Third-harmonic dielectric response of a water-in-oil emulsion

The technique of third-harmonic dielectric spectroscopy has been developed for the study of interfacial dynamics in multiphase complex fluids. It is well suited for systems with structure on the scale of optical wavelengths. Thus, it is particularly useful for the study of opaque systems for which optical techniques are untenable. As a first application, the technique has been used to probe the interfacial dynamics of a low-concentration water-in-oil emulsion. The mechanism responsible for the third-harmonic dielectric response of the emulsion has been modeled and compared successfully with the measurements. Structural information has been extracted as well; the droplet size distribution of the emulsion has been determined by fitting the third-harmonic dielectric response. These results agree with the droplet size distribution obtained by optical microscopy under the assumption of a dynamic surface tension significantly higher than the equilibrium value.