Gelation and Coarsening in Dispersions of Highly Viscous Droplets

Abstract

We study the gelation and coarsening mechanisms in liquid−liquid dispersions made of highly viscous oils (viscosity about 105−106 Pa·s). When a rupturing agent is added to the initially stable emulsion, a gel forms, which further contracts by preserving the geometry of the container. The microscopic observation of the gelation process and the characteristic time for gelation give qualitative insights into the growth mechanism which, in our experiments, is occurring via reaction-limited cluster aggregation (RLCA). The gelation is followed by a contraction process driven by surface tension, which is analogous to the sintering process occurring during the densification of solid powders. The initial stages of densification follow very well the “cylindrical model” for viscous sintering, but deviations are observed at the final stages of densification. We examine the influence of different factors (initial droplet volume fraction, droplet viscosity, rupturing agent nature, and concentration) on the gelation and contraction kinetics. Finally, we discuss the universality of the homothetic-sintering phenomenon.