Study of the monolayer structure and wettability properties of silica nanoparticles and CTAB using the Langmuir trough technique

This study is focused on understanding how the combination of silica nanoparticles with a cationic surfactant (CTAB) may lead to the formation of different solid-like structures at the water/air interface. In fact, the adsorption of CTAB onto the solid particles' surface changes their hydrophilic/lipophilic state which becomes more hydrophobic with increasing the surfactant concentrations. This allows particles to transfer and irreversibly attach to the liquid/fluid interface with the formation of aggregates presenting different kinds of morphologies which depend on the amount of surfactant. This aspect can be found out using a Langmuir trough coupled with a Brewster Angle microscope. moreover, this technique can be a useful tool for obtaining information about the wettability properties of particles at the fluid interface. Indeed, the parameters derived from the compression Pi-A isotherms are strictly related to the value of the three-phase contact angle of the particles. From these experiments it is then possible to evaluate the particle contact angle and better understand the macroscopic structures of the aggregates formed at the water/air interface. (C) 2010 Elsevier B.V. All rights reserved.