Studies on the adsorption of dodecylbenzenesulfonate and cetylpyridinium bromide at liquid/air and bentonite/liquid interfaces

Adsorption of dodecylbenzenesulfonate (DBS) and cetylpyridinium bromide (CPBr) at liquid/air and bentonite/liquid interfaces was studied. The surface excess concentration as well as the area occupied by each adsorbed surfactant molecule at liquid/air interface was calculated. The cationic surfactant (CPBr) was found to adsorb on bentonite surface to a higher extent compared with anionic surfactant (DBS). The adsorption of CPBr exceeded the CEC of bentonite and was assumed to proceed via cation exchange and to be enhanced by the mutual hydrophobic interaction among the hydrocarbon chains. On the other hand, adsorption of DBS was explained to proceed due to specific adsorption. Both surfactants were found to follow the pseudo second order kinetic indicating that the rate of the adsorption is controlled by both the concentration of the surfactant as well as the surface properties of bentonite. The thermodynamic parameters indicated that the adsorption of both DBS and CPBr is of physical nature.