Role of the spacer of Gemini surfactants in solubilization into their micelles

Abstract

We report the role of a spacer chain in gemini surfactants for solubilization of poor soluble compounds to the aqueous medium. Solubilization of n-alkylbenzenes into micellar solutions of alkanediyl-1,s-bis(dimethyltetradecylammonium bromide) (14-s-14,2Br−, s=2, 6, and 12) has been studied in the temperature range from 288.2 to 308.2K. The equilibrium concentrations of all the solubilizates are determined spectrophotometrically. The solubility of the solubilizates remains constant below the critical micelle concentration (cmc) and increases linearly with an increase in the surfactant concentration above the cmc. The hydrodynamic diameter of the micellar aggregates with or without the solubilizates is measured by means of dynamic light scattering (DLS). The enthalpy, entropy, and Gibbs energy changes for the solubilization of n-alkylbenzenes have been calculated to evaluate a driving force of a transfer of the solubilizates into the micelle. These results indicate that the driving force and solubilization site in the aggregates are changed depending on the spacer chain length of surfactants. Furthermore, the inner core of the solubilized aggregates has been investigated by Fourier transform infrared (FTIR) spectra and two-dimensional nuclear Overhauser effect spectroscopy (2-D NOESY).