Nonequilibrium Casimir pressures in liquids under shear



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Ortiz de Zárate Leira, José María and Kirkpatrick, T. R. and Sengers, J. V. (2019) Nonequilibrium Casimir pressures in liquids under shear. European physical journal E, 42 (8). ISSN 1292-8941

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In stationary nonequilibrium states coupling between hydrodynamic modes causes thermal fluctuations to become long ranged inducing nonequilibrium Casimir pressures. Here we consider nonequilibrium Casimir pressures induced in liquids by a velocity gradient. Specifically, we have obtained explicit expressions for the magnitude of the shear-induced pressure enhancements in a liquid layer between two horizontal plates that complete and correct results previously presented in the literature. In contrast to nonequilibrium Casimir pressures induced by a temperature or concentration gradient, we find that in shear nonequilibrium contributions from short-range fluctuations are no longer negligible. In addition, it is noted that currently available computer simulations of model fluids in shear observe effects from molecular correlations at nanoscales that have a different physical origin and do not probe shear-induced pressures resulting from coupling of long-wavelength hydrodynamic modes. Even more importantly, we find that in actual experimental conditions, shear-induced pressure enhancements are caused by viscous heating and not by thermal velocity fluctuations. Hence, isothermal computer simulations are irrelevant for the interpretation of experimental shear-induced pressure enhancements.

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© EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature 2019. We thank J.R. Dorfman for valuable discussions and R. Monchaux for some comments regarding Couette-flow experiments. We are indebted to R. A. Perkins for providing us with the relevant thermophysical-property information for liquid water and liquid argon. The research at the Complutense University was supported by grant ESP2017-83544-C3-2-P of the Spanish Agencia Estatal de Investigación. The research at the University of Maryland was supported by the US National Science Foundation under Grant No. DMR-1401449.

Uncontrolled Keywords:Mode-coupling theory; Long-time tails; Hydrodynamic fluctuations; Stress-tensor; Molecular-dynamics; Viscosity; Hard; Transition; Behavior
Subjects:Sciences > Physics > Thermodynamics
ID Code:58007
Deposited On:12 Dec 2019 12:40
Last Modified:12 Dec 2019 13:28

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