Counterion condensation in Xanthan aqueous solutions in the semidilute and concentrated regime

The dielectric and conductometric properties of aqueous solutions of Xanthan have been investigated from 1 kHz to 1 GHz by means of frequency domain dielectric spectroscopy, at different polyion concentrations from 0.5 to 10 mg/ml, covering both the semidilute and concentrated regimes. The dielectric spectra have been analysed, in these concentration regions, on the basis of a fixed counterion condensation model, considering that a fraction of counterions will remain in the neighbouring of each charged group of the polyion and that this fraction does not change with the degree of ionization and polymer concentration. This assumption, which differs from that given by the Manning model for charged polyelectrolyte solutions, defines the overall dielectric and conductivity behaviour of the system over the whole temperature interval and polymer concentration investigated.