Comparative Study of the Aggregation Behavior of Some Ionic Surfactants with Nonionic Triton X-114 in Water and a Water/2,2,2-Trifluoroethanol Mixture

The influence of 2,2,2-trifluoroethanol (TFE) on the micellar properties of ionic surfactants hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium p-toluenesulfonate (CTAT), sodium dodecyl sulfate (SDS), N-lauroylsarcosine sodium salt (SDDS), and nonionic surfactant Triton X-114 (TX-114) in aqueous solutions was studied using tensiometry, electrical conductivity, fluorimetry, time-resolved fluorescence, and microcalorimetry. With increasing concentrations of TFE, the micellar charge densities of the ionic head groups decrease, causing a decrease in the critical micelle concentration (CMC) of ionic-surfactant solutions (SDS, SDDS, CTAB, and CTAT) in micellar solutions. However, for nonionic surfactant TX-114, the polar headgroup undergoes some conformational changes causing an increase in the value of CMC. Time-resolved fluorescence decay measurements were done to get evidence of penetration of TFE molecules into the stern layer of the micelle. The micellar aggregation number declines with increasing concentration of solvent, indicating a higher concentration of mixed solvent reducing the number of monomers needed for micellization for ionic surfactants, whereas for nonionic TX-114, it indicates some structural changes of the molecule forming the micelle in the presence of TFE.