Creaming, diving and swimming microcapsules driven by chemical reactions

点击翻译按钮获取中文摘要

The new research project is focused on the self-propelling properties of viscoelastic microcapsules, which are used as simple model systems for biological cells. These anisometric particles are produced in a special microfluidic apparatus. Due to the onset of shear forces, which are applied during the synthesis, the capsules attain a drop-shaped geometry with a semispherical head and a small, narrow tail. The directed propulsion of these colloidal particles is stimulated by chemical reactions, which occur in the core of these capsules. A very simple driving mechanism can be realized by incorporation of potassium permanganate crystals into the hollow capsule cavities. If the outer aqueous phase contains hydrogen peroxide, these molecules diffuse through the semi-permeable membranes into the core of the capsules and react then with the solved permanganate ions. The oxygen bubbles, which are formed by this redox-reaction, induce a rapid self-propelling motion of these particles. A large number of additional organic and inorganic chemical reactions shall be used in order to activate well-defined creaming, diving or swimming motions.Oscillating chemical reactions stimulate periodic swelling and shrinking processes of the gel-like capsule membranes. On grounds of the pronounced shape asymmetry this principle might lead to new types of pulsating swimming motions. As the capsules are surrounded by thin, viscoelastic polymer membranes, they react sensitively to the onset of mechanical forces. This special feedback mechanism, which changes the size and shape of the microcapsules during flow, is of foremost interest for the understanding of basic principles of biological microswimmers. The continuous synthesis in the microfluidic apparatus allows the production of a large number of self-propelling capsules. It is, hence, possible, to investigate the swimming motion of capsule swarms. Such experiments shall be performed in the second period of the DFG-priority program. The active capsule motions involve a combination of different phenomena, such as size and shape transitions, swelling processes, osmotic pressures, diffusion of chemical compounds trough the capsule membranes, adsorption and release processes and hydrodynamic interactions. The rheological properties of the capsule membranes can be varied in order to control the swimming motions. The described soft-matter locomotion mechanisms are based on different colloidal principles and lead to the development of new types of self-propelling particles, which can be used for advanced technologies of capsule addressing and processes of controlled drug release.