Thermal storage for electric vehicles (EVs) promises a means to deliver heating and cooling to the cabin without draining electric battery power to maximize driving range. However, thermal energy densities of 0.14 kWht/L and 0.12 kWht/kg for heating and cooling are needed for practical implementation into EVs. We are developing a thermal battery based on an adsorption cycle where the novelty lies in the adsorption bed with zeolites (ZTs) or metal organic frameworks (MOFs) as adsorbents. To maximize the heat and mass transfer of the bed, high thermal conductivity additives to adsorbents are desired. In this work, we integrated carbon nanomaterials, such as graphenes and carbon nanotubes (CNTs) with ZTs or MOFs by the impregnation and/or hydrothermal methods to enhance the thermal conductivity while minimizing decrease in adsorption capacity. Meanwhile, we varied the density of the composites using a hydraulic press. We characterized both the thermal conductivity and adsorption capacity of the various composites. In general, the thermal conductivity was proportional to the density of composites, but the rate of vapor transport was delayed with increasing density. In addition, the thermal conductivities of composites with graphenes (0.75 W/mK) were higher than those with CNTs (0.32 W/mK), which is attributed to the superior adhesion properties of 2-dimensional graphene to adsorbents than that of 1-dimensional CNTs. It is worthwhile noting that no decrease of the adsorption capacities was observed because only a small amount of graphene or CNTs (~3 wt% in the composite) was added, and micropore volume of ZTs or MOFs was not decreased after adding these thermal additives. Moreover, adsorption kinetics was also studied by using a vacuum chamber and an IR camera. We aim to further increase the thermal conductivity by further studying the synergetic effect between graphene and CNT, and by fabricating carbon percolation network within the adsorption bed. Our results provide helpful insights and guidance for the development of high thermal conductivity additives for advanced thermal batteries.

Significant effort has been devoted to the development of advanced electrolytes for use in lithium batteries, such as polymers, gels, inorganic-polymer composites, inorganic-liquid composites (soggy-sands), hybrids, and ionic liquids. We report on the development of a lithiated nanoparticle-organic hybrid composite platform,[1] whereas inorganic nanoparticles are densely cofunctionalized with both neutral oligomers and short ligands terminated with a lithiated anion, then dispersed in a host. The functionalized nanoparticles are essentially nanometric salts whose dispersion in the matrix is enhanced by the oligomeric ligands. The conductivity and lithium transference number of the resulting electrolyte may be tuned by tailoring the chemistry of the tethered anion and host matrix, the loading of the nanoparticle salt, and/or upon addition of a mobile lithium salt.
Electrolytes containing high lithium transference numbers, and thus reduced ion concentration gradients, are desired for application in both lithium-ion and lithium metal batteries. However, ion pair dissociation remains a challenge in electrolytes containing tethered anions, particularly in a low dielectric constant host matrix. In a recent study,[1] we demonstrated that a lithated nanoparticle-organic hybrid composite composed of silica nanoparticles cofunctionalized with polyethylene glycol ligands and short -SO2 BF3Li terminated ligands dispersed in tetraethylene glycol dimethyl ether can achieve an ionic conductivity of 10^(-4) S/cm at room temperature, without the addition of any other dopant lithium salt. Data obtained by dielectric spectroscopy measurements was modeled and used to determine mobile ion concentrations values, thus providing insight into the percentage of dissociated ion pairs as well as the mobility of the ions contributing to conduction. These measurements indicate abnormally high ion mobility, suggesting that an alternative mechanism, such as ion transport along the particle surface or between anion sites, is contributing to conduction.
Further improvements in the ionic conductivity of the lithiated nanoparticle composite electrolytes may be achieved by altering the chemistry of the host matrix. We will report on the analysis of dielectric spectroscopy data that provides insight on mobile ion concentrations, ion mobilities, and transport pathways in these complex composite electrolytes.
1. J. L. Schaefer, et. al., Chem. Mater., 2013.

Graphene has shown a great potential for applications as electrodes in future electronics due to its novel electrical transport properties such as high conductivity and high electron mobility. In the current work, layers of PZT-Epoxy Matrix based composites with Multi-walled carbon nanotube (MWCNT) fillers are stacked over each other on a flexible stainless steel substrate of thickness of 10 mu;m, to enhance the electromechanical properties of the composite thick film. The composite layers are deposited by means of spin coating of a sol-gel comprising of a dispersion of PZT, Epoxy and MWCNT in ethanol over the substrate. Each of the layers in the multimorph are connected with each other by graphene electrodes to enable better transport of electrons between the layers. Each stack is then poled by the corona poling technique at 15-20 kV/mm. The dielectric and piezoelectric properties of the stacked multimorph are then tested and compared to that of a single composite layer. The relationship of the number of composite layers deposited on the stainless steel substrate to the effective electro-mechanical properties is investigated and the effect of the MWCNT volume fraction of the individual layers is studied. Microstructural properties such as agglomeration of MWCNT inclusions, clustering of PZT inclusions in the Epoxy matrix and the contact resistance between the different phases have significant effects on the electromechanical properties of the composite . The present work also includes the analysis of the microstructure of the composites and also the individual phases through SEM and TEM imaging to determine and effects of the aforementioned factors on the composite. The surface properties of the individual layers in the composite multimorph are studied by means of AFM imaging techniques to investigate the effects of the surface roughness and contact resistance between the composite layers, on the effective dielectric and piezoelectric properties of the stacked device.

As electronics devices continue to shrink and the information density continues to rise, the device structure continues to move to ever smaller dimension. To be able to print features as small as 10nm, extreme UV lithography (EUV) is being pursued.
In EUV, a chemical amplification scheme, thin resist (less than 100 nm) and extremely short wavelength (~13.5 nm) light are being explored. In a chemical amplification resist, a photo acid generator (PAG), quencher base (QB) and resist polymer are mixed together to form a thin film on the substrate. Several complicated phenomena, miscibility, thin film densification, acid diffusion, and water diffusion and swelling, all contribute to the lithographic performance significantly. On the other hand, the glass transition and viscoelasticity, which dictate the polymeric behavior, do not follow the traditional bulk properties of the material because the treatment of the materials itself as the whole system breaks down as the physical dimension of the material is approaching its structural dimension (the thickness of a film less than 100 nm). In this talk, we will discuss the effect of acid diffusion and viscoelastic properties in resist films on their lithographic performance.

Solid polymer electrolytes in lithium ion batteries can offer significant advantages compared to conventional liquid electrolytes including safety, stability and thin film manufacturability. However, the major disadvantage of poor ion conductivity especially at room temperature still presents a challenge. Nanoscale fillers are shown to improve ion conductivity up to 3 orders of magnitude although the specific mechanisms are still under debate. In this study, we investigated the mechanisms of lithium ion conductivity enhancement and degradation in polymer nanocomposite electrolytes and proposed a free-volume based model. Agreement between our model predictions and experiments confirm that our postulated mechanisms can explain the dependence of ion conductivity on nanofillers. In addition, a series of molecular dynamics (MD) simulations of polyethylene oxide (PEO)/LiClO4 electrolyte filled with TiO2 nanoparticles were performed using explicit atom models. Results from the MD simulations show that the addition of TiO2 nanoparticles changes the dissociation of LiClO4 salt and the mobility of lithium ions relative to that of unfilled state and the changes appear to be dependent on particle size and surface properties.

Thin films and nanocomposites are among the many new thermoelectric architectures being explored to increase the efficiency of the heat to energy conversion in a material, represented by ZT. Polymer nanocomposites are promising alternatives that offer simple fabrication techniques, reduced cost, and low toxicity compared to traditional inorganic semiconductors. Many of these materials are expected to be anisotropic; therefore the ability to measure the in-plane transport, both thermal and electrical, for these systems is extremely important. Additionally, to obtain a ZT more representative of the candidate materials, the error associated with (i) estimating thermal conductivity using the Wiedemann-Franz law or (ii) assuming that the cross-plane (k_perp;) and in-plane thermal conductivity (k_II) are equal must be reduced. Although measuring electronic properties such as conductivity (σ) is straightforward, measuring k_II directly is challenging. In this talk, will discuss our technique for measuring thermopower, σ, and k_II of the same sample^1-3 and present the first test of this method on thin films consisting of single-walled carbon nanotubes.
1. Rubina Sultan, A.D. Avery, G. Stiehl, and B.L. Zink, Journal of Applied Physics105, 043501 (2009).
2. B.L. Zink, A.D. Avery, Rubina Sultan, D. Bassett, and M.R. Pufall, Solid State Communications150, 514-518 (2010).
3. A.D. Avery, Rubina Sultan, D. Bassett, D. Wei, and B.L. Zink, Physical Review B Rapid Communications83, 100401(R) (2011).

With a hydrophillic interlayer spacing of less than 1 nm, graphene oxide is the ideal testbed for water-based solute permeation. Combined with the ease of synthesis by vacuum filtration, it promises a cheap yet high performance platform for technological applications such as nanofiltration and proton exchange membranes. In this work we present ion diffusion, proton transport and electrophoresis through graphene oxide membranes. We quantify the ionic diffusion coefficients and model the ionic flow through different geometries of the membrane with respect to the flow. Effect of osmotic pressure and size exclusion are discussed. Initial measurements on chemically functinalized graphene oxide are also presented.

Here, we report the realization of ultrahigh thermal conductivity κ metal-nanowire-filled polymer nanocomposites, and unveil the effects of filler fraction on κ and the thermal conductance G_int of their interfaces with metal contacts. Obtaining high κ nanocomposites is a challenge because of difficulties in incorporating high fractions of uniformly dispersed nanofillers and countering low filler-matrix interfacial conductance. Here, we obviate these issues by using < 3 volume% ultrathin sub-10-nm gold nanowire fillers in polydimethylsiloxane [1] to obtain a unprecedented 30-fold increase in κ to ~5 Wm^-1K^-1, which is 6-fold higher than nanocomposites with other nanofillers at comparable filler loadings and exceeds theoretical predictions. We show that low diameter and high aspect ratio are key to forming cold-welded nanowire networks that enhance κ while retaining low elastic modulus of ~ 5 MPa and low electrical conductivity. However, the interfacial thermal contact conductance of copper-contacted nanocomposites is low, e.g., G_int~1.5 kWm^-2K^-1. Rheology measurements reveal that the low G_int is due to a liquid-solid transition that is sensitive to the nanowire loading fraction. In particular, the formation of a percolation network that maximizes κ also causes pre-cure gelation of the polymer, thereby inhibiting the formation of void-free interfaces leading to low G_int. Our results provide a basis and insights for designing processes to increase G_int while maintaining high κ for applications such as device packaging and energy harvesting.
1. N. Balachander, I. Seshadri, R.J. Mehta, L.S. Schadler, T. Borca-Tasciuc, P. Keblinski, and G. Ramanath, “Nanowire-filled polymer composites with ultrahigh thermal conductivity,” Applied Physics Letters, vol. 102, 2013, pp 093117 - 093117-3.

Most scintillators for gamma-ray detection use large single-crystals, which are often difficult and expensive to grow on a large, application-ready scale, or bulk materials such as NaI:Tl, which has decent but relatively inferior resolution and performance. By impregnating higher performance materials, which may be difficult to grow large-scale crystals of, into a nano-porous matrix, we can obtain comparable performance at a small fraction of the cost and processing time.
Two of the top-performing gamma-scintillators are LaBr₃:Ce³⁺ and SrI₂:Eu²⁺. Here we demonstrate the inclusion of such materials into transparent porous matrices, such as highly tunable mesoporous silicas and other porous glasses. We present their performance in terms of photo and radio-luminescence, as well as gamma-ray response.

A Boltzmann transport equation based formalism is developed to analyze the
thermoelectric properties of anisotropic single crystal materials. By
rotating the crystal in all directions and taking an average over all
angles, we developed a formalism to study nano-grained samples prepared by
means of ball-milling and hot-pressing. It was found that the relative
size of the electron mean free path, the cyclotron radius, and the grain
size determines the anisotropy in the thermoelectric response of the
samples under the magnetic field. The theory is compared with the
experimental data obtained for nano-composite samples of Bi2Te3. Two
particular nanograined Bi2Te3 samples were studied. The first sample is
isotropic in the sense that in the absence of the magnetic field, the
electrical and the thermal conductivity tensors are diagonal with
identical elements. The second sample preserves the anisotropic behavior
of Bi2Te3 and is measured to have different thermal and electrical
conductivities in different directions.

Recently, we discovered a new family of two dimensional, 2-D, early transition metal carbides produced by the exfoliation of MAX phases (ternary transition metal carbides). The exfoliation process was carried out by selective etching of the A-group element from the MAX phase, resulting in 2-D Mn+1Xn layers, which were labeled “MXene” to emphasis their similarity to graphene. Eight different carbides and carbonitrides have been produced to date; the properties of a larger number of 2D compounds have been predicted by DFT. DFT simulations showed that band gap of Ti3C2 can be tuned from metallic to semiconductor by changing its surface termination (O, OH and F), and its elastic properties along the basal planes (c11 asymp; 523 GPa) are higher than that of the binary carbide TiC. Herein we focus on the ion intercalation and transport in MXenes and their composites for electrodes of Li-ion batteries and electrochemical capacitors. Recently, we reported on the intercalation of molecules into Ti3C2, Ti3CN, and TiNbC. Hydrazine, urea, DMSO and other organic compounds also intercalated Ti3C2. When dimethyl sulfoxide was intercalated into Ti3C2, followed by sonication in water, it delaminated forming a stable colloidal solution that was in turn filtered to produce MXene “paper”. One of the potential applications for 2-D Ti3C2 is in energy storage systems, such as lithium ion batteries and electrochemical capacitors. Additive-free Ti3C2 anodes produced by filtering an aqueous dispersion of delaminated Ti3C2, showed capacity exceeding that of graphite battery electrodes at low rates, but also capable of charging/discharging at rates approaching 40C with excellent cyclability. Mechanisms of ion transport between MXene layers will be discussed.

Polymer nanocomposites are currently utilized in a variety of high performance applications, most notably by the aerospace industry due to their high strength to weight ratio. However, the epoxy matrix is vulnerable to degradation from ozone during long-term flight in the troposphere and stratosphere. Polyhedral oligomeric silsesquioxanes (POSS) are unique nanoparticles consisting of an inorganic Si8O12 cage which can support up to eight organic functional groups that can substantially affect the solubility of the moiety.[1] The POSS moiety tends to form micron-sized aggregations due to the incompatibility of the inorganic cage within a polymeric system. These aggregations often show surface migration behavior during cure.[2] Molecular simulations can explore the protective potential of such surface aggregation against degradation. Materials Studio® 6.1 was used to create neat POSS layers with octa-methyl, octa-isobutyl and octa-phenyl pendants. The diffusion coefficient for ozone through each of these layers was determined and correlated to the free volume present. Each type of POSS moiety was combined in a amorphous cell with epoxy monomer, diglycidyl ether of bisphenol A (DGEBA), with crosslinker, 4,4&’-diaminodiphenylsulfone (44DDS), and analyzed for mean squared displacement, chi parameter and diffusion coefficient. These parameters are not well understood for POSS in an epoxy system, which hinders laboratory studies of protective POSS surface layers. POSS surface layers with each of the three pendant groups were then annealed over a trimerized epoxy system. Ozone diffusion rates were determined for each nanocomposite layer with special attention paid to the effect of the extent of POSS at the surface on the diffusion coefficients and free volumes.
1. Constantin, F.; Garea, S.A.; Iovu, H. Composites Part B 2013, 44, 558-564.
2. Dintcheva, N.Tz.; Morici, E.; Arrigo, R.; La Mantia, F.P.; Malatesta, V.; Schwab, J.J. Polym. Degrad. Stab. 2012, 97, 2313-2322.

Carbon nanotubes (CNTs) have much attracted to both structural and functional application due to their superior mechanical, electrical and thermal properties. In particular, because of their extraordinary thermal properties such as high thermal conductivity (asymp;3500 Wm-1K-1) and very low coefficient of thermal expansion (CTE), CNTs are considered to be ideal fillers of composites materials for the electronic devices. During the past decades, many investigations of CNT reinforced polymer matrix nanocomposites have been reported and have shown improvement of thermal properties. However, in metal matrix, most of researches have been focused on mechanical property and only a few researches about thermal property have been reported. In this research, the thermal properties of CNTs reinforced Al-Cu matrix nanocomposites were investigated. CNT/Al-Cu nanocomposites were prepared by mixing of CNT/Cu powders and Al powders by high energy ball mill process followed by spark plasma sintering and show a microstructure of homogeneous dispersion of CNTs in the Al-Cu matrix. The thermal conductivity of CNT/Al-Cu nanocomposites decreased as increasing the content of CNTs because of the interface thermal resistance between CNTs and Al-Cu matrix. The coefficient of thermal expansion (CTE) also decreased due to homogeneous dispersion and low CTE value of CNTs.

Dye-sensitized solar cell (DSSC) has been considered as an alternative to a conventional silicon solar cell because of low cost, easy fabrication and relatively high conversion efficiency. Recently, an impressive conversion efficiency of 12% has been achieved in a DSSC with a liquid electrolyte [1]. However, leakage or evaporation of liquid electrolyte is a critical problem that limits the long-term operation and practical use of DSSCs. To overcome these problems, considerable efforts have been made to replace liquid electrolytes with gel polymer electrolytes that exhibit high ionic conductivity and improved stability. However, such gel polymer electrolyte suffers from poor mechanical strength. An activation of a porous polymer membrane in electrolyte solution is an efficient method to solve the problem [2]. Unlike conventional methods such as solution casting and direct dissolution of the polymer in the electrolyte solution, this procedure handles the mechanically robust porous membrane until adding liquid electrolyte to it at last. In this work, we prepared electrospun polyacrylonitrile-based nanocomposite fibrous membrane. The DSSC was then assembled by sandwiching the electrospun membrane between dye-coated TiO2 electrode and Pt counter electrode, and injecting an electrolyte solution into the cell. The electrolyte solution was composed of 0.5M lithium iodide, 0.05M I2 and 0.05M 4-tert-butylpyridine in acetonitrile. The photovoltaic performances of DSSCs are investigated and compared with those of liquid electrolyte-based DSSC. The influence of nano-sized ceramic particle content on the photovoltaic performance of DSSCs is also investigated.
References
1. A.Yella, H.W.Lee, H.N.Tsao, C.Y.Yi, A.K.Chadiran, M.K.Nazeeruddin, E.W.G.Diau, C.Y.Yeh, S.M.Zakeeruddin, M.Gratzel, Science, 334, 629 (2011).
2. D.W.Kim, Y.B.Jeong, S.H.Kim, D.Y.Lee, J.S.Song, J of Power Sources, 149, 112 (2005).

We prepared self-assembled materials consisting of TiO₂ nanoparticles; N, O-carboxymethylchitosan (NOCMCh); and poly(ethylene oxide)(PEO) by the Layer-by-Layer (LbL) technique, aiming to employ them as modified electrode under high lithium ion electroinsertion rate. Electrostatic interaction between the components promoted growth of visually uniform TiO₂/NOCMCh films with highly controlled thickness. Bearing in mind the low charge density of PEO, we prepared a polymeric mixture of NOCMCh and PEO to incorporate the polyether into the self-assembled structure during the preparation of LbL TiO₂/NOCMCh/PEO films. Scanning electron microscopy (SEM) and contact angle measurements between the electrolytic solution and the thin films surface suggested that the polymers affected the mean size of the aggregates and the permeation of the electrolytic solution into the host matrix, providing a better electrolytic connection between the TiO₂ sites. Chronopotentiometric curves and the differential capacities recorded as a function of the potential under several applied current densities showed higher charge capacity and absorbance changes (ΔA) for the TiO₂/NOCMCh/PEO electrode. We employed the potentiostatic intermittent titration technique (PITT), to evaluate the chemical diffusion coefficient (D_c) associated with electron and lithium ion diffusion into the host matrices. To investigate the independent motion of these charge carriers in the absence of an internal electrical field, we also obtained the Wagner factor (W) and the lithium (D_Li) and electron (D_e) self-diffusion coefficients. Spectroelectrochemical measurements also indicated higher coloration front rate due to lithium ion transport in the TiO₂/NOCMCh/PEO electrodes. The electrochemical impedance spectroscopy (EIS) measurements suggested trapping effects and anomalous diffusion, which contributed to a better understanding of the role that polymeric components play in charge transport within the self-assembled materials under high electroinsertion rate.

From metallic copper flakes, monodispersed copper nanoparticles (CuNPs) were successfully prepared using a straightforward and environmentally friendly method by utilizing the ionic liquid such as 1-butyl-3-methyl imidazolium nitrate (BMIM⁺ NO₃^-) and 1-methyl-3-octyl imidazolium tetrafluoroborate (MOIM⁺BF₄^- ). No other reducing agents, capping agents, dispersants were added, making it a green process. The formation of copper particles and the mean diameter (10 nm) of CuNPs were characterized by UV-vis spectra and TEM, respectively. Furthermore, this facile synthetic route allows the in-situ fabrication of facilitated olefin transport membranes due to not only ionic liquid but the highly polarized surface property of CuNPs. It is expected that the free imidazolium cations will interact with olefin molecules and the free anions will positively polarize the CuNPs. The positive charge on the surface of the CuNPs was investigated by the binding energy using XPS. When the MOIM⁺BF₄^-/CuNPs were applied to the separation of propylene/propane mixture (50:50, v/v), the mixed gas permeance increased 12 from 6.9 GPU, nearly twice that of neat ionic liquid. These results suggest that the preparation of positively polarized CuNPs by ionic liquids could be one of the simple but powerful strategies toward olefin separation.

The CO₂ separation is one of the most urgent issues, and polymeric membranes are very attractive for CO₂ separation. Developing the most effective for CO₂ permselective mediums, the introduction of a feasible CO₂ complex site into the membrane matrix could give rise to the carrier-mediated transport, so-called ‘facilitated transport&’. This strategy improves both the diffusivity and the solubility of membrane, resulting in the enhanced mass transport property. Here we report the polymer electrolyte membrane containing potassium (K⁺) which is known to complex with CO₂. Potassium fluoride (KF) was introduced to polyvinylpyrrolidone (PVP) with various concentrations. The chemical environment of prepared membranes was characterized by FT-IR, DSC and XPS. The interaction between the amide group of PVP and K⁺ was confirmed by FT-IR spectroscopy and DSC. Depending on the coordination of K⁺ to PVP, the changes in potassium binding energy were also confirmed by XPS. When the polymer electrolyte membranes (PVP/KF) were applied to the separation of CO₂/N₂ and CO₂/CH₄, the best separation performance (CO₂/N₂ = 4.06 and CO₂/CH₄ = 1.83 with CO₂ permeance of 28.34 GPU) was observed at PVP/KF = 1:0.4 (mol. ratio). These enhanced separation performance compared to that of the neat PVP could be ascribed to the interaction between K⁺ and CO₂ molecules, and it suggests K⁺ plays a role as a CO₂ carrier.

Energetics at organic/metal interface becomes interested in designing new functional materials for novel applications, including the facilitated transport membranes resulted from the carrier-mediated mass transport for gas separations.[1] A new strategy to design facilitated transport membrane has been emerged recently, based on the discovery that surface positive charge on metallic silver nanoparticles (AgNPs) is able to complex with olefin such as propylene.[2] In this study, we report the significantly increased carrier activity of AgNPs in silver-olefin complexation by utilizing tetracyanoquinoidal molecules (TCQs) such as TCNQ and F4-TCNQ. The interactions of AgNPs and TCQs were investigated by UV-vis spectroscopy. The UPS and XPS data revealed vacuum level shifts and dipole formation at the AgNPs/TCQs interface, resulting in the increased work function of the AgNPs from 4.89 up to 5.25 eV. Furthermore, self-assembly of AgNPs in the presence of TCQs was observed in TEM images. As a result, membranes containing AgNPs/TCQs demonstrated a mixed gas selectivity of ca. 100 for a 50/50 (vol%) propylene/propane mixture and showed stable performance for 100 hrs. Also, the AgNPs mediated CO2 transport will be discussed for CO2/N2 and CO2/CH4 separations.
[1] I. S. Chae, S. W. Kang, J. Y. Park, Y-G. Lee, J. H. Lee, J. Won, Y. S. Kang, Angew. Chem. Int. Ed., 2011, 50, 2982.
[2] Y.S Kang, S. W. Kang, H. Kim, J. H. Kim, J. Won, C. K. Kim, K. Char, Adv. Mater., 2007, 19, 475.

We describe how high calcination temperatures introduce anisotropy into inverse opal structures and how this anisotropy effects the optics and wetting. Inverse opals are ordered, porous materials formed from the negative space in a colloidal crystal. Due to their high periodicity, they are three-dimensional photonic crystals, giving interesting optical properties. Due to their high porosity, they form interconnected networks with interesting wetting properties. In this presentation, we describe the mechanism of the geometry changes from high calcination temperatures; further, we describe how this change in geometry can be used to tune the properties of inverse opal films. The optical peak changes predictably with the introduction of anisotropy. Additionally, liquids wet anisotropic inverse opals more easily, and we provide a theoretical understanding of this liquid wetting.

Aerosol filters are typically made of small fibers that are designed to capture small particles from the air. Nano-fibers provide greater filtration efficiency than conventional micro-fibers due to higher surface area and smaller pore sizes. Electrospinning is the most common method to produce nano-sized polymer fibers less than 400 nm in diameter for aerosol filtration. On the other hand, aerosol filter that made of electrospun fibers are associated with a higher pressure drop across the filter. Carbon nanotubes (CNTs) are small diameter fibers that have the potential to be integrated into filters to further increase capture efficiency.
In this study, carbon nanotubes sheets, drawn from millimeter tall carbon nanotube arrays, were integrated between melt-blown polypropylene fabrics to produce aerosol filters. The filtration performance of the novel filters was evaluated using particles with a range in size of 10-300 nm. The results showed that when the number of CNTs layers increased, the filtration efficiency increased dramatically while the pressure drop also increased. In order to meet high efficiency particulate air (HEPA) filter requirements at lower pressure drop, carbon nanotubes were laid in a cross-ply structure within the filter. The results demonstrated that the three layer cross-ply structure provided 99.97% filtration efficiency at 0.3 µm particle size at a 10 cm/s face velocity, making this a viable method for producing HEPA filters with low basis weight using CNTs as the main filtration component. The results also show that these novel CNT filters have filtration properties that are comparable to or better than electrospun filters, because these novel filters have smaller fiber diameters and a low packing density with 99% porosity. At high gas flow rates it was shown that the CNTs were completely trapped between the outer polypropylene fabric layers due to their millimeter length. When combined with glass outer layers the filters can be used in high temperature applications. Due to the continuous nature of the CNT sheet drawing, this process may be a viable method for producing high performance HEPA filters in the future.

A power supply with low environmental impact is essential for sustainable growth; therefore, efforts are necessary, to develop new energy sources. Moreover, there is great interest in producing electricity converted from forms of non-utilized energy at low cost. One example is to obtain electricity from solar, wind, geothermal, and biomass sources. Entropic changes associated with electrolytic solutions mixtures can provide useful work, in accordance with the principles of thermodynamics. Thus, selecting low-irreversibility systems that can convert non-utilized energy into electrical work efficiently is mandatory. In this context, electrical energy can be obtained by treating acid industrial wastes, because the addition of alkaline reagents during the neutralization process increases entropy. Here, we investigated thin self-assembled films originated from phosphomolibydic acid (PMA), poly(3,4-ethylenedioxythiophene/poly(styrenesulfonate) (PEDOT/PSS), and polyallylamine (PAH) as positive electrodes, to possibly apply them in mixing entropy batteries (MEB). Pseudo-capacitive processes involving fast proton electro-insertion into the PMA and PEDOT/PSS host matrices makes these materials potentially applicable in MES in acidic medium. Additionally, the high proton and electron conductivities of PMA and PEDOT, respectively, tend to reduce the overpotential during the charge/discharge processes, which is essential to guarantee minimal energy loss after the complete electrochemical cycle. We used the Layer-by-Layer method (LbL), to decrease the solubility of PMA in aqueous medium due to electrostatic interaction with the prototaned amine group from PAH. Furthermore, the high thickness and nanoarchitecture control provided by this method furnished a thin film and diminished diffusion and ohmic overpotentials as well the contact intimate between PMA and PEDOT/PSS. Consequently, important synergetic effects arose, contributing to a better performance of the MEB proposed in this work. We evaluated the MEB by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy (EIS).

In order to apply various portable devices lightweight forms, such flexible solar panels, fabrication require very low temperature (or near room temperature) processes. Various methods, such as capacitively coupled RF-PECVD, hot wire CVD, very high-frequency PECVD and electron cyclotron resonance CVD have been extensively used for the fabrication of nc-Si thin films. A nano-crystalline (nc)-Si thin film is more stable but possesses lower absorption in comparison to an a-Si thin film for Si thin film based solar cell. For overcoming the weakness of the a-Si:H and nc-Si:H thin film, “nc embedded polymorphous(pm) silicon (nce-p-Si)” is considered as one of alternate. These nc-Si related phases have higher stability than amorphous and higher absorption coefficient than micro-crystal (mu;c) or nc phases. Another issue of flexible device is how to deposit and activate a doped thin film at low temperature because doping process always need high temperature process or post annealing for electrical activation. However, by its inherent structural complexity and its sensitivity to changes in deposition parameter such as high hydrogen dilution ratio, making it very difficult to accurately predict or control the resultant electronic and optical properties. Also the most basic details about how the crystalline volume fraction, impurity levels and dopant location in nano-size grains affect carrier transport are still unresolved.
Recently, we are developing a novel CVD technology with a neutral particle beam (NPB) source, named as neutral beam assisted CVD (NBaCVD), which controls the energy of incident neutral particles (mainly H) in order to enhance the atomic activation and crystalline of thin films at near room temperatures (<80°C). In traditional hydrogenated Si deposition, the gas mixture ratio of H and Si controls the phase of thin films, such as a-Si:H, µc(or nc)-Si:H, while the substrate temperature determines the doping efficiency, mainly. Conversely, the NBaCVD system can control the crystalline phase and the doping efficiency (in this case, the issue includes dopant location inside nano size grain and activation) simultaneously by the energy and flux of impinge neutral particles. During the deposition process, energetic H-neutral atoms transport their energy to the surface of depositing film to enhance crystallization (Xc ~85%) and dopant activation (~1X1020 #/cm3, ~30 cm2/Vs) with low H ratio at near room temperature on the substrate. Also the increase of H enhance transport path (mobility incensement) which is deduced from transition of crystal orientation from [111] to [311] at constant Xc and dopant and impurity location in nano size grain. These properties can explain how the charges transport through grain to grain or grain boundaries.

Magnetic/fluorescent (magnetofluorescent) composite nanoparticles have become one of the most important tools in the imaging modality in vivo using magnetic resonance imaging (MRI) monitoring and fluorescence imaging. In the design of such materials, the fabrication of nanoparticles consisting of nontoxic and safe materials is absolutely critical. We report herein on a simplified procedure to synthesize magnetofluorescent nanoparticles that combine silicon and magnetic iron oxides consisting of magnetite and maghemite. Moreover, the size effect on the magnetic/fluorescence behaviors and the cytotoxicities of obtained nanoparticles are also discussed.
The magnetofluorescent nanoparticles were prepared by the combination of radio frequency (rf) magnetron sputtering process and subsequent rapid thermal annealing process at high temperature. The size of nanoparticles was controlled from 3.0 nm to 8.0 nm by varying the compositional ratio of sputtering targets consisting of silicon chips/magnetite chips/silica disk. After annealing process, the samples were treated in hydrofluoric acid solution in order to form the individual magnetofluorescent nanoparticles. The individual nanoparticles were then co-cultured with HeLa cells (derived from the human cervical cancer cell line) to investigate the cytotoxicity.
Our unique synthetic approach could control the magnetic and fluorescence behaviors by reducing the size, demonstrating that the magnetofluorescent nanoparticles with the mean diameter of 3.0 nm exhibit superparamagnetic behavior and green fluorescence in an aqueous solution, an ambient air and a cellular environment, whereas the nanopaticles with the mean diameter more than 5.0 nm indicate ferromagnetic behavior with near-infrared fluorescence. Additionally, both magnetofluorescent nanoparticles showed not only excellent magnetic responsivity for external applied magnetic field but also good biocompatibility due to the high viabilities of HeLa cells stained with the nanoparticles. Thus, our biocompatible magnetofluorescent nanoparticles would provide an attractive approach for diagnostic imaging system in vivo and area of biochemistry.

ZnO, a wide bandgap semiconductor, has attracted much attention due to its multi-functionality, such as transparent conducting oxide, light emitting diode, photocatalyst, and so on. To improve its performances in the versatile applications, numerous bybrid strategies of ZnO with carbon nanotube (CNT) have been attempted, and various synergetic effects have been achieved in the ZnO-CNT hybrid nanostructures. Most of its multi-functional properties are essentially influenced by electrons, so that understanding the behavior of electrons in the ZnO-CNT hybrid system is of great significance to expand the opportunities in relevant applications.
In this work, we report the temperature-dependent charge transport properties in 2mol% Al-doped ZnO (AZO)-multi-walled CNT (MWCNT) nanocomposite. The AZO-MWCNT nanocomposite was prepared by spark plasma sintering of AZO nanoparticles with MWCNTs, and the uniformly distributed MWCNTs in the nanocomposite were manifested by transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. The AZO-MWCNT nanocomposite exhibited significantly enhanced charge transport behaviors as compared with the AZO nanocomposite, which prepared by the spark plasma sintering without MWCNT. The electron transport in the AZO nanocomposite was determined by the grain boundary scattering due to the Schottky barrier originating from the trapped electrons at the grain boundary. Therefore, it exhibited relatively low Hall mobility even at room temperature (~ 12 cm2/Vs). However, in AZO-MWCNT nanocomposite, the trapped electrons could be released from the grain boundaries by the stimulation of MWCNT, resulting in the lowering of the Schottky barrier. Therefore, not only the significant increase in the carrier concentration, but also single crystal-like Hall mobility (46 cm2/Vs) could be achieved in the AZO-MWCNT nanocomposite. Detailed mechanism for the enhanced charge transport properties in the AZO-MWCNT nanocomposite will be presented.

Carbon-based nanofiller composites have widely been used for achieving improved thermal, mechanical and electrical properties, but it is often difficult to achieve proper properties along a desired direction because fillers are commonly aligned to the processing direction. In this study, we used a directional cooling crystallization method as a fabrication process of polymer matrix having aligned pores of thickness-through. The pores having lamellar morphologies were then used for the impregnation of nanofillers. After a subsequent impregnation method using the adsorption of graphene sheets on the wall surfaces of highly aligned pores, we could produce anisotropic graphene/polyurethane composite materials. The key achievement of this method is that we can control the directionality of thermal and electrical properties in the aligned pore direction of matrix. The major electron pathway was successfully aligned following the pore direction with the coated graphene on the pore wall, while pores are playing a role of blocking electron transfer. This method is simple and requires a relatively small amount of fillers to improve the transport performances. Therefore, controlling the matrix pore morphology can widen the applicability of this process for pressure sensitive materials in processing direction.

Copper is widely used as a key material in the electricity, electronic and information industries because of its good mechanical, thermal and electrical properties. On the other hand, graphenes have recently attracted a great deal of attention due to low density of ~2.2 g/cc as well as superior mechanical, thermal and electrical properties such as Young's modulus of ~1 TPa, fracture strength of ~125 GPa, thermal conductivity of ~5000 W/mK and carrier mobility of ~200,000/vs. In the present study, copper/graphenes nanocomposite is fabricated using a solution process to enhance the mechanical performance and functionalities of copper. Specifically, a solution process was used to disperse graphenes in the copper matrix homogeneously and to induce the strong interface between copper and graphenes. Copper/graphenes composite powder was synthesized via reaction of copper ions and substituent groups in the graphenes: graphene oxides and copper salts are dispersed in ethyl alcohol, thereby producing substituent groups on the surface of the graphene oxides and ionized copper; then, the copper ions are bonded with the substituent groups in the graphenes. To obtain a copper/graphene composite pallet, composite powder was calcinated at 300oC in Ar atmosphere, reduced at 250oC in H2+Ar atmosphere, and then hot pressed at 500oC. The structure and properties of the composite material, varied according to fabrication condition, will be discussed.

Over the past ten years, the exploration of high performance thermoelectric materials has attracted great attention worldwide from fundamental to industrial applications. In recent years progress has been made in developing thermoelctric materials with a high dimensionless figure of merit (ZT) and the related fabrication processes for producing nanostructured materials. Chalcogenide type nanoparicles are semiconducting in nature which is advantageous for use in a wide variety of applications including thermoelectrics, solar cells and solar catalysis. In this study chalcopyrite copper iron sulfide was developed to utilize the interaction between carriers and magnetic moments of Iron as a possible source to achieve high power factor in thermoelectric applications. Chalcopyrite nanomaterials for thermoelectrics offer better sustainability because it is composed of abundant and non-toxic elements. The particles are also highly interesting from a fundamental perspective because the relative composition of copper and iron in the particles can be tuned, resulting in the ability to manipulate the electronic or band gap properties for the desired application. The synthetic technique and compositional/structural nanoparticle characterization will be discussed using techniques such as XRD, XPS, HAADF-STEM, elemental mapping and others. An assessment of the thermoelectric and electronic properties for these materials will also be presented.

Composites of magnetostrictive (MS) and piezoelectric (PE) layers on a cantilever substrate (Sub) are candidates for ultrasensitive magnetic field sensors at room temperature and recently have shown magneto-electric (ME) coefficients of 20 kV/cmOe in resonance. In these composites a magnetic field H causes a mechanical strain in the MS layer. On resonance this excites an oscillation of the cantilever, which is limited by damping. In the static case a static deformation follows. The deformation of the PE layer induces an electric field E and thus an electric potential difference V across the PE layer. Here, we present a theoretical investigation of the influence of the layer sequence, i.e., MS-PE-Sub, MS-Sub-PE, or Sub-MS-PE, on the achievable magneto-electric coefficient. We implemented analytic models for the static and resonant strain-mediated, bending-mode ME effect in thin film composites with different layer sequences. Using these linear elastic models we calculate the ME coefficients αME= dV/dH of the transverse ME effect (E _|_ H ) for varying layer thicknesses for each layer sequence in order to find the maximum achievable ME coefficient. In the resonant case the maximum ME coefficient is observed for the layer sequence MS-Sub-PE. In the static case the maximum ME coefficient is found for the MS-PE-Sub sequence with a similar achievable ME response for the Sub-MS-PE case. These results are explained by considering the neutral plane position, i.e., the plane of zero strain, for varying layer sequences, PE fractions, and substrate thicknesses. In the resonant case, the neutral plane position is dominated by the equation of motion with driving fields constituting small perturbations. In the static case, on the other hand, the cantilever bending is field-dominated and the position of the neutral plane even may be located outside the ME composite. The ME response diminishes for a neutral plane position in the center of the MS layer (no bending excitation, resonant case only) or in the center of the PE layer (electric field sign reversal in the PE layer, resonant and static cases). These effects may be prevented by a thick substrate layer. A thin substrate layer, on the other hand, allows for more efficient bending. The interplay of these factors determines the best layer sequence and the optimum layer thicknesses. The results will be presented for the FeCoBSi-AlN-Si material system, but the general behavior is found to be independent of the specific magnetostrictive, piezoelectric, and substrate materials used in the linear elastic strain-coupled models. The results are compared to finite element method (FEM) calculations.

This work was supported by the German Science Foundation (DFG) within the Collaborative Research Center SFB 855 “Magnetoelectric Composite Materials - Biomagnetic Interfaces of the Future”.

One of the most important challenges in fabricating devices with semiconductor nanocrystals (NCs) lies in identifying appropriate surface ligands that significantly enhance conductivities and carrier mobilities in NC solids. Assemblies of lead selenide (PbSe) semiconductor NCs can be chemically functionalized with compact surface ligands to facilitate stronger interparticle coupling. For this study, we functionalized PbSe NC thin films with chalcogenidometallate (ChaM) clusters and created electrically-conducting, all-inorganic films of NC solids. These ChaM molecules have significantly enhanced electronic performance for CdSe NC solids but have not yet been successfully used to create continuous films of Pb salts (e.g., PbSe) due to their unstable surfaces. We introduce a post-assembly processing approach in which the PbSe nanocrystals are first immobilized on the substrate via a self-assembled monolayer followed by chemical treatment to exchange the insulating oleate ligands with ChaM clusters. After the native ligands are replaced with the ChaMs, the material is annealed at elevated temperatures (180 °C) to form all-inorganic nanocomposites. Quantum confinement in the PbSe nanocrystals is preserved as evidenced by persistent excitonic features in the absorption spectrum. PbSe-ChaM composites exhibit n-type electrical behavior and peak electron mobilities of 1.3 cm2/V-s and 0.44 cm2/V-s, depending on ChaM composition. The enhanced carrier transport that arises from these coupled PbSe NC solids enables their integration into emergent technological applications like NC-based solar cells, thermoelectric devices, and photodetectors.

Photoinduced polymerization of the C60 films was carried out and confirmed by Raman Spectroscopy. The polymerized C60 films are insoluble in common organic solvents. Field dependent mobility of the C60 films was investigated at elevated temperatures using carrier extraction by linear increasing voltage (CELIV) method. The mobility and electron concentration of the polymerized films and pristine C60 films were measured. The experimental details on preparation and photopolymerization of the films and the effect of polymerization on the electron transport characteristics of the C60 films will be presented.

Transport properties have been measured transverse to the plane of sheared and un-sheared thin-film nanocomposites of isotactic Polypropylene (iPP) and carbon nanotubes (CNT) as a function of temperature for 0 and 2 wt% CNT concentrations. The thin-film samples were sheared in the melt at 200 C at 1 Hz in a Linkan microscope shearing hot stage. The thermal and electrical conductivity measurements were performed on the same cell arrangement with the transport perpendicular to the thin-film plane using a DC method. The thermal and electrical conductivity are higher for the un-sheared as compared to the sheared samples with stronger temperature dependence for the latter as compared to the former. Interestingly, the percolation threshold appears smeared in both conductivity measurement likely due to pressing and shear treatment of the films. Our cellular automata simulations of the thermal and electrical transport agree with the measurements and provide information about the microstructure-macroscopic property relation in the thin film nanocomposites. Important for electronics packaging and materials for which those anisotropic properties are highly desired this work presents important advances in understanding the structure-transport property relations.

Nanostructuring has been shown to be an effective approach in reducing lattice thermal conductivity and improving efficiency of thermoelectric materials. A challenge for experimental measurements of thermal conductivity is separating the contributions from both carriers and phonons. Building on the work of Lukas, et al.++ we report measurements of thermal and electrical conductivity of single crystal Cu [100] and W in a magnetic field up to 9 Tesla. Our experiments provide a separation of the lattice/electronic components and makes possible a better theoretical model of the lattice portion of the thermal conductivity in materials. This work is supported by the Solid State Solar-Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center sponsored by the DOE, Office of Basic Energy Science, Award No. DE-SC0001299/DE-FG02-09ER46577.
++K. Lukas, et al., Phys. Rev. B 85 205410 (2012).

The main goal of the research was to examine the effect of electric fields, due to ferroelectric nanoparticles located at the depletion zone, on electronic transport through silicone p-n junction. Voltage-current (I-V) characteristics of a silicon diode with embedded ferroelectric nanoparticles were studied. Samples with different amounts of ferroelectric BaTiO3 (BTO) embedded into the depletion region were prepared. First, p-type silicon wafers were etched with HF to remove native oxide layer. BTO nanoparticles with an average diameter of 15 nm were prepared by phase transfer reaction method and their suspension with different concentrations were drop-casted on the surface of the wafer. The particles were capped with 200 nm of n-type silicone using electron-beam evaporation. Finally, Pt electrodes were sputter deposited on both sides of the wafer (Orion-8 sputtering system, AJA Int.). Samples were poled under electric field of 8kV/cm while cooling from 140 °C down to room temperature. I-V graphs were plotted using a function generator (AFG3022, Tektronix) and oscilloscope (TDS2001, Tektronix) at different frequencies of the applied sinusoidal voltage wave. The results revealed that as the amount of BTO nanoparticles increases, I-V characteristics show hysteretic behavior. The hysteretic properties start at reverse bias region and extend into forward bias region with increasing the concentrations of the BTO particles. Measurements also were repeated at three different frequencies: 10Hz, 100Hz and 1 kHz. As the frequency increased, diode&’s characteristic started changing from an asymmetrical rectifying effect to a symmetrical hysteretic effect. It is believed that the observed interesting hysteretic properties due to electric field from BTO nanoparticles have potential for applications in information storage.

The present work describes a nonchemical technique to produce nanohybrid functional materials by intercalating monodisperse magnetite nanoparticles inside open-ended, electrically-conducting, carbon nanofibers (CNF). Single crystal super paramagnetic magnetite nanoparticles of 10 nm average diameter were incorporated into the CNF internal cavity (dia. < 100 nm). Intercalation was accomplished with the aid of ultrasonication and subsequent self-sustained, concentration-gradient-driven filling. The influence of several experimental parameters, such as sonication mode, sonication time, nanoparticle/CNF ratio, nanoparticle-CNF concentration on intercalation quality were studied using high resolution transmission electron microscopy. This process not only creates magnetically active CNFs but also provides a new platform to study the nano-confinement effects on nanoparticles. CNFs intercalated with magnetic nanoparticles showed strong response and alignment under external magnetic fields. The magnetic tubes were used to prepare polymeric nanocomposite films in the presence and absence of external magnetic fields. These nanocomposite films showed both electrical conductivity and super paramagnetic properties. Nanocomposites with magnetically aligned CNFs showed high degree of anisotropy in electrical and magnetic properties. These magnetic-nanoparticle-filled CNFs have many promising technical applications, such as in magnetically active tunable heat transfer nanofluids, magneto rheological fluids, shock absorbers, sensors etc.

Electronics based on organic materials has been proposed as low cost substitute of silicon with the advantage of making flexible devices. Bio-inspired electronic materials are also attractive for biodegradable or biocompatible devices in sustainable electronics. Biodegradable materials allow fabricating bioresorbable components for use in temporary implantable biomedical electronic devices. Simulating electronic or ionic transport in such materials is essential for designing optimized devices. Transport in disordered media is usually explained in terms of different transport regimes, such as Space Charge Limited Current (SCLC) or Trap Charge Limited Current (TCLC) regimes. These simple models lead to exponential dependencies of current on voltage, e.g., prop;V² for SCLC or prop;V^l+1 for TCLC, with poorly fitted transition regions between transport regimes. Alternatively, transport can be explained by analyzing the density of states (DOS) function, for example, considering a Gaussian distribution of states for free carriers and an exponential function describing trap states. In this work, we propose a semiempirical modeling based on the DOS function calculated from the normalized differential conductivity (dlnI/dlnV) obtained from current-voltage (I-V) curves. This method of computing the DOS function is well known in several spectroscopic techniques and was adapted in this work for modeling transport in nanocomposites. The proposed model is used to fit the current-voltage curves of chitosan/gold and chitosan/silver nanocomposites used in biosensors and fuel cells among other devices and applications. The model allows excellent fitting of experimental curves with a unique expression for the whole voltage range (0-60V) without transition regions.

An accurate description of the carrier hopping topology in the energy domain of hopping systems incorporating a rapidly decreasing density of states and the subsequent energetic position of these systems' so called effective conduction band is crucial for rationalizing and quantifying these systems' thermo-electric properties, doping related phenomena and carrier gradient effects such as the emergence of the General Einstein Relation under degenerate conditions. Additionally, as will be shown, the 'mobile' carriers propagating through such systems can have excess energies reaching 0.3eV above the system quasi-Fermi energy. Hence, since these mobile carriers are most prone to reach systems interfaces and interact with oppositely charged carriers, their excess energy should be considered in determining the efficiencies of energy dependent processes such as carrier recombination and exciton dissociation.
In light of the stated motivations, a comprehensive numerical and analytic study of the topology of hopping in the energetic density of such systems (i.e. the statistics regarding which energy values carriers visit most and in what manner) was implemented and the main statistical features of the hopping process that determine the position in energy of the system's effective conduction band were distilled. The obtained results also help shed light on yet to be elucidated discrepancies between predictions given by the widely employed transport energy concept and Monte Carlo simulations.

Carbon Nanotubes/Polymer composites have been largely investigated in the last decade, due to their enhanced thermal, mechanical and electrical properties. In such materials an insulator to metal phase transition can be induced by adding an amount of Carbon Nanotubes (CNT) sufficient to open a percolation path. The overall conductivity depends critically on the topology of the nanotube network and on the contact resistance between carbon nanotubes. While a large literature about the effects of topological details such as bundling and orientation exists, less effort have been devoted to estimate the contact resistance. An attempt to quantitatively estimate the contact resistance beyond the naive picture of a model metal-insulator-metal junction was only recently [1] by applying Landauer formalism. Nevertheless this model lack atomistic details which, in the case of a Single Wall CNT, can influence the contact resistance by orders of magnitude.
We recently showed that it is possible to quantitatively evaluate the nanotube-polymer-nanotube contact resistance with atomistic details [2] by combining efficient semi-empirical Density Functional Tight Binding (DFTB) method, Green&’s function formalism [3] and classical force field Molecular Dynamics (MD) on large systems. Due to the large intermolecular separation, in the order of Van der Waals radius, special attention to the correct calculation of the electronic structure must be given. Standard semi-empirical parameterization, based on a wave function compression ansatz, can fail in describing weak coupling. The correct couplings, needed to avoid underestimation of the barriers, are evaluated by relaxing the wave function compression parameter or by applying a two steps Fragment Orbital approach. This method is general and allows for description of a large class of composites. Within our model we can evaluate the tunneling barrier and includes flawlessly atomistic details. By thermal averaging over MD trajectories, we can determine a statistical description of the junction resistance. The effect of polymer wrapping and relative alignment is discussed for different polymer matrices. A transition from direct CNT-CNT to a CNT-polymer-CNT tunneling, resulting in different energy barriers, can be defined. The atomistic modelling is used to extract relevant parameters to be used in the mesoscopic modeling. The role of the tunneling model of the contact resistance on the overall conduction of the percolation network is discussed.
[1] Bao, W. S.; Meguld, S. A.; Zhu, Z. H.; Weng, G. J., J. Appl. Phys., 2012, 111, 093726
[2] Penazzi, G.; Carlsson, J. M.; Diedrich, C.; Olf, G.; Pecchia, A.;Frauenheim, T., J. Phys. Chem. C, 2013, 117, 8020-8027
[3] Pecchia, A.; Penazzi, G.; Salvucci, L. & Di Carlo, A., New J. Phys., 2008, 10, 065022

The emergence of the field of stretchable electronics, along with its biomedical applications, has highlighted a challenge: electronic devices are usually made of hard materials, while tissues and cells are soft. Stretchable conductors are needed to enable electronics to meet skin, heart and brain. Existing stretchable conductors are mostly electronic conductors, and struggle to meet demands of diverse applications. Here we describe a class of devices enabled by ionic conductors. These devices are highly deformable and fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kHz and voltages above 10 kV. The electromechanical transduction is achieved without electrochemical reaction. At large stretch and high transmittance, the ionic conductors have lower electrical resistance than all existing stretchable and transparent electronic conductors, including carbon nanotubes, graphene sheets, and silver nanowires. The diversity of ionic conductors creates a large pool of candidates for applications. In addition to conductivity, stretchability and transparency, other attributes can be important in specific applications. For example, many ionic hydrogels are biocompatible, and are conformal to tissues and cells down to molecular level. Life uses primarily ions—rather than electrons—to carry electrical charge. In creating biomedical and engineering devices, it is well to consider the opportunity: the hard and the soft do not necessarily have to meet through electronic conductors; they may as well meet through ionic conductors. This work has been carried out in collaboration with Christoph Keplinger, Jeong-Yun Sun, Choon Chiang Foo, Philipp Rothemund, and George M. Whitesides.

Transport in granular structures, such as nano-crystalline silicon, is limited by the grain boundary scattering and percolation transport. Effective media approaches are typically used to model the behavior of these materials. However, it is difficult to capture the electronic transport for all temperatures and electric fields, and fill factors. In small scale nanocrystalline structures, percolation transport and granularity lead to significant device to device variations. It is possible to model nanocrystalline structures as a random distribution of crystalline domains embedded in an amorphous matrix with temperature and field dependent materials properties assigned to each¹. However, this is a computationally heavy approach as the interfaces of each crystalline structure have to be heavily meshed.
We have developed a mesh-based approach where crystallinity is defined as a material property and grains are grown from random nucleation sites on the mesh. The interfaces of the different grains are identified and a simple boundary resistance model is applied to these interfaces. Using this approach, we have performed 2D finite element simulations in COMSOL multi-physics to study percolation transport, current induced filaments, and the effects of grain boundaries in nano (nc-Si) and polycrystalline (poly-Si) silicon nanowires. Poly-Si and nc-Si nanowires structures are generated in Matlab (with random nuclei, growth rates, and orientations) and imported into COMSOL. Nc-Si is modeled as single crystal grains inside of an amorphous medium while poly-Si is modeled as single crystal grains with grain boundaries. Nanowires are subjected to micro/nanosecond long voltage pulses resulting in self-heating, eventually melting the nanowire from contact to contact as we have observed in our experiments^{2, 3}.
1. S. Fischer, C. Osorio, N.E. Williams, S. Ayas, H. Silva, A. Gokirmak “Percolation transport and filament formation in nanocrystalline silicon nanowires,” Journal of Applied Physics, 113, 164902 (2013)
2. G. Bakan, N. Khan, A. Cywar, K. Cil, M. Akbulut, A. Gokirmak, H. Silva, “Self-heating of silicon microwires: Crystallization and thermoelectric effects,” Journal of Material Research, vol. 26, Issue 9, pp. 1061-1071, 2011
3. G. Bakan, A. Cywar, H. Silva and A. Gokirmak, “Melting and crystallization of nanocrystalline silicon microwires through rapid self-heating,” Appl. Phys. Lett., vol. 94, pp. 251910, 2009

Conjugated polymer nanoparticles are gaining widespread attention as active layer materials for organic-based electronic devices. Typically the nanoparticles are stabilized by charged or nutral surfactants. Efficient charge transport is important for optimal performance of electronic devices. Therefore a key question in the area of conjugated polymer nanoparticles is: Do surfactants impede charge transport in nanoparticle assemblies derived from conjugated polymers? We address this question using assemblies of surfactant-stabilized poly[3-hexylthiophene] (P3HT) nanoparticles. We obtained regioregular P3HT, of high and low molecular weight, nanoparticles stabilized with sodium dodecyl sulfate (SDS) through a mini-emulsion process and we fabricated the nanoparticle assemblies by air-brush spray coating. We determined the hole mobility in various P3HT based nanoparticle assemblies to be on the order of 10^-4 cm^2/V/s using time of flight and the values are comparable to charge carrier mobilities in pristine P3HT films. We have analyzed the transient photocurrent based on dispersive charge transport model. We observed a decrease in trap states upon removing excess surfactant by centrifuging nanoparticle dispersion. Nanoparticle assemblies were confirmed using GWAXS, GSAXS and SEM indicating closed pack when spray coated from centrifuged nanoparticle dispersion compared to spray-coated films from non-centrifuged samples. We believe efficient charge transport through polymer nanoparticle assemblies will essentially be applicable to any solution process organic electronic devices.

Non-destructive evaluation (NDE) techniques have been developed and employed for damage detection of structures such as planes, bridges, etc. to monitor cracks and other damages at pre-critical levels for remediation. Recently, we have developed a novel approach based on carbon nanotube-resistive-heating effect that takes advantage of the effects that damages have on the electric and thermal transport in a material containing aligned carbon nanotubes. When a difference of potential is applied to the CNT-containing composite laminate, the laminate is heated by Joule effect, also known as resistive heating. This heat is transmitted through the laminate causing “hot spots”. This heat flow is impeded in areas of damages and these changes of temperature can be locally visualized with a thermal camera. The power operation depends on the amount of CNTs used, and we demonstrated a spatial resolution superior to the current state-of-the-art in non-destructive evaluation. The implementation of vertically aligned carbon nanotubes remains challenging within medium-size composite laminates. And because of this scaling limitation, most of the work using these nano-architectures was limited to coupon-size samples. We have implemented an approach using commercial grade carbon nanofibers (CNFs) mixed in a thermoset resin. Medium size plates (300x300 mm2) can be fabricated using resin/CNF mixtures and conventional composites fabrication process, such as hand-lay up. In order to assess the resolution of this new approach, defects of different size and depth have been created in the carbon-fiber laminate. This laminate has been analyzed using c-scan and the resistive heating NDE technique. We demonstrate that resistive-heating-based NDE can be achieved using industrial scale carbon nanofibers dispersed in a composite matrix. For first time, medium scale laminates made of carbon nanofibers dispersed in the matrix have been evaluated by both c-scan and thermal resistive heating. High-resolution damage detection has been demonstrated using the resistive heating NDE technique in composites. We were able to detect most of the defects generated in the panel, despite the small size of some of them (4 mm of diameter). The main limitation of this technique is the high voltage it requires to heat the sample when carbon nanofibers are used as a conductive media in the composite matrix. Interestingly, several studies have been conducted in this field using carbon fiber, but there no study used electrical conductive nano-reinforcements. Finally, commercial grade carbon nanofiber and non-resistive non-destructive evaluation can provide a new low-cost and effective inspection route for monitoring future generations of safer vehicles and infrastructure.

Hierarchical nanostructured porous carbons (HNPCs) have unique porous structure, namely, mesopores (2 nm

Efficient water desalination is vital to sustaining the quality of life for populations living without access to sufficient freshwater resources as well as treating the wastewater produced from industrial activities before reuse or being discharged to the environment. In this work, we utilize the flexibility of the layer-by-layer (LbL) assembly process to create composite, cross-linkable polyelectrolyte and clay thin films to serve as a substitute for the polyamide selective layer in commercially-available reverse osmosis (RO) membranes. The spray layer-by-layer (spray-LbL) assembly process enables the deposition of large, asymmetric thin films orders of magnitude faster than possible through traditional dip-LbL processing. Composite thin films were deposited on polyethersulfone nanofiltration (NF) membranes, with the composition and physical properties fine-tuned by manipulating the film assembly conditions such as spray time and pH of the film components, the number of layers deposited, and the time and temperature of the post-deposition heat treatment. Using mathematical modeling on data collected from a dead-end permeation cell, permeability coefficients for water and salt through selective layers of varying film composition were calculated. At operating pressures up to 300 psi (20.7 bar), the water permeability coefficient calculated for these composite thin films was found to be an order of magnitude greater than what was observed for a commercially-available polyamide selective layer. Over the same range of operating pressures, the composite thin films rejected up to 89.6% of the NaCl in solution. These experimental results confirm the viability of using composite polyelectrolyte-clay thin films as selective layers.

Recent work showed that 2D carbon materials can be effectively used as molecular filters in membrane devices for energy and environmental applications. Graphyne, a new 2D carbon allotrope with sp-sp2-hybridized carbon atoms, is a potential 2D polymer with well-defined sub-nanometer pores. Based on an example application of water purification - the removal of contaminants from seawater and wastewater, we use molecular dynamics (MD) simulations to investigate the interplay of mechanical forces, filtration mechanisms, and overall performance, for various graphyne nanoweb membranes with different pore sizes. We carry out biaxial tensile tests of the membrane and verify the superior mechanical robustness of graphyne membranes, which suggests a high tolerance against possible deformations from the membrane installation process in devices. A possible ultimate stress in excess of 15 GPa and an ultimate strain of 1.6 ~ 2.6% is determined for the various graphyne membranes. We also demonstrate its excellent filtration performance with barrier-free water permeations and perfect rejections of the representative contaminants considered here, including hydrophilic inorganic monovalent salts (sodium chloride) and divalent heavy metal salts (copper sulfate), as well as hydrophobic organic chemicals (benzene and carbon tetrachloride). Among the various graphyne membranes, we find that graphtriyne, with an effective pore diameter of 3.8 Å, exhibits the optimal purification performance, because the contaminants rejection rate is more sensitive to pore size than water permeability. In addition, we find that the hydrophobic graphyne membranes exhibit, in average, higher rejection rates for hydrophilic contaminants compared to the hydrophobic ones, as a result of stronger interactions between the hydrophilic species with water molecules. Finally, we find that maximum deformation of the graphtriyne membrane, at the ultimate strain of 1.6% at the point of material failure, has only minor impact on its filtration performance. One of the advantages of using graphyne for water purification is that no chemical functionalization or defects need to be introduced, which maintains the structural integrity of the membrane, and possibly, the long-term device performance. In general, the rational selection of the specific graphyne membranes with certain porosity could allow for a family of molecular filters that selectively remove specific chemicals.

Investigation of localized and quantity controllable coupling between different properties in nanomaterials/nanodevices is of great interest and significance. Such work will dramatically boost the understanding of the material, and develop novel nanodevices with new working principle possessing expanded applications. For a material that simultaneously has semiconductor, photon excitation and piezoelectric characteristics, a coupling between these properties is a new research field called “piezo-phototronics”. The core idea is that the inner-crystal piezopotential can effectively tune/control the carrier generation, transport, separation and/or recombination processes at the vicinity of a p-n junction or metal-semiconductor interface, and thus the electro-optical processes.
First, we realized designing and controlling the electrical transport characteristics of a ZnO micro/nanowire device by piezo-phototronic effect. We fabricated two-end bonded ZnO wire devices to construct a metal-semiconductor-metal structure with Schottky barrier (SB) at the two contacts. Both piezoelectric effect and photoexcitation intensity can tune the I-V transport property of a ZnO microwire device, but they act in opposite directions. By carefully controlling the relative contributions of the effects from piezoelectricity via strain and photon excitation via light intensity, the local contact can be tuned step-by-step, and thus the transport characteristics of the device were well controlled.
Then, we demonstrated the application of piezo-phototronic effect in optimizing the output performance of the photocell. The working mechanism is that by exciting a SB structure using a laser that has photon energy higher than the bandgap of the semiconductor, electron-hole (e-h) pairs are generated at the interface region. If the height of the SB is too high, the generated e-h pairs cannot be effectively separated. If the SB is too low, the e-h pairs are easily recombined even after a short separation. There exists an optimum SB height that gives the maximum output photon current. By using the tuning effect of piezopotential to the SB, we can experimentally find out the optimum choice of the SB height in corresponding to the maximum photon current.
Most recently, we present that the EL properties of Mg-doped p-type GaN thin films can be tuned by the piezo-phototronic effect via adjusting the minority carrier injection efficiency at the metalminus;semiconductor interface by strain induced polarization charges. The external quantum efficiency of the blue EL at 430 nm was changed by 5.84% under different straining conditions which is 1 order of magnitude larger than the change of the green peak at 540 nm. The results indicate that the piezo-phototronic effect has a larger impact on the shallow acceptor states related EL process than on the one related to the deep acceptor states in p-type GaN films.

Aligned nanowire arrays are useful for exploring many types of transport and developing models to understand interactions happening at the nano-scale and potentially take advantage of such. While many nanostructured materials have random or effectively amorphous morphologies, e.g., materials obtained via mixing approaches, more interesting and informative is to study nanostructured materials with texture or morphology control. Aligned nanowire arrays, and materials comprised of such, provides an excellent model system where quantifiable information on morphology can be developed such as fiber waviness and spacing. Such nanowire arrays yield non-isotropic properties, which are useful for model development as well as applications. Recent work in our group has focused on transport properties in aligned carbon nanotube (CNT) arrays where inter-CNT distance can be altered. Morphology quantification studies allow models to be populated and various transport topics have been investigated: particle and polymer transport through the arrays in aqueous solution (bioMEMS), ion transport (supercapacitors and electroactive polymer composites), and electron and phonon transport in polymer nanocomposites. Exemplary dominant structure-property relations include permeability in particle transport studies, and inter-CNT spacing with regard to ion transport along the fiber axis. Future work is suggested towards better quantifying morphology in stochastic arrays such as CNFs/CNTs, as well as developing deterministic nanowire array studies to further improve understanding and verify physical property models, including transport.

Complex oxides have served as promising candidates for discovery of novel functional materials. One of the most successful examples is the mixed-valence lanthanum manganite in which very large magnetoresistance (MR) effects are observed. Among them, La1-xSrxMnO3 (LSMO) is one most-studied compound of the mixed-valence manganite family for its robust and large MR effect above room temperature. However, the volatile electronic properties and the high magnetic fields required to drive the MR change have hindered the potential applications.
In this work, realization of non-volatile control and advanced manipulation of the transport behaviors in colossal magnetoresistance (CMR) materials have been carried out via self-assembled nanostructures. Such goals are achieved by 1) magnetically- and structurally- coupled ferromagnetic-CMR materials, in which the magnetizations could be maintained and tuned even when the magnetic fields are off; 2) the enhanced MR response above room temperature in the nanostructure, where the remnant magnetizations serve the key role to drive the significant change of the non-volatile resistance states. Firstly, self-assembled La1-xSrxMnO3- NiCo2O4 (LSMO-NCO) nanostructures are deposited by using pulsed laser deposition. The spinel-structured ferromagnetic NCO nano-pillars are uniformly embedded in the perovskite-structured LSMO matrix, which is distinguished by atomic force microscopy (AFM) and transmission electron microscopy. HR-XRD and X-ray reciprocal space mapping have been used to confirm the phase-separation and the epitaxial relationships of the two functional materials, where a consistent four-fold symmetry epitaxial correlation for all species has been revealed. Vibrating sample magnetometer and S.Q.U.I.D. have been used to measure the magnetic properties and anisotropy of the nanostructures. X-ray magnetic circular dichroism (XMCD) as a function of magnetic field has further revealed the similar hysteresis-loops of Mn and Co elements in the nanostructure, implying a highly coupled magnetic nature. Such an elegant system enables us to gain advanced control of the CMR materials since the 3-D epitaxial strain and magnetic couplings have served as the bridges across the borders of two functional materials. Magnetotransport as functions of temperatures and magnetic fields have been executed. A significantly enhanced MR has been revealed, which could be explained by spin-polarized tunneling theory. As last step, having established the two aspects mentioned above, we have successfully demonstrated an elegant way to realize a new non-volatile electronic device driven by remnant magnetizations. This system also shed the light to manipulate one order parameter through the other. Such results pave a new pathway to control the intriguing physical properties through the correlations between functional materials, which lead to new generation multifunctional applications and devices.

Thin films of sodium montmorillonite clay and weak polyelectrolytes were prepared by alternately exposing a film to aqueous mixtures of polyethylenimine, poly(acrylic acid), polyethylenimine, and montmorillonite clay. Four of these quadlayers (51 nm thick) exhibit an oxygen permeability below 5x10^-22cm³#9679;cm/cm²#9679;s#9679;Pa (oxygen transmission rate below 0.005 cm³/m²#9679;day). This oxygen barrier is due to a ‘nanobrick wall&’ microstructure comprised of completely exfoliated clay bricks in polymeric mortar. Higher aspect ratio ‘nanobricks&’ can provide even greater barrier and high selectivity for hydrogen. These unique nanocomposites have a barrier that exceeds SiOx and is competitive with metalized films. Similar brick walls have been created with clay and chitosan to produce an environmentally-friendly flame retardant (FR) system for foam. This coating completely stops the melting of flexible polyurethane foam, when exposed to direct flame from a butane torch, with just 10 bilayers (only 4 wt% on foam). Cone calorimetry reveals that this thin film protection reduces the foam's peak heat release rate by more than 50%. These clay-based nanocoatings could prove beneficial for new types of food or electronics packaging or as a replacement for environmentally persistent flame retardants.

The field of materials and microstructure design has progressed significantly in the past two decades. There have been important applications in energy and advanced technology with special attention on synthesis, structural characterization, and physical properties of perovskite oxide nanotubes (PONTs). The TiO₂ nanotubes have been used as template for formation of several ternary metal oxide nanotubes such as barium titanate nanotubes (BaTiO₃) via a hydrothermal reaction and sol-gel process of TiO₂ nanotubes in Ba(OH)2 aqueous solution. Other examples of PONTs include (Ba,Sr)TiO₃ (BST), Pb(Zr,Ti)O₃ (PZT), have been fabricated by using different methods. The application of these nano-heterojunctions can impact Solid Oxide Fuel cell electrolytes leading to a reduction in operating temperatures of SOFC to 350-400 from 700 and above. Engineering of these interfaces can also lead to major cost saving in solar cell. Nano-composites of TiO2 and Fe₂O₃ nano-particles with CNTs with varying size distributions were synthesized and the effect on photovoltaics properties have been examined. The characterization and modeling of these nano-interfaces are also discussed. Using DFT analysis an inverse engineering methodology is introduced to find an optimize the microstructure of the interface. The goals are not only for band gap engineering but also to use the distribution and gradient as design parameters. The implications of the analysis in several applications including SOFC and water splitting is discussed.

Cellulose-based PLA/PBAT polymer blends can potentially be a promising class of biodegradable nanocomposites. Adding cellulose fiber reinforcement can improve mechanical properties of biodegradable plastics, but homogeneously dispersing hydrophilic cellulose in the hydrophobic polymer matrix poses a significant challenge. We here show that resorcinol diphenyl phosphates (RDP) can be used to modify the surface energy, not only reducing phase separation between two polymer kinds but also allowing the cellulose particles and the Halloysite clay to be easily dispersed within polymer matrices to achieve synergy effect using melt blending. Here in this study we describe the use of cellulose fiber and Halloysite clay, coated with RDP surfactant, in producing the flame retardant polymer blends of PBAT(Ecoflex) and PLA which can pass the stringent UL-94 V0 test. We also utilized FTIR, SEM and AFM nanoindentation to elucidate the role RDP plays in improving the compatibility of biodegradable polymers, and to determine structure property of chars that resulted in composites that could have optimized mechanical and reduced thermal transport properties.

Insulating and semiconducting polymers and copolymers/Au nanograins based hybrid multilayers (HyMLs) were fabricated on p-Si single-crystal substrate by an iterative method that involves, respectively, Langmuir-Blodgett and spin-coating techniques (for the deposition of organic film) and sputtering technique (for the deposition of metal nanograins) to prepare Au/HyMLs/p-Si Schottky device. The electrical properties of the Au/HyMLs/p-Si Schottky device were investigated by current-voltage (I-V) measurements in the thickness range of 1-5 bilayers (BL).
At different number of layers, current-voltage (I-V) measurements were performed. Results showed a rectifying behavior. Junction parameters, such as barrier height (BH), from the I-V measurements for example for the PS-b-PMMA based Au/HyMLs/p-Si structure were obtained as 0.67±0.02 eV at 5BL and 0.75±0.02eV at 1BL. It was observed that the BH value of 0.67 eV calculated for the Au/HyMLs/p-Si structure was lower than the value of 0.71 eV of conventional Au/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for Au/p-Si diodes has been achieved using a thin MLs of different polymers based HyMls semiconductor, due to a favored transport of majority carriers at polymer/metal interface. Furthermore, the conduction of minority carriers (electrons) is promoted because of tunneling transport caused by interfaces electronic states produced in the organic layer by the defects originated by the sputtering deposition process.

Memristor shows reversible bi-stable resistance states when the concentration change of oxygen vacancies in oxide changes under electric field. Recently, the memristor has attracted renewed interest for terabit memories, logic operators, neuristors, and nanobatteries. To compete with current Si-based architectures, significant improvements in device uniformity and tunability constitute key challenges for future memristive technology. Here we fabricated nanocomposite films by forming oxide nanocolumns, with average radius of ~10 nm and intercolumnar spacing of ~10 nm, into the other oxide matrix. We found that this so-called nanoscaffold memristor can show extraordinary memristive behaviors without destructive electroforming. Different from conventional single-phase oxide memristors, resistance variations of the nanoscaffold films can be as large as two orders of magnitude with extreme uniformity and tunability. Using electron energy loss spectroscopy, we find oxygen deficiency at vertical interfaces of nanocolumns and matrix, arising from structural incompatibility of two oxides. Using conductive atomic force microscopy, we find that memristive behaviors are confined at vertical interfaces, potentially leading to terabit integration density. These hybrid architectures will create new physical functionalities, e.g., ionic transport and electrochemical phenomena, which may find wide applications in devices and clean energy.

Understanding the microscopic mechanism of amorphous (disordered) to crystalline (order) transformation in complex oxides is central to a range of processes from oxide deposition and growth to material stability and performance during device operation. In this talk, we will discuss how atomistic simulations can be used to probe the nature of amorphous-crystalline transformation in a model system i.e. Ceria-YSZ heterostructures typically used as solid oxide electrolyte in fuel cells. Specifically, we describe an electric field controlled amorphization-recrystallization strategy to manipulate oxide heterostructures. Using molecular dynamics simulations, the effect of electric field assisted annealing (both ac and dc) on the microstructure, composition, and ionic conductivity properties in CeO2/YSZ oxide hetero-structures have been investigated. Amorphization-recrystallization of Ceria-YSZ heterostructures, were performed with and without external electric field of strength 10 MV/cm. AC e-field frequencies in the 1 GHz-1THz frequency range applied along the surface normal direction were studied. Furthermore, DC e-field along three different orientations: in-plane (YZ), normal (X) and 45° resultant (XY) with respect to the oxide hetero-interfaces. The microstructural and compositional differences at the interfaces and in the interior of the oxide heterolayers were evaluated and were found to show a clear correlation with the orientations of the applied field. In particular, the XY configuration displayed a compressive lattice strain of ~9% along with a reduced oxygen vacancy concentration when compared to the others. Ionic density profiles suggest pronounced segregation (~ 60% higher compared to the average value in the interior) of yttrium ions closer to the YSZ/CeO2 interface for the XY configuration. Other configurations exhibit minimal to no such variations. These microstructural differences are found to affect the number of mobile charge carriers and the activation barriers associated with ionic migration through the oxide lattice and consequently influence the ionic conductivity. The diffusion mechanism, the effective diffusion barriers, and ion transport dynamics extracted from these simulations will be presented. Our simulations offer mechanistic insights into electric field effects on ionic conduction in oxide heterostructures while taking into account microstructural and interface proximity effects. In general, our atomistic simulations offer useful insights into the correlation between order-disorder transitions and ion conduction mechanisms that are of importance to solid-state devices used for energy storage and conversion applications.

Cellulose nanocrystals (CNCs) are added into cement paste (CP) as a modification at the nano-scale to improve the mechanical performance. Both isothermal calorimetry (IC) and thermogravimetric analysis show that the degree of hydration (DOH) of CP is improved with CNCs. The first mechanism brought up to explain this phenomenon is the steric stabilization, which is the same mechanism some types of superplasticizer (SP) increase the workability in cement mixing. Rheological, heat flow rate measurements and imaging work are taken to verify this mechanism. The zeta potential measurement, however, indicates that the steric stabilization is not the only or the dominating mechanism in improving DOH. Another new mechanism, referred as short circuit diffusion, is proposed as a complementary for the CNCs to help cement hydration, in which mechanism the CNCs can transport the water from the capillary pores outside the hydration products shell to the unhydrated cement cores and hence cause extra hydrations. Parallel investigations of DOH and flexural strength on the CP with SP prove this thesis and shows that, the short circuit diffusion is more dominating than steric stabilization. For the flexural strength, a ball-on-three-ball test is performed, and the results show a maximum increase in strength of about 30% with only 0.2 % of CNCs with respect to cement. The strength, however, decreases with further increasing the CNC concentrations, which is explained by the agglomerations of CNCs and verified with rheological measurements.

Nanocapsules composed of biocompatible and biodegradable materials are of growing interest for medical and biological applications. An increased bioavailability and an adapted biological distribution turn nanocapsules into advanced biosystems. Nanocapsules can widely be used as carriers for drugs, DNA, enzymes, proteins, or peptides. Of great importance their ability allow a controlled transport of materials in and out of the capsules in order to obtain either specific reaction inside the nanocapsules or a controlled release of the encapsulated material at the place of interest inside the human organism.
The synthesis of nanocapsules made of natural or synthetic monomers or polymers, such as starch, lactic acid, hyaluronic acid and poly(n-butylcyanoacrylate), could be successfully performed using the miniemulsion process. This technique allows the formation of stable nanocapsules whose properties can be tailored individually according to the specific requirements. Following the synthesis, the capsules can be redispersed in an aqueous phase, which provides an opportunity to employ them as “nanocontainers” for various biomedical reactions. The nanocapsule size (between 150 and 500 nm) and stability of the system can be adjusted by varying the amount of monomer, surfactant and cross-linker. Encapsulation of water-soluble fluorescent dyes (e.g. rhodamine SR101, cyanine dyes or infrared dyes) enables the usage of the obtained nanocapsules for imaging. The properties of the shell material including e.g. the molecular weight of the polymer, the crystallinity, the crosslinking density, the shell thickness, the hydrophobicity and the introduction of specific chemical groups can be tailored that way that a selective diffusion of molecules can take place.

Recently, the use of membranes composed of stacked and overlapped graphene or graphene sheets (the latter we call ‘G-O membranes&’) as filters for gases or liquid solutions has been reported. In this talk, the selective ion transport of freestanding G-O membranes is demonstrated. Sodium salts permeated through G-O membranes quickly, whereas heavy-metal salts infiltrated much more slowly. Interestingly, copper salts were almost entirely blocked by G-O membranes, and organic contaminants also did not infiltrate. The temperature-dependent trans-membrane transport properties of alkali and alkaline earth cations through G-O membranes were compared, which revealed that the masses and volumes of selected ions are not the main reasons for the selective ion transport through G-O membranes. The mechanism of the selective ion-penetration properties of the G-O membranes is discussed. The nanocapillaries formed within the membranes were responsible for the permeation of metal ions, whereas the coordination between heavy-metal ions with the G-O membranes restricted the passage of the ions. In addition, the interactions of alkali and alkaline earth cations with G-O membranes are responsible for the selective ion transport through G-O membranes. Finally, the penetration processes of hybrid aqueous solutions were investigated and the results revealed that sodium salts can be separated effectively from copper salts and organic contaminants. The presented results demonstrate the potential applications of G-O membranes in areas such as membrane separation and water purification.

The recently-reported exceptionally fast fluid transport rates in carbon nanotube (CNT) pores of a few nanometer diameters [1] spurred great interest for their application as nanofluidic channels in several areas ranging from desalination and carbon capture, to drug delivery, protein separation and breathable fabrics.
Here, we highlight experimental work performed in our laboratory directed toward: a) a fundamental understanding of the selectivity of these pores for electrolyte solutions; b) the development of breathable and protective fabrics based on CNT arrays. For our studies, we used ceramic [1] or polymeric membranes with well-aligned, a-few-nm wide CNTs as only through-pores. We demonstrate that ion selectivity for single and mixed electrolytes in narrow CNT pores is dominated by electrostatic interactions between carboxylic groups at the CNT tips and the ions in solution. Ion selectivity can be tuned by acting on solution pH [2-3] and by employing a controlled surface functionalization with atomic layer deposition (ALD) without loss of their unique ultrafast fluid transport properties. On the contrary, previous functionalization strategies reported in the literature resulted in a two orders of magnitude flow-rate reduction. Finally, flexible CNT membranes in development for the breathable and protective fabric application provide water vapor transport rates that are comparable to or exceeding state-of-art breathable fabrics at all relative humidities even if the moisture conductive pores are only a-few-nm wide and the membrane porosity <1%. Moreover, these tiny pores enable simultaneous passive protection from biological threats by size exclusion.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
[1] Holt J., Park H.G., Wang Y., Stadermann M., Artyukhin A.B., Grigoropoulos C.P., Noy A. and Bakajin O., “Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes,” Science, 312: 1034 (2006)
[2] Fornasiero F., Park H.G., Holt J.K., Stadermann M., Grigoropoulos C.P., Noy A., Bakajin O., “Ion Exclusion by sub 2-nm Carbon Nanotube Pores”, PNAS, 105 (45):17250-117255 (2008)
[3] Fornasiero F. , In J.B., Kim S., Park H.G., Wang Y., Grigoropoulos C.P., Noy A., Bakajin O., “pH-Tunable Ion Selectivity in Carbon Nanotube Pores,” Langmuir, 26 (18): 14848-14853 (2010)

Separation of carbon dioxide from air, exhaust gas from IGCC is one of the most facing environmental concerns. Among various separation technologies, membrane separation has attracts much attention because of inherent advantages such as high energy efficiency, excellent reliability, and a small footprint. In membrane separation, a membrane thickness plays an important role for molecular separations. Thinner thickness reduces the resistance of gas permeation, but results in leaking gas, meaning less gas selectivity at the same time. In nature system, biological lipid bilayer membrane has very unique, efficient and sophisticated functions, and it simultaneously satisfies both requirements high efficiency and precise selectivity, though it has only several nanometer thickness. Thus, molecular separation by a membrane with ultimate thickness (less than 50 nm) would be possible for precise and efficient gas molecules including carbon dioxide, hydrogen and so on. From this fundamental aspect, we prepared a free-standing and nanometer-thick membrane (nanomembrane) with less than 50nm thickness based on a spin-coating method which is conventionally employed in industrial process. The membrane materials of this nanomembrane is made from conventional polymeric materials. The thickness of a nanomembrane is controllable with the a few nanometers precision by changing the rotation speed of a spin-coating and the concentration of the coating materials. After preparation of a nanomembrane on a sacrificial layer-coated solid substrate, a nanomembrane can be transferred from the solid substrate to different porous support film. Any crack and void of a nanomebrane was not observed even after applying gas with a few hundreds kPa. The membrane By simple changing materials compositions, the permeation and selectivity of a nanomebrane are found to be different without simple gas leaking. This primitive data indicates that design of membrane materials would allow to control the permeability and selectivity of gas by a nanomebrane.

The synthetic architectures of complex nanostructures, including multifunctional hollow capsules, are expected to play key roles in many different applications, such as drug delivery, photonic crystals, nanoreactors, and sensing. Implementation of novel strategies for the fabrication of such materials is needed because of the infancy of this knowledge, which still limits progress in certain areas. We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermal-activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cy-cloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing a real time monitoring of the reaction progress. Additionally, these plasmonic nanoprobes have been shown as an advanced intracellular hybrid SERS sensor for relevant signaling molecules (e. g. NO). After their inner functionalization with a NO chemoreceptor, the sensor is quantitative and can perform in-situ, real-time monitoring of the dynamics of intracellular NO in living cells while remains fully biocompatible. Its sophisticated design prevents the interaction of cytosolic macromolecules within the active optical material and the enzymatic degradation of the sensor. It additionally facilitates the diffusion of small molecules between the interior and exterior thanks to the plasmonic thermal gradients generated upon their illumination.

Development of effective CO2 separation technologies is one of the most critical issues for implementation of CO2 Capture & Storage (CCS) because CO2 capturing covers about 60 % of the total CCS cost. CO2 capturing with solvent absorption has gained current acceptance, and the actual operations have been demonstrated in many countries. However, This technology requires certain amount of energy in releasing CO2 from CO2-capturing solution, which results in developing alternative capturing technologies. Because difference in partial pressure of the interest gas between feed and permeate side drives the separation, membrane separation does not need additional energy and can make CO2 separation much more effective.
In pre-combustion such as integrated gasification combined cycle plant, CO2/H2 gas mixture after water-gas shift reaction has a pressure of 2.4 MPa, which would be preferable for membrane separation. Various membranes for CO2 separation over H2 have been investigated, however, CO2 separation performance has not been implemented due to lack in CO2 selectivity or permeability. In this presentation, poly(amidoamine) dendrimer is used to enhance affinity to CO2 and incorporated in a polymer matrix. The resulting polymeric membrane expressed excellent CO2 separation properties even under pressure. The CO2 permeance is relatively lower than the requirement value and 1.0 x 10-10 m3(STP)/(m2 s Pa). However, the permeance can be enhanced by reducing membrane thickness. The details will be discussed in the presentation.

Over recent years there has been tremendous progress in discovering new organic semiconductors that provide high charge carrier mobilities for both n-type and p-type device operation, good operational stability and other functionalities such as efficient electroluminescene, sensing or memory functions. These materials allow addressing an increasingly broad range of flexible and printed electronic applications based on controlled manufacturing of flexible plastic substrates by a combination of solution processing and direct printing. One of the sources of improvement in performance has been the versatility of organic chemistry to provide a broad range of new molecular structures and the ability to assemble these molecules into ordered structure with minimum degree of disorder. We will review recent insights into the device and charge transport physics of solution-processible small molecule as well as conjugated polymer organic semiconductors, with a particular focus on the microscopic processes that limit the field-effect mobility as well as microstructure-property correlations in these complex materials.