Dynamical Heterogeneities in a Supercooled Lennard-Jones Liquid

Kob, Walter; Donati, Claudio; Plimpton, Steven J.; Poole, Peter H.; Glotzer, Sharon C.

doi:10.1103/physrevlett.79.2827

Cited by 940 publications

(1,011 citation statements)

References 24 publications

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“…We plot P * (V f ) and P * (V s ), the histograms of normalized Voronoi volumes for the 10% fastest and slowest subsets at the cagerearrangement time scale τ* ) 400 s, for a sample with φ ) 0.54 ( Figure 6a); at this time scale, the distribution of displacements is highly heterogeneous. 19,25,26 Although V f > V s , P * (V f ) and P * (V s ) are nearly identical; however, P * (V f ) is shifted almost imperceptibly to higher volumes. The histograms of small-and large-displacement Voronoi volumes for the denser supercooled fluid at φ ) 0.58 plotted at τ* ) 2000 s are also nearly identical (Figure 6b).…”

Section: Resultsmentioning

confidence: 94%

Weak Correlations between Local Density and Dynamics near the Glass Transition

2005

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We perform experiments on two different dense colloidal suspensions with confocal microscopy to probe the relationship between local structure and dynamics near the glass transition. We calculate the Voronoi volume for our particles and show that this quantity is not a universal probe of glassy structure for all colloidal suspensions. We correlate the Voronoi volume to displacement and find that these quantities are only weakly correlated. We observe qualitatively similar results in a simulation of a polymer melt. These results suggest that the Voronoi volume does not predict dynamical behavior in experimental colloidal suspensions; a purely structural approach based on local single particle volume likely cannot describe the colloidal glass transition.

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Section: Resultsmentioning

confidence: 94%

Weak Correlations between Local Density and Dynamics near the Glass Transition

2005

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“…Associations of the temporal scale t * at which the NGP peaks with the time scale for collective motion responsible for the ␣-relaxation process have already been noticed in different glass-forming systems. Studies in supercooled liquids 13,19,22 demonstrated the relation of t * with the lifetime of the dynamic heterogeneities and the cooperative motion necessary for the release of the particles from their cage, which characterizes the early stages of ␣-relaxation. In linear polymer models it was shown 6,9 that NGP peaks in the late-␤/early-␣ regime, while t * was found to follow a similar temperature dependence with that of the ␣-relaxation ͑see Ref.…”

Section: -3mentioning

confidence: 99%

“…At longer length scales and/or later times near the late-␤/early-␣ dynamic range, the so-called "decaging" ͑i.e., escape from the cage͒ process takes place. In this regime, a common feature detected in liquids, 7,13 colloids, 14,15 and polymers 16,17 is the existence of mobility contrast among the glass-forming units. The observed dynamic heterogeneity is characterized by a non-Gaussian distribution in the particle/ monomer displacements r͑t͒ at the relevant spatial and temporal scales, which can be quantified by means of the nonGaussian parameter ͑NGP͒, 18 ␣ 2 ͑t͒ = 3 5 ͓͗r͑t͒ − r͑0͔͒ 4 ͘/͓͗r͑t͒ − r͑0͔͒ 2 ͘ 2 − 1.…”

Section: Introductionmentioning

confidence: 99%

Local polymer dynamics under strong connectivity constraints: The dendrimer case

Karatasos

Lyulin

2006

The Journal of Chemical Physics

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The characteristics of local motion are explored by molecular dynamics simulations in a series of AB 2 -type dendrimer melts. Systems of generations 3-5 were simulated in a wide temperature range, allowing the assessment of effects associated with molecular size, proximity to the detected glasslike transitions, and the strong connectivity constraints imposed by the dendritic topology. Investigation of the mechanisms involved in local motion at short temporal and spatial scales revealed the connection between the non-Gaussian nature of monomer displacements to ␣-relaxation and the caging/decaging process under different degrees of confinement. In the latter mechanism, two characteristic localization lengths were identified: at the low temperature limit spatial localization was realized within approximately 10% of the nearest neighbor distance while at temperatures higher than the glass transition, the existence of an analogous length scale is ascribed to the geometric constraints due to the dense connectivity pattern. As the results from this study are discussed in comparison to the behavior observed in linear polymers and supercooled liquids, new insight is provided on the universal/specific mechanisms involved in local dynamics of different glass-forming systems.

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“…Previous work has revealed the existence of dynamical heterogeneities, associated with the cooperative motion of the particles, as a precursor to the glass transition as well as in the glassy state 22,23,25,29 . Instead of the average global quantities studied above, the existence of dynamical heterogeneities requires a microscopic insight into the structure of the glassy state.…”

Section: Local Fluctuations Of Autocorrelations and Responsesmentioning

confidence: 99%

Dynamic particle tracking reveals the ageing temperature of a colloidal glass

Wang

Makse

2006

Nature Phys

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T he glass transition 1 is considered to be one of the most fundamental problems in statistical physics. Despite decades of effort, a general consensus on the validity of a universal theory for the large variety of glass systems is lacking 2,3 -partly because of difficulties encountered in the experimental testing of the theoretical predictions 4,5 . Here, we present experiments on a colloidal glass made of micrometresized particles in a fluid. We investigate the autocorrelation and response function to monitor the ageing of a colloidal glass. At equilibrium, all the observables are stationary, whereas in the out-of-equilibrium glassy state they have an explicit dependence on the age of the system. We find that the transport coefficients scale with the ageing time as a power law, a signature of the slow relaxation. Nevertheless, our analysis reveals that the glassy system has thermalized at a constant temperature independent of the age and warmer than the bath, reflecting the structural rearrangements of cage dynamics. Furthermore, we find a universal scaling law to describe the global and local fluctuations of the observables.Increasing the volume fraction of a colloidal system slows down the brownian dynamics of its constitutive particles, implying a limiting density, φ g , above which the system can no longer be equilibrated with its bath 1 . Hence, the thermal system falls out of equilibrium on the timescale of the experiment and thus undergoes a glass transition 2 . Even above φ g the particles continue to relax, but the nature of the relaxation is very different to that in equilibrium. This phenomenon of a structural slow evolution beyond the glassy state is known as 'ageing' 3 . The system is no longer stationary and the relaxation time is found to increase with the age of the system, t w , as measured from the time of sample preparation.This picture applies not only to structural glasses such as colloids, silica and polymer melts, but also to spin glasses, ferromagnetic coarsening, elastic manifolds in quenched disorder and jammed matter such as grains and emulsions 2,4,5 . Theories originally developed in the field of spin glasses 6 attempt to develop a common framework for the understanding of ageing. For example, the structural glass and spin-glass transitions have been coupled by the low-temperature extension of the modecoupling theory 4,5,7 . More generally, this approach is related to analogous ideas developed in the field of granular matter such as compactivity [8][9][10][11] , and the inherent structure formalisms 12 , adapted to the energy landscape of glasses 13 .One of the important features of this scenario is a separation of timescales where the observables are equilibrated at different temperatures, even though the system is far from equilibrium. Although theoretical results have flourished, the difficulties in the experimental testing of the fundamental predictions of the theories have hampered the development of an understanding of ageing in glasses [14][15][16][17][18] . Experiments so f...

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Dynamical Heterogeneities in a Supercooled Lennard-Jones Liquid

Cited by 940 publications

References 24 publications

Weak Correlations between Local Density and Dynamics near the Glass Transition

Weak Correlations between Local Density and Dynamics near the Glass Transition

Local polymer dynamics under strong connectivity constraints: The dendrimer case

Dynamic particle tracking reveals the ageing temperature of a colloidal glass

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