Zeta-potentials of self-assembled surface micelles of ionic surfactants adsorbed at hydrophobic graphite surfaces

The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate-SDS and hexadecyltrimethyl ammonium bromide-CTAB) on graphite surfaces were determined both front streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite-liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear. parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite Surface were about -75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature. (C) 2004 Elsevier B.V. All rights reserved.