CO2/N2 Responsive Pickering Emulsion Stabilized by Silica Nanoparticles and a Common Nonionic Surfactant

Responsive emulsions with controllable stability are of growing interests in recent years. These emulsions are usually stabilized by specially synthesized surfactants, polymers, solid particles or their mixtures with switchable functional groups. However, these emulsifiers are inconvenient for extensive utilizations due to their complicated synthesis processes. Here we propose a new approach of using hydrophilic silica nanoparticles activated by a conventional polyoxyethylene nonionic surfactant to prepare responsive Pickering emulsions triggered by CO2/N-2. The addition or removal of CO2 is to simply change the amount of silanols on the particle surface, increasing or decreasing the adsorbing sites for hydrogen bonding with oxyethylene groups. The adsorption amount of the polyoxyethylene nonionic surfactant onto silica nanoparticles can be significantly increased when CO2 is introduced, making the particles hydrophobized in situ and become excellent stabilizers for Pickering emulsions. While N-2 was bubbled at an elevated temperature to remove the dissolved CO2, the substantial desorption of the surfactant from the particle surface can make silica nanoparticles regain their hydrophilic nature, and therefore emulsions stabilized by such particles can be broken.