Swimming of deformable microcapsules and droplets

本研究项目致力于自行式可变形微胶囊或水滴游泳者的理论研究。我们研究了由于水动力和变形能力的相互作用，可变形的自推进胶囊或水滴通常会出现的两个问题：a)由于水动力的作用，自推进微胶囊或水滴在游泳过程中会变形，进而改变周围流体的速度场，从而改变所产生的游泳速度。我们将开发理论和模拟方法，以解决弹性微胶囊或液滴变形、游泳者周围(和内部)流体动力流动的耦合问题，并最终解决导致磷化效应的表面活性剂反应物的扩散问题。特别是，我们研究了胶囊和水滴通过自流推进的游泳者。B)可变形的微胶囊可以使用循环形状变化作为机械游泳机制。将滞后的形状变化与简单的振荡控制参数相耦合，就足以诱导游泳运动。这种由滞回形状变化引起的游泳机制将从理论上研究由温度响应性聚合物凝胶构成的游泳者可能实现的局部膨胀和收缩引发的全局滞回形状变化。

This research project is focused on the theoretical investigation of self-propelling deformable microcapsule or droplet-based swimmers. We study two problems that occur generically for deformable self-propelled capsules or droplets due to the interplay of hydrodynamic forces and deformability: A) Because of hydrodynamic forces, a self-propelled microcapsule or droplet will deform during swimming, which changes in turn the velocity field of the surrounding fluid and, thus, the resulting swimming velocity. We will develop theoretical and simulation methods in order to solve the coupled problem of elastic microcapsule or droplet deformation, of the hydrodynamic fluid flow around (and inside) the swimmer and, eventually, of the diffusion of reactants of surfactants responsible for phoretic effects. In particular, we study capsule and droplet swimmers propelling by autophoresis. B) A deformable microcapsule can use cyclic shape changes as a mechanical swimming mechanism. Coupling a hysteretic shape change to a simply oscillating control parameter suffices to induce swimming motion. This swimming mechanism by hysteretic shape changes will be investigated theoretically with respect to possible realizations by swimmers constructed from thermo-responsive polymer gels undergoing global hysteretic shape changes triggered by local swelling and shrinking.