ADSORPTION OF DODECYL PYRIDINIUM CHLORIDE ON MONODISPERSE POROUS SILICA

The adsorption of a cationic surfactant, dodecyl pyridinium chloride, on monodisperse Stober silica particles dispersed in an aqueous soluti on has been studied as a function of pH and electrolyte concentration. In a previous study it was concluded that the proton charges of these silica particles can be distinguished in charges on the outer surface , charges in the mesopores and charges in a microporous region. From a comparison with the adsorption on non-porous silica it was concluded that dodecyl pyridinium cations can penetrate the mesopores, but are e xcluded from the (highly charged) microporous region. On the outer sur face, adsorption of the cationic surfactant leads to a maximum in the hydrophobicity at about 50% of the maximally adsorbed amount. Charge r eversal has already taken place at about 10% of the plateau value. It was concluded that, after charge reversal, head-on adsorption proceeds until monolayer coverage, after which bilayer formation sets in. (C) 1998 Elsevier Science B.V. All rights reserved.