2018/04/17 by de Zárate, J. M. Ortiz, Kirkpatrick, T. R., Sengers, J. V.
#FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Statistical Mechanics (cond-mat.stat-mech)
paper · doi:10.48550/arxiv.1804.06125
In stationary nonequilibrium states a coupling between hydrodynamic modes causes thermal fluctuations to become long ranged inducing nonequilibrium Casimir forces or 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 enhancement in a liquid layer between two horizontal plates that complete and correct results previously presented in the literature. In contrast to nonequiibrium Casimir pressures induced by a temperature gradient, kinetic theory shows that nonequilibrium contributions from short-range fluctuations are no longer negligible. In addition, it is noted that computer simulations of model fluids in shear observe effects from molecular correlations at nanoscales that have a different physical origin. The idea that such computer simulations probe shear-induced pressures resulting from coupling of long-wavelength hydrodynamic modes is erroneous.