Amphiphilic Copolymers at Liquid-Liquid Interfaces: Diblock vs Multiblock Polymer

Amphiphilic copolymers represent a distinct class of surfactant macromolecules that have been extensively studied due to their surface-active properties. Their ability to reduce interfacial tension helps to create emulsions that are crucial in many industries. Most applications use diblock copolymers as emulsifiers, however, experimental and computational studies suggest that linear multiblock copolymers could have improved emulsifying efficiency. In this work, extensive molecular simulations have been performed to understand how diblock, triblock and pentablock copolymers affect interfacial tension at planar liquid-liquid interfaces. Polymer surface concentration was varied and its effect on the interfacial tension and surface pressure was measured. Polymer structure at the interface was quantified by computing the radius of gyration, relative shape anisotropy parameter, and end-to-end distances. Simulations predict that pentablock copolymers are better at reducing interfacial tension compared to diblocks and triblocks. A possible explanation is given in terms of local densities around the interface, polymer conformations and surface pressure dependence on the block sequence. In addition, free energy profiles for the insertion of a polymer into a saturated interface is computed using advanced sampling techniques.