Gelation and coarsening in dispersions of highly viscous droplets

We study the gelation and coarsening mechanisms in liquid-liquid dispersion s made of highly viscous oils (viscosity about 10(5)-10(6) Pa.s). When a ru pturing agent is added to the initially stable emulsion, a gel forms, which further contracts by preserving the geometry of the container. The microsc opic observation of the gelation process and the characteristic time for ge lation give qualitative insights into the growth mechanism which, in our ex periments, is occurring via reaction-limited cluster aggregation (RLCA). Th e gelation is followed by a contraction process driven by surface tension, which is analogous to the sintering process occurring during the densificat ion 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 age nt nature, and concentration) on the gelation and contraction kinetics. Fin ally, we discuss the universality of the homothetic-sintering phenomenon.