The effect of added salt on adsorption and adsolubilization by a gemini surfactant on silica

Adsorption of a dimeric (1,2-bis(dodecyldimethylammonio) ethane dibromide, 2RenQ) on silica from its aqueous solution has been investigated in presence of added NaBr. The adsorbed amounts of 2RenQ at saturation increase with increasing amount of NaBr added. The dispersion stability of silica suspensions caused by adsorption of 2RenQ is well correlated with the change in zeta potentials. With a constant feed concentration of 2-naphthol, the adsolubilized amounts of 2-naphthol are greater when NaBr is added, but the ratios:of adsolubilized amount of 2-naphthol/adsorbed amount of 2RenQ at maximum adsolubilization decrease with increasing NaBr concentration. This result is interpreted by the change in microviscosity of the 2RenQ adsorbed layer, as estimated by the ESR probe technique. In addition, from a two-step process of adsorption-adsolubilization, it is found that 2RenQ adsorbs on silica much more strongly in presence of added NaBr, keeping 2-naphthol in the adsorbed layers, than when NaBr is not added.