Spontaneous Curvatures of Copolymer Interfaces in Poor Solvents: Monolayer Morphology

Abstract

We compute phase diagrams for dilute AB diblock copolymers in poor solvent in the strong segregation limit (SSL), where we allow for vesicle morphologies with spontaneous curvature and finite radius. We compare monolayer and bilayer structures as well as the possibility of macroscopic phase separation. The phases are in general not thermodynamically stable with respect to macroscopic phase separation, but because of slow kinetics of transitions between states with close free energy, we can assume that the mono- and bilayer structures are sufficiently metastable. Thereby, we can justifiably map transitions between various phases with, e.g., bicontinuous and continuous structures in either solvent or copolymer. We show that the bilayer vesicles can be thermodynamically favorable compared to micellar structures for low volumetric asymmetry of the copolymer such that completely symmetric copolymers do not necessarily lead to lamellar structures or large vesicles without spontaneous curvature.