Thermodynamic scaling of α-relaxation time and viscosity stems from the Johari-Goldstein β-relaxation or the primitive relaxation of the coupling model

2012 ◽  
Vol 137 (3) ◽  
pp. 034511 ◽  
Author(s):  
K. L. Ngai ◽  
J. Habasaki ◽  
D. Prevosto ◽  
S. Capaccioli ◽  
Marian Paluch
Keyword(s):  
Relaxation Time ◽  
Coupling Model ◽  
Β Relaxation

scholarly journals Why is the change of the Johari–Goldstein β-relaxation time by densification in ultrastable glass minor?

2018 ◽  
Vol 20 (43) ◽  
pp. 27342-27349 ◽  
Author(s):  
K. L. Ngai ◽  
Marian Paluch ◽  
Cristian Rodríguez-Tinoco
Keyword(s):  
Relaxation Time ◽  
Coupling Model ◽  
Theoretical Explanation ◽  
Model Based ◽  
Β Relaxation

Coupling-Model-based theoretical explanation of the minor change of JG β-relaxation achieved by ultrastability in contrast to the dramatic change in α-relaxation.

Mechanical Relaxation Studies of Sub-Rouse Modes in Amorphous Polymers

2012 ◽  
Vol 184 ◽  
pp. 52-59 ◽  
Author(s):  
Xue Bang Wu ◽  
Hua Guang Wang ◽  
Chang Song Liu ◽  
Zhen Gang Zhu
Keyword(s):  
Relaxation Time ◽  
Coupling Model ◽  
Amorphous Polymers ◽  
Large Temperature ◽  
Mechanical Relaxation ◽  
Segmental Motion ◽  
Mechanical Spectroscopy ◽  
Segmental Dynamics ◽  
Frequency Scale ◽  
Segmental Relaxation

Mechanical spectroscopy is a powerful tool for the investigation of molecular dynamics of amorphous polymers over a large temperature range and frequency scale. In this work, by using high precision shear mechanical spectroscopy tool, we have investigated the segmental dynamics from local segmental relaxation to sub-Rouse modes in a series of amorphous polymers. We have demonstrated the existence of sub-Rouse modes slower than the local segmental motion in amorphous polymers. The sub-Rouse modes exhibit a similar change of dynamics at the same temperature TB ~1.2 Tg, as the local segmental relaxation through the temperature dependence of relaxation time and relaxation strength. Furthermore, the crossover relaxation time of the sub-Rouse modes at TB is almost the same for all the polymers investigated, i.e. τα'(TB) = 10-1±0.5 s, which is independent of molecular weight and molecular structure. This remarkable finding indicates that solely the time scale of the relaxation determines the change in dynamics of the sub-Rouse modes. According to the coupling model, the crossover is suggested to be caused by the onset of strong intermolecular cooperativity below TB. Hence the results suggest that the sub-Rouse modes and their properties are generally found in amorphous polymers by mechanical spectroscopy, and reveal the cooperative nature of the sub-Rouse modes.

Fast Dynamics in Glass-Formers: Relation to Fragility and the Kohlrausch Exponent

1996 ◽  
Vol 455 ◽  
Author(s):  
K. L. Ngai ◽  
C. M. Roland
Keyword(s):  
Relaxation Time ◽  
Low Temperature ◽  
Specific Heat ◽  
Raman Spectra ◽  
Low Temperatures ◽  
Coupling Model ◽  
Boson Peak ◽  
Specific Heat Data ◽  
Low Temperature Specific Heat ◽  
Heat Data

ABSTRACTFrom the Raman spectra and related inferences from low temperature specific heat data, Sokolov and coworkers have established that the ratio of the quasielastic and vibrational contributions at low temperatures (5∼10K) up to Tg correlates well with the degree of fragility and β of the glass-former. As pointed out by Sokolov (see his contribution in this Volume) such a correlation between the fast dynamics and structural a-relaxation at Tg(i.e., m and β) is intriguing, since at and below Tg, the α-relaxation time τα is more than twelve orders of magnitude longer than the quasielastic contribution and the boson peak. We show in this paper how the Coupling Model (CM) may provide an explanation for this correlation.

Predicting the α-relaxation time of glycerol confined in 1.16 nm pores of zeolitic imidazolate frameworks

2020 ◽  
Vol 22 (2) ◽  
pp. 507-511 ◽  
Author(s):  
K. L. Ngai ◽  
P. Lunkenheimer ◽  
A. Loidl
Keyword(s):  
Relaxation Time ◽  
Relaxation Times ◽  
Coupling Model ◽  
Chem Phys ◽  
Zeolitic Imidazolate Frameworks

Relaxation times of glycerol confined in 1.16 nm ZIF pores found by Uhl et al. [J. Chem. Phys., 2019, 150, 024504] are explained quantitatively by the Coupling Model.

Sign in / Sign up

Export Citation Format

Share Document