Nanoparticles At the Water-Decane Interface: Evidence of Emergent Behavior From Equilibrium Multi-Scale Simulations

Pickering emulsions (emulsions stabilized by solid nanoparticles rather than by surfactants) are finding practical applications in several areas, including cosmetics, drug-delivery, and even in-situ upgrade of bio-oil to fungible bio-fuels [Science 327 (2010) 68]. It is known that solid particles adsorb at water-oil interfaces to reduce the contact area between the two immiscible phases. Stable emulsions are obtained when the particles strongly adsorb at the interfaces. We will report here equilibrium molecular dynamics simulation results employed to differentiate the behavior of silica-based nanoparticles used to stabilize either water-in-decane or decane-water emulsions. We will compare nanoparticles with similar surface properties, but different distribution of the surface groups. Particular attention will be given to Janus as opposed to homogeneous nanoparticles [Langmuir 27 (2011) 5264-5274]. The all-atom simulation results have been used to parameterize dissipative particle dynamics simulations. Using the latter tool, we have obtained interesting morphologies depending on nanoparticle concentration, and water-decane molar ratio in the various simulated systems. The simulation results will be discussed in relation to available experimental data.