Electroacoustic Study of the Crystallization of n-Eicosane Oil-in-Water Emulsions

Abstract

When sodium dodecyl sulfate-stabilized emulsions of n-eicosane are supercooled from about 40 °C, solidification of the droplets occurs below 24 °C; reheating the suspension causes the particles to melt at the normal melting point of 36-37 °C, and the emulsion returns to its initial state without any aggregation or coalescence observed. The crystallization changes the density of the particles and the volume fraction of the suspension. When this is properly considered, the dynamic mobility spectra obtained from electroacoustic measurements can be readily interpreted in terms of the particle size and ζ potential of the droplets with very low fit errors. The droplet size appears, however, to be significantly different at different salt concentrations. This anomalous result is an indication of stagnant layer conduction on the emulsion drops. When this effect is also taken into account, the droplet size becomes independent of the salt concentration. The results then become entirely self-consistent and indicate that the theory, which is used to describe the dynamic mobility, appropriately describes the effect for both solid particles and surfactant-stabilized oil droplets.