Membrane technology has been used in water purification for decades. However, membrane fouling remains a limiting factor. One way to control fouling is through surface modification. Several studies report that increasing surface hydrophilicity can reduce membrane fouling. Surface modification via physical coating (i.e., thin-film composite membrane) was explored in this research to prevent membrane fouling. Before making thin-film composite membranes, it was important to study structure/property relations in a series of potential coating materials. This research aims to contribute to a better fundamental understanding of the structure/property relations which govern water transport, rejection of model foulants (i.e., emulsified oil droplet or protein), and fouling characteristics in hydrogels based on poly(ethylene glycol) diacrylate (PEGDA) and N-vinyl-2-pyrrolidone (NVP). Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by UV-induced photopolymerization of PEGDA crosslinker in the presence of varying amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) when the water content of the prepolymerization mixture was greater than 60 wt%. Visible light absorbance measurements, water uptake, water permeability, and salt kinetic desorption experiments were used to characterize the structure of these phase-separated, crosslinked hydrogels. The films with PIPS exhibited a porous morphology in cryogenic scanning electron microscope (CryoSEM) studies. Dead-end filtration experiments using deionized water and bovine serum albumin (BSA) solutions were performed to explore the fundamental transport and fouling properties of these materials. The total flux of pure water through the films after prior exposure to BSA solution was nearly equal to that of the as-prepared material, indicating that these PEGDA films resist fouling by BSA under the conditions studied. Crosslinked NVP free-standing films were prepared by UV-induced photopolymerization in the presence of water, with NVP as the monomer and N,N’-methylenebisacrylamide (MBAA) as the crosslinker. A series of crosslinked films were polymerized at various prepolymerization water contents, NVP/MBAA ratios and at various levels of UV light intensity in the polymerization. Like PEGDA, the NVP films also underwent phase-separation during polymerization. The influence of monomer/ crosslinker ratio, prepolymerization water content, and UV intensities on membrane morphology and water transport was characterized with CryoSEM, bio-atomic force microscope (Bio-AFM) and dead-end filtration. Molecular weight cutoff (MWCO) measurements were used to characterize the sieving property of crosslinked NVP films polymerized at different UV intensities. UV intensity was found to have an impact on the interconnectivity of crosslinked membranes. Finally, tests of fouling resistance to protein solution (bovine serum albumin) and oily water emulsion were performed. The NVP crosslinked films had good protein and oily water fouling resistance. Overall, both crosslinked PEGDA and NVP films exhibit fouling resistance to oily water emulsions or protein solution. NVP films had more porous structure and higher water permeability than did PEGDA films, while the more compact structure of PEGDA films led to better rejection of model foulants (e.g., protein) than in NVP films. Based on different applications (e.g., oil/water separation, protein filtration), different coating materials must be chosen according to the membrane morphology, transport property, and rejection of model foulants to achieve the highest water flux and foulant rejection in membranes used for water purification. / text

Cross-linked poly(ethylene oxide) (XLPEO) based on poly(ethylene glycol) diacrylate (PEGDA) is an amorphous rubbery material with potential applications for carbon dioxide removal from mixtures with light gases such as methane, hydrogen, oxygen and nitrogen. Changing the polymer network structure of XLPEO through copolymerization has previously been shown to influence gas transport properties, which correlated with fractional free volume according to the Cohen-Turnbull model. This project explores strategic modifications of the cross-linked polymer structure and their effect on the chemical, physical and gas transport properties with an aim to develop rational, molecular-based design rules for tailoring separation performance. Experimental results from calorimetric and dynamic thermal analysis studies are presented, along with pure gas permeability and solubility obtained at 35°C. Incorporation of dangling side chains by copolymerization of PEGDA with methoxy-terminated poly(ethylene glycol) methyl ether acrylate, n=8 (PEGMEA) was previously shown to be effective in increasing fractional free volume of XLPEO through the opening of local free volume elements, which in turn increased CO₂ permeability. Through a comparative study ofshort chain analogs to these co-monomers, incorporation of an ethoxy-terminated co-monomer was shown to be more effective than a comparable methoxy-terminated co-monomer in increasing gas permeability. For instance, copolymerization of PEGDA with 71 wt% ethoxy-terminated diethylene glycol ethyl ether acrylate increased CO₂ permeability from 110 barrer to 320 barrer. Gas permeability increase was not observed when hydroxy or phenoxy-terminated pendants were introduced, which was attributed to reduction in chain mobility due to increased inter-chain chemical interactions or steric restrictions, respectively. Based on these results, incorporation of a co-monomer containing a bulky non-polar terminal group, tris-(trimethylsiloxy)silyl, was examined in order to further increase gas permeability. Addition of 80 wt% TRIS-A co-monomer increased CO₂ permeability of cross-linked PEGDA to 800 barrer. However, the resulting changes in chemical character of the copolymer reduced CO₂/light gas selectivity, even as gas permeability increased. The effect of incorporating a bulky, stiff functional group in the cross-linker chain was studied using cross-linked bisphenol-A ethoxylate diacrylate, which showed 40% increase in permeability compared to cross-linked PEGDA. This study affirmed the importance of polymer chain interaction, in addition to free volume, in determining the gas transport properties of the polymer. / text

Several novel polymer monoliths for the analysis of peptides and proteins were synthesized using polyethylene glycol diacrylate (PEGDA) as crosslinker. Photo-initiated copolymerization of polyethylene glycol methyl ether acrylate and PEGDA yielded an inert monolith that could be used for size exclusion liquid chromatography of peptides and proteins. This macroscopically uniform monolith did not shrink or swell in either water or tetrahydrofuran. More importantly, it was found to resist adsorption of both acidic and basic proteins in aqueous buffer without any organic solvent additives. A strong cation-exchange polymer monolith was synthesized by copolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and PEGDA. A ternary porogen (water, methanol and ethyl ether) was found suitable to prepare a flow-through monolith with moderate pressure drop in aqueous buffer. The resulting monolith showed excellent ion exchange capillary liquid chromatography of peptides using a simple salt gradient. Extremely narrow peaks were obtained for the analysis of synthetic peptides, natural peptides and a protein digest. A peak capacity of 179 was achieved. Although the poly(AMPS) monolith demonstrated extraordinary performance, one main drawback of this monolith was its relatively strong hydrophobicity. A decrease in hydrophobicity was achieved by using more hydrophilic monomers (e.g., sulfoethyl methacrylate or vinyl sulfonic acid). The most hydrophilic poly(vinyl sulfonic acid) monolith provided high resolution cation-exchange liquid chromatography of protein standards and lipoproteins. Use of the new PEGDA biocompatible crosslinker over the conventional ethylene glycol dimethacrylate crosslinker for the preparation of polymer monoliths was found to be advantageous for the analysis of biological compounds in several chromatography modes.