# Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics

## TL;DR

This study experimentally tests the diffusing-diffusivity mechanism by tracking colloidal particles near a surface, confirming that inhomogeneous environments cause non-Gaussian displacement distributions despite linear MSD growth.

## Contribution

First direct experimental validation of the diffusing-diffusivity mechanism in inhomogeneous media using single-particle tracking.

## Key findings

- Displacement distributions become non-Gaussian near surfaces.
- Linear growth of MSD observed despite non-Gaussianity.
- Provides evidence supporting the diffusing-diffusivity model.

## Abstract

The mechanism of diffusing diffusivity predicts that, in environments where the diffusivity changes gradually, the displacement distribution becomes non-Gaussian, even though the mean-squared displacement (MSD) grows linearly with time. Here, we report single-particle tracking measurements of the diffusion of colloidal spheres near a planar substrate. Because the local effective diffusivity is known, we have been able to carry out the first direct test of this mechanism for diffusion in inhomogeneous media.