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 wall, confirming the theory that non-Gaussian displacement distributions can occur despite linear MSD growth in inhomogeneous environments.

Contribution

First direct experimental validation of the diffusing-diffusivity mechanism in inhomogeneous media using near-wall colloidal dynamics.

Findings

Displacement distribution becomes non-Gaussian near walls.

Linear growth of MSD observed despite non-Gaussianity.

Direct evidence supporting the diffusing-diffusivity model.

Abstract

The diffusing-diffusivity mechanism proposed by Chubynsky and Slater [PRL 113, 098302, 2014] 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 wall. 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.