Controlling the structure and dynamics of ionizable polymer thin films is critical to their many applications. As the chemical diversity within one polymer is increased, controlling the structure and dynamics of the polymer, which is a key to their use, becomes a challenge. Here molecular dynamics simulations are used to obtain molecular insight into the structure and dynamics of thin films of one such macromolecule at the interface with water and propanol. The polymer consists of an ABCBA topology with randomly sulfonated polystyrene (C), tethered symmetrically to flexible poly(ethylener- propylene) blocks (B), and end-capped by a poly(t-butylstyrene) block (A). The compositions of the interfacial and bulk regions of films of the ABCBA polymers are followed as a function of exposure time to water or propanol. Because of the polarity of the water molecules, they selectively associate with the ionic segments and cause significant rearrangement of the surface. With time, ionic groups migrate to the interface in the presence of water. In contrast to water, propanol has a polar head group as well as shorter non-polar tail. This allows it to interact with both ionic and non-ionic segments of the polymer membrane. The penetration of propanol into the membrane is significantly faster than for water. Initially, solvent molecules rapidly penetrate membrane for both water and propanol. The water molecules are predominantly associated with ionic clusters, whereas the propanol molecules associate with both the ionic and non-ionic segments. For both, the presence of solvent results in significant rearrangement of the ionic clusters.

Solvent penetration into structured ionomer membranes

2019 Spring National Meeting

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