Theoretical modelling of the motion and deformation of capsules in shear flows.

Mechanical models for capsules freely suspended in another liquid, are devised to predict the deformation, motion, breakup of one particle and also the rheological flow behaviour of a suspension. The capsule is filled with a newtonian liquid, and is surrounded by a thin deformable membrane having otherwise arbitrary mechanical properties. Initially spherical capsules in simple shear flow, are found to deform and orient with respect to streamlines, while their membrane is continuously rotating around the internal liquid. A dilute suspension of such capsules has a viscoelastic constitutive law which depends on the particle physical properties. It is then possible to use such models to interpret experiments in terms of the mean intrinsic properties of a capsule population.