Tailoring Morphologies in Polymeric High Internal Phase Emulsions by Selective Solvent Casting

Abstract

A wide range of different morphologies have been obtained by solvent casting of mixtures of polystyrene (PS) and poly(2-vinylpyridine) homopolymers (PVP) with PS−PVP block copolymer. The curvature of the PS−PVP interface has been investigated as a function of polymer molecular weights, solvent quality, and blend composition. For blends with highly asymmetric composition at equilibrium, simulations based on self-consistent-field theory (SCF) predicted a curvature of the interface toward the minority phase. Casting PS/PVP blends from a common solvent for both PS and PVP resulted in morphologies that were in qualitative agreement with SCF simulations. These morphologies nucleated and grew from an initially fully homogeneous solution. Quite different morphologies resulted when mixtures of separate solutions of PS and PVP in selective solvents were cast, if PS−PVP of the appropriate asymmetry was added to either the PS or PVP solution. Polymeric high internal phase emulsions (polyHIPE) were formed in which the majority phase was dispersed in the continuous minority phase. A requirement for successful polyHIPE formation is that the selective solvent for the homopolymer and majority block of the block copolymer (continuous phase of the polyHIPE) has to be a sufficiently poor solvent for the minority block, thus inducing a strong segregation of the block copolymer at the interface between the two solution phases. A simple way to ensure that this condition is satisfied is to verify that the PS−PVP block copolymers form micelles in the selective solvents. The formation of such micelles was detected using dynamic light scattering.