Composition Distribution-Dependent Miscibility of Amphiphilic Random Copolymer Mixtures in Water

Abstract

Random copolymers intrinsically possess chain-by-chain composition distributions that originate from sequence heterogeneity. Yet they can form macroscopically homogeneous materials and develop intriguing, higher-order self-assembled structures at microscopic levels. Here, we investigate the miscibility and self-assembly behaviors of model amphiphilic random copolymer mixtures in water as a function of composition distributions. We systematically vary the compositional distribution width (σ) and the fraction of the central composition (wR55) by mixing presynthesized random copolymers with different weight ratios. Increasing σ drives a phase transition from homogeneously coassembled, bilayer-folded lamellar mesophases to macrophase-separated, self-sorted states. Introducing a central composition to broadly distributed multinary blends restores macroscopic homogeneity and ordered coassembly, effectively mediating compatibility between compositionally disparate chains. While alternating copolymers with uniform composition distribution do not undergo bilayer folding, the lyotropic mesophase can persist in a ternary blend even under strong shear, suggesting opportunities to use composition distributions as a design parameter of soft matter.