Water-in-water PEG/DEX/protein microgel emulsions: effect of microgel particle size on the rate of emulsion phase separation

Abstract: Protein nanoparticles have been proven to be highly effective stabilizers of water-in-water emulsions obtained from a number of different types of aqueous two-phase systems (ATPS). The stabilizing efficiency of such particles is attributed to their affinity to the water/water interface of relevant ATPS, and emulsion formulations with long-term stability were reported in the recent years. In this study we investigated the macroscopic dynamics of the early-stage time evolution of dextran-in-polyethylene glycol emulsions obtained from a single ATPS and containing beta-lactoglobulin microgel particles of various diameters (ca. 40-190 nm). The results revealed the existence of a threshold in microgel size above which the water-in-water emulsion is stabilized, and that the process of segregative phase separation is determined by the interplay of droplets coalescence and sedimentation. Efficient droplet coalescence inhibition was found for microgel particles larger than 60 nm. Based on previous literature results, we discuss our coalescence-driven phase separation data in the context of the formation of durable particle layers on the emulsion droplets and the resulting droplet-droplet interactions.