Effect of Isopropanol Mixed Solvent on Interaction of Cetyltrimethylammonium Bromide with Bromocresol Green: A Conductometric Study

In present work, the interaction of an anionic dye, bromocresol green (BCG) with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was studied using conductometric method. The effect of alteration of solvent media from water to cosolvent isopropanol and the effect of elevation in experimental temperature on the association behaviour of BCG-CTAB system were studied. The observed CMC and ΔG°m values indicate disfavored micellization of CTAB system in isopropanol. Whereas micellization of CTAB is favoured in the presence of BCG as additive. For BCG-CTAB system micellization becomes more feasible in presence of isopropanol. The observed value of ΔH°m and ΔS°m predicts micellization of CTAB is endothermic and entropy driven in aqueous solution, whereas, in the presence of BCG it becomes exothermic and enthalpy driven. The micellization process of BCG-CTAB system is exothermic and enthalpy driven in isopropanol. The calculated thermodynamic parameters of transfer for the BCG-CTAB system from water to water-isopropanol media at various temperatures (ΔG°m,tr, ΔH°m,tr, ΔS°m,tr) also supports the entropy-enthalpy mutual act in the micellization process of BCG-CTAB system. Present study also reveals that a compensation phenomenon is operative between the enthalpy and entropy of micellization in case of association process involving the CTAB and the BCG-CTAB systems. The hydrophobic stabilization results to increase in spontaneity of micellization of BCG-CTAB system in water while there is a decrease in hydrophobic stabilization in the presence of isopropanol and a decrease in spontaneity of micellization.