Classification of secondary relaxation in glass-formers based on dynamic properties

被引:725
作者
Ngai, KL [1 ]
Paluch, M
机构
[1] USN, Res Lab, Washington, DC 20375 USA
[2] Univ Sci & Technol Lille, CNRS, UMR 8024, Lab Dynam & Struct Mat Mol, F-59655 Villeneuve Dascq, France
[3] George Mason Univ, Dept Chem, Fairfax, VA 22030 USA
[4] Silesian Univ, Inst Phys, PL-40007 Katowice, Poland
关键词
D O I
10.1063/1.1630295
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Dynamic properties, derived from dielectric relaxation spectra of glass-formers at variable temperature and pressure, are used to characterize and classify any resolved or unresolved secondary relaxation based on their different behaviors. The dynamic properties of the secondary relaxation used include: (1) the pressure and temperature dependences; (2) the separation between its relaxation time tau(beta) and the primary relaxation time tau(alpha) at any chosen tau(alpha); (3) whether tau(beta) is approximately equal to the independent (primitive) relaxation time tau(0) of the coupling model; (4) whether both tau(beta) and tau(0) have the same pressure and temperature dependences; (5) whether it is responsible for the "excess wing" of the primary relaxation observed in some glass-formers; (6) how the excess wing changes on aging, blending with another miscible glass-former, or increasing the molecular weight of the glass-former; (7) the change of temperature dependence of its dielectric strength Deltaepsilon(beta) and tau(beta) across the glass transition temperature T-g; (8) the changes of Deltaepsilon(beta) and tau(beta) with aging below T-g; (9) whether it arises in a glass-former composed of totally rigid molecules without any internal degree of freedom; (10) whether only a part of the molecule is involved; and (11) whether it tends to merge with the alpha-relaxation at temperatures above T-g. After the secondary relaxations in many glass-formers have been characterized and classified, we identify the class of secondary relaxations that bears a strong connection or correlation to the primary relaxation in all the dynamic properties. Secondary relaxations found in rigid molecular glass-formers belong to this class. The secondary relaxations in this class play the important role as a precursor or local step of the primary relaxation, and we propose that only they should be called the Johari-Goldstein beta-relaxation. (C) 2004 American Institute of Physics.
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页码:857 / 873
页数:17
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