Facile and scalable synthesis of functional Janus nanosheets – A polyethoxysiloxane assisted surfactant-free high internal phase emulsion approach

Abstract

HypothesisJanus nanosheets, which have two surfaces of different functionalities, exhibit unique interfacial properties. In this work, we propose a facile and scalable technique for preparation of silica-based Janus nanosheets, which is based on formation of high internal phase water-in-oil emulsions stabilized solely by alkyl-substituted polyethoxysiloxanes due to their hydrolysis-induced interfacial activity. ExperimentsJanus nanosheets are then obtained by crushing the silica foams converted from such emulsions. The morphology of Janus nanosheets is investigated by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The chemical structure of functional silica materials is characterized by Fourier transform infrared spectroscopy (FT-IR). The asymmetric structure of silica nanosheets is observed by confocal laser scanning microscopy. FindingsThe resulting nanosheets have a rough hydrophobic surface and a smooth hydrophilic one, and are capable of stabilizing Pickering oil-in-water emulsions. Remarkably, pH-responsiveness of emulsions can be attained using the nanosheets whose hydrophilic surface is substituted with amino groups. Fast oil–water separation is achieved by the Janus nanosheets, which has been demonstrated by the nanosheets with a polystyrene-coated hydrophobic surface. This work paves a new avenue for large-scale production of functional silica-based Janus nanosheets suitable for numerous promising applications.