Suspensions of viscoelastic capsules: effect of membrane viscosity on transient dynamics

TL;DR

This study investigates how membrane viscosity affects the transient deformation and dynamics of dense suspensions of viscoelastic capsules using numerical simulations, revealing complex dependencies on volume fraction.

Contribution

It provides the first systematic numerical analysis of membrane viscosity effects on dense capsule suspensions, highlighting non-trivial interactions with volume fraction and capillary number.

Findings

Membrane viscosity increases resistance to deformation.

Loading times are similar to capsules without surface viscosity at high volume fractions.

The influence of membrane viscosity varies non-linearly with suspension density.

Abstract

Membrane viscosity is known to play a central role in the transient dynamics of isolated viscoelastic capsules by decreasing their deformation, inducing shape oscillations and reducing the loading time, that is, the time required to reach the steady-state deformation. However, for dense suspensions of capsules, our understanding of the influence of the membrane viscosity is minimal. In this work, we perform a systematic numerical investigation based on coupled immersed boundary -- lattice Boltzmann (IB-LB) simulations of viscoelastic spherical capsule suspensions in the non-inertial regime. We show the effect of the membrane viscosity on the transient dynamics as a function of volume fraction and capillary number. Our results indicate that the influence of membrane viscosity on both deformation and loading time strongly depends on the volume fraction in a non-trivial manner: dense suspensions with large surface viscosity are more resistant to deformation but attain loading times that are characteristic of capsules with no surface viscosity, thus opening the possibility to obtain richer combinations of mechanical features.