Probing the association behavior of poly(ethyleneglycol) based amphiphilic comb-like polymer in the presence of cationic surfactant

The interaction between an amphiphilic comb-like polymer—poly(styrene–maleic anhydride) copolymer esterified with brij-35—and a cationic surfactant, N-cetyl-N,N-diethanolyl-N-methyl ammonium bromide (CDMAB), was investigated at pH 6.2. Our earlier experiments (Polymer 42, 7801, 2001) revealed that at this pH the polymer forms intramolecular aggregates and these self-aggregates behave as polyelectrolyte due to the partial ionization of the backbone of the polymer. When surfactant is gradually added to the polymer solution in the present study, binding of the surfactant to the polymer takes place even at lowest surfactant concentration. Initially binding occurs due to electrostatic interaction, leading to compact aggregates. After complete charge neutralization of the polymer backbone, the surfactant hydrophobes are adsorbed into the microdomains formed by the polymer due to hydrophobic interactions. An exothermic enthalpy change is associated with both kinds of interactions, electrostatic as well as hydrophobic.