Silica particles with dynamic Janus surfaces in Pickering emulsion

In Pickering emulsions, solid particles are adsorbed to the oil/water interface, and the dispersed oil or water droplets are stabilized by the particles. The adsorption and wettability of the particles at the liquid-liquid interface play key roles in Pickering emulsion. In this research, the application of the silica particles with responsive surface nanostructures in Pickering emulsion is investigated. Amphiphilic surface micelles (s-micelles) on the silica particles are prepared by polymerization induced surface self-assembly approach. In water, spherical s-micelles with PS cores and quaternized poly(2-(dimethylamino) ethyl methacrylate) (q-PDMAEMA) shells are formed on the silica particles. In toluene, layered surface structures with PS at the top surfaces and q-PDMAEMA embedded in the inner layers, are formed. The silica particles with amphiphilic s-micelles (SiO2-ASM) can be used as stabilizers in Pickering emulsion. Upon addition of SiO2-ASM into O/W emulsion, the interfacial tension decreases significantly, due to the residence of the silica particles at the liquid-liquid interfaces. At the interfaces, the silica particles present dynamic Janus surfaces. On the sides immersed in aqueous phase, hydrophilic surfaces are produced; on the other sides immersed in toluene phase, lipophilic surface structures are formed. Both of confocal laser scanning microscopy and scanning electron microscopy results demonstrate the formation of the silica particles armored liquid-liquid interfaces.