MOLAR-MASS AND IONIC-STRENGTH DEPENDENCE OF THE APPARENT DIFFUSION-COEFFICIENT OF A FLEXIBLE POLYELECTROLYTE AT DILUTE AND SEMIDILUTE CONCENTRATIONS - LINEAR POLY(ETHYLENIMINE)

The ionic strength and the molar mass dependence of the apparent diffusion coefficient of the polyelectrolyte linear poly(ethylenimine) is studied over a wide concentration range in 10, 25, and 100 mM NaCl solutions. At a constant NaCl concentration dilute and semidilute concentration regimes are distinguished with a different dependence of the diffusion coefficient on the polyelectrolyte concentration, the NaCl concentration, and the average molar mass of the polyelectrolyte. At infinite dilution the dependence of the diffusion coefficient on molar mass and on the added NaCl concentration are in good agreement with the theoretical predictions concerning the rms radius of gyration. At dilute concentrations the diffusion second virial coefficient is found to be inversely proportional to the NaCl concentration, which is in agreement with the theory taking into account the coupling of the motions of the small ions and the polyions. In the semidilute concentration regime the apparent diffusion coefficient is shown to follow a power law of the polyelectrolyte concentration and to be independent of the two molar masses investigated. The ionic strength dependence of the apparent diffusion coefficient was not in complete agreement with theory, but was shown to be consistent with previous measurements with NaPSS.