Time dependence of advection-diffusion coupling for nanoparticle ensembles

TL;DR

This study uses evanescent wave microscopy to measure the time-dependent dynamics of nanoparticle dispersion in confined flows, revealing the influence of initial concentration profiles and confirming analytical models.

Contribution

First-time measurement of full Taylor dispersion dynamics at the nanoscale with high spatial resolution, highlighting initial condition effects and validating models.

Findings

Dispersion dynamics depend on initial nanoparticle distribution.

Quantitative agreement with analytical models and simulations.

Identification of master curves describing crossover to steady state.

Abstract

Advection-diffusion coupling can enhance particle and solute dispersion by orders of magnitude as compared to pure diffusion, with a steady state being reached for confined flow regions such as a nanopore or blood vessel. Here, by using evanescent wave microscopy, we measure for the first time the full dynamics of Taylor dispersion, highlighting the crucial role of the initial concentration profile. We make time-dependent, nanometrically-resolved particle dispersion measurements varying nanoparticle size, velocity gradient, and viscosity in sub-micrometric near-surface flows. Such resolution permits a measure of the full dynamical approach and crossover into the steady state, revealing a family of master curves. Remarkably, our results show that the dynamics depend sensitively on the initial spatial distribution of the nanoparticles. These observations are in quantitative agreement with existing analytical models and numerical simulations performed herein. We anticipate that our study will be a first step toward observing and modelling more complex situations at the nanoscale, such as target finding and chemical reactions in nanoconfined flows, dynamical adsorption and capture problems, as well as nanoscale drug delivery systems.