THE BINDING OF CATIONIC SURFACTANTS BY HYDROPHOBIC ALTERNATING COPOLYMERS OF MALEIC-ACID CHARGE-DENSITY DEPENDENCE

The charge density dependence of the binding of a cationic surfactant, dodecylpyridinium chloride (DPCl), by an alternating copolymer of maleic acid with styrene (MASt), and by an alternating copolymer of maleic acid with ethylene (MAE) is reported. Binding isotherms are determined in the presence of a fixed concentration of NaCl, using a potentiometric technique based on surfactant ion selective, solid state membrane electrodes. In the case of MASt, the binding of DP+ ions is considerably enhanced by a decrease in the charge density (degree of neutralization) of the polyion. This effect is attributed to the contribution of the hydrophobic side groups in the polymer to the binding process. In the case of MAE, which is a less hydrophobic polymer, the influence of the charge density on surfactant binding is much less. For MASt-DP+ a nearly linear relationship between the Gibbs energy of binding and the inverse of the charge density is observed, indicating a contribution per phenyl group to the Gibbs energy of binding of -1.6RT, in good agreement with the reported value estimated from other observations in an earlier publication.