Dramatic change of the self-diffusions of colloidal ellipsoids by hydrodynamic interactions in narrow channels*

Abstract

The self-diffusion problem of Brownian particles under the constraint of quasi-one-dimensional (q1D) channel has raised wide concern. The hydrodynamic interaction (HI) plays an important role in many practical problems and two-body interactions remain dominant under q1D constraint. We measure the diffusion coefficient of individual ellipsoid when two ellipsoidal particles are close to each other by video-microscopy measurement. Meanwhile, we obtain the numerical simulation results of diffusion coefficient using finite element software. We find that the self-diffusion coefficient of the ellipsoid decreases exponentially with the decrease of their mutual distance X when X < X 0 , where X 0 is the maximum distance of the ellipsoids to maintain their mutual influence, X 0 and the variation rate are related to the aspect ratio p=a/b. The mean squared displacement (MSD) of the ellipsoids indicates that the self-diffusion appears as a crossover region, in which the diffusion coefficient increases as the time increases in the intermediate time regime, which is proven to be caused by the spatial variations affected by the hydrodynamic interactions. These findings indicate that hydrodynamic interaction can significantly affect the self-diffusion behavior of adjacent particles and has important implications to the research of microfluidic problems in blood vessels and bones, drug delivery, and lab-on-chip.