Tunable Surface Properties of Aluminum Oxide Nanoparticles from Highly Hydrophobic to Highly Hydrophilic

The formation of materials with tunable wettability is important for applications ranging from antifouling to waterproofing surfaces. We report the use of various low-cost and nonhazardous hydrocarbon materials to tune the surface properties of aluminum oxide nanoparticles (NPs) from superhydrophilic to superhydrophobic through covalent functionalization. The hydrocarbon surfaces are compared with a fluorinated surface for wettability and surface energy properties. The role of NPs' hydrophobicity on their dynamic interfacial behavior at the oil-water interface and their ability to form stable emulsions is also explored. The spray-coated NPs provide textured surfaces (regardless of functionality), with water contact angles (θ) of 10-150° based on their surface functionality. The superhydrophobic NPs are able to reduce the interfacial tension of various oil-water interfaces by behaving as surfactants.