Aperiodic tumbling of microrods advected in a microchannel flow

TL;DR

This study experimentally investigates the tumbling dynamics of microrods in microchannel shear flow, revealing behaviors like periodic and aperiodic tumbling influenced by shape, initial conditions, and asymmetries.

Contribution

It provides detailed experimental observations of microrod tumbling, highlighting the effects of asymmetry and initial conditions on their complex motion in microfluidic flow.

Findings

Observation of both periodic and aperiodic tumbling behaviors

Different sensitivities of tumbling trajectories to external perturbations

Loss of phase in periodic trajectories due to center-of-mass drift

Abstract

We report on an experimental investigation of the tumbling of microrods in the shear flow of a microchannel (40 x 2.5 x 0.4 mm). The rods are 20 to 30 microns long and their diameters are of the order of 1 micron. Images of the centre-of-mass motion and the orientational dynamics of the rods are recorded using a microscope equipped with a CCD camera. A motorised microscope stage is used to track individual rods as they move along the channel. Automated image analysis determines the position and orientation of a tracked rods in each video frame. We find different behaviours, depending on the particle shape, its initial position, and orientation. First, we observe periodic as well as aperiodic tumbling. Second, the data show that different tumbling trajectories exhibit different sensitivities to external perturbations. These observations can be explained by slight asymmetries of the rods. Third we observe that after some time, initially periodic trajectories lose their phase. We attribute this to drift of the centre of mass of the rod from one to another stream line of the channel flow.