# Diffusion of Colloidal Rods in Corrugated Channels

## TL;DR

This paper experimentally studies the diffusion of elongated colloidal particles in corrugated channels, revealing complex entropic and hydrodynamic effects, and extends theoretical models to accurately predict particle transport behavior.

## Contribution

It introduces an extended Fick-Jacobs theory for anisotropic particles, accounting for hydrodynamic and entropic effects in corrugated channels, validated by experiments.

## Key findings

- Elongated particles experience reduced accessible space due to shape and confinement.
- The diffusivity matrix depends on particle position and orientation.
- Extended theory accurately predicts mean first passage times.

## Abstract

In many natural and artificial devices diffusive transport takes place in confined geometries with corrugated boundaries. Such boundaries cause both entropic and hydrodynamic effects, which have been studied only for the case of spherical particles. Here we experimentally investigate diffusion of particles of elongated shape confined into a corrugated quasi-two-dimensional channel. Elongated shape causes complex excluded-volume interactions between particle and channel walls which reduce the accessible configuration space and lead to novel entropic free energy effects. The extra rotational degree of freedom also gives rise to a complex diffusivity matrix that depends on both the particle location and its orientation. We further show how to extend the standard Fick-Jacobs theory to incorporate combined hydrodynamic and entropic effects, so as, for instance, to accurately predict experimentally measured mean first passage times along the channel. Our approach can be used as a generic method to describe translational diffusion of anisotropic particles in corrugated channels.