Effect of block copolymer membrane nanostructure on ethanol-water transport measured by infrared spectroscopy

Block copolymers (BCPs) are recognized for exhibiting unique assets, not achievable in homogeneous, single-component materials, by combining the peculiarities of two different homopolymer blocks, in terms of physical, chemical and mechanical properties. Three polystyrene- b -poly(ethylene oxide) (SEO) BCPs with distinct morphologies—lamellar, cylindrical, and spherical—synthesized via anionic polymerization, were investigated for their possible use as membrane materials for ethanol-water transport, aiming to explore sustainable separation processes. Ethanol permeation experiments at 30°C, using water/ethanol feeds with various concentrations, were conducted via in-situ Fourier-transformed infrared spectroscopy (FTIR). Results revealed that ethanol permeability in SEO membranes depends on the feed mixture concentration and the PS-PEO mass ratio. The hydrophilic PEO fraction interacts strongly with both solvents, while the hydrophobic PS moiety, though not dissolvable, is more affine to ethanol. A mass balance model confirmed that at 8.9 mol/L ethanol, permeability increased from 2.7·10 -7 to 8.5·10 -7 cm 2 /s moving from spherical to lamellar structures, while water permeability at 50.1 mol/L rose from 2.0·10 -9 cm 2 /s to 2.1·10 -8 cm 2 /s. Despite the moderate separation performance of the membranes, the study enhances understanding of swelling, morphology, and counter-diffusion effects, contributing to polymer design advancements.