Diffusion of single ellipsoids under quasi-2D confinements

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.