Instability of highly concentrated emulsions with oversaturated dispersed phase. role of a surfactant

Abstract

Instability of highly concentrated emulsions of the water-in-oil type which were investigated in this work is related to the existence of the internal phase as an oversaturated salt solution in water. The principal features of crystallization of these systems were studied by as earlier. This study is devoted to the development of this investigation and based on involving different surfactants and various concentrations of surfactants. It was shown that the originally proposed mechanism of crystallization, which suggested that growing crystals break through interfacial layers, was valid for all highly concentrated emulsions under investigation. Moreover, the Kholmogorov-Avrami kinetic equation with an unusually high exponent value equal to 6 is also applicable to different systems. It was proven that the general relationship between the growth of the yield stress and the degree of crystallization can be formulated for all surfactants studied in the work. The role of a surfactant consists in varying the characteristic time constant for the rate of crystallization. This time constant is much lower for a low-molecular-weight surfactant compared to oligomeric surfactants. This constant noticeably increases with an increase of concentration and the decrease of the average droplet size.