Preparation of a magnetocaloric dual-response SiO2-based green nano-emulsifier by an SET-LRP method and evaluation of its properties

Abstract

In recent years, intelligent nano-emulsifiers have received extensive attention in various fields. In this study, core–shell–shell nanoparticles (Fe3O4@SiO2@PNIPAM) showing magnetic and thermal responsiveness have been successfully prepared as a green nano-emulsifier by single-electron-transfer living radical polymerization (SET-LRP). The emulsifying properties of Fe3O4@SiO2@PNIPAM with different PNIPAM contents in toluene/water systems and the magnetic and thermal responsiveness of Pickering emulsions have been mainly investigated. The research shows that when the content of PNIPAM is higher, Fe3O4@SiO2@PNIPAM has the strongest emulsifying power and the Pickering emulsion is the most stable. After applying a magnet field outside the emulsion, Fe3O4@SiO2@PNIPAM nanoparticles can be separated rapidly, which leads to emulsion demulsification. When the temperature is above the low critical solution temperature (LCST), the PNIPAM chain shrinks and the Pickering emulsion is demulsified. When the temperature returns below the LCST, the emulsion is emulsified again, and a stable emulsion can still be formed. Therefore, the Pickering emulsion made by Fe3O4@SiO2@PNIPAM as an intelligent and efficient green nano-emulsifier can be converted between emulsified state and demulsified state by the control of magnetic field and temperature. These provide a wide range of ideas for Pickering emulsion recycling, industrial oil-containing wastewater separation and enhanced oil recovery.