(606h) Effect of Water Vapor on the Transport and Physical Properties of PS-b-PEO Copolymer Membranes

Poly(styrene - block - ethylene oxide) (PS-b-PEO) membranes are of interest for lithium-air batteries, carbon dioxide separation, and water purification. In contrast to water purification in which high water permeability is desirable, lithium-air batteries require low water permeability for long-term stability. Accurate measurement of water transport is needed to determine the appropriate application(s) for this material. Using FTIR-ATR spectroscopy, we study the transport behavior of water vapor at different water activities in PS-b-PEO and high molecular weight poly(ethylene oxide) homopolymer membranes at 30°C. We also report gravimetric water vapor sorption by PEO and PS-b-PEO membranes over a range of vapor activity (0.05 – 0.95). Equilibrated water content from gravimetric sorption experiments compared closely for both PEO homopolymer membranes and the PEO proportion of PS-b-PEO membranes. The effect of water content on the thermal properties of PS-b-PEO and PEO membranes were studied with differential scanning calorimetry. Our study shows that the glass transition temperature of PS lamellae was not affected below 0.75 water vapor activity. Whereas, PEO crystallinity gradually decreased with increased water vapor activity. The crystalline content of the PEO and the presence of glassy PS lamellae will be used to explain the results of FTIR-ATR transport results.