COUNTERION BINDING ON MICELLES - AN ULTRAFILTRATION STUDY

The association degrees of hydrogen, lithium, rubidium, cesium, cupric, and chromic ions to the anionic micelles of sodium dodecyl sulfate (NaDS) has been examined by using an ultrafiltration (UF) method. It has been found that small monovalent cations (H+, Li+) exhibit no specific adsorption. On the contrary, large monovalent cations (Rb+, Cs+) or multivalent cations (Cu2+, Cr3+) are strongly rejected by the UF membrane exhibiting specific adsorption onto the micelle surface. The model used to fit experimental data is an ionic micelle in which the electric double layer is divided into a diffuse layer outside and a Stern layer inside the shear surface. Assuming a wholly random distribution for both kinds of ions in the diffuse layer, it has been found that adsorption in the Stern layer is well described by a Langmuir isotherm. From this isotherm, ion exchange constants for Rb, Cs, Cu, and Cr with the Na counterion have been determined. For the Cu/Na ion exchange, the variation of the surface potential has been evaluated. © 1991.