Determination of Li~+ Self-Diffusion Coefficients in an Aqueous Suspension of Sulfonated Polystyrene Latex by Pulsed-Field-Gradient, Spin-Echo NMR

摘要

The self-diffusion coefficients of ~7Li~+ in a suspension of sulfonated polystyrene latex particles is determined by pulsed-field-gradient, spin-echo NMR over a wide range of electrolyte concentrations. The self-diffusion coefficient of the Li~+ counterion in the suspension without electrolyte is significantly less than that found in a solution of LiClO_4 at the same bulk concentration. This suggests that a large fraction of the Li~+ counterions are electrostatically bound to the large latex particles. The effective charge on the particles is inferred from this measurement. The self-diffusion coefficient of Li~+ increases upon the addition of NaClO_4 to the deionized suspension. Measuring selectively the dependence of Li~+ diffusion on the amount of added electrolyte characterizes the ion-exchange behavior of the latex suspension. The self-diffusion coefficients determined by NMR agree with prediction of the nonlinear Poisson-Boltzmann equation and gradient-diffusion coefficients of hydrogen counterion determined in the same latex by steady-state voltammetry.