Stabilization of oil-in-water emulsions with graphene oxide and cobalt oxide nanosheets and preparation of armored polymer particles.

Pickering emulsions are emulsions stabilized by particles instead of small molecules or polymers, and commonly consist of oil droplets dispersed into a continuous water phase with particles lying at the fluid-fluid interface. New particle surfactants are important for tuning the composition and properties of assemblies and enabling advanced applications, such as energy harvesting and management. Although most particle surfactants are spherical, graphene oxide (GO) nanosheets and clay platelets have garnered recent attention as 2D (i.e., planar) particle surfactants. Herein, we report the preparation of Pickering emulsions stabilized by a composite of GO nanosheets and cobalt oxide (CoO) nanosheets, and illustrate the impact of GO:CoO ratio, oil identity, and flocculating agent (i.e., salts) on emulsion formation and stability. Distinct effects were noted for salt concentration and identity, as well as GO: CoO ratio. We further illustrate the applicability of these GO-CoO-stabilized emulsions in dispersion polymerization, preparing polystyrene particles armored with both nanosheets. This work provides a method for facilitating oil-in-water emulsions with composite particle surfactants that are stable for at least a week and offers the foundation for using the fluid-fluid interface to architect structures of dissimilar materials.