We present nonlinear dielectric measurements of glass-forming glycerol and propylene carbonate applying electrical fields up to 671 kV/cm. The measurements extend to sufficiently high frequencies to allow for the investigation of the nonlinear behavior in the regime of the so-far mysterious excess wing, showing up in the loss spectra of many glass formers as a second power law at high frequencies. Surprisingly, we find a complete lack of nonlinear behavior in the excess wing, in marked contrast to the α relaxation where, in agreement with previous reports, a strong increase of dielectric constant and loss is found.

This chapter contains sections titled: Introduction Dielectric Spectroscopy The Phenomenology of Glassy Dynamics as Revealed by Dielectric Spectroscopy Broadband Dielectric Spectra of Glass-Forming Liquids Summary References

In the present work, we provide broadband dielectric spectra showing strong electrode polarization effects for various materials, belonging to very different material classes. This includes both ionic and electronic conductors as, e.g., salt solutions, ionic liquids, human blood, and colossal-dielectric-constant materials. These data are intended to provide a broad data base enabling a critical test of the validity of phenomenological and microscopic models for electrode polarization. In the present work, the results are analyzed using a simple phenomenological equivalent-circuit description, involving a distributed parallel RC circuit element for the modeling of the weakly conducting regions close to the electrodes. Excellent fits of the experimental data are achieved in this way, demonstrating the universal applicability of this approach. In the investigated ionically conducting materials, we find the universal appearance of a second dispersion region due to electrode polarization, which is only revealed if measuring down to sufficiently low frequencies. This indicates the presence of a second charge-transport process in ionic conductors with blocking electrodes.

Dielectric loss spectra covering 13 decades in frequency were collected for 2-ethyl-1-hexanol, a monohydroxy alcohol that exhibits a prominent Debye-like relaxation, typical for several classes of hydrogen-bonded liquids. The thermal variation of the dielectric absorption amplitude agrees well with that of the hydrogen-bond equilibrium population, experimentally mapped out using near infrared (NIR) and nuclear magnetic resonance (NMR) measurements. Despite this agreement, temperature-jump NIR spectroscopy reveals that the hydrogen-bond switching rate does not define the frequency position of the prominent absorption peak. This contrasts with widespread notions and models based thereon, but is consistent with a recent approach.

We present the results of broadband dielectric spectroscopy on two glass formers with strong Johari-Goldstein beta-relaxations. In addition to the alpha- and beta-relaxation dynamics, the extension of the spectra up to 1 THz also allows revealing information on the fast beta-process in this class of materials. There is clear evidence for a fast process contributing in the region of the high-frequency loss minimum, which is analyzed in terms of the idealized mode-coupling theory.

We present the temperature dependence of α -relaxation times of 13 glass formers determined from broadband dielectric spectroscopy, also including data from aging measurements. The data sets partly cover relaxation-time ranges of up to 16 decades enabling a critical test of the validity of model predictions. For this purpose, the data are provided for electronic download. Here we employ these results to test the applicability of the Vogel-Fulcher-Tammann equation and a recently proposed new approach that was demonstrated to provide superior fits of a vast collection of viscosity data.