Colloidal TiO2 nanoparticles with near-neutral wettability: An efficient Pickering emulsifier

Colloidal inorganic nanoparticles featured with ultrasmall sizes and near-neutral surface wettability are considered as efficient emulsifiers to stabilize Pickering emulsions. Herein, we demonstrated that colloidal TiO2 nanoparticles synthesized by the well-established sol-gel approach using Ti(OC4H9)(4) as precursor, could be directly used as an efficient Pickering emulsifier without any other additives. The sol-gel TiO2 nanoparticles showed near-neutral wettability at the oil-water interface (theta(ow) (similar to)90 degrees) derived from the surface residual butanol-related species as revealed by TGA/DTA and FT-IR analyses, which should be responsible for the formation of Pickering emulsion with ultrahigh stability. The Pickering emulsions stabilized by size-tunable TiO2 nano-particles under various emulsification conditions were characterized by photography, optical microscopy and rheology measurements. The results suggested that the droplet sizes and rheology properties of the emulsion could be adjusted by tuning the TiO2 nanoparticle sizes. Moreover, as a potential application, we also demonstrated the simple fabrication of TiO2-coated silicone elastic hybrid microspheres through the Pickering emulsion templated polymerization. The present work demonstrated that sol-gel TiO2 nanoparticles could serve as efficient particle emulsifiers for achieving stable emulsions, and may also extend the wide application of colloidal TiO2 nanoparticles based on the Pickering emulsion platforms.