Ultraslow dielectric relaxation process in supercooled polyhydric alcohols

Abstract

Complex permittivity was obtained on glycerol, xylitol, sorbitol and sorbitol-xylitol mixtures in the supercooled liquid state in the frequency range between 10 microHz and 500 MHz at temperatures near and above the glass transition temperature. For all the materials, a dielectric relaxation process was observed in addition to the well-known structural alpha and Johari-Goldstein beta relaxation process [G. P. Johari and M. Goldstein, J. Chem. Phys. 53, 2372 (1970)]. The relaxation time for the new process is always larger than that for the alpha process. The relaxation time shows non-Arrhenius temperature dependence with correlation to the behavior of the alpha process and it depends on the molecular size systematically. The dielectric relaxation strength for the new process shows the effect of thermal history and decreases exponentially with time at a constant temperature. It can be considered that a nonequilibrium dynamics causes the new process.

Slow Debye-type peak observed in the dielectric response of polyalcohols

“…It is seen that we are definitely observing the same process. Our observation thus confirms the observation by Yomogida et al 21 without resorting to such a difficult subtraction of conductivity from the data. However, in contrast to that study, where it was found that the dielectric strength of the "ultraslow process" decreases with time, we found an almost time independent amplitude of the Debye-like process.…”

“…However, these types of subtractions are difficult as one essentially subtracts a huge conductivity contribution to extract a rather small feature in the spectra. The data of Yomigida et al 21 obtained by time domain dielectric spectroscopy and ours are complementary also regarding the covered frequency windows and their obtained peak relaxation times are compared to our data in Fig. 3.…”

“…In fact, it was recently shown for the same polyalcohols that there indeed exists an "ultraslow" process for these materials, 21 but it is only observable if the conductivity is subtracted. However, these types of subtractions are difficult as one essentially subtracts a huge conductivity contribution to extract a rather small feature in the spectra.…”

Response to “Comment on ‘Slow Debye-type peak observed in the dielectric response of polyalcohols' ” [J. Chem. Phys. 134, 037101 (2011)]

“…This, together with the agreement with complementary data by Yomogida et al 3 make us confident that the main conclusions of the original article 2 are right.…”

“…2) or by carefully subtracting the right conductivity contribution in the imaginary part. It should also be noted that not only the present reply and the previous articles 2, 3 on polyalcohols show that the statement 5 that the Debye-like relaxation only exists in monoalcohols is wrong. Recently, a slow Debye-like relaxation has also been observed in water-glycerol mixtures 6 and monosaccharides, 7 proving that this ultraslow process is The dashed line shows the α-relaxation, the dotted line the Debye-like process, and the solid line the resulting total fit using the conductivity obtained from (a), which is indicated by the dashed-dotted line.…”