IN-SITU ANALYSIS OF ALKYL PHOSPHATE SURFACTANT ADSORPTION AT THE ALUMINA AQUEOUS SOLUTION INTERFACE/

Both the extent of adsorption and spatial chain orientation of adsorbe d alkyl phosphate surfactant molecules on alumina were investigated us ing an in situ attenuated total reflection-Fourier transform-infrared technique. The adsorption isotherm was characterized by three distinct regions, and adsorption continued to occur even at pH values higher t han the isoelectric point of alumina. Upon adsorption of surfactant, t he wettability of alumina decreased, followed by a slight increase in the wettability at concentrations greater than 10 ppm, indicating the formation of a second adsorption layer. It was also found that as the surfactant concentration increased, zeta potential reversal occurred, and in a 10 ppm surfactant solution, alumina exhibited negative zeta p otentials across the whole pH range. The profile of zeta potential-pH curves was typical for systems involving chemisorption. The spatial al kyl chain orientation angles of the adsorbed surfactant molecules were found to be in the range 48-41 degrees from the normal to the alumina surface for 1-100 ppm surfactant solutions.