UC Irvine

Emulsions are a group of mixtures made up of two or more immiscible liquids. In 1907, Pickering first described the phenomenon that sufficiently fine-grained solid particles could act as emulsifiers. The solid particles are strongly adsorbed at the liquid-liquid interface to retard droplets coalescence which separates the emulsion into organic and aqueous phase. For a surfactant molecule, the interfacial attachment energy is several kBT which keeps a dynamic equilibrium between interfaces and host solvent, whereas colloidal particles need to overcome hundreds or thousands of kBT to detach from the interface. In various fields, such as food, pharmaceutical, cosmetics and personal care products, particle-stabilized emulsions have received significant attention for their potential applications.

After exposing to power ultrasound, particle-stabilized emulsion system could transit into highly stable gel-like emulsions. The gel-like behavior in these systems is a unique result of the percolating network of droplets that are attached together by a cohesive network of solid particles. The continuous droplet linkage found in particle-stabilized emulsion gels show long-term mechanical stability and resistance to gravitational effects which improve the possibility of improving gel structural life. In addition, the possibility of recoverability for droplet bridging and studies on corresponding microscopic origins and rheological behavior are shown in this work. At macroscopic level, droplet bridging system show stronger structural stability and prolonged mechanical stability.

With a stress-controlled rheometer with cone-and plate geometry, the rheological properties of the emulsion systems were measured. Oscillatory measurement concerning G', the in-phase storage modulus, and G'', the out-of-phase loss modulus were taken into consideration in rheological behavior. The higher the frequency is, the lower the modulus crossover strain is; the larger the ratio (aqueous/ organic) is, the higher the strain of crossover modulus is. In the second time strain sweep tests within entire destroyed samples, it shows a unique rheological behavior comparing to original structure. For a group of ratio of aqueous/organic η in colloidal gels, zero shear modulus G'0 and shear stress τy indicate a signature tendency. At small stress range, Pickering emulsion gels exhibit "creep ringing" vibrating behavior; at large enough stress, the strain increases with increasing stress.