The objective of the present work is to evaluate 1 H NMR as a nondisruptive method for determining the adsorption isotherm of the nonionic surfac-1 H NMR is found to be a suitable method for determining the tant Triton X-405 on polystyrene latex particles and to check if this method adsorption of the nonionic surfactant Triton X-405 on polystyrene could be extended to the same particles swollen with monomer. particles dispersed in D 2 O. In the NMR spectra, free Triton X-405 and Triton adsorbed on the surface can be easily distinguished because of the different chemical shifts. Free Triton appears at EXPERIMENTAL 3.6 ppm, whereas adsorbed Triton shows a signal between 3.48 Due to a large water signal in the proton NMR spectra, the polystyrene and 3.53 ppm, depending on the orientation of the molecules on latex had to be prepared carefully by replacing the water with D 2 O. An the surface. At low concentration, the Triton X-405 chains lie 8.73 g amount of a monodisperse polystyrene latex (Dow Chemical Co., relatively flat on the surface, leading to a broad signal and the 92 nm diameter, 5.74% solids) was placed in a serum replacement cell lowest chemical shift. With increasing Triton X-405 concentration, with 16.32 g of D 2 O. Three successive additions of 35 g of D 2 O were the signal shifts to higher chemical shifts and becomes narrower performed, and 35 g of the serum was recovered after each addition, so due to a decrease in the area occupied by a chain. These experithat most of the water was replaced by D 2 O. At the end of the procedure, ments allow the characterization of the detailed partitioning of 24.42 g of polystyrene latex (2.3% solids) in deuterated water was recov- the Triton X-405 in the water phase and on the particles. This ered and used for the sample preparation. The Triton X-405 (Union Carbide, leads to the determination of the adsorption isotherm. The value 70% solution in water) was dried at 70ЊC for 24 h. Three stock solutions of Triton X-405 in D 2 O and a stock solution of SLS in D 2 O were subsequently determined for the area occupied by one molecule of Triton Xprepared with concentrations of 9.70 1 10 02 , 9.22 1 10 03 , 1.06 1 10 03 , 405 is 172 A ˚2, and the adsorption equilibrium constant, b, is 3.8 and 1.00 1 10 04 M, respectively. The different samples were prepared from 1 10 5 dm 3 mol 01 . ᭧ 1998 Academic Press these solutions to adjust the initial surfactant concentrations. All samples