The Role of Chain Length and Structure in Surfactant Adsorption at Na-Kaolinite

The adsorption of a series of cationic surfactants with different chain lengths and structures on a non-swelling clay surface (sodium kaolinite) has been studied by microelectrophoresis and adsorption isotherms. It was found that an increase in the number of CH 2 groups in the shorter alkyl chain of the double-chain surfactant has much less effect on the adsorption behaviour 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. A comparison of adsorption and micellization leads to an empirical, quantitative description of the effects of alkyl chain length and structure on adsorption. The adsorption mechanism of cationic surfactants on to Na-kaolinite was discussed.