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)2Br) with different chain lengths R and R1 on a nonswelling clay surface (sodium kaolinite) has been studied by microelectrophoresis and adsorption isotherms. An increase in the number of CH2 groups in the shorter alkyl chain of the double-chain surfactant, or the introduction of another kind of alkyl group (phenyl group), was found to have much less effect on the adsorption behavior than changing the length of the alkyl chain in the single-chain surfactants. It is inferred that the effective hydrophobicity of the shorter chains in these double-chain surfactants is reduced by their intramolecular association with the longer chain. Comparison of adsorption and micellization leads to an empirical quantitative description of the effects of alkyl chain length and structure on adsorption. Copyright 1999 Academic Press.