Solid Wettability from Surface Energy Components: Relevance to Pickering Emulsions

TLDR

The study develops a theoretical framework for solid particle wetting at oil–water interfaces based on surface energy components and applies it to predict which particle types can stabilize emulsions of two immiscible oils. The framework models the interfacial energies of solid, oil, and water phases to calculate oil–water contact angles and to forecast particle–oil compatibility for emulsion stabilization. Calculated contact angles for solids of given hydrophobicity across oils of varying polarity agree with experiments, showing that higher oil polarity raises contact angles on hydrophobically modified silica and favors water‑in‑oil Pickering emulsions, while predictions for hydrocarbon–fluorocarbon pairs indicate perfluorinated particles stabilize fluorocarbon‑external emulsions and silica with hydrocarbon groups stabilize hydrocarbon‑external emulsions.

Abstract

A theoretical treatment is developed for the wetting of a solid particle at an oil−water interface in terms of the components of the surface energies of all three phases. Calculated oil−water contact angles for a solid of given hydrophobicity with a range of oils of different polarity show good agreement with experimental data. For a hydrophobically modified silica surface, oils of increasing polarity give higher oil−water contact angles measured through water. The results are in line with the effect of oil type on Pickering emulsion type where more polar oils preferentially give water-in-oil emulsions. The approach is also used to predict the type of solid particles that would be required to stabilize emulsions of two immiscible oils. For hydrocarbon−fluorocarbon pairs, it is predicted that perfluorinated particles would stabilize fluorocarbon-external emulsions while silica particles with a high coverage of hydrocarbon groups should stabilize hydrocarbon-external emulsions.