The -relaxation dynamics of a simple liquid

Gleim, Tobias; Kob, Walter

doi:10.1007/s100510050012

Cited by 48 publications

(52 citation statements)

References 9 publications

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“…7 we recognize that at T = 0.55 this condition is not fulfilled for large values of z and therefore it is not possible to check whether or not the factorization property holds. However, since these correlators are very similar to the one in the bulk, and it has been shown that for the bulk system the factorization property holds [72], we can assume that it does so also for the confined system at large z, if the temperature is sufficiently low. For small values of z it is instead possible to make a direct check on the validity of the factorization property by calculating the function R x (t).…”

Section: B Factorization Property Of Generalized Correlation Functionsmentioning

confidence: 89%

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

2004

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We present the results of molecular dynamics computer simulations of a binary Lennard-Jones liquid confined between two parallel rough walls. These walls are realized by frozen amorphous configurations of the same liquid and therefore the structural properties of the confined fluid are identical to the ones of the bulk system. Hence this setup allows us to study how the relaxation dynamics is affected by the pure effect of confinement, i.e. if structural changes are completely avoided. We find that the local relaxation dynamics is a strong function of z, the distance of the particles from the wall, and that close to the surface the typical relaxation times are orders of magnitude larger than the ones in the bulk. Because of the cooperative nature of the particle dynamics, the slow dynamics also affects the dynamics of the particles for large values of z. Using various empirical laws, we are able to parameterize accurately the z−dependence of the generalized incoherent intermediate scattering function Fs(q, z, t) and also the spatial dependence of structural relaxation times. These laws allow us to determine various dynamical length scales and we find that their temperature dependence is compatible with an Arrhenius law. Furthermore, we find that at low temperatures time and space dependent correlation function fulfill a generalized factorization property similar to the one predicted by mode-coupling theory for bulk systems. For thin films and/or at sufficiently low temperatures, we find that the relaxation dynamics is influenced by the two walls in a strongly non-linear way in that the slowing down is much stronger than the one expected from the presence of only one confining wall. Finally we study the average dynamics of all liquid particles and find that the data can be described very well by a superposition of two relaxation processes that have clearly separated time scales. Since this is in contrast with the result of our analysis of the local dynamics, we argue that a correct interpretation of experimental data can be rather difficult.

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Section: B Factorization Property Of Generalized Correlation Functionsmentioning

confidence: 89%

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

2004

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“…No intricate fit procedure is involved. This approach has therefore been pursued in reciprocal and in real space in several other studies [65][66][67] (see also [68,69] for comparable experimental tests). Figure 5 shows R x q (t) computed from the scattering functions at T = 0.46 with t = 0.610 and t = 86.43.…”

Section: Dynamics Of the Melt In The β-Relaxation Regime In Q-spacementioning

confidence: 99%

Glassy dynamics of simulated polymer melts: Coherent scattering and van Hove correlation functions

Aichele

Baschnagel

2001

The European Physical Journal E

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We report results of molecular-dynamics simulations of a model polymer melt consisting of short non-entangled chains in the supercooled state above the critical temperature Tc of mode-coupling theory (MCT). To analyse the dynamics of the system, we computed the incoherent, the collective chain and the collective melt intermediate scattering functions as well as their space Fourier transforms, the van Hove correlation functions. In this first part of the paper we focus on the dynamics in the β-relaxation regime. The final structural relaxation, the α-relaxation, will be studied in the following second part. The results can be summarized as follows: Without using any fit procedure we find evidence for the space-time factorization theorem of MCT in real and reciprocal space, and also for polymer-specific quantities, the Rouse modes. The critical amplitudes in real space are determined directly from the simulation data of the van Hove correlation functions. They allow to identify the typical length scales of the β-dynamics, and illustrate that it is a localized process. In a quantitative analysis the wave vector dependences of the β-coefficients, i.e., of the non-ergodicity parameter, the critical amplitude, and the next-to-leading order correction coefficients, are studied for all correlators. The β-coefficients show indications of polymerspecific effects on the length scale of the chain's radius of gyration. The agreement between simulation and the leading-order MCT description is found to be good in the central β-regime. Next-to-leading order corrections extend the validity of the MCT approximations to a greater time window and become more important at large wave vectors.

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“…It is e.g. theoretically understood [37] and verified in simulations [38], that systems with qualitatively different hydrodynamic behavior exhibit the same glassy dynamics. To obtain the qualitative behavior of equations (23,26,27), it is therefore sufficient to replace the mode coupling part of the memory function matrix by its leading wave-vector behavior multiplied with a function, which is able to describe glassy dynamics.…”

Section: The Static Correlation Function Ismentioning

confidence: 99%

“…The four parameters K l , K R , K lR and K SR have to be such that the memory matrix remains positive definite for all frequencies. For z = 0 the relation (38) follow and the diagonal elements K l ,K R and G S have to be positive. We also note that the exact relations (41) and (42).…”

Section: The Static Correlation Function Ismentioning

confidence: 99%

On the theory of light scattering in molecular liquids

Latz

Letz

2001

Eur. Phys. J. B

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The theory of light scattering for a system of linear molecules with anisotropic polarizabilities is considered. As a starting point for our theory, we express the result of a scattering experiment in VV and VH symmetry as dynamic correlation functions of tensorial densities $\rho_{lm}(q)$ with $l=0$ and $l=2$. $l$, $m$ denote indices of spherical harmonics. To account for all observed hydrodynamic singularities, a generalization of the theory of Schilling and Scheidsteger \cite{schilling97} for these correlation functions is presented, which is capable to describe the light scattering experiments from the liquid regime to the glassy state. As a microscopic theory it fulfills all sum rules contrary to previous {\em phenomenological} theories. We emphasize the importance of the helicity index $m$ for the microscopic theory by showing, that only the existence of $m=1$ components lead to the well known Rytov dip in liquids and to the appearance of transversal sound waves in VH symmetry in the deeply supercooled liquid and the glass. Exact expressions for the phenomenological frequency dependent rotation translation coupling coefficients of previous theories are derived.Comment: 30 pages including 15 figures, submitted to EPJ B, revised version a detailed discussion on the depolarization ratio is added and the discussion on the hydrodynamic analysis is enlarge

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The -relaxation dynamics of a simple liquid

Cited by 48 publications

References 9 publications

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

Glassy dynamics of simulated polymer melts: Coherent scattering and van Hove correlation functions

On the theory of light scattering in molecular liquids

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