Variable Angle of Incidence Evanescent Wave Spectroscopy of the Adsorption of Quaternized P2VP Polyelectrolyte on Silica

Abstract

The new technique of variable angle of incidence evanescent wave spectroscopy (VIEWS) was applied to the adsorption of low molecular weight, high charge density, quaternarized poly(2-vinylpyridine) (P2VP) onto silica from aqueous solution. The kinetics of adsorption and adsorbed conformations were measured as a function of solution pH for both the iodide and chloride salts of P2VP. The polyelectrolyte was found to adsorb readily above the isoelectric point of silica and increasing surface excesses and decreasing centers of mass of the polyelectrolyte from the interface were observed as the solution pH was raised. These results were attributed to the increasingly favorable electrostatic interactions between the positively charged polyelectrolyte and the increasingly negatively charged silica surface. The iodide salt of P2VP was found to have larger surface excesses and smaller centers of mass from the interface than the chloride salt at the same pH value. This is believed to be an effect of counterion binding to the polyelectrolyte, altering its hydrophobicity. Quaternarized P2VP was found to adsorb in a comparatively flat conformation with no extended polymer structure