A supramolecular approach to probing the influence of micro-phase structure on gas permeability of block copolymer membranes

To gain insight into the correlation between the gas permeability and the micro-structures inside gas separation polymeric membranes, a series of membranes which have similar film thickness but different micro-structure have been fabricated based on block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP). In this work, it has been realized that the micro-structure inside the membrane switched from well-ordered spherical phase to well-ordered cylindrical phase, via simply controlling the hydrogen bonding amounts of the guest molecule M, 12-(1-(dimethyl amino) ethylidene amino) dodecanoic acid. That is, supramolecularly assembling the host copolymer PS-b-P4VP with guest molecule M essentially changes the volume fraction of P4VP/M domains in the membrane. The hydrogen bonding interaction between the P4VP blocks and the molecule M has been confirmed by fourier transform infrared (FT-IR) measurement. The morphologies of the membranes have been investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). After studying the gas permeability of the supramolecularly assembled membranes with the well-ordered microphase structures, we found that the gas permeances for He, N₂, CO₂ of the membranes with well-ordered nanostructure increased in magnitude, which we propose was attributed to the enhanced interface between the different phase domains. An appropriate mechanism has been put forward accordingly. This work provides a new strategy of probing the influence of different micro-phase structure inside block copolymer membranes on gas permeability through supramolecular self-assembly.