The measurement of non-linear dielectric effects with re-entrant cavities

At high field strengths E, the polarization P of a dielectric is nonlinear. The quantity characterising the NDE (nonlinear dielectric effect) is Δε/E². The two major contributions to Δε/E² are the Langevin saturation and the anomalous saturation due to a chemical effect. 1,2-dichloroethane measurements are discussed. The choice of this chemical system as an object of study was determined mainly by the simple equilibrium it offers. The process of interest is the internal rotation from the nonpolar trans conformer to the polar gauche conformer (μ=2.7 D). The transition of g(+) to g(-) is energetically unfavourable. Positive NDE have been reported earlier by Piekara and co-workers (1975), Hopmann (1975) investigated the dynamic features, showing a linear increase in Δtanδ with ω in the range of 7 to 100 MHz, without any indication for relaxation. Experiments in the frequency range of 5 to 100 MHz confirmed Hopmann´s results. Using resonance cavities at 300, 400 and 600 MHz, chemical relaxation of the NDE was clearly shown. All signals were checked for a square dependence on E. Results were corrected for electrode deformation and also for instrumental errors by applying the diethyl ether measurements correction factor