Micro-capsules in shear flow

Abstract

This paper deals with flow-induced shape changes of elastic capsules. The state of the artconcerning both theory and experiments is briefly reviewed starting with dynamicallyinduced small deformation of initially spherical capsules and the formation of wrinkleson polymerized membranes. Initially non-spherical capsules show tumbling andtank-treading motion in shear flow. Theoretical descriptions of the transitionbetween these two types of motion assuming a fixed shape are at odds with the fullcapsule dynamics obtained numerically. To resolve the discrepancy, we expand theexact equations of motion for small deformations and find that shape changesplay a dominant role. We classify the dynamical phase transitions and obtainnumerical and analytical results for the phase boundaries as a function of viscositycontrast, shear and elongational flow rate. We conclude with perspectives ontime-dependent flow, on shear-induced unbinding from surfaces, on the role of thermalfluctuations and on applying the concepts of stochastic thermodynamics to thesesystems.