Demulsification of water-in-oil emulsions stabilized with glycerol monostearate crystals

Abstract: Particle-stabilized emulsions are recognized for their ability to resist breakdown, given the presence of an interfacial particle film that provides a steric barrier. A challenge that has arisen is in strategies to controllably destabilize such emulsions. This presentation highlights a novel approach to break particle-stabilized emulsions by altering the wettability of interfacially-bound particles. Here, we investigated the capacity of a series of six surfactants to destabilize model W/O emulsions stabilized by micron-sized crystals of glycerol monooleate (GMS). The addition of liquid-state, non-ionic surfactants to the external oil phase of the emulsions promoted demulsification of the emulsions. Emulsion destabilization was driven by changes in the wetting behaviour of the interfacially-bound GMS crystals, characterized by a transition in the wettability of hydrophobic GMS crystals from oil-wet to water-wet, rendering them ineffective at stabilizing the starting emulsions. For surfactants to be effective demulsifiers, a strong affinity to the surface of GMS particles and to the oil-water interface was necessary. Cryogenic scanning electron microscopy (cryo-SEM) revealed that addition of demulsifier to the emulsions disrupted the ordering of the interfacial GMS particle film, driving coalescence. Shear interfacial rheology and force tensiometry revealed that addition of demulsifier disrupted the particle-stabilized interfaces, characterized by a drop in interfacial storage modulus and increase in interfacial loss modulus of the otherwise elastic GMS films, with an associated drop in interfacial tension following demulsifier addition. The present work establishes a means of tuning the stability of particle-stabilized W/O emulsions in-situ­­, allowing for the controllable demulsification of otherwise highly stable emulsions for applications such as the controlled release of encapsulated solutes.