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

Viscoelastic capsules consist of a liquid drop core enclosed by a thin membrane that can be engineered with tailored mechanical properties. While the mechanical and rheological properties of purely elastic capsules have been thoroughly studied, only a few studies have focused on understanding the effect of membrane viscosity (MV) on the dynamics of single capsules, and the understanding of its effect on the suspension of capsules is still lacking. This knowledge gap is particularly relevant in the context of blood, which can be considered a suspension of red blood cells (RBCs). Although the impact of MV on single RBCs has recently been investigated, little is known about dense suspensions of RBCs, which is crucial for improving our understanding of blood flow at the macroscale, with important implications for cardiovascular dynamics.

In this contribution, we fill this gap by presenting a numerical investigation of the effect of MV on suspensions of viscoelastic capsules under simple shear flow, using a coupled immersed boundary-lattice Boltzmann implementation. We found that both the deformation and the loading time (i.e., the time it takes for the capsules to deform) are affected by the MV at varying values of the capillary number (Ca) and the volume fraction. Our simulations reveal the non-trivial role played by the MV in these systems. Specifically, while the effect of MV on the deformation and loading time is significant for dilute suspensions, it reduces as the volume fraction increases.