Solubilization of n-alkylbenzenes into gemini surfactant micelles in aqueous medium

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene into micelles of decanediyl-1-10-bis(dimethyltetradecylammonium bromide) (14-10-14,2Br(-)) has been investigated in the temperature range from 288.2 to 308.2 K. The equilibrium concentrations of all the solubilizates are determined spectrophotometrically. The concentration of the solubilizates remains constant below the critical micelle concentration (cmc) and increases linearly with an increase in 14-10-14,2Br(-) concentration above the cmc. Compared to the mother micelle, the solubilized micelles indicate much larger hydrodynamic diameters, which are determined by dynamic light scattering. Therefore, the Gibbs energy change for the solubilization of n-alkylbenzenes has been evaluated by the partitioning of the solubilizates between the aqueous and micellar phases. Furthermore, the enthalpy and entropy changes for the solubilization could be calculated from temperature dependence of the Gibbs energy change. From the thermodynamic parameters, it is found that the solubilization for the present system is entropy-driven and that the location of the solubilizates moves into the inner core of the micelle with an elongation of their alkyl chains. The movement on the location is also supported by the results of absorption spectra, Fourier transform infrared (FTIR) spectra, and two-dimensional nuclear Overhauser effect spectroscopy (2-D NOESY).