(635c) Computation Study On Water and Charge Transport in the Cross-Linked and Sulfonated Poly (1,3-Cyclohexdiene) (xsPCHD) Based Proton Exchange Membranes

Using different computational approaches (Molecular Dynamics Simulation, Confined random walk (CRW) simulation and an analytical theory), this work studied the cross-linked and sulfonated Poly (1,3-Cyclohexdiene) (xsPCHD) hompolymer, xsPCHD-polyethylene glycol (PEG) block copolymer and xsPCHD/PEG blend proton exchange membrane (PEM) molecular level structures and water and charge transport in the membranes. The membrane structure was first studied through pair correlation functions (PCFs) from MD simulation. Interesting results are found for the copolymer and blend membranes. The PEG-water PCF shows PEG has greater affinity to water in the blend than that in the copolymer membrane, suggesting PEG is well mixed with water and serves as a cosolvent in the blend membrane.  The PEG-H₃O⁺ PCFs show that the end OH group of PEG has much stronger affinity to H₃O⁺ while the backbone of PEG has weaker affinity to H₃O⁺ in the copolymer membrane than that in the blend membrane. The features of the PCFs suggest very different proton transport mechanisms in the copolymer and blend membranes. The CRW simulation results show that bigger water clusters formed in the copolymer membrane. The existence of PEG in the blend membrane slows down the water diffusion but helps the structural diffusion of charge. Using a recently developed analytical theory, the proton conductivity is calculated and compared with that of experimental measurements. Good agreement is obtained for homopolymer membrane but the accuracy of the theory is affected when applied to copolymer and blend membrane due to the existence of PEG in these membranes.