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

Abstract 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: The degree of micelle ionization (α) increased with increasing carbon chain length of diols and temperature. The Gibbs free energy ( ) 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 ( ) and entropy ( ) 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 ( ), enthalpy of transfer ( ), and entropy of transfer ( ) values. The enthalpy–entropy compensation parameters were also studied and discussed with proper reasoning.