Thermodynamic Theory for Performance of Graphene Oxide Based Pickering Emulsions

Fine particles can assemble at aqueous-organic interfaces and stabilize droplets to form what is known as a Pickering emulsion. Graphene-based nanomaterials are of potential interest for this application because a large fraction of their atoms reside at the interface.  This allows the stabilization of emulsions at very low mass doses relative to conventional isometric particles. For atomically thin sheets such as monolayer graphene oxide, every atom lies on the interface and interacts with both liquid phases, and stabilization energies can be orders of magnitude higher than spherical nanoparticles at equal mass loading. Experiments show that graphene oxide is an effective stabilizer for a range of organic-in-water emulsions, but few-layer graphene with pristine (hydrophobic) surfaces is much less effective. This trend is consistent with the thermodynamic theory, which provides a basis for optimizing the surface chemistry of a graphene-based material to achieve the highest free energy of stabilization. Other potential advantages of graphene-based emulsion stabilizers include tunable surface chemistry, elastic conformal coverage of curved surfaces, and unfavorable detachment from the interface.