Time-resolved non-linear dielectric responses in molecular systems

Impedance measurements in the 0.1 Hz to 50 kHz range are performed beyond the linear response regime, using a technique where peak fields as high as 450 kV/cm are possible. The main focus is on the effects of the energy that is transferred irreversibly from the external field to a molecular glass-forming liquid. Because the slow degrees of freedom absorb this energy, their heterogeneous configurational temperatures are increased before the heat is transferred to the phonons on the time scale of structural relaxation. We also discuss a time-resolved variant of high-field impedance spectroscopy, where the harmonic field is applied for a number of cycles at a low field, followed by the same signal at a much higher field. Fourier analysis of the resulting voltage and current traces provides a period-by-period time-resolved picture for the response of the configurational temperature with a 5 mK resolution, resulting from a sensitivity on the 5 × 10−5 level for tan δ. It turns out that this energy absorption is responsible for an extremely pronounced non-linearity in the electric field, where the dielectric relaxation can be accelerated by a factor of 2 prior to changing the temperature.