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

摘要

Dielectric relaxation spectroscopy of glass forming liquids normally exhibits a relaxation scenariothat seems to be surprisingly general. However, the relaxation dynamics is more complicated forhydrogen bonded liquids. For instance, the dielectric response of monoalcohols is dominated by amysterious Debye-like process at lower frequencies than the structural a-relaxation that is normallydominating the spectra of glass formers. For polyalcohols this process has been thought to be absentor possibly obscured by a strong contribution from conductivity and polarization effects at lowfrequencies. We here show that the Debye-like process, although much less prominent, is alsopresent in the response of polyalcohols. It can be observed in the derivative of the real part of thesusceptibility or directly in the imaginary part if the conductivity contribution is reduced bycovering the upper electrode with a thin Teflon layer. We report on results from broadband dielectricspectroscopy studies of several polyalcohols: glycerol, xylitol, and sorbitol. The findings arediscussed in relation to other experimental observations of ultraslow (i.e., slower than the viscosityrelated a-relaxation) dynamics in glass formers.