Connection between fragility, mean-squared displacement, and shear modulus in two van der Waals bonded glass-forming liquids

Hansen, Henning Otte; Frick, B.; Hecksher, Tina; Dyre, Jeppe C.; Niss, Kristine

doi:10.1103/physrevb.95.104202

Cited by 21 publications

(12 citation statements)

References 50 publications

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“…For the two van der Waals liquids, the fragility at ambient pressure is m ≈ 80 for PPE 39 and m ≈ 70 for cumene 15 , 40 . The hydrogen-bonding liquid DPG has fragility m ≈ 65 41 , 42 .…”

Section: Methodsmentioning

confidence: 99%

Evidence of a one-dimensional thermodynamic phase diagram for simple glass-formers

et al. 2018

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Glass formers show motional processes over an extremely broad range of timescales, covering more than ten orders of magnitude, meaning that a full understanding of the glass transition needs to comprise this tremendous range in timescales. Here we report simultaneous dielectric and neutron spectroscopy investigations of three glass-forming liquids, probing in a single experiment the full range of dynamics. For two van der Waals liquids, we locate in the pressure–temperature phase diagram lines of identical dynamics of the molecules on both second and picosecond timescales. This confirms predictions of the isomorph theory and effectively reduces the phase diagram from two to one dimension. The implication is that dynamics on widely different timescales are governed by the same underlying mechanisms.

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Section: Methodsmentioning

confidence: 99%

Evidence of a one-dimensional thermodynamic phase diagram for simple glass-formers

et al. 2018

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“…The shoving model was developed for glasses [84], and it is not yet clear whether the model is suitable to describe the viscosity of lubricant-sized molecules in the liquid phase. Some aspects of the model have been experimentally validated for some lubricant-like molecules, such as 5-phenyl-4-ether (5P4E) [85]. While this synthetic polyether has been used as a model lubricant [86], it has a much lower glass transition temperature than conventional lubricants [87].…”

Section: High-pressure Newtonian Viscositymentioning

confidence: 99%

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

2021

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The prediction of friction under elastohydrodynamic lubrication (EHL) conditions remains one of the most important and controversial areas of tribology. This is mostly because the pressure and shear rate conditions inside EHL contacts are particularly severe, which complicates experimental design. Over the last decade, molecular dynamics (MD) simulation has played an increasingly significant role in our fundamental understanding of molecular behaviour under EHL conditions. In recent years, MD simulation has shown quantitative agreement with friction and viscosity results obtained experimentally, meaning that they can, either in isolation or through the use of multiscale coupling methods, begin to be used to test and inform macroscale models for EHL problems. This is particularly useful under conditions that are relevant inside machine components, but are difficult to obtain experimentally without uncontrollable shear heating.

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“…Note that the shear modulus entering eq. ( 8) is the one for short wavelengths, much less temperature-dependent than the one of macroscopic measurements, which is strongly influenced by fast relaxations [25]. Otherwise one could never explain the weak temperature dependence of β [9,21].…”

mentioning

confidence: 93%

Theory of the highly viscous flow

Buchenau¹

2020

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In an undercooled liquid close to the glass transition [1][2][3], the flow begins by many thermally activated back-and-forth jumps, structural Eshelby [4] rearrangements of strained regions. Together, they lead at short times t to the Kohlrausch t β shear relaxation, with β around 1/2, before the jumps become irreversible and the viscous flow begins. The Kohlrausch behavior is not yet well understood. Here, a theoretical explanation is given, starting from an exact result for the irreversible jumps [5], the lifetime distribution of the critical Eshelby region. A new close-packing picture is proposed for the numerically found [6] string motion in soft vibrations and low-barrier relaxations in glasses. It enables a quantitative understanding of the Kohlrausch behavior. A continuity relation between the irreversible and the reversible Kohlrausch relaxation time distribution is derived. The full spectrum can be used in many ways, not only to describe shear relaxation data, but also to relate shear relaxation data to dielectric and bulk relaxation spectra, and to predict aging from shear relaxation data, as demonstrated for a very recent aging experiment [7].

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Connection between fragility, mean-squared displacement, and shear modulus in two van der Waals bonded glass-forming liquids

Cited by 21 publications

References 50 publications

Evidence of a one-dimensional thermodynamic phase diagram for simple glass-formers

Evidence of a one-dimensional thermodynamic phase diagram for simple glass-formers

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

Theory of the highly viscous flow

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