Deformation and orientation dynamics of polysiloxane microcapsules in linear shear flow

In this publication we examined the deformation, the orientation, the surface Young's moduli and the bursting process of different types of polysiloxane microcapsules. It turned out that the rheological properties of these particles were very much influenced by the amount of water, which served as a cross-linking agent for the formation of the polysiloxane membranes. Flexible capsules produced at low water concentrations showed oscillatory motions, which are referred to as swinging modes. At these conditions the orientation angles always displayed positive values. Simultaneously the membranes showed tank-treading motions. Microcapsules formed at elevated water concentrations displayed three types of motion dynamics. At small shear rates tumbling motions occurred in which the inclination angles varied between 90 degrees and +90 degrees. At high shear rates swinging modes with accompanying membrane rotation took place. Between these two fundamental orientation processes we also detected an intermittent mode in which the capsules carried out combined movements similar to tumbling and swinging. Another type of microcapsule displayed shear induced folding processes and swinging motions in shear flow. In separate experiments we compared the flow induced bursting process of the viscoelastic capsules. The experimental results are in good agreement with published theoretical approaches and recent simulations.