Controlling Oil-in-Oil Pickering-Type Emulsions Using 2D Materials as Surfactant

Emulsions are important in numerous fields, including cosmetics, coatings, and biomedical applications. A subset of these structures, oil-in-oil emulsions, are especially intriguing for water sensitive reactions such as polymerizations and catalysis. Widespread use and application of oil-in-oil emulsions is currently limited by the lack of facile and simple methods for preparing suitable surfactants. Herein, we report the ready preparation of oil-in-oil emulsions using 2D nanomaterials as surfactants at the interface of polar and nonpolar organic solvents. Both the edges and basal plane of graphene oxide nanosheets were functionalized with primary alkyl amines and we demonstrated that the length of the alkyl chain dictates the continuous phase of the oil-in-oil emulsions (i.e., nonpolar-in-polar or polar-in-nonpolar). The prepared emulsions are stable at least 5 weeks and we demonstrate they can be used to compartmentalize reagents such that reaction occurs only upon physical agitation. The simplicity and scalability of these oil-in-oil emulsions render them ideal for applications impossible with traditional oil-in-water emulsions, and provide a new interfacial area to explore and exploit.