Time dependence of advection-diffusion coupling for nanoparticle ensembles

Alexandre Vilquin (1) , Vincent Bertin (2) , Pierre Soulard (1) , Gabriel Guyard (3) , Elie Raphaël (1) , Frederic Restagno (3) , Thomas Salez (2) , Joshua D Mcgraw (1)

1 Gulliver (UMR 7083)
2 LOMA - Laboratoire Ondes et Matière d'Aquitaine
3 LPS - Laboratoire de Physique des Solides

Particle transport in fluids at micro-and nano-scales is important in many domains. As compared to the quiescent case, the time evolution of particle dispersion is enhanced by coupling: i) advection along the flow; and ii) diffusion along the associated velocity gradients. While there is a well-known, long-time limit for this advection-diffusion enhancement, understanding the short-time limit and corresponding crossover between these two asymptotic limits is less mature. We use evanescent-wave video microscopy for its spatio-temporal resolution. Specifically, we observe a near-surface zone of where the velocity gradients, and thus dispersion, are the largest within a simple microfluidic channel. Supported by a theoretical model and simulations based on overdamped Langevin dynamics, our experiments reveal the crossover of this so-called Taylor dispersion from short to long time scales. Studying a range of particle size, viscosity and applied pressure, we show that the initial spatial distribution of particles can strongly modify observed master curves for short-time dispersion and its crossover into the long-time regime.

Domaines: Matière Molle [cond-mat.soft]; Mécanique des fluides [physics.class-ph]

Alexandre Vilquin, Vincent Bertin, Pierre Soulard, Gabriel Guyard, Elie Raphaël, et al.. Time dependence of advection-diffusion coupling for nanoparticle ensembles. 2020. ⟨hal-02896493v1⟩