ON THE NATURE OF ALKYLSULFONATE ADSORPTION AT THE RUTILE WATER INTERFACE

The adsorption density of dodecylsulfonate ions at the rutile/water interface was determined at different pH values, together with the surface charge density. The adsorption isotherms consist of four distinct regions. Region 1 (at low concentrations) is characterized by ion exchange of dodecylsulfonate ions with chloride ions in the electrical double layer. In region 2 the adsorbed surfactant ions associate through interaction of their hydrocarbon chains, forming hemimicelles. After reversal of the electrokinetic potential, there is a decrease in the slope of the isotherm in regions 3 and 4. This results from continuous increase in the electrostatic repulsion as the zeta potential becomes negative and the solution concentration approaches the critical micelle concentration. Adsorption phenomena are interpreted in terms of the Stern-Grahame model of the electrical double layer.