Double Phase Inversion of Pickering Emulsion Induced by Magnesium Hydroxide Nanosheets Adsorbed with Sodium Dodecyl Sulfate

Surfactants are often used as a cooperation stabilizer with solid particles for increasing the efficiency of Pickering emulsion. Accordingly, the effects of interaction between surfactants and solid particles on stabilizing Pickering emulsions have been attracting great attention. In this study, magnesium hydroxide (MH) nanosheets adsorbed with different amounts of sodium dodecyl sulfate (SDS) surfactants were designed and used to stabilize paraffin-water emulsions. Using SDS-adsorbed MH nanosheets as a stabilizer, the phenomenon of double phase inversion was found for Pickering emulsion. Pickering emulsion was inverted initially from O/W to W/O at about 0.022 mmol/g of the adsorption amount of SDS on the MH nanosheets, and subsequently back to O/W at about 2.312 mmol/g. The first phase inversion was because of the increased hydrophobicity of modified MH nanosheets, where SDS molecules were monolayer-adsorbed on the MH nanosheets surface. The second phase inversion occurred due to the bilayer adsorption of SDS on MH nanosheets, which converted the modified MH nanosheets hydrophilic again. These results are of great importance to understanding the double phase inversion of Pickering emulsions with the addition of surfactants and finding prospective applications in fields such as reversible drilling fluids and oil extraction.