Fluid Dynamics at the Interface between Soft Elastic Solids

• Applicants: Professor Dr. Gert Heinrich; Dr. Bo Nils Johann Persson
• Subject Area: Polymer Materials
• Term: from 2015 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 272908054

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.

• DFG Programme: Research Grants