Air–liquid interfacial tension and foamability of ionic surfactant solutions containing TiO₂ nanoparticles

Presence of TiO₂ nanoparticles in aqueous surfactant solutions affects air–liquid interfacial characteristics of the system in which they have been dispersed. Foam formation, as a comprehensively applied process for new materials and techniques development, is one of the phenomena affected by changes of interfacial properties of solutions containing surfactants. Therefore, finding the relationship between interfacial properties and foamability is of a great importance for predicting and controlling the behaviours of foaming systems. Herein, using interfacial tension and zeta potential measurements, we studied air–liquid interfacial behaviours of negatively charged anatase TiO₂ nanoparticles in two types of ionic surfactant solutions, i.e. cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS), with their concentrations varied from 1e − 6 M to 1e − 1 M. Foamability studies of these surfactant solutions containing nanoparticles showed that the foam formation was dependent on the type and concentration of the surfactant, and the presence of TiO₂ nanoparticles affected the minimum concentration of surfactants required for the foam formation. These nanoparticles were also found to affect the size distribution of bubbles formed in the foam. In case of the CTAB solutions containing TiO₂ nanoparticles, adsorption of TiO₂ nanoparticles at the air–liquid interfaces prevented bubbles’ coalescence and thus resulted in the formation of foams with smaller bubble sizes in comparison to those of SDS solutions. These findings are important for the formulations of foam-forming materials in which the particles are often used for stabilising foams, providing insight into industrial processes where foaming characteristics need to be controlled.