부산대학교 도서관

Ellipsometry is a powerful experimental technique for studying the surfaces of surfactant solutions both at and away from equilibrium. From a theoretical perspective, there is no simple relationship between ellipsometric parameters at the air−water interface and the surface excess, Γ, of the surfactant. Here we report neutron reflection measurements of the dynamic surface excess, Γdyn, of the cationic surfactants CnTAB (n = 14, 18) in an overflowing cylinder (OFC) as a function of the bulk surfactant concentration, to complement earlier measurements on C16TAB. These results are compared with ellipsometric measurement of the coefficient of ellipticity, ρ, of the surfactant solutions in an OFC in order to generate a calibration curve ρ(Γ). For each surfactant, ρ was found to be a linear function of surface excess. For the shorter homologue, n = 12, surface tension measurements on equilibrium solutions have been used to determine the adsorption isotherm and the surface excess was then compared with the coefficient of ellipticity. Again, the relationship between ρ and Γ is linear. A protocol is described for determining surface excesses ellipsometrically in this class of surfactants, and the errors in the procedure are quantified.