(713g) Rapid Demulsification of Water-in-Oil Emulsions Using Silica Nanoparticles

Our research focuses on investigating the efficiency of fumed silica nanoparticles as potential demulsifiers for water-in-oil emulsions stabilized using a surfactant. From our experimental results, the hydrophobicity of silica nanoparticles determined the efficiency of demulsification. Partially hydrophobic silica nanoparticles had the highest demulsification efficiency followed by hydrophilic silica nanoparticles. Hydrophobic silica nanoparticles did not aid in complete phase separation of water-in-oil emulsions. The observed phenomenon was attributed to the difference in dynamic interaction mechanisms between silica nanoparticles and surfactants. Hydrophilic and partially hydrophobic silica nanoparticles adsorb the surfactants via hydrogen bonding that in turn led to depletion of surfactants at the oil-water interface. Upon addition of hydrophilic silica nanoparticles to the water-in-oil emulsion, the preferential distribution of silica nanoparticles in the water phase led to lower adsorption of surfactants as compared to partially hydrophobic silica nanoparticles, which have higher affinity towards the oil phase. Weak hydrophobic interactions between highly hydrophobic silica nanoparticles and surfactants led to poorer demulsification efficiencies for water-in-oil emulsions stabilized using a non-ionic surfactant. Furthermore, we present observations regarding the effect of salinity on demulsification efficiency of water-in-oil emulsions stabilized using a non-ionic surfactant upon addition of fumed silica nanoparticles of different wettabilities.