MOLAR-MASS DEPENDENCE OF THE APPARENT DIFFUSION-COEFFICIENT OF FLEXIBLE HIGHLY-CHARGED POLYELECTROLYTES IN THE DILUTE CONCENTRATION REGIME

In this study dynamic light scattering experiments have been performed on the flexible highly charged polyelectrolyte sodium poly(styrenesul fonate). The apparent diffusion coefficient was determined for five mo lar masses at a fixed ionic strength of 0.1 M at dilute polyelectrolyt e concentrations. The apparent diffusion coefficients extrapolated to zero polyelectrolyte concentration were compared with theoretical Do v alues calculated with a theoretical procedure based on the translation al friction coefficient of the wormlike chain model of Yamakawa and Fu jii. With the excluded volume theories of Fixman and Skolnick, and Bar rett, the electrostatic persistence length according to Le Bret, and t he counterion condensation theory of Manning, a satisfactory agreement was found for all molar masses. From the polyelectrolyte concentratio n dependence of the apparent diffusion coefficient, the diffusion seco nd virial coefficient could be obtained. The molar mass dependence of the diffusion second virial coefficient was found to be linearly propo rtional to the molar mass and could be interpreted with small ion-poly ion coupled mode theories.