Ultramicroelectrode voltammetric measurement of the hydrodynamic radii and shear plane of micellar particles for sodium dodecylsulfonate in aqueous NaCl solution

Ultramicroelectrode voltammetric measurements have been carried out to determined the micellar hydrodynamic radii (R-h(0)) and h shear plane location of sodium dodecylsulfonate (SDS) in the aqueous solutions containing different NaCl concentrations at 298.2 +/- 0.1 K. The results suggest that R-h(0) decrease initially due to collapse of the shear plane toward the micellar hard-sphere surface, and then R-h(0) increase gradually due to electrolyte-induced linear spherical expansion of the micellar particles with the increase h of NaCl concentration. It is found that, the shear plane thickness is from 0.06 to 0.75 nm in aqueous electrolyte solutions and is very close to the hard-sphere surface of SDS micelle particles relative to the outer boundary of electric double layer. The relationship between the shear plane thickness and Debye-Huckel length is shown to be a simple linear function with the shear plane collapsing toward the micellar surface as the electric double layer collapses with added electrolyte. (C) 2004 Published by Elsevier B.V.