Water-in-oil high internal phase Pickering emulsions formed by spontaneous interfacial hydrolysis of monomer oil

Hypothesis: Alcohols can strongly reduce the interfacial tension between immiscible liquids, thus facili-tating the formation of emulsions. By combining non-surface-active hydrophobic particles with medium-chain alcohols, stable water-in-oil (w/o) high internal phase Pickering emulsions (HIPPEs) can be easily prepared without high-energy emulsification methods. Experiments: The emulsions containing acrylate monomer as the oil phase were prepared at different pH values in the presence of hydrophobic silica particles. Further, by replacing monomer oil with organic sol-vents (e.g., toluene) and a certain concentration of alcohol, the promoted particle adsorption at the oil- water interface has been systematically investigated. The morphology and interfacial structure of HIPPEs were visualized by confocal laser scanning microscopy (CLSM). Finding: At high pH, stable water-in-acrylate monomer HIPPEs can be formed using commercial fumed silica nanoparticles alone with simple stirring or vortexing. The hydrolysis of the acrylate group at high pH can generate alcohols in situ which adsorb at the oil-water interface to reduce the interfacial tension and promote particle adsorption to hinder droplet coalescence. The novel strategy for forming stable and processable HIPPEs can be universally applied to different hydrophobic silica particles with the help of various alcohols as the co-stabilizer, which provides a flexible approach for the fabrication of lightweight, closed-cell solid foams for a range of applications. (c) 2022 Elsevier Inc. All rights reserved.