Fluidics of micro-capsules in shear flow: Dynamical shape transformations and role of membrane roughness

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This proposal deals with a theoretical analysis of the fluidics of micro-capsules in external shear flow. Micro-capsules are thin hollow elastic capsules either prepared artificially such as polyamid capsules and polyelectrolyte shells or occuring in nature such as red-blood-cells. These capsules deform in hydrodynamic flow depending on their visco-elastic properties. For micro-capsules in unbounded shear flow, we will focus on the role of a non-zero bending rigidity for the experimentally observed shear-induced crumpling. The role of a confining geometry will be studied for micro-capsules interacting on nano-scales with a substrate. The competition between attractive interactions causing elastic deformations and the flow-induced hydrodynamic lift, which depends both on this deformation and the thin lubricating layer between substrate and capsule, can lead to a dynamical unbinding transition. As methods, we will use both an analytical approach for small deviations from a spherical shape and a numerical boundary-integral technique which incorporates the full hydrodynamics into a non-local equation of motion for the capsule shape for which the molecular architecture of the membrane enters the boundary conditions.