Abstract
The flow behavior of particle stabilized oil-in-water emulsions with different dispersed volume fractions was analyzed in steady shear on a rotational rheometer employing a coaxial cylinder geometry. The dispersed phase of the emulsion was a mixture of equal volumes of a polar oil, isopropyl myristate, and a nonpolar oil, dodecane. The continuous phase was an aqueous suspension of hydrophilic colloidal silica particles of 8nm diameter with the pH adjusted to pH2 in order to stabilize the emulsion [Binks and Whitby, Colloids Surf., A 253, 105–115 (1995)]. Droplet diameters were of the order of a few micrometers, and droplet surfaces apparently show dense particle coverage. We show that the markedly different interfacial structure in particle stabilized emulsions when compared to surfactant stabilized emulsions is reflected in the rheological behavior. To illustrate these differences, the rheological behavior of a comparable surfactant stabilized emulsion with the particles in the aqueous phase replaced by Tween 20, was also investigated. The rheological characterization revealed a domain of shear thickening in the particle stabilized emulsions at high droplet phase volumes that is not observed for the classical surfactant stabilized emulsions.
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