Micellar size and phase behavior in n-octyl-β-d-thioglucoside/Triton X-100 mixtures: The effect of NaCl addition

The temperature and NaCl concentration dependence of the size of mixed micelles of n-octyl-β-d-thioglucoside (OTG) and Triton X-100 (TX100), two non-ionic surfactants belonging to the alkyl glucosides and polyoxyethylene alkyl ether families, respectively, has been investigated using the dynamic light scattering technique. Micellar size increases with temperature, with this micellar growth occurring faster when the temperature approaches the cloud point temperature. The extent of this growth is less pronounced at higher relative proportions of OTG in solution. In addition, the cloud point temperature was investigated for aqueous and NaCl solutions of OTG and Triton X-100 mixtures. The experimental results can be explained assuming the clouding process to be a liquid–liquid phase separation which takes place as a result of reduced hydration of the head group in the surfactant molecules caused by the temperature rise. The thermodynamic parameters of the clouding phenomenon have been calculated using the phase-separation model and considering the cloud point to be the threshold temperature for solubility. This study found that the enthalpy–entropy compensation relationship holds for this process.