Slowing-down of non-equilibrium concentration fluctuations in confinement

Abstract

Fluctuations in a fluid are strongly affected by the presence of a macroscopic gradient making them long-ranged and enhancing their amplitude. While small-scale fluctuations exhibit diffusive lifetimes, larger-scale fluctuations live shorter because of gravity, as theoretically and experimentally well-known. We explore here fluctuations of even larger size, comparable to the extent of the system in the direction of the gradient, and find experimental evidence of a dramatic slowing-down in their dynamics. We recover diffusive behaviour for these strongly-confined fluctuations, but with a diffusion coefficient that depends on the solutal Rayleigh number. Results from dynamic shadowgraph experiments are complemented by theoretical calculations and numerical simulations based on fluctuating hydrodynamics, and excellent agreement is found. The study of the dynamics of non-equilibrium fluctuations allows to probe and measure the competition of physical processes such as diffusion, buoyancy and confinement.

Includes see Supplementary Material. Submitted to PRL

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• Giant Casimir effect in fluids in non-equilibrium steady states
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Cited by in corpus (4)

• Equilibrium and non-equilibrium concentration fluctuations in a critical binary mixture
• Nonequilibrium fluctuation-induced Casimir pressures in liquid mixtures
• Staggered Scheme for the Compressible Fluctuating Hydrodynamics of Multispecies Fluid Mixtures
• Rheology modulated non-equilibrium fluctuations in time-dependent diffusion processes