Emulsion behavior control and stability study through decorating silica nano-particle with dimethyldodecylamine oxide at n-heptane/water interface

Emulsions have been widely applied in subterranean enhanced oil recovery processes, cosmetics and chemistry engineering fields, etc. Current research interests are focusing on improving the stability of emulsion by involving surfactants or colloidal materials. This work aims to enhance the emulsion stabilization by introducing silica nanoparticles (SNP) surface-hydrophobilized/hydrophilized by adding dimethyldodecylamine oxide (OA-12) and to reveal the dynamic behaviors of such composites on the liquid-liquid interface. The synergistic effect between SNPs and OA-12 in solution and on oil/water interface were studied by measuring the zeta potential, interfacial rheology and emulsion viscoelastic rheology, etc. It was found that the oil/water interface viscoelastic modulus are augmented by modified silica nano-particles and at the same time emulsions acquired significant long-time stability. Furthermore, phase transformation was induced with the increase of the concentration ratio between OA-12 and silica nano-particle, the emulsion type change from o/w, then to w/o and back to o/w. It is suggested that the inversions are induced by the mounting adsorption of OA-12 molecules on SNPs, which changes the hydrophilic-lipophilic balance of particle surfaces.