Nature and properties of the Johari-Goldstein beta-relaxation in the equilibrium liquid state of a class of glass-formers

Previous dielectric relaxation measurements of glycerol and propylene carbo nate and new results on propylene glycol performed below the conventional g lass transition temperatures T-g after long periods of aging all show that the excess wing (a second power law at higher frequencies) in the isotherma l dielectric loss spectrum, develops into a shoulder. These results suggest that the excess wing, a characteristic feature of a variety of glass-forme rs, is the high frequency flank of a Johari-Goldstein beta -relaxation loss peak submerged under the alpha -relaxation loss peak. With this interpreta tion of the excess wing assured, the dielectric spectra of all three glass- formers measured at temperatures above T-g are analyzed as a sum of a alpha -relaxation modeled by the Fourier transform of a Kohlrausch-Williams-Watt s function and a beta -relaxation modeled by a Cole-Cole function. Good fit s to the experimental data have been achieved. In addition to the newly res olved beta -relaxation on propylene glycol, the important results of this w ork are the properties of the beta -relaxation in this class of glass-forme rs in the equilibrium liquid state obtained over broad frequency and temper ature ranges. (C) 2001 American Institute of Physics.