Silica nanoparticles catalyse the formation of silica nanocapsules in a surfactant-free emulsion system

Abstract

In this paper we report on a new green emulsification technique that utilizes a hydrophobic silica precursor polymer, hyperbranched polyethoxysiloxane (PEOS), for efficient stabilization of oil-in-water emulsions without any additional classical surfactants due to its hydrolysis-induced interfacial activity. Remarkably, in such an emulsion system methyl-functionalized silica nanoparticles can catalyse the conversion of PEOS to a mechanically strong silica shell at the oil/water interface. Thus, the oil phase is encapsulated in monodispersed silica nanocapsules with almost 100% efficiency. This process depends strongly on the pH value of the aqueous phase, which controls the interfacial activity of both PEOS and silica nanoparticles as well as PEOS hydrolysis and condensation. The catalytic effect of the silica particles is the result of a delicate interplay between their interfacial activity that allows immersing catalytically active silanolate groups in the PEOS-containing oil phase and the repulsion between charged surfaces of these particles and the resulting silica nanocapsules that splits them apart. We believe that this technique opens new avenues not only for the preparation of functional inorganic nanocapsules, but also for the design of a new type of heterogeneous catalysts.