Morphology of soft and slippery contact via fluid drainage

TL;DR

This paper investigates how fluid drainage and elastic deformation influence contact formation between soft materials and rigid surfaces in fluid environments, revealing the roles of surface roughness and coating thickness.

Contribution

It provides a detailed characterization of elastic deformation and fluid drainage in soft coatings with nanometer roughness, highlighting the effects of coating thickness and surface roughness on contact mechanics.

Findings

Deformation profiles differ from elastic half-space models when coating thickness is comparable to hydrodynamic radius.

Surface roughness promotes fluid drainage without significantly changing elastic deformation.

Coupling between elasticity and slip can trap fluid pockets in the contact region.

Abstract

The dynamic of contact formation between soft materials immersed in a fluid is accompanied by fluid drainage and elastic deformation. As a result, controlling the coupling between lubrication pressure and elasticity provides strategies to design materials with reversible and dynamic adhesion to wet or flooded surfaces. We characterize the elastic deformation of a soft coating with nanometer-scale roughness as it approaches and contacts a rigid surface in a fluid environment. The lubrication pressure during the approach causes elastic deformation and prevents contact formation. We observe deformation profiles that are drastically different from those observed for elastic half-space when the thickness of the soft coating is comparable to the hydrodynamic radius. In contrast, we show that surface roughness favors fluid drainage without altering the elastic deformation. As a result, the coupling between elasticity and slip (caused by surface roughness) can lead to trapped fluid pockets in the contact region.