Polymer adsorption in shear

大自然已经开发了多种方法来移动粘性介质中的细胞和动物，或者在许多情况下是类似的问题，移动动物体内的流体。Schwerpunktprogramm特别感兴趣的是纳米到微米尺度，其中惯性力通常比粘性力小，定义了所谓的小雷诺数区域。产生流体动力阻力的典型策略包括a）旋转聚合物螺旋（所谓的鞭毛）或B）击打通常形成相当密集的接枝区域（所谓的纤毛）的直的和半柔性的聚合物。我们将从理论上研究运动的聚合物（和支持细胞表面）和聚合物的弹性，这导致在大驱动力的形状变形的流体动力学相互作用之间的复杂耦合。虽然基本的流体动力学方程在低雷诺数区域是线性的，但与弹性自由度的耦合导致了非线性，非线性对产生定向阻力起着重要的作用，但迄今为止一直被忽视。在第一部分中，我们将分析和理解旋转鞭毛和跳动纤毛的两种生物学相关情况，并具体计算聚合物作为施加扭矩的函数的形状变形。这些计算将使用包括完整流体动力学相互作用的布朗动力学代码进行。在该项目的第二部分，我们将以仿生方式开发使用跳动的合成纤毛在微流体芯片内泵送流体的策略。这些可以例如通过硫醇结合的DNA-寡聚体形成，其使用从接枝表面施加的电势周期性地移动。

Nature has developed a multitude of methods to move cells and animals within a viscous medium, or, which is in many cases an analogous problem, to move fluids within an animal. Of particular interest to the Schwerpunktprogramm is the Nano- to Micrometer scale, where inertia forces are typically small compared to viscous forces, defining the so-called small-Reynolds-number regime. Typical strategies of producing hydrodynamic drag involve either a) rotating polymeric spirals (so called flagellae) or b) beating straight and semiflexible polymers that normally form quite densely grafted areas (so-called ciliae). We will theoretically study the intricate coupling between the hydrodynamic interactions within the moving polymer (and with the supporting cell surface) and the elasticity of the polymers, which leads to shape deformations at large driving forces. Although the underlying hydrodynamics equations are linear in the low-Reynolds-number regime, the coupling to elastic degrees of freedom leads to non-linearities that play an important and hitherto neglected role for the production of directed drag. In the first part, we will analyze and understand the two biologically relevant situations of a rotating flagella and beating cilia, and in specific calculate the resulting shape deformations of the polymers as a function of applied torque. These calculations will be done using a Brownian-Dynamics-code including full hydrodynamic interactions. In the second part of the project we will in a biomimetic fashion develop strategies for pumping fluids within micro-fluidic chips using beating synthetic ciliae. These can for example be formed by thiol-bound DNA-oligomers, which are periodically moved using an electric potential applied from the grafting surface.