Nearly constant dielectric loss of polyhydric alcohols

Complex permittivity measurements have been performed on a series of polyhydric alcohols (glycerol, threitol, xylitol and sorbitol) and mixtures of glycerol–xylitol and xylitol–sorbitol in the frequency range between 100 Hz and 1 MHz at temperatures from 293 K down to 50 K. It was found that all the systems including the mixtures show the nearly constant dielectric loss (NCL) at temperatures far below the glass transition temperature. The parameters describing the NCL depend on the number of carbons in the molecules. This relation can also be applied for the mixture with the mean values for the number of carbons. The parameters describing the behavior of the α process, such as the fragility index, depend the number of carbons in this series of polyhydric alcohols. Degree of freedom in the intermolecular interactions connected with the fragility index can be considered to relate to the NCL. This is consistent with the caged dynamics as a possible microscopic origin for the NCL. Although the fast β process is not denied by the NCL, coexistence of these processes being able to explain the dielectric loss minima, should be examined experimentally in future.