The nonequilibrium dynamics of a binary Lennard-Jones mixture in a simple shear flow is investigated by means of molecular dynamics simulations. The range of temperature T investigated covers both the liquid, supercooled, and glassy states, while the shear rate γ covers both the linear and nonlinear regimes of rheology. The results can be interpreted in the context of a nonequilibrium, schematic mode-coupling theory developed recently, which makes the theory applicable to a wide range of soft glassy materials. The behavior of the viscosity is first investigated. In the nonlinear regime, strong shear-thinning is obtained, with in the supercooled regime. Scaling properties of the intermediate scattering functions are studied. Standard “mode-coupling properties” of factorization and time superposition hold in this nonequilibrium situation. The fluctuation-dissipation relation is violated in the shear flow in a way very similar to that predicted theoretically, allowing for the definition of an effective temperature for the slow modes of the fluid. Temperature and shear rate dependencies of are studied using density fluctuations as an observable. The observable dependence of is also investigated. Many different observables are found to lead to the same value of suggesting several experimental procedures to access It is proposed that a tracer particle of large mass may play the role of an “effective thermometer.” When the Einstein frequency of the tracers becomes smaller than the inverse relaxation time of the fluid, a nonequilibrium equipartition theorem holds with where is the velocity in the direction transverse to the flow. This last result gives strong support to the thermodynamic interpretation of and makes it experimentally accessible in a very direct way.
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8 April 2002
Research Article|
April 08 2002
Nonequilibrium dynamics and fluctuation-dissipation relation in a sheared fluid
Ludovic Berthier;
Ludovic Berthier
CECAM, ENS-Lyon, 46, Allée d’Italie, 69007 Lyon, France
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Jean-Louis Barrat
Jean-Louis Barrat
Département de Physique des Matériaux, UCB Lyon 1 and CNRS, 69622 Villeurbanne, France
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J. Chem. Phys. 116, 6228–6242 (2002)
Article history
Received:
October 11 2001
Accepted:
January 22 2002
Citation
Ludovic Berthier, Jean-Louis Barrat; Nonequilibrium dynamics and fluctuation-dissipation relation in a sheared fluid. J. Chem. Phys. 8 April 2002; 116 (14): 6228–6242. https://doi.org/10.1063/1.1460862
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