Estimation of degree of counterion binding and thermodynamic parameters of ionic surfactants from cloud point measurements by using triblock polymer as probe

Cloud point (CP) was measured for ternary mixtures of different ionic surfactants such as sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) plus triblock polymer (TBP) ((PEO)2(PPO)15.5(PEO)2) plus water, keeping the concentration of TBP constant and varying the surfactant concentration from pre- to postmicellar regions. These experiments were also performed in the presence of different fixed amounts of NaBr to evaluate the salt effect on the clouding behavior of these ternary mixtures. The CP value of TBP exhibits a drastic change at the cmc of each surfactant. The cmc values thus obtained both in the absence and in the presence of NaBr were used to evaluate counterion binding (β) with the Corrin-Harkins method. β values were also 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 reported in the literature.