Dielectric Relaxation Spectroscopy of Aliphatic Ionene Bromides and Fluorides in Water: The Role of the Polyion's Charge Density and the Nature of the Counterions

Abstract

Dielec. relaxation spectroscopy (DRS) has been chosen to study the dielec. properties of ionene bromides and fluorides in water. The best model for describing the exptl. data in the range of frequencies 0.05 < v/GHz < 89 was the one that considered two relaxing species: (i) counterions and (ii) the bulk water. From the redn. of the water amplitude, S2, effective hydration nos. could be derived. Relaxation times of counterions, τ1, decreased with the increasing concn., which was a consequence of stronger electrostatic screening in more concd. solns. Fluoride counterions were to a lesser extent affected by the polyion than bromide counterions. It seemed that charged sites of the polyions had a much greater influence on the F- counterions than the chains of -CH2- units between them. For ionene bromides, however, the influence of polyion's charges and of hydrophobic parts of the backbone manifested itself in a more complex manner. High hydration nos. in the case of Br- counterions as well as the insensitivity of τ1 on the charge d. of the polyion indicated that the role of the solvent could not be disregarded in these systems.