P1: Adhesion and Friction between Solid and Soft Matter at Multiple Scales

Adhesion and friction involving fluids or viscous matter, such as encountered in adhesives or in lubrication, are processes that determine everyday life, from human interaction with the environment to the function and reliability of machinery. The project focusses on three archetypal systems that all pose unsolved problems from a multiscale modeling perspective: Pressure sensitive adhesives (PSAs) that achieve tack through a soft viscoelastic medium at the interface of the contacting bodies, classical lubrication of hard substrates as employed in mechanical machinery and lubrication of soft substrates often found in biological systems such as synovial joints. In these systems, molecular interactions determine the viscoelastic response of the confined adhesive or lubricant, but the entrainment conditions are determined by long-range elastic deformation. Adhesion and friction at the macroscopic scale is therefore an inherent multi-scale problem.

Predictive models for the deformation and energy dissipation in these systems are presently not available. The complexity of the problem requires a recursive guidance of the sampling at mechanically relevant conditions at one scale by the other. Mesoscopic models capture geometrical properties of interfaces, such as roughness and gradients in substrate elasticity, and provide information on the deformation of interface and solid.

The goal of this project is to recursively couple these mesoscale calculations to molecular dynamics models of the adhesive or lubricant, thereby bypassing the need for explicit constitutive equations that are presently used for these types of problems.