Diffusion of single ellipsoids under quasi-2D confinements

TL;DR

This study investigates how quasi-2D confinement affects the translational and rotational Brownian motion of ellipsoidal particles, revealing significant changes in diffusion anisotropy due to wall effects.

Contribution

It provides experimental measurements of diffusion coefficients of ellipsoids in quasi-2D environments, highlighting the impact of confinement on diffusion anisotropy.

Findings

Wall confinement alters diffusion anisotropy significantly.

Diffusion along the short axis is substantially slowed by confinement.

The ratio D_a/D_b exceeds two under certain confinement conditions.

Abstract

We report video-microscopy measurements of the translational and rotational Brownian motions of isolated ellipsoidal particles in quasi-two-dimensional sample cells of increasing thickness. The long-time diffusion coefficients were measured along the long ($D_a$) and short ($D_b$) ellipsoid axes, respectively, and the ratio, $D_a/D_b$, was determined as a function of wall confinement and particle aspect ratio. In three-dimensions this ratio ($D_a/D_b$) cannot be larger than two, but wall confinement was found to substantially alter diffusion anisotropy and substantially slow particle diffusion along the short axis.