An electrical circuit model of the alpha-beta merging seen in dielectric relaxation of ultraviscous liquids.

We present a new model for dielectric data in the alpha-beta merging region. The model is constructed using electrical circuit analogies. It leads to an interpretation of the merging region as one where the total relaxation upon cooling separates in two relaxation processes, consistent with a view where the relaxing entities involved are the same for the two processes. We use this alpha-beta model to fit dielectric data in the merging region of two different molecular liquids. These fits are performed under the assumption that the intrinsic high-frequency behavior of the alpha relaxation is a -1/2 power law and that both the alpha and the beta process separately obey time temperature superposition. We get good quality fits in the entire frequency and temperature range studied. This supports the view that alpha relaxation high-frequency slopes that are found to be numerically smaller than 1/2 can be attributed to the influence of the beta relaxation.

Prevalence of approximate square root(t) relaxation for the dielectric alpha process in viscous organic liquids.

This paper presents dielectric relaxation data for organic glass-forming liquids compiled from different groups and supplemented by new measurements. The main quantity of interest is the "minimum slope" of the alpha dielectric loss plotted as a function of frequency in a log-log plot, i.e., the numerically largest slope above the loss peak frequency. The data consisting of 347 spectra for 53 liquids show prevalence of minimum slopes close to -1/2, corresponding to approximate square root(t) dependence of the dielectric relaxation function at short times. The paper studies possible correlations between minimum slopes and (1) temperature (quantified via the loss peak frequency); (2) how well an inverse power-law fits data above the loss peak; (3) degree of time-temperature superposition; (4) loss peak half width; (5) deviation from non-Arrhenius behavior; (6) loss strength. For the first three points we find correlations that show a special status of liquids with minimum slopes close to -1/2. For the last three points only fairly insignificant correlations are found, with the exception of large-loss liquids that have minimum slopes that are numerically significantly larger than 1/2. We conclude that--excluding large-loss liquids--approximate square root(t) relaxation appears to be a generic property of the alpha relaxation of organic glass formers.