Multiblock Copolymers at Liquid-Liquid Interfaces: Effect of the Block Sequence on Interfacial Tension and Polymer Conformation.

Abstract

Block copolymers of amphiphilic nature represent a distinctive class of macromolecules that have been extensively studied due to their intriguing surface-active properties. Their ability to reduce interfacial tension and create disperse phases, such as emulsions, has made them crucial in industries that rely on the interfacial effects of these molecules. Experimental and computational studies have reported the effects of changing various properties associated with the polymeric chains including stiffness, molecular weight, and other structural attributes. In this work, extensive molecular simulations were performed to understand how the sequence of an AB multiblock copolymer impacts the interfacial tension between two immiscible liquids. To efficiently explore a range of surface concentration values and four different block copolymer sequences, a coarse-grained model was employed. Simulation results indicate that at a fixed composition, block sequence has a strong effect on the rate of interfacial tension reduction as polymer surface concentration increases. Of all studied sequences, the alternating sequence was able to greatly reduce the interfacial tension at low surface concentrations, whereas pentablock and triblock sequences were able to reduce it even more than the alternating sequence, but it required a higher polymer surface concentration to achieve this. To correlate polymer conformations with interfacial effects, several structural descriptors were computed to quantify the conformations adopted by the macromolecules at the interface.