scholarly journals Structural order as a genuine control parameter of dynamics in simple glass formers

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Hua Tong ◽  
Hajime Tanaka
Keyword(s):  
Glass Transition ◽  
Order Parameter ◽  
Liquid Structure ◽  
Coarse Grained ◽  
Glassy Dynamics ◽  
Slowing Down ◽  
Structural Order ◽  
Particle Level ◽  
Complex Structural ◽  
Unified Description

AbstractGlass transition is characterised by drastic dynamical slowing down upon cooling, accompanied by growing spatial heterogeneity. Its rationalisation by subtle changes in the liquid structure has been long debated but remains elusive, due to intrinsic difficulty in detecting the underlying complex structural ordering. Here we report that structural order parameter characterising local packing capability can well describe the glassy dynamics not only macroscopically but also microscopically, no matter whether it is driven by temperature or density. A Vogel-Fulcher-Tammann (VFT)-like relation is universally identified between the structural relaxation time and the order parameter for supercooled liquids with isotropic interactions. More importantly, we find such an intriguing VFT-like relation to be statistically valid even at a particle level, between spatially coarse-grained structural order and microscopic particle-level dynamics. Such a unified description of glassy dynamics based solely on structural order is expected to contribute to the ultimate understanding of the long-standing glass-transition problem.

All-atomistic molecular dynamics study of the glass transition of amorphous polymers

2021 ◽  
Author(s):  
Zhiye Tang ◽  
Susumu Okazaki
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Spatial Scale ◽  
Degrees Of Freedom ◽  
Main Chain ◽  
Polymer Materials ◽  
Coarse Grained ◽  
Mode Analysis ◽  
Radius Of Gyration ◽  
Chemical Structures

Glass transition is an important phenomenon of polymer materials and it has been intensively studied over the past a few decades. However, the influencing factors arising from the chemical structures of the polymers are often ignored due to a continuous or coarse-grained description of the polymer. Here, we approached this phenomenon using all-atomistic molecular dynamics (MD) simulations and two conventionally used polymer materials, polycarbonate (PC) and poly-(methyl methacrylate) (PMMA). We reproduced the glass transition temperatures (Tg) of the two materials reasonably well. Then we characterized and investigated the glass transition process by looking at the changes of potential energy, dihedral transition, and thermal fluctuation of the individual degrees of freedom in the systems, over the entire temperature range of glass transition. As previously reported, the dihedral angles stop their conformational changes gradually at the Tg, especially for the main chain dihedrals, and sidechain rotations immediately rooting from the main chain. The volumetric change during the temperature decrease is confirmed to be because of conformational adjustment, probably due to the tendency of chain stretching for the maintenance of the radius of gyration, and the loss of thermal energy. The strength of motions of single degrees of freedom and polymer chains, and overall slow motions obtained by normal mode analysis (NMA) shows that different motions at different spatial scale may gradually stop at distinct temperature in the MD simulation temporal and spatial scales. Presumably, the small spatial scale do not contribute to the glass transition at the experimental scale since the timescale is much longer than their relaxation time.

scholarly journals Coarse-graining for fast dynamics of order parameters in the phase-field model

2018 ◽  
Vol 376 (2113) ◽  
pp. 20170203 ◽  
Author(s):  
D. Jou ◽  
P. K. Galenko
Keyword(s):  
Master Equation ◽  
Thermodynamic Equilibrium ◽  
Phase Field ◽  
Order Parameter ◽  
Field Model ◽  
Local Thermodynamic Equilibrium ◽  
Phase Field Model ◽  
Coarse Graining ◽  
Order Parameters ◽  
Coarse Grained

In standard descriptions, the master equation can be obtained by coarse-graining with the application of the hypothesis of full local thermalization that is equivalent to the local thermodynamic equilibrium. By contrast, fast transformations proceed in the absence of local equilibrium and the master equation must be obtained with the absence of thermalization. In the present work, a non-Markovian master equation leading, in specific cases of relaxation to local thermodynamic equilibrium, to hyperbolic evolution equations for a binary alloy, is derived for a system with two order parameters. One of them is a conserved order parameter related to the atomistic composition, and the other one is a non-conserved order parameter, which is related to phase field. A microscopic basis for phenomenological phase-field models of fast phase transitions, when the transition is so fast that there is not sufficient time to achieve local thermalization between two successive elementary processes in the system, is provided. In a particular case, when the relaxation to local thermalization proceeds by the exponential law, the obtained coarse-grained equations are related to the hyperbolic phase-field model. The solution of the model equations is obtained to demonstrate non-equilibrium phenomenon of solute trapping which appears in rapid growth of dendritic crystals. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.

Revisiting Anomalous g-Factors for Charged Leptons in a Fractional Coarse-Grained Approach With Axiomatic Local Metric Derivatives

2020 ◽  
pp. 171-197
Author(s):  
José Weberszpil ◽  
José Abdalla Helayël-Neto
Keyword(s):  
Electromagnetic Field ◽  
Order Parameter ◽  
Mass Parameter ◽  
Type Equation ◽  
External Electromagnetic Field ◽  
Coarse Grained ◽  
Low Level ◽  
Relativistic Regime ◽  
Charged Leptons ◽  
The Right

This contribution sets out to extend the concept of helicity so as to include it in a fractional scenario with a low-level of fractionality. To accomplish this goal, the authors write down the left- and the right-handed Weyl equations from first principles in this extended framework. Next, by coupling the two different fractional Weyl sectors by means of a mass parameter, they arrive at the fractional version of Dirac's equation, which, whenever coupled to an external electromagnetic field and reduced to the non-relativistic regime, yields a fractional Pauli-type equation. From the latter, they are able to present an explicit expression for the gyromagnetic ratio of charged fermions in terms of the fractionality parameter. They then focus their efforts to relate the coarse-grained property of space-time to fractionality and to the (g-2) anomalies of the different leptonic species. To do this, they build up an axiomatic local metric derivative that exhibits the Mittag-Leffler function as eigenfunction and is valid for low-level fractionality, whenever the order parameter is close to 1.

A geometrical criterion for glass transition in soft-sphere fluids

Soft Matter ◽  
2018 ◽  
Vol 14 (34) ◽  
pp. 7075-7082 ◽  
Author(s):  
Yuxing Zhou ◽  
Scott T. Milner
Keyword(s):  
Glass Transition ◽  
Hard Spheres ◽  
Glassy Dynamics ◽  
Soft Sphere

Supercooled monodisperse WCA fluids have been simulated using the crystal-avoiding method. After mapping to hard spheres, we find that the “T1-activity” (a geometrical criterion for neighbor rearrangement) of particles is correlated with glassy dynamics.

Investigation of coarse-grained models across a glass transition

2020 ◽  
Vol 18 (2-3) ◽  
pp. 185-199 ◽  
Author(s):  
Ryan J. Szukalo ◽  
W. G. Noid
Keyword(s):  
Glass Transition ◽  
Coarse Grained
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