Abstract: The binding of cationic surfactant dodecyloxypropyl-β-hydroxyltrimethyl ammonium bromide(C₁₂NBr) on different polyanions, such as hydrolytic polyacrylamide (HPAM), hydrophobic modifiedpolyacrylates(AMB, AMBA), were investigated by using a potentiometric technique and surface tensionmeasurements at (30.0±0.1)℃.The binding isotherms of C₁₂NBr to HPAM show a cooperative charac-teristic nature: the binding suddenly occurs and is soon saturated within a very narrow concentration range.The sudden onset of binding is referred to as the critical aggregation concentration(c_ac), in analogy withcmc in micelle formation.The c_ac value, however, is 1.5 orders of magnitude lower than the c_mc.Thebinding of C₁₂NBr to hydrophobic modified polyelectrolytes has begun at very low cf and show noncoopera-tive.For the two polyelectrolytes AMB and AMBA, a slow and continuous increase in β with the increaseof cf is observed.This is caused by the presence of hydrophobic microdomains formed by the polyelec-trolytes concentration of surfactant.The surface tension is otherms of C₁₂NBr/HPAMexhibit two aggrega-tion concentration c_T1, c_T2, and c_T1<c_mc<c_T2.But from the surface tension of mixture of c₁₂NBr and hy-drophobic modified polyelectrolytes, we get a 1ower c_mc.It is because that C₁₂NBr molecules interact withpolymer by electrostatic on air-solution interface, and form ordered compact structure of surfactant-poly-mer complex.

Key words: Polyeletrolytes, Surfactant, Binding isotherm, Complex