(385o) Tunable Polymer Synthesis Towards Membrane Applications

Research Interests: Polymer Membranes, Polymer Synthesis and Characterization

Fuel cell devices such as photoelectrochemical CO₂ reduction cell (PEC-CRC) convert CO₂ into various products such as alcohol (methanol) and carboxylate ions (formate and acetate). These devices require ion exchange membranes that prevent crossover (transport) of product species, while maintaining sufficient ionic conductivity. Additionally, the transport of a particular product species is affected due to the presence of other products. Therefore, understanding the impact of membrane structure towards product (solute) transport is essential. Previously, our group observed increased acetate transport when it is in co-transport with fast diffusing methanol to poly(ethylene glycol) diacrylate (PEGDA) based crosslinked membranes. The addition of uncharged monoacrylate poly(ethylene glycol) phenyl ether acrylate (PEGPEA) monomer decreases acetate transport. Furthermore, the addition of charged monoacrylate 3-sulfopropyl methacrylate potassium salt (SPMAK) enhances ionic conductivity but also increases undesirable acetate and methanol transport. At certain compositions of SPMAK and PEGPEA, acetate transport is suppressed in co-transport with methanol, which is favorable to PEC-CRC. The two main factors that affect the solute transport in these crosslinked membranes are water uptake and fixed charge concentration, and it is important to isolate and investigate their individual impact on solute transport. Therefore, tunable crosslinked membranes with different PEGDA chain lengths, varying SPMAK content and three different uncharged monomers of increasing chain length, namely phenyl acrylate (PA), ethylene glycol phenyl ether acrylate (EGPEA) and PEGPEA are utilized. Membranes with constant water uptake, varying charge concentration, and varying water uptake, constant charge concentration were prepared. The membranes were then characterized for their water uptake and transport property experiments performed using in-situ ATR FTIR spectroscopy. The results indicate that increasing water uptake drastically increases solute transport as compared to fixed charge concentration. We also found at certain fixed charge concentration of 1.24mol charged monomer/L of sorbed water, solute transport decreases while ionic conductivity increases, which is a favorable observation. In the future, membranes with different fixed charge groups will be prepared to investigate the role of multiple charged groups of same or opposite charges towards solute transport.

Additionally, research on polymer synthesis, particularly PEGDA of varied molecular weight and block/gradient copolymers of polystyrene-polyisoprene were synthesized for membrane applications. Polymer characterization were carried out using NMR and GPC. The prepared PEGDA polymers were used to investigate freezing dynamics of polymer-water droplets of different concentrations, potentially of use in oil and gas industries and membrane applications. The block/gradient copolymers of polystyrene-polyisoprene can be utilized to prepare thin film membranes for coating and template applications.