We employ temperature
modulated DSC (TMDSC) to determine the dependence of the fictive temperature
on cooling rate for a series of polychlorinated biphenyls (PCB). From the
slopes of semi-logarithmic plots of cooling rate vs.
fictive temperature, the latter normalized by the fictive temperature for
an arbitrary cooling rate, we determine the enthalpic fragilities. Despite
significant differences in glass transition temperature and chemical structure
(specifically chlorine content), the PCB have the same fragility. The value
of the fragility determined using TMDSC is consistent with the fragility previously
determined using dielectric relaxation spectroscopy.
Data are presented for three glass formers, each having an excess wing in the low temperature dielectric loss spectra. Two
polychlorinated biphenyls, whose α relaxations have equivalent temperature dependences, exhibit excess wings that are clearly
different. Comparison of the spectra for glycerol at atmospheric pressure and at P=0.9 GPa reveals a different response of the α relaxation and the excess wing. These findings cannot be reconciled with the
notion that the excess wing is an inherent part of the α relaxation. Interpretation of the spectra as a superposition of distinct
α and β processes, however, is consistent with the observed behavior.