# Inhomogeneous diffusion in confined colloidal suspensions

## TL;DR

This paper studies how confinement between rough walls affects the movement and behavior of colloidal particles in a fluid.

## Contribution

The study provides new insights into inhomogeneous diffusion and scattering functions in confined colloidal systems using experiments and simulations.

## Key findings

- Confined colloidal suspensions show inhomogeneous diffusion coefficients.
- Surface roughness significantly impacts dynamical properties of colloidal systems.
- Non-zero off-diagonal elements in scattering functions are observed and modeled.

## Abstract

We have performed confocal microscopy experiments and computer simulations of colloidal suspensions with moderate volume fraction confined between two quasi-parallel, rough walls [A. Villada-Balbuena et al., Soft Matter, 2022, 18, 4699–4714]. Here we investigate many facets of the dynamical properties of the system, such as confined and inhomogeneous diffusion, mean first-passage times and generalized incoherent scattering functions. We observe that the experiment features strong footprints of the confinement in the dynamical properties, such as inhomogeneous diffusion coefficients and non-zero off-diagonal elements in the incoherent scattering function which we can quantitatively model and analyze with computer simulations. This allows us, for example, to systematically investigate the impact of surface roughness. Our comparative study therefore advances the fundamental understanding of the impact of confinement on dynamics in fluids and colloidal suspensions.

Confining fluids leads to inhomogeneous structural and dynamical properties. We investigate inhomogeneous diffusion and generalized scattering functions of colloidal fluids using confocal microscopy and molecular dynamics simulations.