Creaming, diving and swimming microcapsules driven by chemical reactions

新的研究项目集中在粘弹性微胶囊的自推进特性上，这些微胶囊被用作生物细胞的简单模型系统。这些不等轴颗粒在特殊的微流体装置中产生。由于在合成过程中施加剪切力，胶囊获得具有半球形头部和小窄尾部的滴状几何形状。这些胶体颗粒的定向推进受到发生在这些胶囊核心的化学反应的刺激。通过将高锰酸钾晶体结合到中空胶囊腔中，可以实现非常简单的驱动机制。如果外部水相含有过氧化氢，则这些分子通过半透膜扩散到胶囊的核心中，然后与溶解的高锰酸盐离子反应。由这种氧化还原反应形成的氧气泡引起这些粒子的快速自推进运动。应使用大量额外的有机和无机化学反应以激活明确的乳状液分层、潜水或游泳运动。振荡化学反应刺激凝胶状囊膜的周期性溶胀和收缩过程。基于明显的形状不对称性，这一原理可能导致新型的脉动游泳运动。由于胶囊被薄的粘弹性聚合物膜包围，它们对机械力的发生反应敏感。这种特殊的反馈机制，它改变了流动过程中的微胶囊的大小和形状，是最感兴趣的生物microswimmer的基本原理的理解。在微流体装置中的连续合成允许生产大量的自推进胶囊。因此，有可能研究胶囊群的游动运动。此类实验应在DFG优先计划的第二阶段进行。主动胶囊运动涉及不同现象的组合，例如尺寸和形状转变、溶胀过程、渗透压、化合物通过胶囊膜的扩散、吸附和释放过程以及流体动力学相互作用。可以改变胶囊膜的流变学性质以控制游泳运动。所描述的软物质运动机制基于不同的胶体原理，并导致新型自推进颗粒的发展，其可用于胶囊寻址的先进技术和受控药物释放的过程。

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.