Coadsorption of poly(styrenesulfonate) and cetyltrimethylammonium bromide on silica investigated by attenuated total reflection techniques

Adsorption of poly(styrene sulfonate) (PSS) and cetyltrimethylammonium bromide (CTAB) on silica from mixed solutions of the polyelectrolyte and surfactant has been studied. The surface excess of the polyelectrolyte was determined by ultraviolet attenuated total reflectance (UV-ATR) monitoring of the 224 nm styrenesulfonate absorbance band. Complementary information was derived from infrared attenuated total reflectance (IR-ATR) on the same system. Deconvolution of the 2920 cm(-1) asymmetric and 2850 cm(-1) symmetric methylene bands common to both surfactant and polyelectrolyte gave the adsorbed amount of surfactant, as well as a measure of adsorbed polyelectrolyte. The surface excesses of both polymer and surfactant were determined in situ for different pH values and solution histories. The adsorbed amount of both species was highly dependent on pH and on the order of addition of the polyelectrolyte and surfactant. These results are interpreted in terms of competing interactions between the polyelectrolyte and the surface and between the surfactant and the surface and in terms of cooperative surfactant/polyelectrolyte solution interactions.