Shape diagram of vesicles in Poiseuille flow

TL;DR

This paper investigates how fluid membranes influence vesicle shapes in Poiseuille flow, revealing that membrane effects can reverse typical parachute shapes and depend on channel aspect ratio and flow patterns.

Contribution

It introduces a phase diagram of vesicle shapes in channels, highlighting the impact of membrane properties and flow asymmetry on shape formation.

Findings

Shapes are wider in the narrowest channel direction.

Flow patterns significantly influence membrane deformation.

Membrane presence reverses typical parachute shape formation.

Abstract

Soft bodies flowing in a channel often exhibit parachute-like shapes usually attributed to an increase of hydrodynamic constraint (viscous stress and/or confinement). We show that the presence of a fluid membrane leads to the reverse phenomenon and build a phase diagram of shapes --- which are classified as bullet, croissant and parachute --- in channels of varying aspect ratio. Unexpectedly, shapes are relatively wider in the narrowest direction of the channel. We highlight the role of flow patterns on the membrane in this response to the asymmetry of stress distribution.