Pickering emulsions stabilized with magnetite, gold, and silica nanoparticles: Mathematical modeling and experimental study

Abstract

Stability of O/W emulsions with magnetite/silica and gold/silica nanoparticles was investigated experimentally and by mathematical modeling using the Langevin dynamics method. Experimentally studied emulsions with magnetite/silica nanoparticles were stable to creaming and coalescence (at pH 8). Results of numerical modeling showed that silica and magnetite nanoparticles aggregated with the formation of chain-like heteroaggregates that were attached to the surface of oil droplets and located into the bulk of the aqueous phase. A gel-like network of aggregated particles was formed that prevented droplet creaming and coalescence.In emulsions with gold/silica nanoparticles, numerical simulations revealed that chain-like heteroaggregates of silica and gold nanoparticles existed for short periods. Over time, these heteroaggregates shrank, and oil droplets were covered with bulky protruding structures of aggregated nanoparticles. The heteroaggregates that were not attached to the oil droplets did not combine to form a gel-like network, so such emulsions were unstable to creaming. However, bulky heteroaggregates on the surface of oil droplets prevented them from approaching and fixed droplets at some distance from each other. This was in agreement with experimental results. The aqueous phase partly separated from emulsions with silica/gold nanoparticles. The oil phase fraction increased in the residual emulsion but was less than the dense packing of droplets.