Sequential Adsorption of Triton X-100 and Sodium Dodecyl Sulfate onto Positively and Negatively Charged Polystyrene Latexes.

Individual and sequential adsorption of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant Triton X-100 on cationic and anionic polystyrene latexes has been examined. Both latex samples, although charged differently (-16.2 and +11.0&mgr;C cm(-2)), must be considered hydrophobic polymer colloids. The adsorbed amounts of both surfactants on cationic and anionic latexes were found to be different as a consequence of the dissimilar interfacial properties of these two surfactants. In addition, a comparison between the two surfactants showed that SDS is more easily replaced than Triton X-100 when sequential adsorption on both latexes was studied. It was found that the electrophoretic mobility of surfactant latex complexes depends on the addition sequence order of both surfactants. In relation to colloidal stability, when a layer of a nonionic surfactant is adsorbed on the surface of latexes, the electrosteric mechanism explains the experimental results. If SDS is adsorbed the stabilization or unstabilization is a consequence of the changes in the electrical repulsion between particles. However, when both surfactants are adsorbed, the assumption of additivity is not correct; that is, the electrostatic repulsion (V(R)) and the steric repulsions (V(osm) and V(vr)) are not totally independent. Copyright 2001 Academic Press.