Remarkable efficacy of graft block copolymers as surfactants for reducing interfacial tension

Abstract

Graft copolymers as surfactants have the ability to improve the interfacial properties of polymer blends or fluid mixtures. This is related to the topologies of the grafts. Based on dissipative particle dynamics (DPD) simulations, we investigated the interfacial properties (interfacial density, interfacial thickness and interfacial tension) of oil/water systems and their dependence on the topological structure and the concentration of graft copolymers. Importantly, a quantitative scaling relationship between the variation in the interfacial tension Δγ_S and the concentration C_S was first established as Δγ_S = kC_S^N. The exponent N is mainly influenced by the graft number, for example N = 1.54 for A₈(B₈)₁ (1 graft) < N = 1.63 for A₈(B₄)₂ (2 grafts) < N = 1.73 for A₈(B₂)₄ (4 grafts). This means that graft copolymers with more grafts have a higher efficacy for reducing the interfacial tension at the same concentration. Further analysis by Gibbs adsorption isotherm is in accordance with the results of our simulated density profiles, which testifies the credibility of our established relationship. This work provides a standard model for experimental applications of graft copolymers as surfactants, especially for reducing the interfacial tension.