INTERFACIAL PROPERTIES OF MIXED SILICA

In the last decades, the investigation on the interfacial properties of complex systems composed by particles and surfactants has become increasingly important. In fact, such systems are employed in many technological fields (e.g. oil recovery, cosmetics and food industries) since the presence of solid particles effectively increases the stability of foams and emulsions, avoiding the droplet/bubble coalescence. The particle attachment at the liquid interfaces mostly affects the interfacial properties of these systems since changes of the interfacial tension and of the dilational rheology may occur. Moreover, the particle-surfactant interactions can provide the formation at the interface of aggregated layers with viscoelastic character. In this work, some results on systems composed by a cationic surfactant (CTAB) and silica nanoparticles are presented [1, 2]. The CTAB adsorption onto the particle surface changes their wettability and, consequently, their affinity to the liquid interface. Different degrees of particle hydrophobicity are so obtained. Three techniques have been used for investigating the interfacial properties of these systems: drop/bubble profile analysis, capillary pressure tensiometry and electrocapillary waves. In this way, information on the interfacial tension and dilational viscoelasticity have been obtained. In particular, adopting such different devices allowed us to investigate the rheological behaviour of the composite systems in a wide frequency range, from 10-2 Hz to 103 Hz, which provided a better understanding of the dynamic mechanisms occurring in the interfacial layer. Moreover, the Langmuir film balance technique coupled with the Brewster Angle Microscopy has been utilized for studying the influence of the hydrophobicity grade of the particles on the thermodynamic and structural properties of the mixed layer, evaluating P-A isotherms by compression and expansion experiments and observing the 2-D structures forming at water/air interface. [1] F. Ravera, E. Santini, G. Loglio, M. Ferrari, L.iggieri, J. Phys. Chem. B, 110 (2006) 19543 [2] F. Ravera, M. Ferrari a, L. Liggieri , G. Loglio, E. Santini, A. Zanobini, Coll. & Surf. A, 323 (2008) 99 Corresponding author: e.santini@ge.ieni.cnr.it