CO₂-Switchable Pickering Emulsion Using Functionalized Silica Nanoparticles Decorated by Amine Oxide-Based Surfactants

Abstract

Herein, we describe a novel CO2-switchable oil-in-water Pickering emulsion stabilized by functionalized silica nanoparticles with a trace amount of myristylamidopropyl amine oxide (C14PAO), which is commercially available, and readily biodegradable. C14PAO in the current system has been demonstrated to be CO2-responsive. Upon alternately bubbling CO2 and N2 under mild conditions (30 °C, 40 mL min–1), C14PAO is reversibly switched between cationic and nonionic forms, and is thereby adsorbed on or desorbed from the surface of the particles. In this way, interfacially active particles are formed and adsorbed on the surface of oil droplets, stabilizing the emulsion (CO2), or disrupted and desorbed from the surface of oil droplets, breaking the emulsion (N2). As compared to the traditional acid/base cycle, switching the current system with CO2/N2 multiple times does not lead to any evident changes in either macroscopic appearance or microscopic size. Moreover, this CO2-responsive Pickering emulsifier can be recycled when fresh oil was added after removing the original oil, and theoretically the cycling can be maintained, conforming to the principle of green and energy-saving processing. It offers a green, efficient, and recyclable container for oil product transportation, especially in high temperature area. Such a strategy is also suitable for other amine oxide-based surfactants, and does not require complicated organic synthesis.