Radius of gyration of a polyion in salt free polyelectrolyte solutions measured by S. A. N. S.

Abstract

In this paper measurements of the radius of gyration of a polyion in salt free semi-dilute polyelectrolyte solutions are presented. We have used neutron scattering to extract the form factor of a single polyelectrolyte chain from the total correlation function by using a specific labelling associated with an extrapolation method. Assuming that the wormlike chain model takes into account the local flexibility of the chain due to electrostatic interactions along the chain, we have extracted, from the radii of gyration, values for the persistence length bt. Both Rg and bt decrease with increasing polyion concentration, c p. We can distinguish two concentration regimes : at low concentration, Rg decreases as cp-½ and bt as c p-1 and at high concentration R g decreases as cp-¼ and bt , as cp-½. These two regimes for the variation of bt with cp are well described by a calculation of Le Bret for the electrostatic contribution to the persistence length of the polyion.