Effect of Silica Nanoparticles on Liquid-Liquid and Liquid-Air Interfacial Properties

The effect of particles at fluid interfaces is a topic of increasing interest especially for the application in the field of emulsions and foams. Colloidal nanoparticles are in fact utilised, often in association with surfactants, as stabiliser of such dispersed systems in different industrial fields. Particle stabilised foams and emulsions are also common in natural products and processes. In order to understand better the basic mechanisms underlying this stabilising effect, it is necessary to pay attention to the behaviour of the interfacial layer in these systems and in particular to the dilations properties of composite interfaces, which have been so far poorly investigated. In this work an experimental study is presented based on the measurement of surface properties of liquid/liquid and liquid/air systems, in the presence of colloidal nanoparticle. To this aim two drop tensiometers based on the drop profile acquisition and on the pressure acquisition are used. The coupling of these two methods allows the measurement of the dynamic and equilibrium interfacial tension and of the dilational visco-elastic modulus in a range of frequency from 0.001 to 100 Hz. The systems studied were CTAB aqueous solution at water/air and water/hexane interface in presence and in absence of colloidal suspension of spherical monodisperse silica nanometric particles. The measurements refer to different surfactant and solid concentrations. The effect of nanoparticles on the investigated interfacial properties is then interpreted according to proper thermodynamic and kinetic models