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.

Self-diffusion of nonspherical particles fundamentally conflicts with effective sphere models

“…This lack of theoretical validation is surprising given the strongly increased interest in nonspherical systems in the last 15 years due to its relevance for inter alia the assembly of complex structures [8], as well as for the understanding of macromolecular crowding in biology [9], and its role for cellular reaction pathways [10]. Recent experimental colloidal examples studied the self-diffusion of ellipsoids in channels [11], in quasi-2D confinement [12], through obstacle arrays [13], and random energy landscapes [14], as well as the anisotropic collective diffusion of magnetic ellipsoids in external fields [15,16], and the influence of particle shape on flow in microchannels [17,18]. Besides ellipsoids, dynamics of rod-like particles has been studied in recent years, including fast self-diffusion of long rods through smectic phases of short rods [19], thermodiffusion of rods [20,21] and strongly hindered diffusion in long stiff ribbon-like peptide aggregates [22].…”