Hydrophobicity enhancement in micelles of Triton X-165 by the presence of the cosolvent 2,2,2 trifluoroethanol (TFE)

Abstract This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar properties of Triton X-165 (TX-165) in aqueous solutions. The results obtained from various experimental techniques are used to interpret the interactions in the systems studied. The added TFE has strong effect on lowering the cloud point (CP) in the solutions of TX-165. This effect is consistent with partial dehydration of the oxyethylene groups in the micelle. The decrease of both the critical micelle concentration (CMC) and the CP with the increase of TFE concentration is justified by the interaction between TFE molecule and the oxyethylene group of TX-165, by the low hydrogen bond ability of the hydroxyl oxygen atom of TFE and by the water structure maker effect of TFE. The micelle aggregation number determined by fluorescence decreases initially with the increase of TFE concentration and then increases for the highest TFE concentrations. Fluorescence quenching data indicate that about 45% of pyrene probe is accessible to the quencher (TFE). The results of viscosity are consistent with ellipsoidal shape of TX-165 micelles. The changes in the intrinsic viscosity with increasing TFE concentration may reflect changes in the solvation of micelles and conformational changes in the polar head groups in the micelle. These factors affect the packing of the monomers and the micelle aggregation number. The TFE cosolvent confers hydrophobicity to the micelles of TX-165.