Solvent Response of Ionic Co-Polymers at Interface

Ionizable co-polymers constitute effective media for controlled ion transport. Their response to the environment affects a large range of applications from biotechnology to clean energy. Though the interplay between highly segregating blocks is known to drive rich variety of phases, their response to solvents remains an open question. The higher the blocks segregation is, the more distinctive their response becomes. Here the response of a symmetric pentablock co-polymer (A-B-C-B-A) with a center polystyrene sulfonate (PSS) block tethered to polyethylene propylene (PEP), terminated with a t-butyl styrene(t-PS), to solvent triggers was studied for two PSS sulfonation 26% and 52% . Thin films of the order of 10-20 nm were spin coated on SiO₂ and their morphology was followed as a function of exposure time to toluene using atomic force microscopy. The pristine films of 26% consist of co-continuous domains. With exposure time to toluene the hydrophobic domains expend about 10% of their initial size within the first 20min. In contrast, the 52% sulfonation film forms well defined isolated assemblies that increase two folds within the first 20min. For both polymers however, the ionic networks remain unperturbed where the packing of the hydrophobic blocks is affected.