Modes of interaction and thermodynamic behavior of aggregation of CTAB + BSA mixtures in diols media: effects of diols composition and temperature

The micellization of cetyltrimethylammonium bromide (CTAB) and bovine serum albumin (BSA) mixture has been studied conductometrically in aq. solutions of different diols (1,2-propanediol (1,2-PrD), 2,3-butanediol (2,3-BD), and 1,5-pentanediol (1,5-PD)) media over the temperature range from 298.15 K to 323.15 K to gain insight into the mode and degree of interaction amongst the investigated constituents. The critical micelle concentration (cmc) values of the CTAB + BSA mixtures were attained initially low but enhanced with the rise in temperature in all the media studied. The values of the CTAB + BSA mixtures in the different diols media followed the order: cmc1,5−PD>cmc1,2−PrD>cmc2,3−BD. The degree of micelle ionization (α) increased with increasing carbon chain length of diols and temperature. The Gibbs free energy (ΔGm0) values associated with the micellization of the CTAB + BSA mixture were negative and revealed a lowering of the spontaneity of micellization with increasing carbon chain length of the diols. The enthalpy (ΔHm0) and entropy (ΔSm0) changes of micellization revealed that the micellization was exothermic and mainly an enthalpy-controlled process in aq.1,2-PrD and 2,3-BD media while the process being endothermic, and entropy controlled in the 1,5-PD medium. The contribution of the solvent to the thermodynamic parameters was assessed from free energy of transfer (ΔGm,t0), enthalpy of transfer (ΔHm,t0), and entropy of transfer (ΔSm,t0) values. The enthalpy–entropy compensation parameters were also studied and discussed with proper reasoning.