Time dependence of advection-diffusion coupling for nanoparticle ensembles*

Advection-diffusion coupling can enhance particle dispersion by orders of magnitude as compared to pure diffusion, with a steady state being reached for confined flow regions such as a blood vessel. Whereas the classical Taylor model predicts the long-time limit of this dispersion in a closed space, we address the question of the dynamics in the first instants after release and the corresponding crossover towards the long-time limit. Here by using evanescent wave microscopy, we make time-dependent, nanometrically-resolved particle dispersion measurements varying particle size, velocity gradient, and viscosity in a submicrometric flow domain. We measure the full dynamical approach and crossover into the steady state, revealing a family of universal curves, depending on the initial spatial distribution of the particles. Such laws are essential in predicting and optimizing the efficiency of drug delivery, among others.
https://hal.archives-ouvertes.fr/hal-02896493