Solvent Tuning of Cluster Morphology in Ionic Block Copolymer Solutions

Ionic block copolymers find broad uses in transport-controlled applications. Tuning ionic clusters formed in solutions that can propagate into membranes offers a path to tailor performance. Here micellar structures of a symmetric ABCBA co-polymer resolved by SANS, as the polarity of the solvent is changed by adding propanol to cyclohexane, are reported. C is a randomly sulfonated polystyrene, B is hydrogenated polyisoprene, and A is poly (t-butyl styrene). Core-shell aggregates dominate the solutions of the pure solvents with the ionic blocks residing in the core of the micelle. The packing of the ionizable segments is significantly tighter in a hydrophobic environment than in a hydrophilic one. The corona however is more compact in the hydrophilic environment. A transitional region is observed as the fully miscible solvents are mixed with elongated structures dominating the solution.