Abstract
At short times, microparticle motion couples with the ambient fluid, which can transiently store and return kinetic energy. Here, numerical experiments reveal that this hydrodynamic memory effect hedges against space- and time-varying forces. As a result, hydrodynamic memory can boost the transport efficiency of driven microparticles beyond what is expected from standard Langevin theory.
Highlights
In the pioneering work of Alder and Wainwright [1], molecular dynamics simulations of hard-spheres liquid argon revealed a long-time tail in the velocity autocorrelation function, which decays as t−3/2
This retarded force is known as the Basset history force, which underlies the slow t−3/2 decay associated with hydrodynamic memory
When fluid inertia is taken into account, the Basset history force moderates momentum and energy flow between bead and environment, smoothing the bead’s response [Figs. 2(a) and 2(b)]
Summary
Seyler Department of Physics, Arizona State University, Tempe, Arizona 85287, USA. Steve Pressé * Department of Physics and School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA (Received 15 June 2019; published 7 October 2019). At low Reynolds number, the Basset-Boussinesq-Oseen (BBO) equation correctly describes nonuniform particle motion, capturing hydrodynamic memory effects associated with this slow algebraic decay. Using the BBO equation, we numerically simulate driven single-particle transport to show that memory effects persist indefinitely under rather general driving conditions. When driving forces do not vary smoothly, hydrodynamic memory substantially lowers the effective transport friction. This enables coasting over a spatially uneven potential that otherwise traps particles modeled with pure Stokes drag. Our results provide direct physical insight into the role of particle-fluid coupling in nonequilibrium microparticle transport
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