Surfactant Adsorption Kinetics by Total Internal Reflection Raman Spectroscopy. 1. Pure Surfactants on Silica

Abstract

Total internal reflection Raman spectroscopy provides a sensitive probe of surfactants adsorbed at an interface. A visible laser passes through a silica hemisphere and reflects off the flat silica-water interface. An evanescent wave probes ∼100 nm of solution below the surface, and the Raman scattering from this region provides chemically specific information on the molecules present. Here we look at both equilibrium and kinetic aspects of the adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the nonionic surfactant Triton X-100 in single-component systems. We use the well-defined wall jet geometry to provide known hydrodynamics for the adsorption process. The well-defined hydrodynamics allows us to model the mass transport of surfactant to the surface which is coupled with a kinetic model consistent with the Frumkin isotherm to produce a complete model of the adsorption process. The fit between this model and the experimental results provides insight into the interactions on the surface.