# Controlling effective dispersion within a channel with flow and active walls

## TL;DR

This paper explores how flow profiles and active or pulsating channel walls influence Taylor dispersion, providing analytic expressions to control solute transport in biological and artificial systems.

## Contribution

It derives closed-form expressions for effective dispersion considering active walls and flow profiles, revealing regimes of dispersion enhancement or suppression.

## Key findings

- Active walls can decrease or increase dispersion depending on conditions.
- Dispersion regimes include entropic slowdown, shuttle dispersion, and Taylor dispersion.
- Analytic formulas enable targeted control of solute transport.

## Abstract

Channels are fundamental building blocks from biophysics to soft robotics, often used to transport or separate solutes. As solute particles inevitably transverse between streamlines along the channel by molecular diffusion, the effective diffusion of the solute along the channel is enhanced - an effect known as Taylor dispersion. Here, we investigate how the Taylor dispersion effect can be suppressed or enhanced in different settings. Specifically, we study the impact of flow profile and active or pulsating channel walls on Taylor dispersion. We derive closed analytic expressions for the effective dispersion equation in all considered scenarios providing hands-on effective dispersion parameters for a multitude of applications. In particular, we find that active channel walls may lead to three regimes of dispersion: either dispersion decrease by entropic slow down at small Peclet number, or dispersion increase at large Peclet number dominated either by shuttle dispersion or by Taylor dispersion. This improves our understanding of solute transport e.g. in biological active systems such as blood flow and opens a number of possibilities to control solute transport in artificial systems such as soft robotics.