Microphase Separation Induced by Complexation of Ionic−Non-Ionic Diblock Copolymers with Oppositely Charged Linear Chains

Abstract

We develop a theory of microphase separation in a solution precipitate of flexible AB block copolymers consisting of charged (A) and neutral (B) blocks which are complexed with oppositely charged linear chains (C) via electrostatic interactions. We analyze regimes of selective solvents: the solvent is Θ for the A blocks and the C chains, whereas it is poor for the B blocks. Despite the selectivity, stoichiometric complexes precipitate because of fluctuations induced electrostatic attraction. Depending on composition of the diblock copolymer, selectivity of the solvent and fraction of charged groups, direct and inverse spherical, cylindrical and lamellar structures can be stable in the precipitant. Phase diagrams are constructed in the strong segregation approximation. Morphological transitions induced by changes of solvent quality and fraction of charged groups are predicted.