Electrical properties of plasticized polyelectrolytes

Previous work on polymeric systems containing dissolved electrolytes (R. M. Fuoss, J. Amer. Chem. Soc., 61, 2329 (1939); D. J. Mead and R. M. Fuoss, ibid., 67, 1566 (1945): W. N. Maclay and R. M. Fuoss, ibid., 73, 4065 (1951)) has shown that such systems, as usually measured, exhibit an ionic conductance which depends on the voltage used, in the measurements and on the duration of the test. Furthermore, the dielectric constant is unexpectedly high and the total a.c. loss factor is much greater than that caluclated from the d.c. ionic conductance. Our present work shows that much of the variation in d.c. conductance can be ascribed to electrode polarization. By partially quaternizing poly-4-vinylpyridine with methyl bromide, plastic electrolytes were obtained in which only the halide ion is mobile. By addition of dibutyl tartrate as a plasticizer, it was possible to vary the internal viscosity and hence the conductance for a given electrolyte content. When measured between colloidal graphite or tin foil - vaseline contacts, these materials show the familiar variation of d.c. conductance with voltage and time. But if they are measured between bromidized silver electrodes (which are reversible to bromide ion), steady d.c. conductances are obtained., which, incidentally, are as much as ten times the maximum obtained with conventional electrodes. It is therefore to be concluded that much of the variation observed in insulation resistance measurements is due to surface effects rather than to volume properties of the insulation compound itself. With the reversible electrodes, the a.c. properties also showed a more normal behavior: the dielectric constant and loss factor of the plastics containing ions were indeed greater than the constants for non-electrolytic plastics, but the enormous anomalous values no longer appear. With surface effects eliminated by the use of reversible electrodes, the residual ionic effect on volume properties can now be studied. It shows a dispersion which may be due to ionic acceleration during each half cycle: an out-of-phase component in conductance would naturally appear as a capacitance tern in the equivalent parallel R - C circuit.