Hydrodynamic lift of vesicles under shear flow in microgravity

TL;DR

This study investigates how vesicles move away from walls in shear flow under microgravity, confirming theoretical predictions about lift forces through experimental data collected via holographic microscopy.

Contribution

It provides experimental validation of the hydrodynamic lift force scaling for vesicles in shear flow under microgravity conditions, aligning with existing theoretical models.

Findings

Vesicles are pushed away from walls with a lift velocity proportional to shear rate and vesicle size.

Lift velocity depends on vesicle aspect ratio as predicted by theory.

Experimental data matches the theoretical scaling law for lift forces.

Abstract

The dynamics of a vesicle suspension in a shear flow between parallel plates has been investigated under microgravity conditions, where vesicles are only submitted to hydrodynamic effects such as lift forces due to the presence of walls and drag forces. The temporal evolution of the spatial distribution of the vesicles has been recorded thanks to digital holographic microscopy, during parabolic flights and under normal gravity conditions. The collected data demonstrates that vesicles are pushed away from the walls with a lift velocity proportional to $\dot{\gamma} R^3/z^2$ where $\dot{\gamma}$ is the shear rate, $R$ the vesicle radius and $z$ its distance from the wall. This scaling as well as the dependence of the lift velocity upon vesicle aspect ratio are consistent with theoretical predictions by Olla [J. Phys. II France {\bf 7}, 1533--1540 (1997)].