A matter of shape: contact area optimization in soft lubrication

TL;DR

This paper investigates how the shape of a deformable object affects contact formation with a rigid surface in soft lubrication, revealing that shape can be optimized to control contact and fluid entrapment.

Contribution

It demonstrates that shape significantly influences contact and fluid entrapment in soft lubrication, providing a new perspective for designing contact interfaces.

Findings

Sharper profiles maximize contact at the center.

Blunter shapes tend to trap bubbles in central dimples.

Classical contact mechanics can predict pressure distributions in thin viscous films.

Abstract

We study the fluid-mediated approach of a deformable axisymmetric object towards a rigid substrate, focusing on how its shape influences contact formation. For low approach velocities and large Stokes numbers, we show that sharper profiles (e.g., conical) maximize contact at the center and avoid fluid entrapment, while blunter ones form central dimples that trap bubbles. We also find that the resulting pressure distributions in the presence of thin viscous films can be predicted remarkably well by classical (dry) contact mechanics. These findings reveal shape as a design parameter for contact optimization in soft matter, adhesion, and elastohydrodynamics. Finally, we also theorize the possibility of a mechanical equivalence between shape and approach velocity.