DIFFUSION OF POLYELECTROLYTE IN PRESENCE OF ADDED SALT

The diffusion process of polyelectrolyte in the presence of added salt is analyzed based on the assumption that the Donnan equilibrium is always maintained between the sample solution and the solvent. The apparent diffusion coefficient determined by an interference optical system is given as a function of the concentrations of both polyelectrolyte and added salt. Consequently, it is shown that the polymer concentration dependence of the apparent diffusion coefficient is expressed by an equation valid for two-component systems if the polymer solution is dialyzed against the solvent. That is, the second virial coefficient of the sample solution can be expressed by the sum of the concentration dependence coefficients of both sedimentation and diffusion divided by the molecular weight. The diffusion coefficient of poly(sodium styrenesulfonate) in sodium chloride solutions is determined by a Rayleigh optical system to be compared with the theory. The second virial coefficient calculated from the concentration dependence coefficient of diffusion thus obtained and that of sedimentation reported previously is found to agree with the value determined by the light-scattering method.