Guihua Yu, Univ of Texas-Austin
Haiqing Lin, SUNY Buffalo
Ho Bum Park, Hanyang University
BM7.1: Charged Membranes for Water Purification
Monday PM, November 28, 2016
Hynes, Level 2, Room 202
9:00 AM - *BM7.1.01
Ion Solubility, Diffusion, Permeation and Conductivity in Charged Polymers
Benny Freeman 1
1 University of Texas at Austin Austin United StatesShow Abstract
Charged polymer membranes are widely used for water purification applications involving control of water and ion transport, such as reverse osmosis and electrodialysis. Efforts are also underway worldwide to harness separation properties of such materials for energy generation in related applications such as reverse electrodialysis and pressure retarded osmosis. Additional applications, such as energy recovery ventilation and membrane-assisted capacitive deionization, rely on polymer membranes to control transport rates of water, ions, or both. Improving membranes for such processes would benefit from more complete fundamental understanding of the relation between membrane structure and ion sorption, diffusion and transport properties in both cation and anion exchange membrane materials. Ion-exchange membranes often contain strongly acidic or basic functional groups that render the materials hydrophilic, but the presence of such charged groups also has a substantial impact on ion (and water) transport properties through the polymer.
We are exploring the influence of polymer backbone structure, charge density, and water content on ion transport properties. Results from some of these studies will be presented, focusing on transport of salt, primarily NaCl, through various neutral, positively charged and negatively charged membranes via concentration gradient driven transport (i.e., ion permeability) and electric field driven transport (i.e., ionic conductivity). One long-term goal is to develop and validate a common framework to interpret data from both electrically driven and concentration gradient driven mass transport in such polymers and to use it to establish structure/property relations leading to rational design of membranes with improved performance.
Ion sorption and permeability data were used to extract salt diffusion coefficients in charged membranes. Concentrations of both counter-ions and co-ions in the polymers were measured via desorption followed by ion chromatography or flame atomic absorption spectroscopy. Salt permeability, sorption and electrical conductivity data were combined to determine individual ion diffusion coefficients in neutral, cation exchange and anion exchange materials. Manning’s counter-ion condensation models and the Mackie/Meares model were used to correlate and, in some cases, predict the experimental data.
9:30 AM - BM7.1.02
Facile Construction of Anion Exchange Membranes with 3D Interconnected Ionic Nano-Channels by the Self-Organization of Polymerizable Ionic Liquid
Xinpei Gao 1 , Liqiang Zheng 1
1 Key Laboratory of Colloid and Interface Chemistry Shandong University Jinan ChinaShow Abstract
Anion-exchange membranes (AEMs) for alkaline fuel cells have triggered great interest in the energy field because of their distinct advantages in terms of enabling the use of non-precious metal catalysts, better oxygen reduction kinetics and fuel flexibility. However, the current AEMs often suffer from low OH− conductivity and poor chemical stability. Among the various strategies to improve the hydroxide ion conductivity, construction of a microphase separated morphology composed of hydrophilic ion nanochannel and a hydrophobic phase has been demonstrated as the most important strategy. Although several trials to construct microphase separated membranes using block copolymers, comb-shaped polymers, and graft polymers have been reported, achieving membranes with highly ordered and well-defined ionic nano-channels is still challenging.
The uses of molecular self-assembly to create nanostructured liquid-crystalline (LC) materials with highly ordered and well-defined ionic channels has been shown to be good candidates for efficient ion transportation. In particular, bicontinuous cubic liquid crystals are of considerable interest because of their 3D interconnected and well-defined periodical channel networks. The fixation of LC nanostructures within a polymeric film provides a considerate solution to achieve simultaneous enhancement of many required AEM properties. In this talk, our recent studies will be presented regarding the facile construction of AEMs with LC nanostructures via the self-assemble of polymerizable ionic liquids. Hexagonal, lamellar and bicontinuous cubic LC samples were prepared by the self-organization of polymerizable amphiphilic imidazolium-based ionic liquids. And for the first time, AEMs with hexagonal, lamellar and bicontinuous cubic nanostructures were fabricated through in-phase photopolymerization of liquid crystals. The AEMs performance in terms of ionic conductivity, hydration behavior, and chemical stability were characterized, which turned out to be closely related with the LC nanostructures retained after photopolymerization.
9:45 AM - BM7.1.03
Adhesive Interaction of Polyzwitterion Brushes Containing Inverse Phosphorylcholine Group
Motoyasu Kobayashi 1
1 Kogakuin University Tokyo JapanShow Abstract
Methacrylate monomer having an inverse phosphorylcholine at the side chain (MiPC) was synthesized by N,N-dimethylaminoethyl methacrylate, 2-chloro-2-oxa-1,3,2-dioxaphospholane, and isopropanol with 25% yield. Surface-initiated atom transfer radical polymerization of MiPC was carried out in methanol at 50 °C for 2 h to give poly(MiPC) brush with a 110 nm thick (dry state) on silicon wafer. The resulting poly(MiPC) was water soluble, however, the surface free energy was estimated to be 40.8 mN m-1 by Owens-Wendt method based on a water contact angle of 71 degree. When the poly(MiPC) brush was immersed in water, the thickness of brush increased from 110 to 171 nm due to the swelling of brush and hydrophilicity of poly(MiPC). Adhesion force of poly(MiPC) brush in water was also measured to be 30 nN by force curve measurement using a propylsilane-modified silica probe (d = 20 mm), indicating that poly(MiPC) brush has a relatively large hydrophobic interaction in spite of its hydrophilicity.
10:00 AM - BM7.1.04
Water-Polymer Distribution and Mobility in Hydrated Aromatic Ionomers under Confinement
Shudipto Dishari 1 3 , Christopher Rumble 1 , Mark Maroncelli 1 , Joseph Dura 2 , Michael Hickner 1
1 The Pennsylvania State University University Park United States, 3 Chemical and Biomolecular Engineering University of Nebraska–Lincoln Lincoln United States, 2 National Institute of Standards and Technology Gaithersburg United StatesShow Abstract
The response of ionomer thin films and bulk membranes to humidity is distinctly different. Hydration of fuel cell ionomers in supported thin films leads to complex multimodal interactions among water, polymer chains and substrate and these interactions may lead to interesting mechanical and transport properties. However, the properties of ionomers in thin film format are still not well understood. This understanding is crucial to explore the properties of the ionomer-catalyst interface of fuel cell electrodes. In this work, thin films of sulfonated aromatic ionomer, S-Radel were investigated to know how thickness and hydration lead to changes in density, water-polymer distribution and mechanical properties. A fluorescent rotor probe was incorporated into the polymer films (~25-250 nm thick) to predict the stiffness of the films using time resolved fluorescence. The density values obtained from quartz crystal microbalance and spectroscopic ellipsometry showed a similar trend with thickness to those obtained from neutron reflectometry. A ~25 nm thick film had lower density as compared to a ~250 nm thick film which corroborated with greater mobility and lower stiffness of thinner film observed at dry state. When the same sample was hydrated, film density and interfacial water volume fraction significantly increased. A very thin pure water layer was found at the substrate interface of the ~25 nm thick sample from neutron reflectometry. On the other hand, thicker films were less water-rich at the interface as compared to thinner samples. The water distribution near substrate interface in the aromatic s-Radel films was distinctly different from that in fluorocarbon based Nafion films seen in previous work. Antiplasticization, or stiffening of the films upon hydration, was observed at different extents from fluorescence lifetime of rotor probes. The plasticization properties appeared to be controlled by film thickness, film density, and water mobility.
10:15 AM - BM7.1.05
Exploration of Zwitterionic Hydrogels for Desalination and Energy Production from Salt Waters by Mechanical Stress
Sui Zhang 1 2 , Rohit Karnik 1
1 Mechanical Engineering Massachusetts Institute of Technology Cambridge United States, 2 Chemical and Biomolecular Engineering National University of Singapore Singapore SingaporeShow Abstract
Salty waters (e.g., seawater) are important sources for drinkable water production through various desalination technologies, such as reverse osmosis and distillation. Meanwhile, salinity gradients between two solutions of different concentrations offer great potential for renewable energy production, which has been demonstrated by pressure retarded osmosis (PRO) as well as other processes. However, challenges exist for both desalination and osmotic energy production, such as insufficient energy efficiency, serious fouling and relatively high costs, etc.
Alternative routes to achieve desalination or energy production from salty waters remain interesting to the community; one possible approach is by mechanical stress. Hydrogels are a group of materials that might respond differently to the changes in salt concentration or mechanical stress. For example, charged hydrogels absorb both ions and water when immersed in salt solutions and may release solutions with lower concentration upon application of mechanical stress, thereby achieving desalination; they also change their volume towards different salt concentration, which can be utilized to produce energy if mechanical stress is applied. In this study, we chose zwitterionic hydrogels because of their hydrophilic, super water-absorbing properties and their outstanding anti-fouling capability. Fundamental understanding on the structure-swelling-mechanical strength behaviors will be provided, and the potential of such hydrogels for desalination and energy production will be explored and discussed.
11:00 AM - *BM7.1.06
Ion Containing Block Copolymers for Emerging Energy Applications
Carl Willis 1
1 Kraton Polymers Houston United StatesShow Abstract
In 2010, Kraton Polymers started producing a grade line of ion containing, styrenic block copolymers under the tradename of Nexar(R) Polymers. The polymers are made by a 3 step process. In the first step, a 5 block copolymer is prepared by a living anionic polymerization technology - sequential addition of 1) t-butylstyrene, 2) isoprene, 3) styrene, 4) isoprene, and finally, 5) t-butylstyrene; the living anionic polymerization method affords polymer segments that are nearly monodispersed in molecular weight. In the second step of the synthesis, the isoprene segments are selectively hydrogenated to remove the C=C unsaturation. In the final step, the pentablock copolymer is selectively sulfonated in the polystyrene segment (center block).
The sulfonated polystyrene segment in these polymers gives the material unique structure and unusual performance features. Solutions of these polymers tend to be structured. In non-polar solvents, spherical micelles are formed with the ion microphase in the core of the structure. In polar solvents, spherical micelles are also formed but have the ion microphase on the outside of the micelle. Under some conditions with mixtures of polar and non-polar solvent blends, a different species is formed that has been hypothesized to be of a vesicle nature. Due to the structured nature of these polymer solutions, they have interesting rheological features.
The Nexar Polymer solutions have been cast into membranes which have found utility in energy recovery ventilation applications. By running fresh air over one side of the membrane and spent air over the other side of the membrane, water vapor can be transferred from on air stream to the other. In this way, humidity can be regulated in the incoming air stream with the result that the air can be conditioned at a substantially reduced cost. Regulation of humidity in the conditioned air can improve comfort, as well.
The Nexar Polymer solutions have also been printed onto fabrics and the resulting coated fabrics made into garments that provide an improved micro-climate for the wearer. This technology provides a mechanism for cooling the person wearing the garment when working in a hot climate.
At present, we are developing methods for spray coating these polymers onto porous and irregularly spaced surfaces - microporous membranes and various carbon powder coated structures.
Ongoing research is addressing opportunities for these polymers in water transport and water treatment applications. Various energy storage and energy generation applications are being examined, as well.
This presentation will focus on the science that supports these technologies.
11:30 AM - BM7.1.07
Self-Cleaning Membranes from Comb-Shaped Copolymers with Photoresponsive Side Groups
Papatya Kaner 1 , Xiaoran Hu 1 , Samuel Thomas 1 , Ayse Asatekin 1
1 Tufts University Medford United StatesShow Abstract
We introduce a new self-cleaning, photoresponsive membrane that can remove pre-deposited foulant layers upon exposure to UV light, exhibit UV-triggered surface morphology changes, and sustain stable pore size and permeance throughout. We first synthesized novel comb-shaped graft copolymers at two side-chain lengths with polyacrylonitrile (PAN) backbones and photoreactive side-chains using atom transfer radical polymerization (ATRP). The side-chains undergo a light-induced transition between a hydrophobic spiropyran (SP) state and a zwitterionic, hydrophilic merocyanine (MC) state, allowing photo-regulated control over membrane features. We used these comb-shaped copolymers to produce thin film composite (TFC) membranes by coating a commercial PVDF membrane with a thin layer of the copolymer solution. Changes in fingerprint IR peaks pertinent to SP and MC forms upon light treatment confirm the structural difference between the two forms at a molecular level. Prior to any photo-treatment, as-coated membrane surface consists mainly of hydrophobic SP groups, which promote the adsorption of hydrophobic solutes on pore channel walls, reducing flow rate. Upon reversing the photochemical response by irradiation with UV light, the SP groups are converted to hydrophilic MC groups that release the adsorbed molecules and permit water passage once again. This “self-cleaning” behavior is shown by measuring pre- and post-UV water permeability after fouling with model protein bovine serum albumin (BSA). We found that flux decline through a BSA-fouled membrane can be fully recovered back to its original value by a simple, non-mechanical intervention of exposure to UV light. In addition, despite the as-coated membrane, the UV-induced MC form membrane surface is fouling resistant, indicated by zero flux decline after two hours of protein filtration. To better understand how polymer self-organization controls the responsive behavior, the light-induced changes in surface topography and hydrophilicity are analyzed.
11:45 AM - BM7.1.08
Inverse Opal-Templated Multiscale Architectured Nanomembranes with Tunable Separation Properties
Pil Jin Yoo 1
1 Chemical Engineering Sungkyunkwan University Suwon Korea (the Republic of)Show Abstract
Membrane has been used from time immemorial to purify water. Advances made in membrane technology for more than a century have to do with either enhancing separation efficiency of the membrane or improving the permeation flux. Enhancing the separation efficiency, however, inevitably led to reducing the permeation flux, and improving the permeation flux resulted in a loss in the separation efficiency. This inherently built-in dilemma has to be dislodged for the filtration membrane to fully reach its potential. In this presentation, we suggest multiscale porous membranes that allow for high permeation flux without sacrificing separation efficiency. In order to create the multiscale architectured membranes, primary structure is first prepared by assembling closely packed colloidal particles, filling the gaps with a suitable material, and dissolving out the particles to form inverse opal structure. Then, secondary nanostructures are incorporated inside the structured template to elaborately tune the pore size, tortuosity, and interfacial properties. Embedded nanostructures can be created by layer-by-layer assembly of polyelectrolyte multilayers, microphase separation of block copolymers, or self-assembly of another colloidal particles, etc. Finally, the constructed multiscale architectures are utilized for water-treatment applications, such as ultrafiltration of nanoparticles or nanofiltration of metallic ions. Due to the perfectly ordered characteristics of the multiscale architecture, it offers advantages of reduced tortuosity as well as pore size uniformity, resulting in high permeability and selectivity simultaneously.
1) D. K. Rhee, B. Jung, Y. H. Kim, P. J. Yoo, ACS Appl. Mater. Interfaces 6, 9950-9954 (2014).
2) Y. M. Lee, B. Jung, Y. H. Kim, W.-S. Choe, P. J. Yoo, Adv. Mater. 26, 3899-3904 (2014).
3) Y. H. Kim, H. Kang, S. Park, D. Y. Ryu, P. J. Yoo, Adv. Mater. 26, 7998-8003 (2014).
4) G. H. Choi, F. Caruso, P. J. Yoo, ACS Appl. Mater. Interfaces 8, 3250-3258 (2016).
12:00 PM - BM7.1.09
Fabrication of Hierarchically Porous Membranes by Photofluidization of Azopolymers for Oil/Water Separation
Hong Suk Kang 1 , Shu Yang 1
1 University of Pennsylvania Philadelphia United StatesShow Abstract
Access to clean water and separation of oil/water mixtures have become urgent global issues due to the increased incidents of oil spills, water contamination, and water shortage. Separation oil/water via membranes with selective oil/water absorption is a relatively recent development. While simple oil/water mixtures can be separated by gravity, separation of surfactant stabilized oil/water emulsions is especially challenging. Meanwhile, to enhance selectivity of the membrane, smaller nanopores are preferred; while to achieve high permeation flux, micropores are preferred. Therefore, it is highly desirable to create a membrane with precisely controlled, hierarchical pores over a large area in a simple yet efficient way. Here, we utilize photofluidization of electrospun fiber network from azopolymer (polydisperse orange 3, PDO3), to fine-tune the pore size ranging from nano- to micron-scale. It is well known that azopolymers can undergo trans- to cis- isomerization under irradiation by visible light; even below the glass transition temperature (Tg), the polymer chains can move around, leading to photofluidization. This nature of azopolymers is caused by the repeated photo-isomerization of azobenzene molecules attached to the main chain of the polymer and their resulting anisotropic alignment in the direction perpendicular to the light polarization. First, we fabricate the microporous membranes by electrospinning of the azopolymers. Subsequently, we partially melt the fiber scaffold to shrink the pore size far below micron level by controlling the laser (l = 532 nm) irradiation time. Lastly, we demonstrate that the fabricated membranes can be utilized to separate submicron-sized water-in-oil emulsions with high separation efficiency (> 99.95 %).
12:15 PM - BM7.1.10
Influence of Nanoparticles on Phase Segregated Morphology of an Immiscible Polymer Blend Thin Film
Anuja Das 1 , Rabibrata Mukherjee 1
1 Indian Institute of Technology Kharagpur Kharagpur IndiaShow Abstract
Over the recent years, nanoparticle filled polymeric systems have attracted significant interest due to the fact that addition of such particles can drastically change the properties of the polymers, along with imparting its own functionality. In this regard, nanoparticle filled polymer blend thin film is getting greater attention as it has tremendous potential when implemented using functional polymer in the field of bulk heterojunction solar cells (BHJ). Unlike a homopolymer thin film, a polymer – polymer blend thin film on spin coating forms a laterally phase segregated morphology instead of smooth flat film. The effect of addition of nanoparticles on the phase-segregated morphology and on the stability of such systems is highly complex compared to its homopolymer counterparts and involves a richer physics as it deals with additional polymer–polymer interfaces. Hence, we present here a fundamental study on influence of addition of nanoparticle in the two-phase region of a polymer blend thin film.
With this work, we investigate the influence of organic nanoparticles on a phase-segregated morphology of a spin casted immiscible polymer blend on a flat substrate. For this fundamental study, poly(styrene) (PS) - poly(methylmethaacrylate) (PMMA) were chosen as immiscible polymers and fullerene (C60) as the organic nanoparticle (NPs). PS and PMMA being UCST blends, phase segregates at room temperature. Atomic Force Microscope images of ascast PS-PMMA blend reveals that on addition of nanoparticles, the lateral phase segregation of the domains reduces. From our initial experiments it was observed that on increasing the concentration of NP, lateral phase segregated domains reduces gradually. Moreover, beyond a critical concentration (Cn-NP*), the phase segregation was completely arrested leading to a flat film. By ellipsometric studies, thickness of the polymer blend with nanoparticle before and after selective phase removal hinted vertical phase separation instead of a typical lateral phase separation. Hence, from the results we qualitatively understand that the nanoparticles while spin coating, migrates towards the polymer–polymer interfaces and impart stability to the interface, thereby arresting the lateral phase segregation process during the latter stages of spin coating. This interfacial stability led to a vertical phase segregation of the PS and PMMA forming a polymer–polymer bilayer. This study can help us build a technique that is fast, simple yet novel to obtain coatings of multifunctional polymers.
Keywords: Polymer Blend, Thin Film, Phase Segregation, Nanoparticles, Fullerene, Thin Film Coatings, Interfacial Stability.
12:30 PM - BM7.1.11
Zwitterionic Random Copolymers for Next-Generation Membranes—Self-Assembly for Pore Size Control, Fouling Resistance and Molecular Imprinting
Ayse Asatekin 1
1 Tufts University Medford United StatesShow Abstract
Zwitterionic groups, defined as functional groups with equal numbers of positive and negative electrostatic charges, strongly resist biomacromolecular adsorption due to their high degree of hydration. This has led to their incorporation into membranes to prevent fouling by various methods, especially by grafting from and surface functionalization of existing porous membranes. In addition, however, zwitterionic groups have interesting self-assembly capabilities due to their high dipole moments and strong intra- and inter-molecular interactions. Our group aims to better understand how zwitterion-containing amphiphilic copolymers self-assemble, and utilize their behavior to develop membranes with improved capabilities: controlled, monodisperse pore size, controlled selectivity, high flux, fouling resistance, and scalable manufacture. We have prepared high flux, fouling resistant, size-selective membranes whose selective layers are made of random copolymers of zwitterionic and hydrophobic monomers. We have shown that within certain composition ranges, these copolymers self-assemble to form bicontinuous networks of nanochannels that allow water passage, and filter out solutes larger than the channel size. Membranes made by coating a thin layer of these copolymers onto a porous support exhibit fluxes as high as 21 L/m2.h.bar, which can be further be improved by better coating methods. Based on the rejection of anionic and neutral dyes of varying sizes, they show size-based selectivity with a cut-off around 1 nm. This pore size closely matches the size of the zwitterionic nanochannels, measured to be ~1.3 nm in diameter by transmission electron microscopy (TEM). These membranes also exhibit exceptional fouling resistance, showing little to no flux decline and essentially complete flux recovery with a water rinse upon the filtration of foulants such as protein solutions and oil suspensions. Well-designed membranes show no flux decline even in week-long fouling experiments with oil suspensions. This resistance arises from the presence of chemically dissimilar domains (hydrophobic and zwitterionic) of ~1 nm size, which frustrates the adsorption of foulants such as proteins. Furthermore, molecular imprinting approaches can be used to control and alter the selectivity of these membranes, further expanding their potential applications. These are the first examples of membranes that gain their selectivity from the self-assembled nanostructure of zwitterionic groups, in addition to exploiting this functionality for fouling resistance. These membranes are highly promising for a wide range of applications, including energy-efficient separations in the chemical and biochemical industries and industrial wastewater treatment.
BM7.2: Nanostructured Membranes for Separation
Ho Bum Park
Monday PM, November 28, 2016
Hynes, Level 2, Room 202
2:30 PM - *BM7.2.01
Polymers of Intrinsic Microporosity (PIMs)—High Free Volume Polymers for Energy-Efficient Separations
Peter Budd 1
1 University of Manchester Manchester United KingdomShow Abstract
Polymers of intrinsic microporosity (PIMs) are glassy polymers which possess high free volume and high internal surface area as a consequence of their relatively rigid, contorted macromolecular backbones. They comprise fused ring sequences interrupted by spiro-centres or other sites of contortion. PIMs have a high affinity for gases such as carbon dioxide, and for small organic species. The first commercial application of a PIM is in a sensor developed by 3M that acts as an end-of-life indicator for vapour-adsorbing cartridges. PIMs are being investigated as adsorbents and membrane materials for a variety of industrial separation processes, including gas separations (e.g., carbon dioxide capture) and organophilic liquid separations (e.g., bioalco