Solvation and Entropic Regimes in Ion-Containing Block Copolymers

Abstract

The phase behavior of ion-containing block copolymers is studied using a field-theoretic model consisting of fully mobile ions immersed in a heterogeneous dielectric medium. Two distinct thermodynamic regimes are found to emerge, resulting from the competition between ion translational entropy and solvation free energy. In the regime dominated by entropy, the disordered phase is stabilized by the addition of ions. In the regime dominated by solvation free energy, the disordered phase is destabilized, leading to a “chimney”-like channel of stable ordered phases at sufficiently large ion concentrations. The two regimes are demarcated by the parameter λB, which quantifies the variation in solvation energy upon transferring ions between different dielectric domains. Estimates of λB for experimental systems suggest that the majority of block copolymer electrolytes fall within the solvation regime.