The addition of equimolar amounts of cryptand 222 to solutions containing either sodium dodecyl sulfate (SDS) or sodium decyl sulfate (SdecS) was shown to lower the critical micelle concentration (cmc) of both surfactants by a factor of nearly 5, as measured by surface tension plots and changes in the fluorescence characteristics of pyrene. The cmc values for C222Na+DS- and C222Na+decS- were calculated to be 1.4 and 6.8 mM, respectively. In addition, cryptand complexation of the sodium counterions diminishes the hydrophobicity of the micellar hydrocarbon core. These findings were interpreted as the result of differences in the counterion location: the sodium counterions reside in the outer side of the micelle head-group region while the more hydrophobic sodium cryptate counterions are interspersed among the head groups, acting like spacers, decreasing interionic repulsions in the Stern layer, and favoring a greater extent of water penetration into the micellar structure.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry