Foams stabilized by Laponite nanoparticles and alkylammonium bromides with different alkyl chain lengths

We investigated the behavior of foams stabilized by Laponite nanoparticles combined with alkylammonium bromides with different alkyl chain lengths. A four-region model based on electrostatic and hydrophobic interactions adequately explains the adsorption of the cationic surfactants on the negatively charged Laponite particles. The results indicate that chain length has a minimal influence on surfactant adsorption via cation exchange, but a longer alkyl chain length can induce a stronger hydrophobic interaction among the adsorbed alkylammonium molecules and hence a higher surfactant adsorption. Adsorption of surfactants on the Laponite particles is crucial to foam stability. Surfactant addition initially transforms particles from anionic to uncharged and hydrophobic and subsequently to cationic as a result of adsorption. The foam experiments indicate that the most hydrophobic particles, possessing an adsorbed monolayer of surfactant, yield foams which are completely stable to disproportionation and coalescence. As the surfactant chain lengths increase from C12 to C16, the characteristic features of the adsorption isotherm are lowered by approximately an order of magnitude. For surfactants with longer alkyl chain surfactants, stable foams are obtained at lower concentrations.