Competitive Adsorption of the Anionic Surfactant SLS and the Nonionic Surfactant Triton X-405 on Polystyrene Latex Particles

Abstract

The competitive adsorption of an anionic surfactant (SLS) and a nonionic surfactant (Triton X-405) on monodisperse polystyrene particles (92 nm) was studied and quantified using a variety of experimental techniques (filtration, desorption via serum replacement, 1H NMR spectroscopy). All experiments were performed at 25 °C using a cleaned polystyrene latex (2% solids). In the competitive adsorption of a 1/1 molar ratio of SLS to Triton X-405 on the polystyrene particles, Triton X-405 adsorbed preferentially at total surfactant concentrations in the aqueous phase below 2.5 × 10-3 M, due to its low free energy of adsorption. At higher surfactant concentrations, the particle surface became saturated with Triton X-405, and cooperative interaction between the two surfactants took place. An excess amount of the two surfactants was noted on the surface. Triton X-405 was observed to adsorb on polystyrene particles precovered with SLS. Approximately 20% of the SLS was removed from the surface below 7.0 × 10-4 M Triton X-405 aqueous concentration. However, cooperative adsorption occurred at higher concentrations, and a large excess of the two surfactants was noted on the surface at saturation. SLS was also shown to adsorb on polystyrene particles precovered with Triton X-405. The adsorption was small at SLS aqueous concentrations below 2.5 × 10-3 M. At higher concentrations, more of the SLS was adsorbed, and an excess surfactant content was present at the surface. No significant effect on the adsorption of Triton X-405 was noted for increasing SLS concentrations in the system. Competitive desorption experiments were performed with the two surfactants using serum replacement. SLS was found to desorb more readily than Triton X-405. The particle surface composition was richer in Triton X-405 as the total surfactant concentration in the system decreased.