Nanophase-Segregated Structures and Transport Properties in Sulfonated Poly(arylene ether sulfone) Multiblock Copolymer Membrane for Proton Exchange Membrane Fuel Cell

Abstract

Multiblock sulfonated poly(arylene ether sulfone) membranes with various block lengths are investigated using molecular dynamics simulation methods. Three different polymers are modeled to have unique block lengths. The resulting blocks include (X5Y5)4, (X10Y10)2 and (X20Y20)1, where five, ten and twenty monomeric units, respectively, are consecutively connected to form a block. Each block is then alternatingly connected to another block type. All other molecular variables such as molecular weight, equivalent weight, and number of water molecules are controlled to have the same value among the three polymers. Despite the variation of the block length, the equilibrated structures of the membranes appear very similar. Through pair correlation function analysis, every aspect of the detailed local structures is nearly identical, indicating no effect of block length. Accordingly, the transport of both water and hydronium is also similar regardless of block length variation. The similarities between the membranes, regardless of block length, are attributed to the presence of hydrophilic keto and sulfone groups in the hydrophobic blocks. The even distribution of hydrophilic groups throughout the hydrophobic phase leads to more dispersed water molecules and a poorly developed water phase. Therefore, more contrast in hydrophobicity/hydrophilicity between the blocks is suggested to induce more nanophase-segregation.