Interfacial Tension of Particle-modified Interfaces and the Mechanism of Emulsion Formation

Abstract

Emulsions stabilized by adsorbing fine particles are called Pickering emulsions, and are attracting attention as a technique for stabilizing emulsions without using a surfactant. The stabilization of the oil-water interface by the fine particles should follow a change in the interfacial tension, but it is not systematically understood. The purpose of this study is to clarify the effect of particle adsorption on the interfacial tension at the oil-water interface. Monodisperse and spherical particles were used to make it easier to analyze the effects of the particles. In the measurement of the interfacial tension, a quasi-elastic light scattering method was employed to avoid the effect of the probe contacting the interface. The interfacial tension at the decane/water interface was measured as a function of the number of adsorbed particles; the interfacial tension decreased with the amount of dispersed particles. The decrease in interfacial tension was much larger than the stabilization free energy due to the adsorption of the particles, or the repulsive interaction between the adsorbed particles, suggesting that the decrease is due to synergetic effects of structural change of the interface.

Graphical Abstract

Experimental setup of quasi-elastic light scattering measurement based on optical heterodyne spectroscopy. The light scattered at the oil-water interface with a certain scattering angle is detected together with a portion of original light (local light) to give frequency shift by the scattering with capillary wave.