Underwater friction for soft-hard contacts

Presence of lubricating liquid between two contacting surfaces has a profound influence on adhesion and friction. The current understanding in this area is summarized using a Stribeck curve that relates friction to velocity, viscosity, and applied load. Originally constructed for a hard-hard contact, the Stribeck curve has been extended to explain friction behavior in lubricated soft-hard contacts. Further, recent findings suggest that the underlying factors governing lubricated friction are microscopic contact area and the distribution of liquid trapped between the contacting pairs.

In this study, we are using a soft elastomer (crosslinked PDMS) with a smooth solid substrate (OTS monolayer) and varying parameters such as surface wettability, elastic modulus, and velocity. We measure the effect of these parameters on the dynamic evolution of the microscopic contact area and the local entrapped water during sliding along with the in-situ friction force measurements. This study provides insight into the changes in friction coefficients across a broad velocity range underwater. These results have implications in the fields of bio-tribology, smart underwater robotics, haptics, and tire traction.