(634e) Fluid -Fluid Interfaces Stabilized By Solid Particles in Pickering Emulsions

Monoglycerides are commonly used emulsifiers for water-in-oil emulsions and are relevant to pharmaceutical and food applications. In this work, we investigate the stabilising action of Monoglyceride, a model emulsifier, deposited at the air-water and oil-water interface and quantify the elastic properties. The elasticity of the interface provides a steric barrier against the phase separation of fluids in an emulsion. Generally, the emulsion is prepared by first dissolving the emulsifier in the oil phase at a high temperature, which is then cooled to a chosen temperature. At this temperature, the polar phase is added, and this mixture is homogenised such that the droplets of the polar phase are dispersed throughout the continuous oil medium. The mixture is then cooled to room temperature with a specified cooling rate. The micron-sized emulsifier particles solidify at the liquid-liquid interface, forming a network of particles that provide a barrier against phase separation in the emulsions.

We hypothesise that the strength of these networks is strongly dependent on the surface concentration of the emulsifier particles at the interface and the cooling rate at which the emulsion mixture is cooled to room temperature. To test this hypothesis, we prepare the monoglyceride-stabilized oil-water interface in a DuNuöy ring setup so that the elastic modulus of the interface is measured at various composition and cooling rates. We obtain a power-law-like behaviour of the elastic modulus with respect to the surface concentration and find that, for a given surface concentration, the interfacial modulus increases with increasing cooling rates.

In parallel, we prepare water-in-oil Pickering emulsions, which are stabilised by the encapsulation of the water droplets by Monoglycerides at various surface concentrations. The emulsions are prepared by employing various cooling rates. We perform an accelerated stability test of these emulsions by centrifuging the prepared emulsions. The stability of the emulsion is quantified based on the degree of separation of the water phase.

From our understanding of the interfacial elastic properties and the stability studies, we propose a model that can predict the emulsion stability for a given set of compositions and the cooling rate parameters typically followed in the industry.

The methodology proposed in this work can potentially reduce the need for numerous cumbersome Designs of experiments (DoE) used by formulators in the food, pharmaceutical, and cosmetic industries.