Estimation of degree of counterion binding and related parameters of monomeric and dimeric cationic surfactants from cloud point measurements by using triblock polymer as probe

The cloud point (CP) measurements of aqueous solutions of a triblock polymer (TBP) [(PEO)2.5(PPO)31(PEO)2.5], in the presence of varying amounts of cationic surfactants (monomeric and dimeric alkylammoniumbromides) covering premicellar to postmicellar regions, have been carried out. A plot of CP vs surfactant concentration allowed us to evaluate apparent critical micelle concentration (cmc*), which has been found to decrease with an increase in the amount of salt. The cmc* values thus obtained in the absence and presence of salt allowed us to evaluate counterion binding (β) by using the Corrin–Harkins method. β values have been further used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the β values evaluated using this method, especially at low [TBP], are in good agreement with those already reported in the literature.