Effect of pentanol adsorption on the forces between bilayers of a cationic surfactant

Abstract

Measured interaction forces between adsorbed bilayers of a double-chained quaternary ammonium ion surfactant were found to be in remarkable agreement with the predictions of the nonlinear Poisson-Boltzmann equation for fully ionized bilayers. Addition of pentanol at 50% and 100% water saturation induced a strong, short-range, attractive force acting at bilayer separations up to 5-6 nm. This attractive component was found to be quite similar to that observed between adsorbed hydrophobic monolayers and is apparently due to a hydrophobic interaction between the bilayer surfaces in the presence of pentanol. The observation that several hours were required before the added pentanol changed the interaction leads us to postulate that (slow) penetration into the adsorbed bilayer is a necessary requirement for surface adsorption of pentanol. The relevance of these results to the role of cosurfactants in microemulsions is discussed, as are implications for current theories of the double layer. Show more