Characteristic lengths and the structure of salt free polyelectrolyte solutions. A small angle neutron scattering study.

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chain S( q) and the structure factor S( q). Two lengths are deduced from these two factors: the persistence length b which characterizes the electrostatic interactions along the chain by a fitting of S( q) with calculation of the scattering function for a wormlike chain, and from S( q), q which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions ( b ∝ C, q ∝ C) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range. [ABSTRACT FROM AUTHOR]