Interaction between amine oxide surfactant layers adsorbed on mica

Abstract

A surface-force apparatus has been used to determine the interaction between two mica surfaces immersed in water solutions of a non-ionic surfactant dimethyldodecylamine oxide (DDAO). These interactions could be associated with three different adsorption states as the surfactant concentration was increased : hardly any adsorbed surfactant, a monolayer and a bilayer. The study has also been aimed at determining any temperature dependence in the interactions between bilayer-coated surfaces. In addition to the surface-force measurements. quantifications of the amount of adsorbed surfactant on mica sheets were made using X-ray photoelectron spectroscopy. The contact angles were also determined for the same mica samples. From these results we suggest an adsorption mechanism based on positively charged surfactant molecules adsorbing into the negatively charged mica substrate. No temperature dependence is found of the forces between bilayer-coated surfaces and this is consistent with the absence of any temperature-induced phase separation of the DDAO–water system.