DETERMINATION OF THE ADSORPTION-ISOTHERM OF THE NONIONIC SURFACTANT TRITON X-405 ON POLYSTYRENE LATEX-PARTICLES USING H-1-NMR

H-1 NMR is found to be a suitable method for determining the adsorptio n of the nonionic surfactant Triton X-405 on polystyrene particles dis persed in D2O. In the NMR spectra, free Triton X-405 and Triton adsorb ed on the surface can be easily distinguished because of the different chemical shifts, Free Triton appears at 3.6 ppm, whereas adsorbed Tri ton shows a signal between 3.48 and 3.53 ppm, depending on the orienta tion of the molecules on the surface. At low concentration, the Triton X-405 chains lie relatively hat on the surface, leading to a broad si gnal and the lowest chemical shift. With increasing Triton X-405 conce ntration, the signal shifts to higher chemical shifts and becomes narr ower due to a decrease in the area occupied by a chain. These experime nts allow the characterization of the detailed partitioning of the Tri ton X-405 in the water phase and on the particles, This leads to the d etermination of the adsorption isotherm, The value determined for the area occupied by one molecule of Triton X-405 is 172 Angstrom(2), and the adsorption equilibrium constant, b, is 3.8 X 10(5) dm(3) mol(-1). (C) 1998 Academic Press.