SILICA NANOPARTICLE - AMINE SURFACTANT

In several natural phenomena and in technologies related to the production of highly stable emulsions and flotation, the association of nanoparticles and surfactants at bubble or drop surfaces is of great importance. For a better understanding of these phenomena, new experimental studies addressing the thermodynamic and dynamic properties of these complex interfacial layers are needed. Here the interfacial properties of aqueous dispersions of silica nanoparticles against a hexane solution of an oil-soluble (fatty) amine surfactant have been investigated. In this system, the initially hydrophilic particles interact with surfactants only at the water-hexane interface. The process of nanoparticle attachment to the liquid interface is driven by surfactant adsorption. The dynamic interfacial tension of this system was measured in the presence and absence of 1 wt% silica particles in the aqueous phase and as a function of the amine concentration. The interfacial rheology of the same systems was investigated by measuring the dilational viscoelasticity as a function of the area perturbation frequency. To better investigate the affinity of silica particles with the adsorption layer at liquidliquid interface, related to the wetting properties of silica particles, contact angles of drops of hexane solution on a silica plate immersed in water were measured. The interpretation of the results allows identification of different regimes in the interactions between the surfactant and particles at the oil-water interface. These regimes depend on the surfactant concentration and correlate with variations in the structure and stability of the corresponding water/hexane emulsions. References [1] C.P. Whitby, D. Fornasiero, J. Ralston, J. Colloid Interface Sci., 323 (2008), 410. [2] F. Ravera, E. Santini, G. Loglio, M. Ferrari, L.iggieri, J. Phys. Chem. B, 110 (2006) 19543 [3] F. Ravera, M. Ferrari a, L. Liggieri , G. Loglio, E. Santini, A. Zanobini, Coll. & Surf. A, 323 (2008) 99 Corresponding author: f.ravera@ge.ieni.cnr.it