Dielectric behaviour of stiff polymers in solution when subjected to high voltage gradients

Abstract

We report measurements of dielectric saturation on solutions of poly-γ-benzyl-L-glutamate and ethyl cellulose. Saturation effects of considerable magnitude were observed, particularly with the former polymer. Measurements were made by the simultaneous application of high static and low alternating fields to these macromolecules in solution. When poly-γ-benzyl-L-glutamate was the solute, this technique has enabled us to observe, for the first time field-induced changes in the dielectric relaxation times. The influence of such variables as field strength, concentration, average molecular weight and average dipole moment on both the dielectric saturation and critical frequency shifts are reported. We present a unified theoretical approach to dielectric saturation which embraces some of the previous theories, and on the basis of this approach discuss the observed results. Complete agreement between experimental observations and theoretical predictions for the poly-γ-benzyl-L-glutamate system is only possible if the calculated dipole moment of the macromolecule under high field is considerably larger than its measured low-field value. Some possible implications of this conclusion are considered.