Diffusion of Solvent in Swollen Latex Particles

Pulsed field gradient (PFG) NMR spectroscopy was used to measure the translational diffusion coefficient of solvent toluene in spheres made from polystyrene (latex). The latex spheres had a bimodal size distribution that was measured using transmission electron microscopy and image analysis. Analysis of the PFG data using the equations of Murday and Cotts (J. Chem. Phys. 48, 4938, 1968) for diffusion restricted to a sphere demonstrated the need, in general, to incorporate the entire size distribution of the latex particles into the analysis when the particle sizes are sufficiently polydisperse. The values of self-diffusion coefficients obtained from this analysis were significantly higher than those predicted by bulk diffusion studies. This discrepancy could not be attributed to an inaccuracy in the approximation, inherent in the Murday and Cotts equations, that the distribution of the phases of the magnetization vectors confined to a sphere is Gaussian and could suggest the presence of heterogeneities within the latex particles.