possibly ocean waves for large-scale blue energy. [1]: Y. Zi, et al, ACS Nano, 2016, 10 (4), pp 4797–4805

Over the last decade, flexible and stretchable electronics has emerged as the next-generation functional devices and has attracted extensive interests from both academia and industry. To achieve stretchable, self-powered electronic systems, however, the development of stretchable energy generation devices deserves more attention. In this work, a type of highly stretchable triboelectric nanogenerators made from conventional, inelastic materials such as nanopatterned FEP and PET thin films, is presented. Its stretchability originates from the rationally designed interlocking kirigami structure instead of constituent materials, and thus enables stretchable triboelectric nanogenerators to be made from materials without intrinsic stretchability. The fabricated devices sustain an ultrahigh tensile strain up to 100% and are capable of harvesting energy from various types of motions such as stretching, pressing and twisting owing to the shape-adaptive thin film design. Energy harvested from the as-fabricated devices has been used for powering a LCD screen and lighting LED arrays. Furthermore, the thin-film-based devices have also been demonstrated for self-powered acceleration sensing and self-powered sensing of book opening and closing. This work introduces traditional kirigami into the development of stretchable triboelectric nanogenerators and verifies its promising applications in both power generation and self-powered sensing.

We have described the development of a permanent biocompatible electrode material for supercapacitors that circumvents the need for passivation by using body fluid electrolytes in an open configuration device. To reduce toxicity and improve capacitance, a composite of MnO₂ nanoparticles (NPs) embedded in multi walled carbon nanotubes (MWCNTs) serves as the positive electrode, and phosphidated activated carbon (pAC)—phosphidation enhances the biocompatibility—serves as the negative electrode. To minimize the risk of leakage and the limited operation life compared to other energy storage devices that contain toxic electrolytes, we applied this device to open systems using body fluids containing various ions (Na⁺, K⁺, Ca²⁺, Cl^-, and HCO₃^-) as electrolytes with a minimal loss of capacitance. By assembling implantable devices with biocompatible two electrodes, our technique avoids the problem of performance degradation and toxicity which limits number of reactions which can be carried out in body fluids. The bio-functionalized two electrodes successfully are implanted in the body of rat that enables stable performance of supercapacitor using body fluids. These findings establish the plat form towards biocompatible and potential material for implantable energy storage device in implantable electronic medical devices.

A novel composite structured film impregnated with cellulose nanocrystal flakes (CNCFs) as effective dielectric is demonstrated to enhance the generator performance and energy conversion efficiency based on vertical contact separation mode. This facile and scalable technique provides a promising solution for developing large-scale and practical self-powered devices, and stimulates the development of green high performance triboelectric generator. The orientated and uniform distributed CNCFs made it possible to fabricate cellulose composite structured triboelectric generators (CTGs, 1.5cm×1.5cm) with an open-circuit voltage of 320 V and a closed-circuit current density of 5 µA cm^-2, resulting in a high output power of 8.7 mW under period compression, giving a 10-fold power enhancement in comparison with a pure film based triboelectric nanogenerator (TGs). The enlarged friction area between CNCFs and PDMS matrix and improved flexibility of PDMS composites films enhanced the electric output performance (i.e., open-circuit voltage, closed-circuit current, instantaneous power, and energy conversion efficiency). The enhanced power of CTGs was capable of instantaneously lighting up as many as 100 multicolor commercial LEDs.

Luminescence is a type of cold body radiation caused by external stimuli such as mechanical stress, photo-absorption, electric field and chemical reactions. Distinct types of stimuli yield corresponding important applications that cover a wide spectrum of areas including lighting, displays, disinfection, medical imaging and horticulture. Here, we report a novel motion-driven luminescence. It is essentially a type of triboelectrification-induced electroluminescence (TIEL) that converts dynamic motions into luminescence upon extremely gentle mechanical interactions. The TIEL relies on the coupling between triboelectrification and electroluminescence. Tribocharges resulting from relative dynamic interactions between two dissimilar materials can abruptly and significantly alter the surrounding electric potential by as high as hundreds of volts within milliseconds. Such a drastic change of the electric potential can excite the electroluminescence (EL) of underlying phosphor along the motion trajectory. The TIEL possesses prominent features. First, it is non-destructive to materials and thus has excellent stability, repeatability and durability. Second, it can be excited by extremely weak stimuli. The threshold stress is as low as less than 10 kPa, three orders of magnitude smaller than that for elastico-triboluminescence; and the threshold velocity is less than 1 cm/s. Third, the stress responsivity in a low-stress region (<20 kPa) reaches up to 0.03 kPa-1, presenting a 750-fold enhancement over the ETL. In addition, the light emission is achieved in atmospheric pressure instead of vacuum. As a demonstration of potential applications of this novel effect, position locating and motion tracking in a high-spatial resolution are achieved with the assistance of a software interface. Therefore, the TIEL is a new approach for a variety of applications including security surveillance, electronic commerce, anti-counterfeiting and illumination.

References
X. Y. Wei et al. Dynamic triboelectrification-induced electroluminescence and its use in visualized sensing Advanced Materials, DOI: 10.1002/adma.201600604.

Poly(vinylidene fluoride) (PVDF) has been extensively investigated due to its piezoelectric and ferroelectric properties as well as its excellent thermal and chemical stability. Due to these attractive properties, PVDF has found applications ranging from energy harvesting in electromechanical devices to battery electrolytes and chemically inert lining in pipelines. The β crystal form of PVDF has the highest piezoelectric response. One of the most common methods for enhancing the fraction of β-PVDF is uniaxially stretching PVDF films. In this work, mechanically isotropic and uniaxially oriented samples of PVDF are investigated using simultaneous tensile testing and Brillouin light scattering. This unique combination of techniques enables concurrent measurement of the adiabatic longitudinal modulus and the isothermal tensile modulus of a sample under uniaxial tensile strain. The longitudinal modulus can be measured in the direction parallel or perpendicular to the applied strain as well as any direction in between. Changes in these two moduli are related to stress- and strain-induced microstructural developments such as crystallization, crystallite alignment, and the formation of fibrils. The results from this work provide deeper insight into the effects of processing conditions on the formation of β-PVDF. The technique provides a means for structural characterization that can be more generally applied to polymeric materials.

Traditional solar power applications largely avoid using the infrared spectrum. Nevertheless, this region makes up almost half (~45%) of the solar power spectrum and therefore represents an untapped resource. Temperature control of buildings represents a significant cost for both businesses and private consumers. We are interested in using thermochromic materials as building coatings to help moderate solar infrared absorption and thereby offset temperature control costs for buildings. Our initial effort in this study has been to characterize materials which might represent starting points for our research. We designed and 3D-printed an optical test platform to perform reflectance measurements with an ultraviolet-visible-near infrared spectrometer over a spectral range from 350-1100nm. The test platform was constructed so that the temperature can be adjusted in real time using Peltier modules. In our experiments, temperature measurements were made using thermocouple probes and an infrared remote thermometer. We examined candidate thermochromic materials including liquid crystals and fluoran-type leuco dyes, measured spectra for both materials at temperatures from 15-40°C, and integrated to obtain overall reflectance data. The total reflectance of the liquid crystal sample never exceeded 5%, whereas the reflectance of the leuco dye samples was around 15% below the transition and nearly 50% above the transition. The reflectance and reflectance transition for the liquid crystal samples were both less than for the leuco dye samples, from which it can be concluded that the leuco dye samples are better candidates for building coatings. Both of the studied materials exhibited reflectance transitions in the visible spectrum, but lacked a strong transition in the infrared spectrum. Our next step will be to chemically modify existing leuco dye structures and to immobilize the leuco dyes in polymer matrices in order to more efficiently access and switch the near- and mid-infrared wavelengths of the solar spectrum. We seek a recursive approach linking synthesis, analysis, and simulation.

Bulk heterojunction polymer solar cells (PSCs) have attracted wide scientific attention since their emergence, because of their low cost and easy fabrication as well as flexibility. However, the device performances remain inferior to inorganic solar cells, hindering their widespread use in practical device applications. A detailed understanding of the multiscale structure-properties-performance relationships of these systems is required to overcome the current limitations of the PSCs. In particular, fundamental understanding of the electrical and optoelectronic properties of the active layer of PSCs as well as their dependence on nanoscale features in their morphology is indispensable to advance the device performances.

In this work, photoconductive atomic force microscopy (AFM) is applied in conjunction with highly sensitive nanoscale morphology imaging to establish connections between the morphology and the electrical properties of the active layer of PSCs. Morphology information is acquired by tip scanning in tapping mode. After applying a bias through a conductive AFM cantilever with tip radius of ~10 nm, I-V curves are acquired at selected locations across the region of interest. A 532 nm green laser is focused tightly through a top-illumination to illuminate the sample area around the tip of the cantilever in contact with the sample. With this approach, the morphology, electrical properties and optoelectric performances are studied simultaneously with nanoscale resolution. This work provides a deeper insight of the intrinsic correlation of nanostructure, local electrical properties and optoelectric performances of the device of which the active layer is made from blends of polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7): indene-C60 bisadduct (ICBA) in a binary (chlorobenzene (CB)/1, 8-diiodooctane (DIO)) solution

The formation of two-dimensional (2D) polyaniline (PANI) has attracted considerable interest due to its expected electronic and optoelectronic properties. Although PANI has been discovered over 150 years ago, obtaining an atomically well-defined 2D PANI framework has been a longstanding challenge. Here, we describe the synthesis of 2D PANI via the ‘direct’ pyrolysis of hexaaminobenzene trihydrochloride single crystals in solid state. The 2D PANI consists of three phenyl rings sharing six nitrogen atoms, and its structural unit has the empirical formula of C₃N. The topological and electronic structures of the 2D PANI were revealed by scanning tunnelling microscopy and scanning tunnelling spectroscopy combined with a first-principle density functional theory calculations. The electronic properties of pristine 2D PANI films (undoped) showed ambipolar behaviours with a Dirac point of –37 V and an average conductivity of 0.72 S/cm. After doping with hydrochloric acid, the conductivity jumped to 1.41 × 10³ S/cm, which is the highest value for doped PANI reported to date. Although the structure of 2D PANI is analogous to graphene, it contains uniformly distributed nitrogen atoms for multifunctionality; hence, we anticipate that 2D PANI has strong potential from wet-chemistry to device applications beyond linear PANI and other 2D materials.

Obtaining the control over optoelectronic properties in organic semiconductors with doping is essential for advancing relevant device applications. Here we investigate the electron transport, photoresponse, photocurrent, and nanomorphology in a model system P(NDI2OD-T2) n-doped with a moderately air-stable ruthenium organometallic dimer, RuCp*Mes. We found that the electron mobility of P(NDI2OD-T2) diodes can be enhanced by more than one order of magnitude with reduced thermal activation energy using with RuCp*Mes dopants. This reduction is rationalized by the fill up of tail electronic states by doping induced mobile carriers. N-doping with RuCp*Mes also helps improve electron injection at the Schottky contacts in nanoscale transport measurements obtained by conductive atomic force microscopy (c-AFM). Upon irradiation, we observed an enhancement of photocurrent after doping by using photoconductive AFM, which is a combined result of enhanced electron injection and mobility, leading to improving charge sweep-out rate. We found that the RuCp*Mes dopants are homogenously distributed throughout the P(NDI2OD-T2) film at moderate doping concentrations. Our results demonstrate an opportunity of using air-stable molecular n-doping to modulate charge transport properties for solution-processed organic optoelectronic devices.

Lithium-ion batteries (LIBs) have been commercially applied in various portable electronic devices nowadays. Ever increasing interests are inspired to study on improving the power density, efficiency and safety of LIBs. It is recognized that developing proper electrode materials is one of the key steps in the process to optimize the practical implementation of LIBs. A major challenge for LIBs is the complicated thermodynamic equilibrium because of the inevitable side-reactions occurred at electrode/electrolyte interface. A promising strategy is to develop composite material with tunable surface chemistry. Carbon has been commonly utilized as a component to associate with various anode and cathode materials, due to its superior electrochemical stability, electronic conductivity, tunable microstructure and low cost. The principle for introducing carbon to fabricate composite is to address the limitation of single active material without excessive interference. Therefore, it is necessary to develop a general and controllable approach by using facial techniques.

In this work, we propose a design to build a hierarchical architecture for efficiently encapsulating the active material in porous carbon matrix. To confirm the viable design, pristine anatase TiO₂ nanoparticles of 5 nm size are synthesized and used as active material. The obtained TiO₂ nanoparticles are confined in the porous carbon matrix which is derived from pyrolyzing poly(acrylonitrile-co-styrene). As an essential component in the design, the carbon matrix derived from the polymer not only offers a continuous and porous matrix for promoting electron/ion transfer and accommodating active material, also buffers the possible internal stress upon cycling. The physiochemical properties of the carbon, e.g. graphitization and porosity are studied in details via varying carbon fractions in composites at various pyrolysis temperatures. When applied as anode material for LIBs, the TiO₂/carbon composites enable excellent capacity, stable rate and cycling performance. Applying the design to develop composite active materials for LIBs allows a promising utility of insulate material with high theoretical capacity, such as silicon for cathode, to build highly performed LIBs.

Nanostructures of oxide semiconductors, particularly titanium oxide and zinc oxide, have been widely studied as promising candidates for optoelectronic applications including sensors, solar cells, and energy storage devices. As an effective method for generating nanostructures over large areas, nanostructures of block copolymers have been intensively investigated because they self-assemble into periodic nanostructures, of which the size and morphology can be controlled by the molecular weight and composition of copolymers. Their thin films and micelles have been utilized for the fabrication of inorganic nanostructures including metals and oxides. Furthermore, nanostructures of diblock copolymers can be ordered into specific orientations by the directed self-assembling technique. In this study, we employed diblock copolymer templates having lamellar or cylindrical nanodomains to fabricate nanostructures of titanium oxide and zinc oxide with sol-gel methods. The fabricated nanostructures of titanium oxide were further utilized in photovoltaic devices of perovskites. In addition, we oriented nanodomains of diblock copolymers by directed self-assembly in order to obtain well-aligned oxide nanostructures which were applied to hard templates, sustainable with organic solvents or at high temperatures, for assemblies of functional polymeric nanostructures.

Optical microcavities play an important role for the next-generation light technology. Recently, we succeeded in fabricating spherical microcavities from π-conjugated polymers (CPs) by simple self-assembly process.^[1,2] We found that the microcavities show whispering gallery mode (WGM) resonant photoluminescence (PL) upon focused laser excitation, where PL generated inside the sphere is confined via total internal reflection at the polymer/air interface.^[3–8] The resonance occurs when the wavelength of the light is an integer multiple of the circumference of the microsphere.
The CP-based microcavities have benefits to the conventional microcavities in the following points: [1] simple and low-energy fabrication process to obtain well-defined microspheres, [2] the microcavities function as both cavity and emitter, [3] the microcavities have high refractive index and photoabsorptivity, and [4] potent use for electrically-driven WGM and laser oscillation. In this presentation, recent results on the fundamentals of the self-assembly of the CPs, resonant PL from the CP microspheres, intra- and intersphere light energy conversion, and the future prospects to realize light-, electrically-, and chemically-driven WGM and lasing will be presented.

References
1) T. Adachi, et al., J. Am. Chem. Soc. 2013, 135, 870−876.
2) L. Tong, et al., Polym. Chem. 2014, 5, 3583−3587.
3) K. Tabata, et al., Sci. Rep. 2014, 4, 5902/1−5.
4) S. Kushida, et al., Macromolecules 2015, 48, 3928−3933.
5) S. Kushida, et al., ACS Nano 2016, 10, 5543–5549.
6) D. Braam, et al., Sci. Rep. 2016, 6, 19635/1–6.
7) S. Kushida, et al., RSC. Adv. 2016, 6, 52854–52857.
8) Y. Aikyo, et al., Chem. Lett. 2016, in press.

Surface patterning of polymers with nanometer dimensions is critically important to advances in nanoscience and energy technology. The nanoimprint technique may play a future role in polymer surface patterning as a replacement for projection type photolithography because of its advantages of simple, low-cost, and high-throughput production. The resolution limit of nanoimprinting has attracted much attention from both scientific and industrial field. In this work, we presents the following exciting results on nanoimprint fabrication of 0.3 nm-high atomically stepped flexible & conducting polymer sheets coated with ITO thin films or Au nano-patterns [1-3].
The atomic-scale surface patterning with a vertical resolution of 0.3 nm was performed on poly(methyl methacrylate) (PMMA) polymer sheets as well as thermostable polyimide sheets by thermal nanoimprinting using an atomically stepped sapphire template (α-Al₂O₃ single crystal). The present 0.3 nm-high atomic step & terrace surface morphology of the polymer sheets was stable for over a year.

On the 0.3 nm-high atomic step-and-terrace surface of the flexible and transparent polyimide sheet, the smooth and atomically stepped indium tin oxide (ITO) transparent conducting thin films could be deposited, leading to development of the new nanostructured polymer electrodes for energy-conversion devices.

Large area Au-nanoarrays of dot or mesh were produced onto the 0.3 nm-high stepped ultra-smooth PMMA sheets by applying a nanocontact-print technique using the Au-film coated pillar or mesh molds.

We will also report the electrical and optical properties of the 0.3 nm-high atomically stepped polymer sheets coated with ITO thin films or Au nano-patterns as well as thermal stability and the influence of the nanoimprint conditions on the pattern transfer.
[1] G. Tan et al., Appl. Phys. Express, 7 (2014) 055202.
[2] M. Yoshimoto, Applied Physics A, 121 (2015) 321
[3] G. Tan et al., Polymer Journal, 48 (2016) 225.

Flexible thermal conductors are used to provide tailored heat transfer pathways in a variety of advanced energy conversion devices ranging from thermoelectric generators and solar cells to wearable and high-performance microelectronics. Interfaces in such devices require materials to provide low-resistance heat transfer pathways between heat sources and heat sinks while offering mechanical flexibility to maintain device integrity under thermomechanical stresses. Nanostructured hybrid inorganic-organic composites provide an opportunity to combine the mechanical flexibility of a polymer with the high conductivity of inorganic fillers. In this work, we demonstrate a method to synthesize and implement polymeric composites containing a dense array of vertically-aligned copper nanowires that retain the high thermal conductivity of the nanowires while preserving the mechanical flexibility of the polymer matrix. The high aspect ratio nanowires accommodate bending and other mechanical deformation of the composite while the vertical alignment of the nanowires ensures percolation and minimizes the length of the conduction pathway. The nanowire arrays are synthesized using templated electrodeposition and infiltrated with a polymer matrix to generate a fully-dense multifunctional composite. This process allows for the facile synthesis of nanostructured composites over macroscale areas larger than ~1 cm² as required for practical implementation in many devices. The effective thermal conductivity is measured to be as high as 70 W m^-1 K^-1 for 25% dense nanowires in PDMS, an increase of more than two orders of magnitude compared to unfilled PDMS. In contrast, the mechanical flexibility is primarily derived from the interstitial PDMS matrix surrounding the high aspect ratio nanowires, which provides elasticity and flexibility to the otherwise ductile nanowires. The effective properties of composite media are functions of both the composition (i.e. how much of each constituent material is present) and the morphology (i.e. how the different constituent materials are arranged within the composite). We describe the transport phenomena and mechanical properties of these composites through multiscale models that capture both the macroscale effective medium characteristics and the nanoscale effects on conduction, mechanics, and inorganic-organic interfacial interactions. Furthermore, the use of a percolating metallic conduction pathway also enables the composites presented here to be used as flexible electrodes due to the high electrical conductivity. We expand the analysis to examine the broader materials design space for multifunctional polymeric composites having complex nano-architectures and morphologies to create unique property combinations not found in nature for advanced energy conversion technologies.

Semiconductor nanocrystals, or quantum dots (QDs), are promising color converter in fabrication of white light emitting diodes (WLEDs) due to their unique optical properties. Generally, when QDs are used in fabrication of WLEDs, QD/polymer hybrid nanocomposite is used to protect QDs and LED chip from harsh environment. When QDs are incorporated in polymer matrix, however, aggregation of QDs occurs as the concentration of QDs increases. Aggregation of QDs can lead to reduction of LED efficiency caused by increase in reabsorption and light scattering. In addition, reabsorption between QDs can shift emission band to a longer wavelength, which makes color control in WLED difficult. To overcome this problem, it is important to adjust inter-particle distance between individual QDs by using various dispersion strategies. Herein, we have fabricated highly luminescent and stable QD/poly(methyl methacrylate) (PMMA) nanocomposite at high QD concentration by using a matrix-free method. CdSe/ZnS QDs were functionalized by PMMA polymeric ligands to prepare nanocomposites. We investigated optical properties of QD/PMMA nanocomposites using polymeric ligands with different end groups (thiol, amine, and carboxylic acid) and molecular weights. We could fabricate QD/PMMA nanocomposites with high quantum yield at QD concentration as high as 30% (w/w), which exhibited high transparency without change in emission wavelength. Finally, QD/PMMA composite was coated onto polyethylene terephthalate (PET) film and then applied to WLEDs. We confirm that WLED based on the matrix-free QD/PMMA nanocomposites exhibited superior LED efficiency to conventional WLEDs.

Introducing plasmonic structures is a viable way to enhance the performance of optoelectronic devices by improving surface plasmon couplings. In this study, we combined block-copolymer lithography and nano-imprinting lithography to fabricate metal electrodes with highly effective multiple-patterned plasmonic nanostructures. The metal electrodes were then used as back reflectors in organic photodiodes (OPDs). The multiple-patterned electrodes exhibited increased light absorption compared to conventional flat electrodes, increasing the light responsivity of OPDs from 0.82 AW^-1 to 5.91 AW^-1 under 532-nm-wavelength light illumination at an intensity of 20 µW cm^-2. Theoretical study and near-field scanning optical microscopy revealed strong surface plasmon coupling of these nanostructured electrodes. Moreover, the multiple-patterned OPDs fabricated on a plastic substrate showed highly stable device performance. Furthermore, flexible 8×8 photosensor arrays were successfully fabricated and used for detecting incident photonic signals with high resolution. These results demonstrate that the developed multiple patterns provide a versatile and effective route for developing high-performance organic optoelectronic devices.

Polyvinylidene fluoride (PVDF) has been widely investigated as a sensor and transducer material due to its high piezo-, pyro- and ferroelectric properties. In this study, we demonstrate a force sensor based on a kind of electrospun composite fibers mat, the structure of which is composed of PVDF as the matrix, zinc oxide (ZnO) nanoparticles and graphite nanoplatelets (GNPs). By this sensing device, the mechanical energy can be converted into electrical signals upon different loading rates. And the device also shows long-term working stability. Moreover, we use optical microscopy (OM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) to demonstrate the effects of the electrospinning technique and the addition of ZnO and GNPs on the β-phase composition of PVDF. These results imply promising applications for practical energy harvesting devices and wearable self-powered sensors.

Self-powered energy harvesters using triboelectric effect and electrostatic induction have been widely studied, leading in the materials viewpoint to numerous material pairs for facile charge separation upon repetitive contacts with elaborate topological structures. Here, we demonstrate a simple but robust triboelectric platform based on a molecularly engineered surface triboelectric nanogenerator by self-assembled monolayers (METS). Triboelectric surface charge density of a substrate was readily controlled by the variation of end-functional groups of self-assembled monolayers (SAMs). In particular, by employing fluorine terminated SAMs, we develop a METS with the maximum open circuit voltage and short circuit current of 105 V and 27 μA, respectively, under relatively gentle mechanical contacts with the 3N vertical force at 1.25 Hz. The power density of the device was 1.8 W/m² at the load resistance of 10 MΩ more than 60 times greater than that of an unmodified dielectric/Al device. In addition, our method with SAMs was winded to various types of wearable fabrics such as silk, cotton, and poly(ethylene terephthalate) (PET) and a PET film, and the results of single friction-surface triboelectric nanogenerators with these materials propose a facile and universal guideline for designing triboelectic materials.

The uniform dispersion of Si materials in a carbon nanospheres while maintaining the nanomorphology of Si is required to achieve higher performance lithium-ion batteries (LIBs). Carbon-coated silicon nanoparticles embedded in uniformly dispersed carbon nanospheres (C-Si/CSs) were assembled by a simple mixing approach. We obtained high silicon contents up to 56 wt.% for the composite electrodes. The C-Si/CS anodes delivered a reversible specific capacity of 1230 mAh/g for 56 wt.% Si and 953 mAh/g for 44 wt.% Si at 800 mA/g after 150 charge/discharge cycles. The capacity retention after 150 cycles was 73% for the 56 wt.% Si and 86% for 44 wt.% Si C-Si/CS electrodes, while the bare C-Si without CSs displayed only 32% retention. This high capacity retention of the C-Si/CS composite electrodes reveals that the CSs effectively buffered the mechanical stress induced by the large volume change of Si during the lithiation/delithiation. Moreover, the high capacity retention reveals the high electrical conductivity of the electrodes, provided by the assembled morphology the CSs and the carbon-shell on the silicon nanoparticles (SNPs). The use of CSs with C-Si is a facile method to obtain a uniformly-dispersed mixture and can be readily scaled for practical applications.

Polymer-ceramic fiber-like structures have been fabricated by the electrospinning method and the as-spun fiber mats have been characterized structurally, compositionally and morphologically and their mechanical properties have been investigated for potential use as artificial muscles. To this end, poly(vinylidene fluoride-co-hexafluoropropylene), an electroactive polymer, and barium titanate (BaTiO₃), an archetypal ferroelectric and piezoelectric material, have been selected to fabricate hybrid organic inorganic system with a fiber-like morphology which provides the best combination of properties for a true muscle-like behavior. The effect of addition of BaTiO₃ colloidal nanocrystals on the structure and properties of fibers was investigated by different experimental techniques and the performance of the polymer nanofibers reinforced by BaTiO₃ colloidal nanocrystals for potential use as artificial muscles were studied. The structure and performance of nanofiber composites were characterized by different techniques including atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA), dielectric spectroscopy and electromechanical response. The results revealed a high increase in the stiffness and actuation strains of samples containing BaTiO₃ nanoparticles compared to those of pristine polymer nanofibers. In which, the PVDF-HFP/BaTiO₃ nanocomposites containing 4% BaTiO₃ exhibited Young’s modulus value of 24.9MPa and actuation strain of 3.51% at a low electric field of 10MV/m which was about 3 times higher than what was measured for PVDF-HFP nanofibers. These results suggested a method for fabricating materials with fibrous structures and modulating their properties by addition of high dielectric inorganic nanofillers.

Our studies involve the time dependence of diiodopolyene chains produced by photochemical irradiation with the reactants and product constrained to narrow parallel channels of a urea inclusion complex. We used Raman scattering spectroscopy to characterize the time dependence of the resulting conjugated polyene chains and to understand their internal quantum behavior. We discuss a quantum chemical simulation of these observations using the simplest model.

Organic π-electron systems like linear conjugated polyenes, and their infinite chain version polyacetylene, have low energy π-π* electronic excited states. For linear conjugated polyenes, one of these excited states gives rise to a very strong “allowed” transitions exhibiting a progression in two normal modes of motion both involving C-C stretching. One of these is due to the C=C bond stretching of the bond-alternate polyene chain and positioned near 1500 cm^-1; the other is due to the C-C single bonds and is found near 1100 cm^-1. The length of an absorption progression reflects the change in geometry along each these two degrees of freedom associated with the electronic excitation. If there is no change in geometry the transition is strictly “vertical” and has only the 0-0 transition. This is observed in large cyclic π-electron molecules and is anticipated for polyacetylene.

Given the nature of these excitations in finite linear conjugated polyenes, it is expected and observed that the strongest Raman excitations are due to these motions – at approximately the same vibrational frequencies – in the ground electronic state. The vibronic theory of Raman scattering for such a case gives “A-term” or Condon scattering which depends on a change in geometry upon electronic excitation. There are also higher order terms in the vibronic expansion that involve changes in the electronic transition dipole moment with displacement along normal modes. To a good approximation these can be ignored for linear conjugated polyenes.

Calculations of the pre-resonance Raman spectra for diiodopolyenes with up to 44 carbons based on the Gaussian implementation of A-term Raman scattering reproduce the following observations made in the experiments in order of increasing irradiation time:
●appearance of strong C=C peaks near 1500 and 1100 cm^-1 with the 1500 cm^-1 mode being the strongest
●increase in the relative intensity of the 1100 cm^-1 feature relative to the 1500 cm^-1 feature
●loss of all Raman intensity for extensive photochemical conversion
This last phase of the overall process is anticipated because, as polyacetylene forms, the one electron excitation dominating the Raman enhancement decreases in its ability to generate a geometry change and eliminates the dominant A-term Raman scattering.[1]

[1] E. J. Heller, Y. Yang, and L. Kocia, ACS Cent. Sci. 1, 40 (2015).

Emerging energy applications require polymer-based materials (insulators, dielectric films) that can operate at substantially higher electric fields (voltage per thickness), far beyond what is achievable with the current state of the art. Here, tailored hierarchical composite morphologies are used to obtain such non-trivial highly-enhanced performances in polymer-matrix dielectric composites. Polyethylene and polyethylene/montmorillonite nanocomposite films, are compared to delineate the contributions of crystal alignment vs. nanofiller alignment, as mechanisms that can increase the high-field electrical breakdown strength (E_BD). The crystal alignment increases E_BD to the same degree in both the polymers and the composites (75% to 150% increase in E_BD, much like as in biaxially oriented polyolefin films). The aligned fillers provide an extra marked increase in E_BD, beyond all increases due to crystal orientation, acting as aligned barriers to the motion of charges. For low filler loading composites (below the filler percolation), fillers act as independent barriers, synergistically adding to any crystal orientation effects (yielding 140% to 240% increase in E_BD). Above percolation (higher filler loadings), fillers provide a substantially higher E_BD improvement, due to a superior barrier mechanism from establishing a macroscopic filler/crystal network (up to 370% increase in E_BD).

Manufacturing of commercial capacitor dielectric films employs biaxial stretching to improve the dielectric breakdown strength (E_BD) of semicrystalline polyolefins. This methodology capitalizes on the strain-induced orientation of the crystallites in these films, and necessitates high purity and high crystallinity polymers, where E_BD is to be substantially improved. Here, we employ aligned high aspect ratio (pseudo-2D) nanofillers as an alternate method to yield equally large E_BD improvements, but for a LLDPE polymer matrix that possesses neither high crystallinity nor high purity. Specifically, extrusion blown polyethylene/montmorillonite nanocomposite films were cold-stretched to various strains, to further align the nanoparticles parallel to the film surface. A systematic series of films with increased alignment of the filler and of the crystalline lamellae (quantified through Hermans orientation order parameter from 2D X-ray diffraction studies) are studied, and the aligned structure is correlated to the electric field breakdown strength (quantified through Weibull failure studies). It is shown that the aligned pseudo-2D nanofillers, act as barriers to electrical treeing, further improving E_BD beyond any crystal orientation contributions. Along these lines, aligned nanofillers yield ultra-high E_BD polyethylene-based composite films, matching or exceeding the performance of high end BOPP films.

Polymer based organic photovoltaic systems holds the promise for the cost effective, lightweight solar energy conversion devices, which could benefit from simple solution processing of active layers. A novel small molecule (SM) of low band gap based on acenaphthoquinoxaline was characterized. It was soluble in polar solvents like N, N-dimethylformamide (DMF). Using SM and PCBM we have prepared blend solution. As cast as well as blend films have been prepared on ITO plates using spin coating unit. Blend films were annealed at 373K for 10 minutes. As cast, blend and annealed films were characterized using X-ray diffraction, Keithley electrometer, Uv-Vis spectrophotometer and Atomic force microscopy to determine their structural, electrical, optical and morphological studies.

Recently supercapacitors have gained immense attention as prominent energy storage device due to high power density and remarkable efficiency. However due to high self discharge the durability of supercapacitor needs to be addressed further. Recently we have used combination of high dielectric constant nonconducting polymers composites (NC) to Improve leakage current. Further in this work we have used facile chemical polymerization approach to synthesis PVDF, poly (o-aminophenol) (PoAP)-nanodiamond composites as dielectric layer. The G–PANI/Nonconducting Polymer composites(NC) has been characterized by using structural techniques e.g. scanning electron microscopy (SEM), XRD, Raman spectroscopy, electrical conductivity, respectively. The electrochemical behavior of prepared material has also been studied using electrochemical techniques e.g. cyclic voltammetry, impedance and chornopotentiometry. Here we report the excellent retainability of device with the incorporation of nonconducting polymers (NC)-composites layer over 200000 cycles with minimal loss in capacitance and almost no loss in film appearance. Dielectric stability has also been observed at various discharging current of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6A/g respectively with almost no notable difference in capacitance which renders remarkable durability of device with satisfactory improvement in leakage current.

The direct carbonization of 3D porous patterns has attracted interest for its use in obtaining carbon materials. In the case of carbonization of nanopatterned polymers, the polymer flow and subsequent pattern change may occur in order to relieve their high surface energies. Here, we introduce direct carbonization of 3D polymer pattern by supportive pyrolysis. With this method, 3D porous patterns were successfully converted to carbon patterns while maintaining their porous features. The fabricated 3D carbon pattern with micrometre-thick, submicrometre-pore-patterned was applied for supercapacitor electrodes. A facile doping process was subsequently employed to introduce nitrogen atoms into the carbon, which was intended to further enhance the carbon’s capacitive properties. The nitrogen-doped, 3D carbon pattern electrodes exhibited an areal specific capacitance of 32.7 mF/cm² at 0.5 mA/cm² when used as supercapacitor electrodes, which is approximately 20 times greater than that of commercially available MWCNT films of similar thickness measured under the same conditions. Our 3D carbon structures and fabrication approach will be beneficial in energy storage and conversion devices and in the development of various mobile and wearable biosensors.

Ionic liquids (IL’s) have been suggested for applications as diverse as solubilizing cellulose, antimicrobial treatments, and electrolytes in batteries due to their molten salt properties. We have recently discovered that a polymerized cation (such as imidazolium) is an excellent host for any associated anion. As a result, polymerized ionic liquids (PILs) are useful as vectors for the inclusion of a massive variety of functionalities ranging from multi-valent ions for batteries to magnetic anions. Moreover, PIL block copolymers allow orthogonal control over mechanical and morphological properties, ultimately leading to a conceptual framework for processable, tunable, multifunctional materials. In this talk, I will discuss the design of polymerized ionic liquids (PILs) based on imidazolium cations which exhibit high ionic conductivities of multivalent ions in the solid state. I will also discuss new functional materials and applications enabled by PIL chemistry.

Alkaline fuel cells (AFCs) that employ solid-state anion exchange membranes (AEMs) as the electrolyte separator are of great interest as they produce high power densities at low operating temperatures (< 200 °C) and enable the use of non-platinum electrodes (e.g., nickel), significantly reducing cost relative to proton exchange membrane fuel cells. Several challenges limiting the wide scale use of membrane-based AFCs is the alkaline chemical stability and ion transport of polymers used as AEMs. Recently, polymerized ionic liquid (PIL) block copolymers with a range of chemically stable heterocyclic cations have become candidates to investigate for AFCs. PIL block copolymers constitute an emerging class of polymers and a distinct set of block copolymers that synergistically combine the advantageous properties of both PILs and block copolymers and are synthetically highly versatile with numerous cation and anion chemistries available. Specifically, the unique physiochemical properties of PILs, such as high solid-state ionic conductivity, high chemical, thermal and electrochemical stability, and widely tunable physical properties (e.g., via anion exchange), are incorporated in the block copolymer architecture, which allows for self-assembly into a range of nanostructures, where morphology type and domain size are tunable. In this talk, the synthesis, alkaline chemical stability, and ion transport of numerous PIL block copolymers developed in our research group will be discussed. More specifically, both the cation and backbone chemistry have a significant effect on alkaline chemical stability and various chemistries and chain architectures have a significant impact on ion conductivity. The AFC performance of PIL block copolymers as both the electrolyte and ionomer in the catalyst layer will also be discussed.

The poor electronic and lithium ion conductivity of lithium ion battery (LIB) active materials requires them to be in particulate form and suspended in an inactive binder with conductive carbon additive. The nature of this electrode matrix is limiting because ion and electron transport relies on uptake of liquid electrolyte and percolation thresholds, respectively, as well as unfavorable organic-inorganic interactions ultimately forming discontinuous pathways. This presentation works to address these issues by replacing the traditional materials with an all-functional, all-polymer composite, consisting of (electronic) conducting polymer PEDOT:PSS and Li ion-conducting polymer PEO. It was found that with increasing PEO/descreasing PEDOT content, the conductivity was actually enhanced (100x). To elucidate this structure-function phenomenon, the morphology was first investigated using TEM and AFM. They revealed a dual-phase system, which we hypothesize is driven by hydrophilic-phobic interactions. The revealed morphology was a more continuous network of domains compared to neat PEDOT:PSS, to which the improved conductivity can be attributed. Using wide-anlge XRD and DSC, it was found that the presence of PEDOT:PSS suppresses crystallization of PEO (only 1% crystallinity for 64 wt% PEO), which implies that the polymer interactions result in long-range domain formation rather than segregated regions of PEDOT in a crytallized PEO matrix. The electrochemical properties of this material were also investigated under LIB conditions, and it is shown that its stability is comparable to conventional materials, with some added charge storage due to the capacitance of PEDOT.

Poly(ionic liquid)s (PILs) have attracted substantial attention due to the unique combination of properties such as σ_DC, thermal and electrochemical stability, improved processability and practically unlimited ability in macromolecular design¹.
A broad range of 1,2,3-triazolium-based PILs (TPILs)^2,3 have been synthesized by merging copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), step growth or chain growth polymerizations together with efficient 1,2,3-triazole quaternization and ion metathesis. Among them, TPILs obtained through Click chemistry are particularly attractive since they afforded TPIL ionenes having σ_DC values matching the best PILs reported so far (1.0 x 10^-6 S cm^-1 at 25°C) and significantly higher than conventional ionenes. Comparison with non-regioisomeric analogs obtained by an accelerated solvent- and catalyst-free monotopic approach has shown that regiochemistry of the 1,2,3-triazolium groups has no significant impact on thermal and ion conducting properties of TPILs⁴.

In order to sharpen the structure/proprieties relationship of TPIL ionenes while trying to achieve the highest possible σ_DC and electrochemical stability, we present here TPILs bearing bis(trifluoromethylsulfonyl)imide (TFSI) anion obtained from two novel α-azide-ω-alkyne monomers using both sequential CuAAC/quaternization or monotopic approaches⁵.
To maximize the volume fraction of charge carriers and σ_DC, new TPILs having short hexanoyl or diethylene glycol spacers were synthesized. Although the shortening of the spacers afforded materials with higher T_g, the obtained materials exhibit σ_DC values up to 1.0 x 10^-5 S cm^-1 at 25 °C which is comparable to that of their longer structural analogues. It is also shown that these polyelectrolytes exhibit good electrochemical stability (up to 5.9 V vs Ag+/Ag), which is among the best known for PILs.

1. Yuan J.; Mecerreyes D.; Antonietti M. Prog. Polym. Sci., 2013, 38, 1009-1036.
2. Abdelhedi-Miladi I.; Obadia M. M.; Drockenmuller E. Macromol. Chem. Phys., 2014, 215, 2229-2236.
3. Obadia M. M.; Drockenmuller E. Chem. Comm., 2016, 52, 2433-2450.
4. Obadia M. M.; Montarnal D.; Drockenmuller E. Macromol. Rapid Commun., 2014, 35, 794-800.
5. Colliat-Dangus G.; Obadia M. M.; Drockenmuller E. Polym. Chem., 2015, 6, 4299-4308.

Lithium-ion batteries are the best approach at present for supplying mobile electrical power. While metallic lithium is known to be the ideal high-capacity anode material because of light weight and high electronegativity, it is unusable for rechargeable batteries because growth of lithium dendrites during recharging, short-circuits the device.

A long-proposed solution replaces the liquid battery electrolyte with a solid having sufficient mechanical strength to suppress lithium dendrite formation during battery cycling (Monroe & Newman 2005, Tarascon & Armand 2001). We are pursuing nanoconfinement as an approach for strengthening solid polymer electrolytes. We present studies of model ionic conduction devices made by confining polyethylene oxide (PEO) within nanometer-scale volumes fabricated by high-resolution lithography and plasma etching. We are investigating this system for its potential to provide high ionic conductivity and strong barrier properties for battery applications. We fabricated porous and grating templates using both interference lithography and electron-beam lithography with controllable feature sizes ranging from ~200 nm to as small as ~20 nm, and controllably filled them with PEO incorporating lithium salts. We compare measurements of the nanoconfined ionic conductivity with the molecular structure obtained via synchrotron grazing incidence wide-angle X-ray scattering (GIWAXS) studies.

Gel electrolytes or ‘ion gels’ based on ionic liquids and structuring polymers offer a number of advantages for printed electrochemical devices such as electrochromic displays, sensors, and capacitors. These advantages include large electrochemical windows, good ionic conductivity, optical transparency, chemical inertness, good solvent processability with essentially zero vapor pressure in the final gel state, and readily tunable mechanical and electrochemical properties. This talk will begin with a discussion of several strategies for the preparation and characterization of rubbery ion gel networks with elastic moduli in the range of 1 kPa-10 MPa and rupture strains up to 300%. The second half will feature applications in simple electrochromic displays and sensors that have utility in printed, flexible electronics.
A specific example that will be discussed involves mixtures of ionic liquids (e.g., EMI TFSI) and a gelating A-B-A triblock polymer such as polystyrene-b-polymethylmethacrylate-b-polystyrene, which form a two-phase composite. The ionic conductivity of the conductive phase is sensitive to the choice of ionic liquid and the Tg of the soluble B-block; the strength of the physically cross-linked insulating phase depends on the Tg of the insoluble A blocks. The modulus of the gel is tuned through the relative molecular weights of the A and B blocks. Electrochemical function is introduced by adding redox-active molecules to the conducting phase. Using this strategy, multi-colored electrochromic or electrochemiluminescent displays can be fabricated on plastic that operate with sub-2 V supply voltages.

The emerging needs for high-power, lightweight and flexible electronics require the use of polymer film based solid-state capacitors with pulsed power. Despite the high power density of film capacitors due to fast charge/discharge rates (ms-μs), their energy storage densities fall significantly short of rising demand in advanced applications. Improvements in the energy storage densities over current performance metrics are reliant on increasing the permittivity (ε_r) and/or breakdown strength (E_BD) of the dielectric and necessitates the development of new materials and processing methods. Experimental and simulation studies have shown that the presence of barriers within the dielectric can significantly enhance the E_BD by hindering electrical tree propagation during breakdown. In this regard, co-extruded multilayer composite films have shown much promise to improve the E_BD over that of individual components.
In this work, we report a new material design and processing strategy for fabrication of multilayered, multicomponent, barrier dielectric films using self-assembling diblock copolymers (BCP). BCPs are versatile materials which self-assemble into highly ordered periodic nanostructures (5-100 nm), offering extraordinary tunability of dielectric contrast, orientation, layer thickness and interfacial width, from the intrinsic nanoscale molecular level to macroscopic thickness for device-level compatibility. Directed self-assembly (DSA) using a themal-gradient based Cold Zone Annealing-Soft Shear (CZA-SS) method was applied to model lamellae-forming PS-b-PMMA BCP films to obtain highly oriented multilayered dielectric films, as confirmed by cross-sectional TEM, Neutron Reflectivity and X-ray scattering measurements. Dielectric breakdown measurements of the BCP films revealed a ~20-50% enhancement in E_BD for the self-assembled multilayer BCP films as compared to unordered single-phase as-cast films, suggesting that the breakdown pathway is highly selective to the BCP nanostructure. The enhancement in E_BD was attributed to the “barrier effect”, where the multiple interfaces between the component PS and PMMA lamellar blocks act as barriers to the dielectric breakdown through the film.
As such, the effects of block molecular weight, lamellar thickness and number of layers on the breakdown strength of multilayered BCP films were also studied. Dielectric spectroscopy measurements on the BCP samples revealed no deleterious changes to the permittivity or dielectric loss with self-assembly. Thus, using the simple but robust self-assembly approach, the breakdown strength of films was significantly increased without compromising on other dielectric properties. Given that the energy density scales as the square of the breakdown strength (U~ E_BD²), this novel concept of DSA aligned BCP dielectric films provides a new nanomaterial paradigm for designing high energy density polymer film capacitors.

Safety is one of the major issues preventing the large-scale application of lithium-ion batteries. Recently, researches aimed at reducing safety hazard in lithium-ion batteries have a particular focus on the polymer electrolytes to replace the flammable organic solvents. The solid-polymer electrolytes (SPEs) are generally based on neat, high-molecular weight polymers without solvent, which is benefit for the promising safety characteristic. Nevertheless, the low room-temperature ionic conductivity of SPEs, which is usually in the range of 10^-8 to 10^-6 S/cm, is a major obstacle for their application in devices. While the gel-polymer electrolytes (GPEs), as a combination of polymer matrix and liquid organic electrolytes, can share both the cohesive and diffusive properties of solids and liquids, respectively. But the mechanical strength is inevitably reduced with the increasing content of liquid. To address these issues, substantial research efforts have been undertaken to enhance ionic conductivity while maintain their manifold advantages.
Poly(ionic liquid)s (PILs), as a new family of functional polymers, are generally prepared by conventional or controlled radical polymerization of ionic liquid (IL) monomers bearing vinyl groups. The presence of an IL moiety in the repeating unit of PIL chains can integrate some desirable characteristics of IL into the polymeric matrix, such as thermal stability, high ionic conductivity, negligible vapor pressure, wide electrochemical window etc. Therefore, PILs can be considered as attractive candidates as potential polymer electrolytes for lithium-ion batteries.
In this presentation, two kinds of advanced polymer electrolytes based on PILs are discussed. A novel zwitterionic PIL with cation and anion combined covalently are used to promote Li-ion dissociation and improve ionic conductivity. Firstly, GPEs containing zwitterionic PILs as polymer matrix and propylene carbonate (PC) as solvent are prepared. The ionic conductivity of neat PIL is 10^-5 S/cm and increases to 10^-3 S/cm with the addition of PC. Both the dissociation of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in the presence of zwitterion and the ion-dipole interaction between Li-ion and PC are expected to play significant roles for the enhancement of ionic conductivity. Secondly, a new type of single Li-ion conductor based on zwitterionic PILs, polyanionic lithium salts and poly(ethylene oxide) (PEO) are prepared by a simple solution-casting method. The zwitterionic moiety of PILs are expected to promote the ion dissociation in polyanionic lithium salts, in which more Li-ions would be highly mixed with PEO, so that ionic conductivity could be further improved. Meanwhile, the incorporation of PILs also favorably enhances the degree of amorphous phases in PEO, which is required for ionic conduction. We believe that the two kinds of polymer electrolytes would provide new perspective to design novel lithium-ion conductors based on PILs.

Lithium batteries are electrochemical devices for storing energy. Among the different options, solid polymer electrolytes allow for batteries with high energy densities but modest specific power. This is a direct consequence of an excessive complexation of Li ⁺ ions by the rigid polymer chains. One way to improve these properties is therefore to swell the polymer electrolyte with smaller entities such as plasticizers.

In this context, ionic liquids are a good option, because this new class of electrolytes has many proven benefits. These ionic liquid/polymer blends appear as a new class of materials in which the properties can be easily modulated.
In this communication, we show in particular that the confinement of ionic liquids in block copolymers leads to nanostructured architectures that can be exalted to lead to anisotropic phase in which ion mobility becomes strongly anisotropic also. A feature of these systems is that they can be easily and almost perfectly oriented by mechanical stress. In particular, the phase diagrams of mixtures of ionic liquids with PEO/PPO copolymers present composition domains in which 1D or 2D phases are obtained. The long-range structure of these new anisotropic materials are studied by X-ray diffraction, and quadripolar NMR is used to monitor molecular and ionic motions and anisotropies. Self-diffusion coefficient are measured by NMR pulsed field gradient to decipher the long range mobility and probe the size of the correlation domains. These measurements allow to determine the quality of alignment of phases.¹
However, improvement of the properties of these materials requires a deep understanding of the salt solvatation in these complex environments. Our approach involve to combine experimental and theoretical methods to address the structural and dynamic aspects in these materials.² In parallel, molecular dynamics studies are performed to highlight the role of site solvation and ion pairs on the transport properties.³



References:

[1] P. Judeinstein, S. Huet, P. Lesot, RSC Adv., 2013, (3), 16604.
[2] P. Judeinstein, F. Alloin, Spectra Analysis, 2014 (300) 46.
[2] B. Coasne, L. Viau, Vioux A., J. Phys. Chem. Lett., 2011 (2), 1150.

Solid ceramic-polymer nanocomposite electrolytes incorporating ceramic nanoparticles into polymeric matrices have attracted much attention as an alternative to replacing liquid electrolytes for high energy-density Li batteries. In this study, liquid-feed flame spray pyrolysis synthesized amorphous Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) nanoparticles with an average particle size of 65 nm are dispersed in poly(ethylene) oxide (PEO) matrices as active fillers. LATP is a Li superionic conductor with conductivities of 7 × 10^-4 S cm^-1 in crystalline form. Even amorphous LATP has a room temperature conductivity of 10^-5 S cm^-1. We performed a parametric study by varying the lithium concentration, particle loading up to 20 wt.%, and PEO molecular weight with different ceramic fillers. TiO₂ with an average size of 21 nm and fumed silica with and average size of 0.2-0.3 µm are used as passive fillers for comparatison. IR spectroscopy, Raman, XRD, SEM, DSC and impedance spectroscopy are used to identify the structural and chemical origins that underlie the performance of these nanocomposite electrolytes.
We achieved the highest ionic conductivities of 1.70*10^-4 S cm^-1 at 20°C with PEO-LiClO₄ containing 10 wt. % LATP nanoparticles. Nanoparticles are mono-dispersed and form no agglomerates. Systems with inert fillers show comparable glass transition temperature and degree of crystallinity. However, for the LATP filled nanocomposite we observe up to two orders of magnitude enhancement in ionic conductivity. Accordingly, the main cause for ionic conductivity enhancement appears to be the chemical nature of nanoparticle and its ability to suppress crystallization in the polymer. The activation energies for LATP filled nanocomposites are much lower than those for the reference samples, which suggests a different conduction mechanism created by polymer-LATP interphase, which provides extra pathways for lithium ions and a source for additional lithium supply.

Charged block copolymers (BCPs) are solid-state ionic materials which self-assemble into nanostructures, enabling both fast single-ion (such as Li or Na) transport and structural integrity. Their ionic conductivity highly depends on the morphology of self-assembled BCP microdomains at the molecular level. Here we carry out mesoscopic simulations based on a modified dissipative particle dynamics framework, combined with directly computed small-angle X-ray scattering patterns, to predict the phase diagrams of charged BCPs, considering both screened electrostatic interactions and explicit ionic diffusion. We estimate and confirm the phase diagram of charged A-B diblock copolymer systems under various f_A (A-block ratio) and χ (Flory-Huggins parameter) values. The phase diagram of charged BCPs exhibits a significant shift to the left compared to neutral BCPs with inversed A-rich phases present at much lower f_A values, and such degree of shifting is correlated with the counterion concentration and valence. This is because counterions bind electrostatically to the A block, and therefore, contribute to additional excluded volumes. These findings are consistent qualitatively with self-consistent mean field theory (SCFT) results on charged BCP systems. We then calculate the ion diffusivity and conductivity (via the Nernst-Einstein equation) in representative lamellar, regular/inversed cylindrical and regular/inversed gyroid phases to understand how ions transport and conduct in charged BCPs. We use the diffusivity tensor, computed by velocity correlation functions to determine the principal diffusivities in randomly oriented microdomains. We find that the A-rich inversed cylindrical phase exhibits the highest, and meanwhile, isotropic ion conductivity, even though such a phase occupies a small region in the phase diagram. Ion conductivities in the lamellar and regular B-rich cylindrical phases are highly anisotropic, while that in the regular/inversed gyroid phases is isotropic. We also determine the activation energy barriers for ion transport in various phases using the transition-state theory to design the best charged BCP morphology and operating condition for their practical application as solid-state superionic conductors.

Printable energy storage facilitates innovation in the manufacture of flexible electronics in that it will enable direct integration of a power source into a device during the fabrication process. To enable such advancement, we demonstrate a universal approach to develop free-standing and flexible electrodes for printable, high-performance Li-ion batteries. This simple approach utilizes a well-dispersed and directly castable mixture of active material, carbon nanofibers, and polymer to make printable electrode inks. The unique composite properties are mainly attributed to the formation of a 3D nanofiber network that acts as the conductive additive, embedded charge collector, and porous, structural scaffold to facilitate Li⁺ diffusion. Free-standing electrodes of three common Li-ion battery active materials (Li₄Ti₅O₁₂, LiFePO₄, LiCoO₂) are prepared, each showing excellent cyclability and rate capability. To complement this component, we demonstrate a dry phase inversion technique representing a step toward controlled, printed porosity in Li-ion battery electrolytes. Our approach utilizes a solvent/weak non-solvent system to generate porosity within a polymer matrix and a ceramic Al₂O₃ filler to fine tune the pore size distribution to impart desirable tortuosity within the membrane. These electrolytes offer electrochemical performance on par with commercial separator films even at current rates as high as 5C, with better thermal stability and electrolyte wetting. This material can also be printed directly over an electrode layer without sacrificing performance in either layer. Additionally, the phase inversion process is applicable to composite electrode inks, yielding electrodes with increased electrochemical properties and better flexibility over those prepared with good solvent alone. This technology for both electrolyte and electrode inks is an enabling step toward direct integration of flexible power in confined areas or on non-planar device surfaces.

Polymer dielectrics are an important family of enabling materials for electrostatic capacitors relying on their low mass density, ease of processing, flexibility, and reliability associated with high dielectric strength and graceful failure mechanism. However, the development of polymer dielectrics has turned out to severely lag behind many emerging needs such as electric vehicles and aerospace power conditioning where high operating temperatures are required. The intrinsic weaknesses of existing high-temperature polymer dielectrics are seemingly unsolvable within the regime of current knowledge of polymer engineering. In this work, we show that by fabricating a multilayer-heterostructured polymer nanocomposite film, a dielectric constant of ~6 at 1 kHz electric field frequency can be achieved without compromising the high electric field operation capability at 150 °C, a temperature oriented to many important high power applications such as electric vehicles and pulsed power technologies. This K value, being almost three times that of biaxially oriented polypropylene (K = 2.2), accompanied with the high-dielectric strength of polymer-based dielectrics, leads to a record dischargeable energy density at 150 °C, which far exceeds that of previous polymer-based dielectric materials under the same conditions. Moreover, high power densities and the capability in surviving continuous operation under both high temperatures and electric fields of the multilayer-heterostructured polymer nanocomposites are demonstrated through fast discharge tests. With substantially improved collective performance, these multilayer-heterostructured polymer nanocomposites are expected to find widespread application in advanced electronics and power modules where harsh operating conditions are present.

Conductive polymers, such as polypyrrole (PPy), have both redox activity for charge storage and conductivity for facilitation of charge transportation. Redox-active small organic molecules, such as quinone (QN) derivatives, have potentials for charge storage with high capacity and tunable redox potential. However, the redox-active molecules are not fully applied to the active materials because of their solubility to electrolyte and low conductivity. In the present study, composites of the redox-active molecules and the conductive polymers were prepared by three different methods. The conductive polymers act multiple roles, such as active material for charge-storage, host for incorporation of redox-active molecules, and conductive path.
The three types of the PPy/QN composites, such as the host-guest structure, the sea-island structure, and the core-shell structure, were synthesized by the three different methods based on morphogenesis of PPy. The hierarchical PPy consisting of nanoparticles 50 nm in size was used as the host for incorporation of the QN derivatives as the guest. The host-guest composite was synthesized by incorporation of QN into the interspaces between the nanoparticles. The sea-island composite of the PPy connected nanoparticles as sea and the QN as island was obtained by the polymerization of pyrrole containing QN on the surface of oxidant crystal. The composite with sea-island structure was formed by simultaneous polymerization and crystal growth. The core-shell structure was obtained by the PPy coating on the surface of the QN crystals.
The PPy/QN composites showed enhanced electrochemical properties as an active material of redox capacitor. The composite with sea-island structure showed the highest electrochemical performance, namely 200 F g^-1 at the current density of 5 A g^-1. In contrast, the mixture of the commercial PPy and QN showed 80 F g^-1 at 5 A g^-1. The composite electrode exhibited improved cycle stability than typical QN electrode. The redox reaction of both PPy and QN proceeds on the high current density. The PPy contributes to ensure the conductivity for the redox reaction of QN. The dissolution of redox active molecules to electrolyte is inhibited by incorporation of PPy. These results indicate the combination of conductive polymers and redox-active molecules is efficient strategy for development of organic electrode with the enhanced performances.

A thermally stable separator based on Al₂O₃-coated PE with a multi-functional urethane acrylate (UA) binder was prepared by a dip-coating and thermal curing process. The UA binder showed a good miscibility with a co-binder, PVdF, and effectively formed the cross-linked structure within PVdF matrix, which was not achieved when a low molecular weight tetra-acrylate (TA) was used as a cross-linkable binder. The UA film composed with PVdF showed more stable thermal property in the electrolyte at a high temperature than the TA film composed with PVdF, and maintained the tensile storage modulus to a certain degree even above the PVdF melting point, which represents that UA forms the well cross-linked structure within PVdF matrix and is very suitable binder for our ceramic coating system to improve the thermal stability of separators.
A high cross-linking density achieved by the multi-functionality of UA ensured the thermal stability of separator up to 200^oC by making ceramic particles firmly bound within the coating layer. The thermal shrinkage at 200^oC of the pristine PE and the ceramic-coated separator with PVdF binder alone was 98.5% and 76.4% respectively, however, the ceramic-coated separator with UA binder was only 1.9%. The Al₂O₃-coated separator with UA binder also showed more gradual decrease of tensile storage modulus with temperature and higher mechanical integrity than the ceramic-coated separator with PVdF binder and the pristine PE, this is because the firm cross-linked structure of UA within the ceramic coating layer effectively makes up for the thermal weakness of a PE fabric. A high polarity of UA rendered a good wettability with organic liquid electrolytes so effectively reduced the bulk resistance of cell assembled with the separator, and the separator with UA binder showed higher ionic conductivity than the ceramic-coated separator with PVDF binder and the PE fabric. The battery performance was evaluated with a LiCoO₂/graphite full cell (1C=2300mAh) under a voltage range between 3.0 and 4.3V at a constant charge/discharge current density of 1C/1C. The cell of the Al₂O₃-coated PE with UA binder exhibited less capacity fade than the cells of PVdF binder and PE separator, and the capacity retention after 500 cycles was 86.16%, 81.94%, and 76.16% respectively. This result suggests that the Al₂O₃ coating on the separator surface plays a critical role in improving the cycle performance, and especially the binder system in ceramic-coated separator is an important factor for the battery performance.

Sustainable, low-cost and long-cycle-life rechargeable batteries are key enabling components for grid integration of renewable energies. The concept of using organic materials as electrode materials for lithium battereies is as old as that of inorganic ones. The first commercialized primary lithium battery was in fact based on the Li-CFx chemsitry. Now that intercalation materials have reached their intrinsic limits, organic redox materials are called upon for stationary energy storage due to the attractive features of high theoretical capacity (>400 mAh/g), potentially low-cost (no expensive elements), recyclable, and tunable properties that can be designed by modifying chemical structures. In this talk, we will report organic carbonyol compounds as a class of sustainable, low-cost, and universal electrode materials that enable multiple long-cycle-life aqueous batteries. These organic compounds can address the key limitations of anode materials in aqueous rechargeable battery with little to no compromise to what make these batteries attractive. We will also report our recent progress on aqueous flow batteries and all-solid-state-Na-ion batteries based on organic redox materials.

We developed a new diacetylene containing photopolymerizable ligand molecule, tailored for application in nanoelectronic devices based on gold nanoparticles (AuNPs).[1] It consists of (i) a diacetylene unit which undergoes photopolymerization, (ii) a sufficiently long alkyl chain to build up a dense monolayer via self-assembly, (iii) a terminal thiol group for proper binding to a AuNP surface, and (iv) a carboxylic end group for terminal binding ability and electrostatic stabilization. Applying this ligand molecule, AuNPs in the size range of 12-13 nm were prepared and the diacetylene unit was polymerized upon UV irradiation leading to a polymeric ligand shell stabilizing the metallic core. Investigations including colloidal stability towards NaCl, DTT displacement reactions, and temperature were performed with this tailor-made polydiacetylene/metal particles and indicate an extraordinary high degree of steric and electrostatic stabilization.
Moreover, individual or at least a few of these particles were immobilized in between nanoelectrodes, thus forming nanoelectronic devices, which enabled us to investigate the electron transport properties of the applied diacetylene-polymer. The high stability of this multidentate polymeric organic/inorganic hybrid structure and the integration into a nanoelectrode device represents a key step towards the application in molecular nanoelectronics.
[1] Liffmann et. al., RSC Adv., 2015,5, 102981-102992

When elemental sulfur is polymerized with 1,3-diisopropenylbenzene (DIB), the resulting organosulfur copolymers are capable of realizing enhanced capacity retention as the active cathode material in Li-S batteries. In this presentation we will reveal how the incorporation the DIB cross-linking agent dramatically alters the morphology at the nanoscale of the composite cathodes in comparison to traditional cathodes made from elemental sulfur. These cathodes are characterized by a suite of high-spatial resolution analytical electron microscopy techniques in both their initial pristine state as well as after the transformations that accompany the charge-discharge cycling. The use of elemental sulfur in the composite cathode leads to heterogeneous structures composed of aggregated carbon nanoparticles poorly mixed with the sulfur domains, forming a loosely percolated network of electrically conductive pathways and extended multiscale porosity and cracking. Replacing the elemental sulfur with the organosulfur copolymers improves the compatibility between the carbon nanoparticles and the sulfur domains down to sub-5 nm length scales, resulting in the organosulfur copolymers intimately wetting the carbon nanoparticles. This increases the compositional homogeneity and improves the interfacial contact between electrochemically active sulfur compounds and the electrically conductive carbon nanoparticles. There also appears to be concomitant improvements of the physical-mechanical stability of the composite cathodes that leads to less cracking but still preserving extended mesoscale and nanoscale porosity. Together these factors lead to increased capacity and enhanced cycle life in the final Li-S battery assembly. We will then explore how the incorporation of MoS₂ flakes into the composite cathodes further alters this morphology and leads to additional improvements in cycle life.

In recent decades, block copolymer-inorganic hybrid co-assembly has emerged as a scalable, tunable route to the synthesis of crystallographically ordered, mesoporous inorganic materials. These materials have found numerous applications in catalysis, energy conversion and storage, and other areas. One notable area in which block copolymer-directed assembly has made few inroads, however, is the production of high-purity electronic materials useful for advanced energy conversion, storage, and transmission devices. For example, superconductors with mesoscale ordering and porosity are expected to have properties very different from their bulk counterparts. The exploration of these properties has been limited, however, by the lack of tunable, versatile, and robust wet-chemical synthesis methodologies to mesostructured superconductors. We report the synthesis of gyroidal NbN superconductors from gyroidal block copolymer self-assembly-derived niobium oxide. The resulting materials have a Tc of about 7.8K, a critical current density of 440 A cm ^-2 at 100 Oe and 2.5K, and a mesoscale lattice with the I4₁32 (alternating gyroid) structure with d₁₀₀ spacings between 27 and 36 nm. We expect that block copolymer-inorganic hybrid co-assembly will prove to be a scalable, tunable platform for exploration of the impacts of mesoscale order and porosity on superconducting properties.

Hydrogels are cross-linked polymer with a three-dimensional (3D) structure, which can absorb large quantities of water without dissolving. Among them, conducting polymer hydrogels (CPHs) represent a unique class of materials that synergize the advantageous features of organic conductors and hydrogels, which have been used in many applications such as bioelectronics and energy storage devices.
Conductive polymer hydrogel exhibited attractive features for electronic applications, for example: (a) high conductivity; (b) good biocompatibility due to its similarity to extracellular environment; (c) CPHs can be used as a processing platform for fashion conducting polymer into porous and 3D structured thin films due to the in situ solution gelation and microstructure formation process; (d) the simple chemistry of CPHs synthesis is compatible to fast and low cost patterning fabrication such as screen printing and inkjet printing; (e) CPHs can be used as advanced interface between soft and hard materials; (f) CPHs can interface between ion transport phase and electron transportation phase, and low the impedance.
In this talk, we provides a brief overview of current research activities in the synthesis, processing and electronic device of three-dimensional (3D) nanostructured CPHs, and their applications in bioelectronic, switchable RF ID and electronic skin devices.
Reference
1. L. J. Pan, G. H. Yu, D. Y. Zhai, H. R. Lee, W. T. Zhao, N. Liu, H. L. Wang, B. C. Tee, Y. Shi, Y. Cui and Z. N. Bao, Proc. Natl. Acad. Sci. USA, 2012, 109, 9287.
2. L. J. Pan, A. Chortos, G. H. Yu, Y. Wang, S. Isaacson, R. Allen, Y. Shi, R. Dauskardt and Z. N. Bao, Nature Commun., 2014, 5, 3002.
3. L. L. Li, Y. Q. Wang, L. J. Pan, Y. Shi, W. Cheng, Y. Shi, G. H. Yu, Nano Lett., 2015, 15, 1146.
4. Y. Q. Wang, Y. Shi, L. J. Pan, M. Yang, L. L. Peng, S. Zong, Y. Shi, G. H. Yu, Nano Lett., 2014, 14, 4803.
5. L. L. Li, Y. Shi, L. J. Pan, Y. Shi, G. H. Yu, J. Mater. Chem. B 2015, 3, 2920.

Organic semiconductors based on π-conjugated polymers and oligomers have shown considerable promise for applications in optoelectronic devices such as light emitting diodes and organic solar cells. A wide variety of organic polymers and oligomers have been studied in the last few decades. Polythiophene is one of the most promising and widely used materials among these. We have recently developed a simple route for the synthesis of thiophene based oligomers from plant extracts. In this presentation we will be revealing the fabrication details and the results of our study on the structural properties carried out using nuclear magnetic resonance and infrared spectroscopy as well as the performance of this material as the absorber layer in organic-inorganic hybrid solar cells. Simulations performed using finite difference time domain method for understanding the visible light propagation through the material and determining the optimum solar cell configuration required for maximizing the performance will also be discussed.

Melanin is a broad term that denotes pigments of diverse structures and origins derived by the oxidation and polymerization of tyrosine in animals or phenolic compounds in lower organisms. It has different biological functions, such as thermoregulation, photoprotection and metal chelation. Especially, eumelanin is the black-brown subgroup derived at least in part from the oxidative polymerization of L-dopa via 5,6-dihydroxyindole intermediates. It is mainly composed by 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and their redox forms. In the human skin, eumelanin absorbs and scatters solar radiation[1].
Being stable, low-cost and environmentally benign, melanin is interesting for many different technologies, e.g. in DSSCs. Eumelanin absorbs in the whole UV-vis region, with a monotonic decrease of absorbance from the UV to the near IR. This behavior has been described, among a number of hypotheses, with the “chemical disorder model”. Here, eumelanin is depicted as a complex polymeric material that contains a range of chemically distinct chromophores that absorb at different wavelengths [2-3].
Unfortunately, natural eumelanin is insoluble in common organic solvents. Indeed, natural melanin has a complex supramolecular organization characterized by the presence of particles of 100-200 nm. Therefore, reaching the intimate contact between the melanin dye and the inorganic semiconductor (titanium dioxide) to ensure the proper operation of the DSSC, in particular the effective photosensitization, is challenging.
Here, we report on a new synthetic approch [4] based on the polymerization of the eumelanin monomers on the surface of the mesoporous TiO₂ photoanode, to produce controlled thin layers of melanin-like polymer. Such polymerization allowed a strong control of the thickness and of the composition of the polymer. The great affinity between the indolic–OH groups of DHI (and DHICA) and the TiO₂ surface ensures the intimate contact, as verified by solid state NMR. EPR and photoelectrochemical measurements allowed us to reveal the complex electronic features of the interfaces. We are presently working to develop DSSCs and to test their performances.

[1] Santato, C. et al. Melanins and melanogenesis: from pigment cells to human health and technological applications, Pigment Cell Melanoma Res., 2015, 28, 520-544;
[2] Meredith, P. et al. Towards structure–property–function relationships for eumelanin, Soft Matter, 2006, 2, 37-44;
[3] Buehler, M. J. et al. Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin, Nature Commun., 2014, 5, 3859-3868.
[4] Panzella, L. et al. Surface-Functionalization of Nanostructured Cellulose Aerogels by Solid State Eumelanin Coating, Biomacromol., 2016, 17, 564-571.

Covalent organic frameworks (COFs) represent an emerging class of crystalline, porous materials exhibiting unique structural and functional diversity. By combining multidentate building blocks via covalent bonds, two- or three-dimensional frameworks with defined pore size and high specific surface area in conjunction with appreciable thermal and chemical stability can be constructed.[1] Crystallinity and porosity are of central importance for many properties of COFs, including electronic transport. Here we present two different approaches for strongly enhancing both aspects. The introduction of a modulator that competes with one of the building blocks during the solvothermal COF growth results in highly crystalline frameworks with greatly increased domain sizes of several hundreds of nanometers (Figure 1).[2]
In a second approach we have developed a synthetic concept to allow consecutive COF sheets to lock in position during crystal growth, and thus minimize the occurrence of stacking faults and dislocations. [3]
As an example we report a photovoltaic device that exclusively utilizes a crystalline organic framework with an inherent type II heterojunction as active layer. The novel boronate ester linked COF comprises ordered columns of electronically separated donor and acceptor moieties. Oriented films of this COF were applied in the construction of a photovoltaic device where the COF itself provides the photoactive junction, which was found to promote charge separation upon photoexcitation of either building block.[4] Based on the degree of morphological precision that can be achieved with COFs and the enormous diversity of molecular building blocks, these materials show great potential as model systems for organic heterojunctions and might ultimately provide an alternative to the current bulk heterojunctions.
References
[1] Côte, A. P.; Benin, A. I.; Ockwig, N. W.; O'Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Science 2005, 310, 1166.
[2] Calik, M.; Sick, T.; Dogru, M.; Döblinger, M.; Datz, S.; Budde, H.; Hartschuh, A.; Auras, F.; Bein, T. J. Am. Chem. Soc. 2015, DOI 10.1021/jacs.5b10708.
[3] Ascherl, L.; Sick, T.; Margraf, J.; Lapidus, S. H.; Calik, M.; Hettstedt, C.; Karaghiosoff K.; Döblinger, M.; Clark, T.; Chapman, K. W.; Auras, F.; Bein, T. Nature Chem. 2016, 10.1038/NCHEM.2444.
[4] Calik, M.; Auras, F.; Salonen, L. M.; Bader, K.; Grill, I.; Handloser, M.; Medina, D. D.; Dogru, M.; Löbermann, F.; Trauner, D.; Hartschuh, A.; Bein, T. J. Am. Chem. Soc. 2014, 136, 17802.

Optical microresonators play an important role for various applications such as lasers, chemo- and biosensors, and optical communications. Whispering gallery mode (WGM) is one of resonating modes in optical resonators, which confines photons inside a cavity via total internal reflection and resonates by self-interference of photons. Among the WGM resonators, microspherical polymer resonators are beneficial, since simple self-assembling processes easily fabricate well-defined microstructure. So far, two types of polymer-based spherical optical microresonators are reported; one is fluorescent dye-doped microspheres made of non-conjugated polymers such as polystyrene (PS), and the other composed of π-conjugated polymers which itself have fluorescent properties. The wavelength of the resonance depends on the properties of the fluorophores, hence, different dyes/polymers are necessary if the various color photoluminescence (PL) is required.
In this presentation, we report on polymeric spherical microresonators that exhibit multicolor resonant PL by doping with a single fluorescent dye, boron dipyrrine (BODIPY). Typical BODIPY exhibits green PL in a diluted solution. The PL color changes depending on the aggregated state of BODIPY; yellow PL from the BODIPY monomer in a solid state, orange PL from the excimer state in the J-type aggregates, and red PL by a modulation of reflectivity from crystalline BODIPY. By taking advantage of the multicolor PL, we succeed in fabricating BODIPY-doped PS microspheres that exhibit multicolor WGM resonant PL. The PL colors can be selectively controlled with a wide range from green to red. Furthermore, coupling of the microspheres with different PL colors by a micromanipulation technique showed WGM cavity-mediated long-range, multistep FRET cascade. Such energy transfer system and multistep color conversion will be valuable for application to novel micro-optical communications.

Atomic layer deposition (ALD) is conventionally used to deposit smooth and conformal coatings from the gas phase onto surfaces. ALD onto nonreactive organic films, however, may lead to precursor infiltration into the sample and subsurface deposition. Hence, ALD into polymer films could be used for the preparation of inorganic-in-organic nanocomposite materials. Nevertheless, harnessing this approach requires deep understanding of the mechanisms that govern the infiltration, nucleation, and growth with respect to the processing and properties of the organic matrix. To do so we exposed films of a nonreactive polymer, poly(3-hexylthiophene-2,5-diyl) (P3HT) with different extents of crystallinity to ALD cycles of ZnO precursors at different deposition temperatures and examined the effect on the ZnO nucleation and growth inside the polymer film. We found that in the case of nonreactive polymer matrices, the inorganic uptake is significantly affected by the rate of nucleation which is determined by the retention of the precursors in the matrix. Moreover, the retention in the film is facilitated by the presence of crystalline domains, probably due to physisorption of the precursor molecules. This retention dependent mechanism is further supported by temperature dependence and deposition in amorphous/semicrystalline bilayers where the precursors diffused through the top amorphous layer but ZnO is deposited strictly in the bottom semicrystalline layer due to the preferred retention. Revealing the general growth mechanism in nonreactive polymer matrices offers new approaches for nanoscale characterization and engineering of hybrid materials, as will be demonstrated for hybrid and organic photovoltaics.

Triboelectric nanogenerators have been invented as a highly efficient, cost-effective and easy scalable energy-harvesting technology for converting ambient mechanical energy into electricity. Four basic working modes have been demonstrated, each of which has different designs to accommodate the corresponding mechanical triggering conditions. A common standard is thus required to quantify the performance of the triboelectric nanogenerators so that their outputs can be compared and evaluated. Here we report figure-of-merits for defining the performance of a triboelectric nanogenerator, which is composed of a structural figure-of-merit related to the structure and a material figure of merit that is the square of the surface charge density. [1] The structural figure-of-merit is derived and simulated to compare the triboelectric nanogenerators with different configurations. A standard method is introduced to quantify the material figure-of-merit for a general surface. This study is likely to establish the standards for developing TENGs towards practical applications and industrialization. [1]: Y. Zi et al, Nature Communications, 6:8376, 2015.

Triboelectric nanogenerator (TENG) is emerging as an intriguing technology for converting mechanical energy into electricity with merits of high output, simple design and low cost. The working principle of TENG is based on the combined effect triboelectrification and electrostatic induction. According to this mechanism, controlling the charge density on the triboelectric surface is the most fundament strategy for improving the performance of TENG. Nowadays, surface modification of triboelectric polymer is the predominant approach to regulating the charge density. However, the operation of TENGs requires intimate contact and sometimes friction between triboelectric materials, which inevitably induces wearing of the surface. In this regard, surface modification/engineering yields little contributions toward the performance gain in long-term operation. One essential solution is to extend the property engineering from mere surface to the bulk of the material.
Atomic layer deposition (ALD) is a powerful thin film growth technique on the basis of sequential self-limiting surface reactions. When implemented to certain polymers, the large permittivity of metalorganic precursors allows deep infiltration of inorganic compounds during ALD process, leading to inorganic/organic hybrid materials. This process is known as sequential infiltration synthesis (SIS). It has been successfully used to convert block co-polymer nanopatterns into more durable inorganic patterns and to improve the polymeric lithography resistance to subsequent etching. Inspired by these developments, we expect SIS could effectively tailor the internal composition and electrical properties of polymer films, which may provide an ultimate solution for triboelectric material design in the development of high-performance TENGs. Here, we present an internal AlO_x doping of several polymers via SIS, including polydimethylsiloxane (PDMS), polyimide (Kapton) and poly(methyl methacrylate) (PMMA).[1,2] We showed that SIS can introduce AlO_x molecules ~3 μm deep into these polymers, which effectively tuned the bulk electrical property of the film. TENG devices using the modified polymer films exhibited 8 times larger power output; and this enhancement remained effective after the surface of polymer film was polished off for more than 2 μm. This polymer doping approach paves a new path to bulk electrical property modification of polymer films, demonstrating a promising strategy for improving the performance of functional polymer based devices, such as TENGs.
Reference
1. Y. Yu, Z. Li, Y. Wang, S. Gong, X. Wang. Adv. Mater., 27, 4938-4944, 2015.
2. Y. Yu, X. Wang. Extreme Mech. Lett., doi:10.1016/j.eml.2016.02.019, 2016.

Structural defects such as entanglements and voids, low carrier concentrations, and weak Van der Waals inter-chain interactions result in thermal conductivities (κ) in polymers (0.1-0.5 Wm^-1K^-1) that are much lower than those of metals (20-400 Wm^-1K^-1) and ceramics (2-50 Wm^-1K^-1), thus limiting their use in fields such as microelectronics, power electronics, LED packaging, vehicles, and heat exchangers, where they would otherwise prove to be highly beneficial owing to their light weight, corrosion resistance, and low-cost manufacturability. Common methods to enhance polymers’ thermal conductivity include blending with high-κ metal or ceramic fillers and inducing chain extension through mechanical stretching, nanoscale templating, etc. These methods impart unwanted optical and electrical properties, increased weight, and/or high cost (high-κ fillers), or are difficult to practically implement in mass production (e.g., mechanical chain extension).

We present two design approaches to realize high κ in amorphous all-polymeric material systems. In the first approach, we envision replacing weak VdW interactions between polymer chains with hydrogen bonds that are 10-100x stronger. Such inter-chain connections should furthermore be made via short linker units to reduce thermal resistance, and should be present at a concentration sufficient to provide a continuous pathway for heat flow through the material. These parameters were met by a designed material blend of two different polymers: one, a short-chain stiff polymer (Poly(N-acryloyl piperidine), PAP) interpenetrating into the second long-chain flexible polymer (Polyacrylic acid, PAA) matrix and holding it in a more extended conformation through strong hydrogen bonds. The polymers were mixed in certain ratios of PAP and PAA in an organic solvent, and thin polymer blend films were deposited by spin-casting. The highest κ measured was 1.72 Wm^-1K^-1 for the monomer molar ratio of 30% PAP, which is one order of magnitude higher than that of the constituent PAP (κ = 0.19 Wm^-1K^-1) and PAA (κ = 0.22 Wm^-1K^-1) polymers.

In the second approach, we tested the idea that polymer chain extension even if not directionally oriented can be used to fabricate amorphous films with enhanced κ. This was achieved using a polyelectrolyte (PAA) which can be ionized at different conditions of acidity or basicity, resulting in a tunable charge density on the polymer chain and hence chain conformation (coiled-up at low pH to expanded above the pKa value) driven by Columbic repulsion between like charges. Thin films were spin-cast from polymer solutions of different pH. Thermal conductivity increased linearly with the degree of PAA ionization from 0.2 Wm^-1K^-1 at pH 1 to ~1 Wm^-1K^-1 at pH 10, demonstrating that extended polymer chains can result in significantly enhanced κ even in an amorphous film. This research showcases the potential of molecular engineering of polymers to enhance their thermal transport properties.

Plastics are normally thermal insulators and not ideal in heat transfer applications, despite that they are light and of low cost. Polyethylene (PE) is the basic ingredient for 60% of plastics. Bulk PE typically exhibits a very low thermal conductivity (k ~ 0.3 W/mK). However, the presence of strong covalent carbon-carbon bonds along PE chains suggest that individual molecular chains could be highly thermally conductive. Some of the authors had demonstrated before PE nanofibers with thermal conductivities of 104 W/mK, exceeding that of many pure metals. In this talk, we will present the recent development of high thermal conductive PE films by aligning the molecular chains using a roll-to-roll drawing procedure. We will present the fabrication process and show structural characterization results that confirm the presence of highly oriented PE chains of high crystallinity. Additionally, we will discuss the results of thermal conductivity measurements of the PE films. These high thermal conductivity PE films exhibit a unique functional combination of electrical, mechanical and optical properties not possible with any other heat transfer materials, which could be used in thermal management of in microelectronic devices and other applications.

This work was supported by the U.S. Department of Energy/Office of Energy Efficiency and Renewable Energy/Office of Advanced Manufacturing Program (DOE/EERE/AMO) under award number DE-EE0005756.

We report on the design, fabrication and characterization of flexible polymer metamaterials that provide passive radiative cooling and light diffusing by utilizing optical resonant effects in polymer microfibers with tailored sizes and material composition. New types of fabrics made of such materials can help people feel cooler by allowing thermal emission from the skin to pass through the clothes rather than being trapped inside. The micro-structured polymer fabrics can be made opaque to the visible light yet transparent to the infrared thermal radiation from the human body. They can also be designed to be largely transparent across both visible and infrared frequency bands for applications in other wearables such as e.g. laboratory gloves. In contrast, conventional fabrics mostly block thermal radiation emitted by the skin, contributing to overheating at high ambient temperatures. We identified synthetic polymers that support few vibrational modes as promising materials to reduce intrinsic material absorption in the IR wavelength range. Individual fibers were designed to minimize reflection in the IR by virtue of weak Rayleigh scattering. They can be simultaneously made optically opaque in the visible wavelength range by engineering strong Mie scattering. Compared to conventional personal cooling technologies, microstructured polymer fabrics can provide fully passive means to cool the human body regardless of the person’s physical activity level. The anticipated effect of the clothes made of such fabrics will be the increase in the body radiative cooling power leading to significant energy savings and reduction of air conditioning costs. We will also report on our on-going research on improving optical, thermal, and mechanical characteristics of these new types of flexible metamaterials as well as on new applications beyond indoors personalized cooling.

Semiconductor colloidal quantum dots are promising candidates for next generation energy efficient applications. Their near unity photoluminescence quantum yield, and tunable optical properties i.e. tunable photoluminescence profile with change in their composition or size, make them important agents as light harvesting agents. Thanks to their exotic optical properties, colloidal quantum dots have been used in wide range of applications in optoelectronics including photovoltaics, lasers and light emitting diodes.
Although a mature level of material quality have been attained with the synthesis of quantum dots, niche applications require these colloidal quantum dots as in their film form, in which difficulty arises due to their transfer to a host media or a substrate. In general, colloidal quantum dots are used after spin coating, spray coating, dip coating, inkjet printing or drop casting. However these substrate integrated methods do not make these nanocrystals readily available to be used for versatile applications. In this regards, polymeric composites of quantum dots are promising agents as they would offer free standing forms of nanocrystals ready to be employed for versatile applications.
In this work, we propose and demonstrate the synthesis, characterization and fabrication of color converting CdSe/ZnS quantum dots in their flexible polymeric film. The colloidal quantum dots with photoluminescence quantum efficiencies reaching 90% in solution have been extensively characterized including transmission electron microscopy, X-ray diffractometer, time resolved photoluminescence measurement set up and X-ray photoelectron spectroscopy in their synthesized form. When green and red emitting nanocrystal sheets are hybridized with blue light emitting diodes, these colloidal quantum dot sheets provide remarkably high enhanced NTSC (National Television Standards Committee) color gamut of 122.5% (CIE-1931) for display applications. On the other hand using a fourth color component as yellow emitting sheet, these flexible emitting platform offers color rendering index of 88.6, luminous efficacy of optical radiation value of 290 lm/W_opt and color temperature of 2763 K when used for lighting applications [1]. The utilization of the flexible emitting polymeric platforms will serve for next generation energy efficient applications.
Acknowledgement: This work have been supported by TUBITAK project no's 114E107, 5140079.
[1] Y. Altintas, S. Genc, M. Y. Talpur, E. Mutlugun,Nanotechnology 27 295604 (2016).