Surface properties of binary TiO2 - SiO2 nanoparticle dispersions relevant for foams stabilization

This work focuses on the surface properties of binary dispersions of nanoparticles, namely Titania (TiO2) and amorphous silica (SiO2), associated to a short chain ionic surfactant (CTAB) which has the role of modifying their amphiphilicity, inducing the segregation of particle-surfactant complexes at the liquid interface. The foams produced by these dispersions are also investigated. The adsorption of these complexes at water-air interfaces has been investigated by surface tension and dilational rheology measurements. The results obtained, discussed on the basis of the main characteristics of the two types of particles, allow us to understand the role of the dispersion composition and, especially, of the cationic surfactant in the determination of the surface activity of the different complexes and of the properties of the mixed NP layers at the water- air interfaces. In particular, important synergetic effects on the interfacial properties have been observed, when both types of particles are adsorbed. These effects reflect in an enhanced stability of the corresponding foams. In addition, the study evidences the possibility to formulate binary dispersions in order to drive selectively the adsorption of one type of particles at the liquid interface, which can be particularly significant for the formulation of particle-stabilized foams with tailored lamella and cell surface composition/structure.