Synergistic effects of surfactants and heterogeneous nanoparticles at oil-water interface: Insights from computations

Hypothesis: Nanoparticles (NPs) can reduce the interfacial tension (IFT) of the oil-water system containing surfactants by reducing the interfacial area available to surfactants. The ability to reduce the IFT when surfactants are present in addition to NPs depends on the localization of the NPs on the interface, which is related to the nature of the NPs and the interaction between NPs and surfactant molecules. Experiments: Systems of NPs and surfactants on the oil-water interface were studied using dissipative particle dynamics (DPD). Heterogeneous NPs with different properties and interface coverage were placed on the interface with various surfactant concentrations. The IFT and the surfactant density profiles across the interface were analyzed. Findings: At constant surfactant concentration, adding NPs reduced the IFT: while with the absence of surfactant, NPs expressed no effect on the IFT. Among different types of heterogeneous NPs, the most effective were those that maximized their footprint on the interface, reducing thus the interfacial area available to surfactants. The interactions of the NPs with the surfactant molecules determined exactly which pattern of heterogeneity was most favorable. Based on these results, suggestions for designing NPs for maximum synergistic effects with surfactants were formulated. (C) 2019 Elsevier Inc. All rights reserved.