Micro-Capsules in Shear Flow

TL;DR

This paper investigates how elastic capsules change shape and move in shear flow, highlighting the importance of shape dynamics and providing phase diagrams for different flow conditions.

Contribution

It introduces a new theoretical approach that accounts for shape changes in capsule dynamics, resolving previous discrepancies between theory and numerical simulations.

Findings

Shape changes are crucial for accurate capsule dynamics modeling.

Phase boundaries depend on viscosity contrast and flow rates.

Analytical and numerical results clarify motion transitions.

Abstract

This paper deals with flow-induced shape transitions of elastic capsules. The state of the art concerning both theory and experiments is briefly reviewed starting with dynamically induced small deformation of initially spherical capsules and the formation of wrinkles on polymerized membranes. Initially non-spherical capsules show tumbling and tank-treading motion in shear flow. Theoretical descriptions of the transition between these two types of motion assuming a fixed shape are at variance with the full capsule dynamics obtained numerically. To resolve the discrepancy, we expand the exact equations of motion for small deformations and find that shape changes play a dominant role. We classify the dynamical phase transitions and obtain numerical and analytical results for the phase boundaries as a function of viscosity contrast, shear and elongational flow rate. We conclude with perspectives on timedependent flow, on shear-induced unbinding from surfaces, on the role of thermal fluctuations, and on applying the concepts of stochastic thermodynamics to these systems.