M. Tyagi, S. Murthy
Feb 16, 2001
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Influential Citations
38
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Journal
Journal of Chemical Physics
Abstract
Cycloheptanol, cyclo-octanol, cyanoadamantane and cis-1,2-dimethylcyclohexane are known to form plastic crystals which can be supercooled to show a glass transition at a temperature Tg. The molecular dynamics in different plastic phases is studied in their supercooled states using dielectric spectroscopy (frequency range: 106 Hz–10−3 Hz) and differential scanning calorimetry (DSC) over a wide temperature range. The kinetic freezing of the various dielectric processes have been critically examined in relation to the Tg found in the DSC experiments. The plastic phase I of cyclo-octanol shows two Tg’s: one at 148.5 K and the other at 164 K, the former of which is not found in well annealed phase I. The dielectric α-modes correspond to the latter. Cycloheptanol exhibits many Tg’s for the different plastic phases. Unlike the cyclic alcohols, the dielectric spectra of cyanoadamantane and cis-1,2-dimethylcyclohexane is clearly found to follow the Havriliak–Negami equation, both of which interestingly show very l...