Nanoparticles, Surfactants and Interfaces with Coarse-Grained Computations

Interfacial phenomena play a critical role in various applications of environmental and industrial importance.1 For example, oil spill cleanup, remediation of soil contaminated with organic compounds, chemical flooding of hydrocarbon reservoirs,2,3 separations in the chemical industry and drag delivery4,5,6 depend on interface behavior. Either surfactants or nanoparticles (NPs) can stabilize oil-water interfaces, but the stabilization mechanism is different. For surfactants, the interfacial tension (IFT) is reduced.7,8 For NPs the IFT does not change, but the oil-water interfacial area changes. In this work, we will describe the use of coarse-grained computational techniques to investigate the synergisms between NPs and surfactants at the oil-water interface. Such computations provide molecular-scale information about the system studied, but in cases where molecular dynamics are impractical. The Dissipation Particle Dynamics (DPD) method9,10 employed herein allows the simulation of systems of oil (i.e., dodecane or heptadecane) and water with surfactants, such as the non-ionic Octaethylene glycol monododecyl ether (C12E8), and NPs. The wetting properties of the NPs and their shape can be tuned in the simulations, so that both homogeneous particles and anisotropic NPs, such as Janus NPs (polystyrene-gold) or carbon nanotubes (CNTs) can be simulated. We will discuss the computational technique, its implementation for specific physical systems and its verification, as well as recent results on the stability of droplets and interfaces in oil-water systems.