One-step processing of highly viscous multiple Pickering emulsions

Hypothesis: Solid-stabilized Pickering emulsions have attracted a lot of attention recently due to their surfactant-free character, and exceptional stability. At the moment, how the viscosities of the liquid phases impact the processing of Pickering emulsions remain to be clearly understood - it is however an important parameter to consider when developing chemical engineering processes employing these multiphase liquids. Our first assumption was that the amount of emulsified dispersed phase would drastically decrease as viscosity increases. Experiments and findings: In this work, we demonstrate that double water-in-oil-in-water (W/O/W) Pickering emulsions are obtained in a single processing step when using very high viscosity silicone oils (>= 10,000 cSt) and a single type of sub-Ism silica particles modified with two grafted silanes and sodium alginate. The formation of water sub-inclusions proceeds via a phase-inversion mechanism. These sub inclusions are subsequently stabilized and retained in the oil phase due to its viscosity, limiting sub inclusions mobility, and the presence of adsorbed particles forming dense layers at oil-water interfaces, acting as barriers. The process we present is simple, requires a minimum number of components, and allows the preparation of multiple emulsions which could then be used to efficiently protect and/or transport a variety of sensitive encapsulated compounds. (C) 2019 Elsevier Inc. All rights reserved.