COADSORPTION OF PHENOXYALCOHOLS AND CATIONIC SURFACTANTS WITH VARIOUS HEADGROUPS AT THE SILICA WATER INTERFACE

The adsorption of neutral molecules on fine silica particles in the presence of four cationic surfactants (adsolubilization) has been studied as a function of both solute and surfactant concentration. The necessary adsorption isotherms of the cationic surfactants trimethyltetradecyl and trimethyhexadecylammonium bromides and hexadecylpyridinium and benzyldimethyltetradecylammonium chlorides on silica have also been investigated at low pH and ionic force. It is shown in the case of phenoxyalcohols that the adsorption profile of the solutes is very similar to that of the surfactants: at low alcohol concentration a plateau adsorption is observed followed by a rapid increase of adsolubilization above a solute threshold concentration and a new plateau at higher concentration. This type of isotherm was obtained at low surfactant concentration; it may be fitted with the same theoretical adsorption isotherms as the cationic surfactants. The partition coefficient of the phenoxyalcohols between various adsorbed surfactant aggregates and water were determined. They were shown to be of magnitude similar to that observed between classical cationic micelles and water. Benzene, acetophenone, and phenol were also investigated with the same substrates and were found not to be adsolubilized with the present chemical systems. Some of the conditions for adsolubilization of neutral molecules are discussed. (C) 1994 Academic Press, Inc.