USE OF SURFACTANT-SPECIFIC ELECTRODES IN THE STUDY OF ADSORPTION OF CATIONIC AMPHIPHILIC IONS ONTO CLAYS

The adsorption isotherms of dodecyltrimethylammonium ions (DTA(+)) ads orbed onto a laponite clay colloid were studied in water and in NaBr s olution (at 0.1, 0.3, and 0.5 mol . liter(-1)), at 298 K, using amphip hilic ion-specific electrodes, This potentiometric method can be used to measure concentrations in situ and to follow the decrease in the am ount of surfactant in the solution as the surfactant is adsorbed onto the day, This paper describes a method for characterizing adsorption i sotherms of DTA(+) onto laponite by determining the amount adsorbed at a fired surfactant activity in solution. By repeating this process fo r various DTA(+) activities, the adsorption isotherm can be plotted, A dsorption isotherms obtained with or without NaBr in the solution were continuous curves which increased with the surfactant activity. The f ield of study is limited by the CMC value for the surfactant and the c urves have a common intersection point, which can be attributed to the isoelectrical point of the laponite/adsorbed surfactant system, This method can be generalized to other cations and obviously to other soli ds. (C) 1995 Academic Press, Inc.