Effects of chain length and structure of cationic surfactants on the adsorption onto Na-Kaolinite

The adsorption of a series of alkylammonium bromides (RR1N(CH3)(2)Br) with different chain lengths R and R-1 on a nonswelling clay surface (sodium kao linite) has been studied by microelectrophoresis and adsorption isotherms. An increase in the number of CH2 groups in the shorter alkyl chain of the d ouble-chain surfactant, or the introduction of another kind of alkyl group (phenyl group), was found to have much less effect on the adsorption behavi or than changing the length of the alkyl chain in the single-chain surfacta nts. It is inferred that the effective hydrophobicity of the shorter chains in these double-chain surfactants is reduced by their intramolecular assoc iation with the longer chain. Comparison of adsorption and micellization le ads to an empirical quantitative description of the effects of alkyl chain length and structure on adsorption. (C) 1999 Academic Press.