Small particles can be activated via a synergistic effect with surfactants and adsorbed to the air–water interface to generate and stabilize foams, which has been applied extensively to develop new materials and techniques. Here, we studied the synergistic effects of TiO₂ particles with ionic surfactant SDS (sodium dodecyl sulfate), ionic AOT (sodium di-2-ethylhexylsulfosuccinate), and cationic CTAB (cetyltrimethylammonium bromide) in aqueous solution, and their impacts on the foamability and foam stability were assessed by measuring the foam volume and observing the number of particles adsorbed onto the foam surface. The results showed the interactions of TiO₂ particles with SDS and CTAB surfactants were synergistic in both foamability and foam stability. The degree of synergy of the CTAB–TiO₂ mixed system was stronger than that of the SDS–TiO₂ mixed system as a whole. However, the interaction of TiO₂ with AOT (a double carbochain anionic surfactant) in the TiO₂–AOT mixed system was generally not synergistic. Unexpectedly, a maximum synergistic effect among these mixed systems occurred in the TiO₂–AOT system at an AOT concentration of approximately 5 mM. This study provides further understanding for the mechanism of foaming and stability of foam modulated by surfactant and colloidal particles and provides a useful reference for future applications.

Nano/submicron particles can be activated by surfactants and aggregate at the air-water interface to generate and stabilize foams. Such systems have been applied extensively in the food, medicine, and cosmetic industries. Studying particle charging behavior in a particle/surfactant/water system is a fundamental way to understand the activation of the particle surface. This paper presents an investigation of the charging behavior of polystyrene (PS) particles dispersed in aqueous solutions of the surfactant sodium di-2-ethylhexylsulfosuccinate (AOT). The results showed that zeta potential of PS was related to the AOT concentration with two different concentration regions. Below the critical micelle concentration (CMC), the charging of PS particles was effected by AOT ions; while above the CMC, it came from both AOT ions and AOT micelles. This behavior was different from that observed for PS in aqueous salt solutions. Additionally, the particle concentration and size were found to affect the zeta potential differently in the two AOT concentration regions. By analyzing these results, the charging mechanism of the PS/AOT/water system was revealed to be preferential adsorption. In summary, the study disclosed the internal connection between the PS charging in aqueous AOT solution and the activation of PS particles, as well as their influence to foam formation and stability.