Abstract:

Non-aqueous emulsions have a wide range of applications in cosmetics, drug-controlled release, and the preparation of functional nanoparticles. However, due to the weaker polarity of non-aqueous solvents, these emulsions often exhibit inferior stability compared to their aqueous counterparts. In this experiment, the properties of quaternary ammonium surfactants in glycerol were investigated through surface tension measurements, to further enhance the stability of n-decane/glycerol emulsions, hydrophilic nanoparticles SiO₂ were modified in situ using double tailed quaternary ammonium surfactants Di-C₁₂DAB and Di-C₁₆DAB. Stable n-decane/glycerol Pickering emulsions were successfully prepared. These emulsions were stable at 45 ℃ for over six months, and no significant changes in droplet size occurred. The minimum droplet size of the emulsion was only 2-3 μm. Contact angle measurements showed that the wettability of the silica surface was tremendously affected by the concentration and the alkyl chain length of the double-tailed surfactants. In the presence of Di-C₁₂DAB, the contact angle of glycerol on the silica surface increased monotonically with the surfactant concentration. This explains the phenomenon that the Pickering emulsions containing Di-C₁₂DAB and silica particles were stable within the contact angle range of 80°-120°. Comparatively, the contact angle of the glycerol on the silica surface in the presence of Di-C₁₆DAB first increased with surfactant concentrations and then decreased, reaching a maximum at 0.6 mmol/L. It can be concluded that Di-C₁₂DAB formed monolayers at the surface of silica particles within all investigated concentrations. On the contrary, Di-C₁₆DAB formed monolayers at concentrations below 0.6 mmol/L and formed double layers at concentrations above 0.6 mmol/L, leading to a non-monotonic change in the contact angle with respect to concentration. Using these stable non-aqueous Pickering emulsions as templates, polymer microspheres with a particle size of 2-3 μm were successfully prepared with high yield. This work is helpful to expand the potential applications of non-aqueous emulsions in the encapsulation of drug, controlled release, material preparation, and cosmetic formulations.

Key words: non-aqueous emulsions, Pickering emulsions, stability, double tailed surfactant