ADSORPTION AND ADSOLUBILIZATION BY MONOMERIC, DIMERIC, OR TRIMERIC QUATERNARY AMMONIUM SURFACTANT AT SILICA WATER INTERFACE/

Adsorption of monomeric, dimeric, or trimeric quaternary ammonium surf actant on silica from its aqueous solution has been investigated by me asuring adsorption density, zeta potential, and dispersion stability. The monomeric (dodecyltrimethylammonium bromide, 1RQ), dimeric (1,2-bi s(dodecyldimethylammonio)ethane dibromide, 2RenQ), and trimeric dodecy lbis[2-dimethyldodecylammonio)ethyl]ammonium tribromide, 3RdienQ) surf actants are used in this study. The amounts adsorbed at saturation dec rease with increasing dodecyl chain number of the surfactants from 1RQ to 2RenQ and 3RdienQ. Silica suspensions by adsorption of the surfact ants exhibit a process of dispersion-flocculation-redispersion with th e surfactant concentration for the three surfactants which can be corr elated with the change in zeta potentials. ESR measurements using meth yl 12-doxylstearate show that the microviscosities in 2RenQ- and 3Rdie nQ-adsorbed layers are greater than that in the 1RQ-adsorbed layer. Un der a constant feed concentration of 2-naphthol, the adsolubilized amo unts of 2-naphthol increase, reach a maximum, and then decrease with t he surfactant concentration for the three surfactants. The ratio of ma ximum amount of 2-naphthol adsolubilized to the adsorbed amount of sur factant on silica increases with an increase in the dodecyl chain numb er of the surfactants from 1RQ to 2RenQ and 3RdienQ. In addition, from a two-step process of adsorption-adsolubilization, it is suggested th at 2RenQ and 3RdienQ adsorb on much stronger than 1RQ, keeping 2-napht hol in their adsorbed layers. (C) 1996 Academic Press, Inc.