Membranes based on sulfonated block copolymers have shown potential for water purification, but the structure and performance of these materials have not been studied as a function of hydration cycles. In this work, we investigate the structure, mechanics, and transport properties of sulfonated pentablock copolymer membranes after cycles of soaking in water and drying in air. Two membrane thicknesses are compared (15 μm and 30 μm). All as-prepared films have a disordered micelle-like structure of isolated sulfonated domains. The thicker as-prepared films absorb more water, exhibit higher proton conductivity and show enhanced ductility compared with thinner films, which is consistent with a reduced surface to volume ratio. Through successive hydration cycles, the sulfonated domains progressively merge into a continuous network, and the normalized proton conductivity (conductivity/water content) increases due to the formation of this transport pathway. However, while cycling increases the absolute proton conductivity and water content in thicker films, the opposite trend is observed in thinner films. This discrepancy is attributed to cycling-induced mechanical instabilities that drive severe buckling in thinner films, leading to large strains that reduce water uptake and associated proton conductivity. This mechanical degradation is also detected in tensile tests, which show that thinner films lose 20% of their ductility with each successive cycle and cannot support any additional strain after four cycles. These systematic studies demonstrate that wet-dry cycles can lead to complex changes in the structures and performance of amphiphilic block copolymer films, which may complicate their design for applications in water treatment or proton-conducting layers in electrochemical devices.

Structure, properties and performance of sulfonated pentablock terpolymer membranes as a function of hydration cycles

255th National Meeting (2018)

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