Shear-induced clustering of gelling droplets in aqueous biphasic mixtures of gelatin and dextran

The flow-induced morphology of aqueous mixtures of gelatin and dextran was investigated during gelation of the dispersed phase. Mixtures with 5% volume fraction of the gelatin-rich phase dispersed in the dextran-rich phase were sheared in a translating parallel plate apparatus coupled with an optical microscope. Gelation of the dispersed phase was brought about by decreasing mixture temperature under flow. As a consequence of gelation, the dispersed phase aggregated, forming clusters of gelled, partially coalesced, spherical particles. Cluster size was found to depend on the shear rate applied during gelation and on the temperature profile. Indeed, smaller clusters were formed: (a) under faster flows, (b) if the temperature was decreased to lower levels, and (c) if gelation was induced under quiescent conditions and the flow started only afterwards. By acting on these parameters, it is possible to suppress or enhance cluster formation and to tune cluster size. When the temperature was increased again above the gelation temperature, the gelled particles melted and the clusters rapidly coalesced.