Combined effects of nanoparticles and surfactants upon foam stability

We investigate effects of surfactants with different charges (anionic, cationic, and non-ionic) on foam stability in the presence of charge-stabilized silica (SiO2) nanoparticles. Toward this aim, a comprehensive series of experiments on a Hele-Shaw cell and a foam column is conducted at bubble and bulk-scale respectively, that is, investigating the phenomenologies of foam coarsening by gas diffusion and bubble coalescence, and separately by gravitational drainage. Our results show that nanoparticles, despite their ability to position themselves at liquid–gas interfaces and thus limit the resulting surface tension coefficient, do not necessarily have a positive effect on foam stability; the nature and magnitude of this effect depends strongly on the nature of the surfactant, its concentration and the concentration of nanoparticles. In less stable systems, significant coarsening occurs. Both results from bubble-scale and the bulk-scale experiments suggest that compatibility experiments are pre-requisite to foam stability analysis to test the compatibility between surfactants and nanoparticles.