Liquid-liquid interfacial properties of mixed nanoparticle-surfactant systems

In this study the effect of particles of nanometric dimensions on the interfacial properties of liquid-liquid systems is addressed. The nanoparticle transfer and the consequent attachment to the fluid interface are mainly governed by their hydrophobic/lipophilic character. For this reason a model particle-surfactant system has been investigated, namely a nanometric colloidal silica dispersion plus CTAB, where the role of the cationic surfactant is varying the particle surface properties adsorbing on them. The interfacial properties of the dispersion against hexane were determined as a function of the surfactant concentration, measuring the interfacial tension and the dilational viscoelasticity versus frequency. These results were then crossed with a study on the behaviour of micrometric oil droplets inside the same dispersions, as well as on the morphology of the respective nanoparticle stabilised emulsions. By this multiple investigation it was possible to find out that diffusion transport of particles from the bulk to the interface plays an important role, as well as the reorganisation of the mixed parlicle-surfactant layer. Moreover from these results the irreversible aspect of the nanoparticle attachment to the fluid interface was also evidenced which, under particular conditions, can provide the formation of a solid-like layer. (c) 2007 Elsevier B.V. All rights reserved.