Fluid Dynamics at the Interface between Soft Elastic Solids

接触固体与表面粗糙度之间界面的流体动力学是一个具有重要实际意义的课题，例如轮胎与路面的摩擦、雨刮器叶片的噪音产生、注射器中橡胶塞的粘滑运动或密封件的泄漏率。对于流体润湿界面（无脱湿过渡）的系统，可以通过所谓的流体流动因素考虑表面粗糙度对流体流动的影响。结合Bruggeman有效介质理论和Persson接触力学理论，提出了计算流体流动系数的方法。然而，该理论不包括流体压力分布引起的凸起变形。在捆绑提案中的这个单独项目：橡胶和（不规则）粗糙表面之间的脱湿和粘附：从分子基础到工程接触，我们将扩展理论以包括这种效应，并研究其在不同应用（混合润滑和流体挤压）中的影响。在许多应用中，薄流体膜是不稳定的，但至少在低滑动速度下会经历脱湿过渡，这可能对滑动接触的摩擦或静态或动态密封的泄漏率产生深远的影响。例如，疏水性（如涂蜡）玻璃上的雨刷片在低滑动速度下会发生脱湿过渡，导致粘滑运动、雨刷动作不良和噪音。我们将把流体动力学理论扩展到除湿系统。我们将首先确定将发生脱湿的临界滑动速度v = vc，并研究（负）扩散压力（脱湿的驱动力）对v < vc时流体流动动力学的影响。我们还将进行模型实验来验证理论，并分析我们的合作伙伴在捆绑提案中获得的理论结果。最后的目标是获得在具有随机粗糙度的界面上计算润湿和非润湿流固组合的流体流动的数值程序。

Fluid dynamics at interfaces between contacting solids with surface roughness is a topic of huge practical importance, e.g., for tire-road friction, noise generation of wiper blades, stick-slip motion of the rubber stopper in syringes or the leak-rate of seals. For systems where the fluid wets the interface (no dewetting transition) the influence of the surface roughness on the fluid flow can be taken into account via so called fluid flow factors.We have developed methods for how to calculate the fluid flow factors, combining the Bruggeman effective medium theory with the Persson contact mechanics theory. However, this theory does not include the deformations of the asperities by the fluid pressure distribution. In this individual project in the bundled proposal: Dewetting and Adhesion between Rubber and (irregular) Rough Surfaces: From Molecular Basics to Engineering Contacts, we will extend the theory to include this effect, and study its influence in different applications (mixed lubrication and fluid squeeze-out). In many applications a thin fluid film is not stable but will undergo a dewetting transition, at least for low sliding speeds, which can have a profound effect on the friction of sliding contacts, or the leak-rate of static or dynamic seals. A dewetting transition occurs, for example, for wiper blades on hydrophobic (e.g. wax coated) glass at low sliding speed resulting in stick-slip motion, bad wiper action and noise. We will extend the fluid dynamics theory to dewetting systems. We will first determine the critical sliding velocity v = vc below which dewetting will occur, and study how the (negative) spreading pressure (driving force for dewetting) influence the fluid flow dynamics for v < vc. We will also perform model experiments to test the heory, and also analyze theoretically results obtained by our partners in the bundled proposal. The final objective is to obtain numerical procedures for calculating fluid flow at interfaces with random roughness for both wetting and non-wetting fluid-solid combinations.