O/D emulsions stabilized by quaternary ammonium gemini surfactants together with alumina nanoparticles

Oil-in-dispersion (O/D) emulsions are the focus in many fields due to their new microstructures and new functions. Herein, O/D emulsions were successfully prepared using series of cationic gemini surfactants 12-s-12 (s = 2, 3, and 6) and alumina nanoparticles. The microstructures and type of emulsions were identified using optical microscopy, zeta potential and contact angle methods. Gemini surfactants with two head groups carry more charges than that of conventional surfactants when adsorbed at the oil-water interface. The O/D emulsions can be stabilized at lower surfactant concentrations compared with the conventional single-headed surfactants. In the presence of 0.1 wt% alumina nanoparticles, gemini surfactants 12-s-12 (s = 2, 3, and 6) can stabilize emulsions at the concentration of 3 x 10(-4) mM (1.84 x 10(-5) wt%), 6 x 10(-4) mM (3.76 x 10(-5) wt%) and 1 x 10(-3) mM (6.68 x 10(-5) wt%), respectively. Addition of excessive organic salts such as sodium salicylate and sodium p-methylbenzenesulfonate shielded the head group charges of gemini surfactants, leading to gemini surfactants to behave as nonionic surfactants Adsorption of surfactants at the alumina nanoparticles occurred, resulting in the transformation from the O/D emulsions to Pickering emulsions. This work shows the advantages of preparing O/D emulsions using gemini surfactants and also provides a new methods of emulsion type transformations by adding excessive oppositely charged organic salts.