Effect of shear and interfacial fat crystallization on release of water-soluble dye from water-in-oil emulsions

Abstract

The microstructure and associated dye release behaviour of water-in-oil (W/O) emulsions stabilized with either a liquid or solid-state interfacial layer were studied under static and shear conditions. The emulsions contained high-melting fat crystals in the oil continuous phase which provided network stabilization. Two surfactant types were used to generate and stabilize the emulsions: Polyglycerol polyricinoleate (PGPR), a liquid-state surfactant at room temperature, and monoacylglycerols glycerol monostearate (GMS) and glycerol monooleate (GMO) which are solid at the same temperature. The latter two surfactants resulted in droplets exhibiting interfacial crystallization, whereas only network stabilization was present in the PGPR-based emulsion (i.e., no interfacial crystallization). Release of Rhodamine B, a water-soluble dye, from the dispersed aqueous phase of the W/O emulsions into an agar gel was quantified using confocal microscopy. Emulsions stabilized with liquid surfactant displayed greater dye release compared to the GMS and GMO emulsions. The PGPR emulsions also showed higher shear-mediated dye release than under quiescent conditions, whereas no such differences were seen with the GMS and GMO emulsions. Ultimately, the interfacial structure of the dispersed aqueous droplets was the dominant factor controlling the release of water-soluble dye from these W/O emulsions.