Competitive adsorption of the anionic surfactant SLS and the nonionic surfactant Triton X-405 on polystyrene latex particles

The competitive adsorption of an anionic surfactant (SLS) and a nonionic su rfactant (Triton X-405) on monodisperse polystyrene particles (92 nm) was s tudied and quantified using a Variety of experimental techniques (filtratio n, desorption via serum replacement, H-1 NMR spectroscopy). All experiments were performed at 25 degrees C using a cleaned polystyrene latex (2% solid s). In the competitive adsorption of a 1/1 molar ratio of SLS to Triton X-4 05 on the polystyrene particles, Triton X-405 adsorbed preferentially at to tal surfactant concentrations in the aqueous phase below 2.5 x 10(-3) M, du e 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 ads orb on polystyrene particles precovered with SLS. Approximately 20% of the SLS was removed from the surface below 7.0 x 10(-4) hi Triton X-405 aqueous concentration. However, cooperative adsorption occurred at higher concentr ations, and a large excess of the two surfactants was noted on the surface at saturation. SLS was also shown to adsorb on polystyrene particles precov ered with Triton X-405. The adsorption was small at SLS aqueous concentrati ons below 2.5 x 10(-3) M. At higher concentrations, more of the SLS was ads orbed, and an excess surfactant content was present at the surface. No sign ificant effect on the adsorption of Triton X-405 was noted for increasing S LS concentrations in the system. Competitive desorption experiments were pe rformed 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.