Effects of solid particle content on properties of o/w Pickering emulsions

The control of droplet size and stability of oil-in-water Pickering emulsions stabilized by hydrophobized fumed silica was investigated. Three regimes were observed according to the silica content: instability at low silica content, stable emulsions with droplet size controlled by the silica content, and emulsions of constant size set by the emulsification process at high silica concentrations. The oil-to-silica ratio was the relevant parameter of the size control in the medium concentration regime. Centrifugation experiments and particle size distribution measurements gave evidence of the presence of excess silica present as dispersion in the aqueous phase in the high silica content regime. Adsorption of silica to the droplet surface did not follow adsorption equilibrium; strong adsorption prevailed. Lastly, aggregation of silica particles appeared a crucial parameter. Oil adsorption and capillary condensation of oil within the silica aggregates provided a supplementary mechanism of silica aggregation that contributed to the stability of emulsions.

Particle size distribution and ultracentrifugation experiments show control of o/w Pickering emulsion droplet size by silica content, till a regime with excess silica is reached.Figure optionsDownload high-quality image (82 K)Download as PowerPoint slideResearch highlights
► Comprehensive investigation of o/w Pickering emulsions stabilized by hydrophobically modified silica particles is presented.
► Droplet size is controlled by the oil-to-silica ratio.
► Coverage of oil droplets by silica particles is not constant.
► Silica is fully adsorbed to oil droplets till saturation of the interface.
► Excess silica is observed in the aqueous phase at high silica content.