ELECTROSTATIC SURFACE-POTENTIAL AND CRITICAL MICELLE CONCENTRATION RELATIONSHIP FOR IONIC MICELLES

The relationship between the micellar interfacial electrostatic potential (‘I'probe), as measured by reliable acid-base indicator techniques, and the critical micelle concentration (cmc) for dodecyltrimethylammonium bromide/NaBr, dodecyltrimethylammonium chloride/NaCl, sodium dodecyl sulfate/NaCl, sodium dodecyl sulfate/NaC104, and sodium decyl sulfate/NaC104 systems has been examined. For these dilute micellar systems, it has been found that probe|/unit change in log cmc is circa 59 mV at 25. A thermodynamic treatment, appropriate for the objective of interpreting the relationship between ‘I'probe and the cmc, demonstrates that this form of behavior is consistent with ‘I' obe being equal to the mean electrostatic potential at the micellar surface, i.e., the thermodynamic or Nernst interfacial potential (*0) of the micelle. Furthermore, it is consistent to regard the aqueous surfactant monomer species as the potential-determining ion in the charged micellar systems. © 1990, American Chemical Society. All rights reserved.