Swimming of deformable microcapsules and droplets

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This research project is focused on the theoretical investigation of self-propelling deformable microcapsule or droplet-based swimmers. We study two problems that occur generically for deformable self-propelled capsules or droplets due to the interplay of hydrodynamic forces and deformability: A) Because of hydrodynamic forces, a self-propelled microcapsule or droplet will deform during swimming, which changes in turn the velocity field of the surrounding fluid and, thus, the resulting swimming velocity. We will develop theoretical and simulation methods in order to solve the coupled problem of elastic microcapsule or droplet deformation, of the hydrodynamic fluid flow around (and inside) the swimmer and, eventually, of the diffusion of reactants of surfactants responsible for phoretic effects. In particular, we study capsule and droplet swimmers propelling by autophoresis. B) A deformable microcapsule can use cyclic shape changes as a mechanical swimming mechanism. Coupling a hysteretic shape change to a simply oscillating control parameter suffices to induce swimming motion. This swimming mechanism by hysteretic shape changes will be investigated theoretically with respect to possible realizations by swimmers constructed from thermo-responsive polymer gels undergoing global hysteretic shape changes triggered by local swelling and shrinking.