Dielectric Properties of Polyelectrolytes in Solution

Abstract

Dielectric measurements belong to the oldest techniques used by physical chemists to gain information about molecular properties and molecular behaviour. Dielectric investigations are generally focused on two main aspects: (1) the equilibrium value of the electric permittivity (or dielectric constant) e which is related to the equilibrium polarization of the system under the influence of an external field; (2) the dispersion or frequency dependence of s which is related to the change in time of the polarization when the external field is established or switched off. Both the equilibrium or static electric permittivity and the dielectric dispersion of polyelectrolyte solutions have been subjects of experimental investigations of which Oncley’s pioneering work on protein solutions should be mentioned [1]. Owing to experimental difficulties measurements in the past have often been limited to a small frequency range but more recently experiments covering a much broader domain have become available. (In our own laboratory experiments are performed between 2.5 kFlz and 100 MHz; Minakata and Irnai [2] claim to have measured between 30 Hz and 6 MHz). Although it should be ideal to measure dielectric properties at frequencies as low as possible, determinations of s below 50 kHz become increasingly difficult for two different reasons: (1) the conductivity contribution of the solution admittance becomes predominant; (2) the effects of electrode polarization which has to be corrected for increase very rapidly with decreasing frequency. Special experimental equipment is necessary and correction methods must be devised to take care of the influence of the electrode effects.