Stabilization of Silicone Oil-in-Water Emulsions by Ionic Surfactant and Electrolytes: The Role of Adsorption and Electric Charge at the Interface

The stability of silicone oil-in-water emulsions in the presence of a cationic surfactant (viz. cetyltrimethylammonium bromide) and salts containing mono-, di-, and trivalent ions (viz. NaCl, CaCl2, and AlCl3) is reported in this work. Addition of salt enhanced the adsorption of surfactant at the oil-water interface and had a significant effect on the zeta potential. The evolution of droplet size with time was measured by dynamic light scattering. The experimental data were fitted by a model based on drop coalescence. The stability of the emulsions increased in the presence of salt. The effectiveness of the salts investigated was in the sequence AlCl3 > CaCl2 > NaCl. Coalescence of a single silicone oil drop at a flat oil-water interface was studied. Addition of salt increased the drop coalescence time.