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Abstract: A relation between equilibrium, steady-state, and waiting-time dependentdynamical two-time correlation functions in dense glass-forming liquids subjectto homogeneous steady shear flow is discussed. The systems under study showpronounced shear thinning, i.e., a significant speedup in their steady-stateslow relaxation as compared to equilibrium. An approximate relation thatrecovers the exact limit for small waiting times is derived following theintegration through transients ITT approach for the nonequilibriumSmoluchowski dynamics, and is exemplified within a schematic model in theframework of the mode-coupling theory of the glass transition MCT. Computersimulation results for the tagged-particle density correlation functionscorresponding to wave vectors in the shear-gradient directions from bothevent-driven stochastic dynamics of a two-dimensional hard-disk system and frompreviously published Newtonian-dynamics simulations of a three-dimensionalsoft-sphere mixture are analyzed and compared with the predictions of theITT-based approximation. Good qualitative and semi-quantitative agreement isfound. Furthermore, for short waiting times, the theoretical description of thewaiting time dependence shows excellent quantitative agreement to thesimulations. This confirms the accuracy of the central approximation usedearlier to derive fluctuation dissipation ratios Phys. Rev. Lett. 102,135701. For intermediate waiting times, the correlation functions decay fasterat long times than the stationary ones. This behavior is predicted by ourtheory and observed in simulations.



Autor: Matthias Krüger, Fabian Weysser, Thomas Voigtmann

Fuente: https://arxiv.org/



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