Adsorption of a cationic surfactant on Na-montmorillonite: Inspection of adsorption layer by X-ray and fluorescence spectroscopies

The adsorption of the cationic surfactant BDDAC on a hydrophilic smectite ( montmorillonite) surface has been investigated, especially in the range of low coverage ratios where surfactant ions are adsorbed through cation-excha nge with the counterions of the clay. The surfactant colons (Cl-) were foun d to be adsorbed simultaneously with the cationic part after a complete alk yl ammonium ion-exchange of montmorillonite (CEC). We observe that organocl ay particles remain flocculated in aqueous medium in almost all the range o f adsorption isotherms up to 1.38 CEC and afterward redisperse incompletely . The intercalation of surfactant in the interlamellar space was followed b y X-ray measurements. Fluorescence spectroscopy was used to obtain informat ion about the adsorption layer at the interface. A calculation from geometr ical considerations and from adsorption isotherms shows that below 1.38 CEC , there is a flat double layer in the interlamellar space and after this am ount of adsorbed surfactant, an interstratified clay-surfactant mixed syste m is formed. (C) 1999 Academic Press.