Polymer-coated cationic silica nanoparticles for slow-release Pickering emulsions

Abstract

Silica nanoparticles were functionalized with amine and quaternary ammonium groups using a two-step chemical surface modification, to allow coating with anionic polymers for emulsion stabilization. This strategy proved to render high colloidal stability in aqueous dispersions and strong electrostatic interactions with polyacrylic acid and poly(sodium 4-styrene sulfonate), over a wide pH range. These hybrid nanoparticles stabilized Pickering emulsions at very low concentrations (0.01 wt%), without added surfactants. Most stable emulsions were obtained with nanoparticles coated with polyacrylic acid, due to synergy of strong interfacial adsorption of nanoparticles enhanced by the long polymeric chains and the weak polyelectrolyte character of the polymer. These nanoparticles were able to prevent diffusion of N,N′-diethyl-m-toluamide (DEET), a common insect repellent, from oil-in-water emulsions into a model media. The release profile followed typical zero-order kinetics, demonstrating the potential of using the polymer-coated nanoparticles developed in this work in DEET formulations to achieve extended repellent action.