Rotational dynamics of simple asymmetric molecules

Fragiadakis, D.; Roland, C. M.

doi:10.1103/physreve.91.022310

Cited by 12 publications

(9 citation statements)

References 38 publications

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“…It is apparent in figure 5 that the Debye model is a very good approximation for the non-associated system at room temperature. Upon cooling the system, only one primary relaxation process is detected, similarly to the results obtained for slighlty asymmetric Lennard-Jones molecules [20]. The Debye model is less satisfactory at low temperatures, and the Davidson-Cole approach, shown in figure 6, produces better results.…”

Section: Dynamic Dielectric Propertiessupporting

confidence: 60%

“…On the other hand, the influence of temperature on the dielectric properties of the non-associated liquid at very low temperatures will also be studied. It has been previously obtained that systems composed by Lennard-Jones rigid asymmetric diatomic molecules exhibit both structural and secondary relaxation processes in rotation below an onset temperature [19,20]. We intend to check on the dielectric relaxation behaviour of a system made up by sligthly asymmetric diatomic molecules, with an added constant dipole moment.…”

Section: Introductionmentioning

confidence: 99%

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Influence of hydrogen bonds and temperature on dielectric properties

Urbina

Sesé

2016

Phys. Rev. E

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Dielectric properties have been evaluated by means of Molecular Dynamics simulations on two model systems made up by dipolar molecules. One of them mimics methanol, whereas the other differs from the former only in the ability of forming hydrogen bonds. Static dielectric properties such as permittivity and the Kirkwood factor have been evaluated, and results have been analyzed by considering the distribution of relative orientations between molecular dipoles. Dipole moment time correlation functions have also been evaluated. The relevance of contributions associated to autocorrelations of molecular dipoles and to cross-correlations between dipoles belonging to different molecules has been investigated. For methanol, the Debye approximation for the overall dipole moment correlation function is not valid at room temperature. The model applies when hydrogen bonds are suppressed, but it fails upon cooling the non-associated liquid. Important differences between relaxation times associated with dipole auto and cross-correlations as well as their relative relevance are at the root of the Debye model breakdown. *

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Section: Dynamic Dielectric Propertiessupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Influence of hydrogen bonds and temperature on dielectric properties

Urbina

Sesé

2016

Phys. Rev. E

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“…This was done in the same way as in the 3D systems in refs. [31,32,33,34]; to wit, the energy parameters are those of the KA liquid, i.e., = = = 1.0, = = = 1.0, and = = = = 1.5. To set , we use the original KA parameters for the larger A and C particles, while the smaller B and D particles have a size 62.5% that of A and C, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Model systems most often used to study glassy dynamics are mixtures of spherical particles, which do not show a JG relaxation, at least up to the timescales accessible by molecular dynamics simulations. Instead, we simulate a rigid, asymmetric dumbbell-shaped molecule, the simplest shape that captures the characteristics observed experimentally for the JG process [31,32,33,34]. The simulations were done for a two dimensional molecule, so that clustering can be more clearly depicted.…”

Section: Introductionmentioning

confidence: 99%

Role of structure in theαandβdynamics of a simple glass-forming liquid

Fragiadakis

Roland

2017

Phys. Rev. E

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The elusive connection between dynamics and local structure in supercooled liquids is an important piece of the puzzle in the unsolved problem of the glass transition. The Johari-Goldstein β relaxation, ubiquitous in glass-forming liquids, exhibits mean properties that are strongly correlated to the long-time α dynamics. However, the former comprises simpler, more localized motion, and thus has perhaps a more straightforward connection to structure. Molecular dynamics simulations were carried out on a two-dimensional, rigid diatomic molecule (the simplest structure exhibiting a distinct β process) to assess the role of the local liquid structure on both the Johari-Goldstein  and the  relaxation. Although the average properties for these two relaxations are correlated, there is no connection between the  and  properties of a given (single) molecule. The propensity for motion at long times is independent of the rate or strength of a molecule's β relaxation. The mobility of a molecule averaged over many initial energies, a measure of the influence of structure, was found to be heterogeneous, with clustering at both the  and  timescales. This heterogeneity is less extended spatially for the  than for the  dynamics, as expected; however, the local structure is the more dominant control parameter for the  process. In the glassy state, the arrangement of neighboring molecules determines entirely the relaxation properties, with no discernible effect from the particle momenta.

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“…However, many experimental results have shown that some β-relaxation processes are closely related to the structural relaxation process. Very recent molecular dynamics simulation results for asymmetric diatomic molecular glass formers demonstrate that the α-relaxation process has a close relationship with a secondary relaxation process known as the Johari-Goldstein β-relaxation (J-G) process [4][5][6][7]. This type of secondary relaxation process is generally considered to be universal in nature as it appears in a variety of glass formers such as supercooled liquids, metallic glasses, polymeric glasses and plastic crystals.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of the secondary relaxation process in soft colloidal suspensions

Saha¹,

Joshi²,

Bandyopadhyay³

2015

EPL

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A universal secondary relaxation process, known as the Johari-Goldstein (JG) β-relaxation process, appears in glass formers. It involves all parts of the molecule and is particularly important in glassy systems because of its very close relationship with the α-relaxation process. However, the absence of a J-G β-relaxation mode in colloidal glasses raises questions regarding its universality. In the present work, we study the microscopic relaxation processes in Laponite suspensions, a model soft glassy material, by dynamic light scattering (DLS) experiments. α and β-relaxation timescales are estimated from the autocorrelation functions obtained by DLS measurements for Laponite suspensions with different concentrations, salt concentrations and temperatures. Our experimental results suggest that the β-relaxation process in Laponite suspensions involves all parts of the constituent Laponite particle. The ergodicity breaking time is also seen to be correlated with the characteristic time of the β-relaxation process for all Laponite concentrations, salt concentrations and temperatures. The width of the primary relaxation process is observed to be correlated with the secondary relaxation time. The secondary relaxation time is also very sensitive to the concentration of Laponite. We measure primitive relaxation timescales from the α-relaxation time and the stretching exponent (β) by applying the coupling model for highly correlated systems. The order of magnitude of the primitive relaxation time is very close to the secondary relaxation time. These observations indicate the presence of a J-G β-relaxation mode for soft colloidal suspensions of Laponite.

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Rotational dynamics of simple asymmetric molecules

Cited by 12 publications

References 38 publications

Influence of hydrogen bonds and temperature on dielectric properties

Influence of hydrogen bonds and temperature on dielectric properties

Role of structure in theαandβdynamics of a simple glass-forming liquid

Characteristics of the secondary relaxation process in soft colloidal suspensions

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