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

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Ngai, K. L. and Lunkenheimer, P. and León Yebra, Carlos and Schneider, U. and Brand, R. and Lodl, A. (2001) Nature and properties of the Johari-Goldstein β-relaxation in the equilibrium liquid state of a class of glass-formers. Journal of chemical physics, 115 (3). pp. 1405-1413. ISSN 0021-9606

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Official URL: http://dx.doi.org/10.1063/1.1381054


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Abstract

Previous dielectric relaxation measurements of glycerol and propylene carbonate and new results on propylene glycol performed below the conventional glass transition temperatures T_(g) after long periods of aging all show that the excess wing (a second power law at higher frequencies) in the isothermal dielectric loss spectrum, develops into a shoulder. These results suggest that the excess wing, a characteristic feature of a variety of glass-formers, is the high frequency flank of a Johari–Goldstein β-relaxation loss peak submerged under the α-relaxation loss peak. With this interpretation 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 α-relaxation modeled by the Fourier transform of a Kohlrausch–Williams–Watts function and a β-relaxation modeled by a Cole–Cole function. Good fits to the experimental data have been achieved. In addition to the newly resolved β-relaxation on propylene glycol, the important results of this work are the properties of the β-relaxation in this class of glass-formers in the equilibrium liquid state obtained over broad frequency and temperature ranges.


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© 2001 American Institute of Physics. This work was supported by the Deutsche Forschungsgemeinschaft, Grant No. LO264/8-1 and partly by the BMBF, contract No. 13N6917. The part of the work performed at the Naval Research Laboratory was supported by the Office of Naval Research.

Uncontrolled Keywords:Dielectric alpha-relaxation; Supercooled liquids; Forming liquids; Propylene carbonate; Secondary relaxations; Kohlrausch exponent; Coupling model; Transition; Dynamics; Spectroscopy.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
ID Code:31104
Deposited On:26 Jun 2015 07:30
Last Modified:10 Dec 2018 14:58

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