Infrared study of the adsorption of non-ionic surfactants on silica

Abstract

An infrared study of the adsorption of octylphenolethoxylates with an average of 1, 10 and 70 oxyethylenic groups at the silica–carbon tetrachloride interface is reported. The adsorption occurred mainly via hydrogen bonding between the oxygen atoms of the hydrophilic chain and the free silanols. No chemisorption was found to take place. The surfactant molecules presented a flat configuration at low coverage, but at increasing coverage they were adsorbed in a more upright configuration as fewer oxyethylenic groups were able to interact with surface silanols owing to steric crowding. Finally, at saturation, the last molecules were adsorbed vertically through the terminal hydroxy group.