Microscopic Theory of Softness in Supercooled Liquids

Nandi, Manoj Kumar; Bhattacharyya, S. K.

doi:10.1103/physrevlett.126.208001

Cited by 22 publications

(15 citation statements)

References 48 publications

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“…Therefore, we deduce that the value of Δ r p /Δ r X relative to unity is directly related to the nonmonotonic behavior predicted for Δ r m,c , β F el,p , and τ α,p /τ 0 as a function of βε mp . As an important reminder, recall that Δ r X is a structural quantity while Δ r p is a dynamical property, so the above results further reinforce the core thesis of the ECNLE , and SCCH , theories that structure determines dynamics, consistent with recent experimental, − machine learning, and simulation − studies.…”

Section: Penetrant Relaxation In the Deeply Supercooled Glassy Regimesupporting

confidence: 77%

Theory of the Effects of Specific Attractions and Chain Connectivity on the Activated Dynamics and Selective Transport of Penetrants in Polymer Melts

Mei

Schweizer

2022

Macromolecules

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We generalize and apply a microscopic force level statistical mechanical theory of activated spherical penetrant dynamics in glass-forming liquids to study the influence of semiflexible polymer connectivity and penetrant–polymer attractive interactions on the penetrant hopping rate. The detailed manner that attractions of highly variable strength and spatial range modify the penetrant size and polymer melt density (from the rubbery state to slightly beyond the kinetic glass transition) dependences of penetrant activation barriers is established. Of special interest are possible nonadditive consequences of physical bonding and steric caging, the degree of coupling of penetrant hopping and the Kuhn segment scale alpha relaxation process, the relative importance of local caging and long-range matrix collective elasticity as a function of penetrant size, and implications for optimizing transport selectivity. With increasing attraction strength, the repulsive caging-restriction effect on penetrant mobility is predicted to grow, in contrast to the effect of the equilibrium penetrant–matrix solvation shell size, which decreases. The former dynamical effect results in a significant enhancement of the importance of the local cage barrier, while the latter effect results in a decrease of the importance of the nonlocal collective elastic barrier. These two competing effects have a very strong influence on selective penetrant transport for different sized penetrants: selectivity varies nonmonotonically with attraction strength in the deeply supercooled state but decreases monotonically in the rubbery state and at fixed attraction strength, exhibits a nonmonotonic variation with the matrix packing fraction. By comparing results based on modeling the matrix as semiflexible polymer chains with analogous calculations using the same dynamical theory but for a disconnected hard sphere matrix, the effect of chain connectivity is revealed and found to have quantitative, but not qualitative, consequences on penetrant-activated dynamics.

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Section: Penetrant Relaxation In the Deeply Supercooled Glassy Regimesupporting

confidence: 77%

Theory of the Effects of Specific Attractions and Chain Connectivity on the Activated Dynamics and Selective Transport of Penetrants in Polymer Melts

Mei

Schweizer

2022

Macromolecules

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“…However, it is unclear how their differences in the integrals of pair correlation functions result in different dynamics. While recent theories and experiments and/or simulations point to the importance of structural causes in glass formation − and even crystallization, , the connection between structure and dynamics remains unclear.…”

mentioning

confidence: 99%

Local-Average Free Volume Correlates with Dynamics in Glass Formers

Mei

Zhuang

et al. 2022

J. Phys. Chem. Lett.

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Glass formers exhibit a pronounced slowdown in dynamics, accompanied by progressive heterogeneity as they approach the glass transition. There is intense debate over whether the dramatic slowdown is caused by dynamical heterogeneity and whether the enhanced dynamical heterogeneity originates from structural causes. However, the connection between dynamical heterogeneity and the spatial distribution of the single-particle free volume (a purely static structural quantity) was found to be rather weak, which raises the question of whether dynamic heterogeneity has a purely structural origin. Here, by introducing the concept of local-average free volume, we present numerical evidence that long-time dynamic heterogeneity shows significantly enhanced correlation with the average local free volume over a length scale of a few neighboring shells. Our results resolve the long-standing controversy about whether free volume plays an important role in particle rearrangements associated with the activated hopping relaxation. The concept of “local average” can be applied to other local structural descriptors to better correlate with dynamic heterogeneity in glass-forming liquids.

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“…Dynamic heterogeneity has also been discussed in connection with theories for physical aging [24,26,41,66,83,90]. A simple way to understand how spatial heterogeneity may influence the dynamics is via elastic models of glass-forming liquids [91][92][93]: because a liquid is disordered, there must be regions of varying softness [94,95], leading to different barriers for molecular rearrangements [83,96] and thus spatially varying levels of activity in the form of molecular motion.…”

Section: Role Of Dynamic Heterogeneitiesmentioning

confidence: 99%

Distance-as-time in physical aging

Douglass¹,

Dyre²

2022

Preprint

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Although it has been known for half a century that the physical aging of glasses is described by a linear thermal-history convolution integral over the so-called material time, the microscopic interpretation of the material time remains a mystery. We propose that the material time increase over a given time interval reflects the distance traveled by the system's particles. Different possible distance measures are discussed, starting from the standard mean-square displacement. The viewpoint adopted implies a "geometric reversibility" and a "unique-triangle property" characterizing the system's path in configuration space during aging, both of which properties are inherited from equilibrium and confirmed by computer simulations of an aging binary Lennard-Jones system. The simulations show that the slow particles control the material time. This motivates a dynamicrigidity-percolation picture of physical aging; specifically the material time is proposed to be a function of the slowest quartile particles' inherent square displacement. This collapses well numerical data for the potential energy during aging in the sense that the normalized relaxation function following any temperature jump is almost the same function of this material time. The standard Tool-Narayanaswamy equation for physical aging is arrived at by assuming that when time is replaced by distance, an aging system is described by the same expression as that of linear-response theory.

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Microscopic Theory of Softness in Supercooled Liquids

Cited by 22 publications

References 48 publications

Theory of the Effects of Specific Attractions and Chain Connectivity on the Activated Dynamics and Selective Transport of Penetrants in Polymer Melts

Theory of the Effects of Specific Attractions and Chain Connectivity on the Activated Dynamics and Selective Transport of Penetrants in Polymer Melts

Local-Average Free Volume Correlates with Dynamics in Glass Formers

Distance-as-time in physical aging

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