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 (C _P) 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 C _P 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.