Interfacial Tension of Graft Block Copolymers at Immiscible Homopolymer Interfaces

Abstract

Graft multiblock copolymers are emerging as effective compatibilizers for immiscible polymer blends, leveraging the large parameter space offered by their branched architecture to surpass traditional linear diblock copolymers in compatibilization potential. We report the results of coarse-grained molecular dynamics simulations of AB graft copolymers at a strongly segregated A/B interface, focusing on the impact of graft copolymer loading at the interface and the copolymer architecture on the resulting interfacial tension of the system, which is correlated to copolymer conformation. At relatively low copolymer loadings, distributing the total grafting beads into a greater number of grafts enhances the copolymer interfacial coverage, effectively minimizing unfavorable homopolymer-homopolymer contacts and reducing interfacial tension. At relatively high copolymer loadings, once the interface is saturated with copolymers, molecules with a high number of grafts exhibit a greater penetration perpendicular to the interface, characterized by bending of the backbone and increased deviation of backbone beads from the interfacial plane. Our results demonstrate the existence of an optimal junction density beyond which the copolymers aggregate at the interface, leading to a plateau in interfacial tension as junction density increases further.