Sticking without contact: Elastohydrodynamic adhesion

TL;DR

This paper develops a theoretical framework for viscous adhesion in wet conditions, revealing how fluid-induced forces can cause sticking without contact and lead to snap-off in elastic solids.

Contribution

It introduces a novel theoretical model describing viscous adhesion between elastic solids immersed in fluid, extending the understanding beyond classical dry contact theories like JKR.

Findings

Viscous forces induce significant elastic displacements during separation.

A nonlinear adhesion force grows as t^(2/3) during initial separation.

Snap-off occurs via a finite-time singularity, similar to dry contact models.

Abstract

The adhesion between dry solid surfaces is typically governed by contact forces, involving surface forces and elasticity. For surfaces immersed in a fluid, out-of-contact adhesion arises due to the viscous resistance to the opening of the liquid gap. While the adhesion between dry solids is described by the classical JKR theory, there is no equivalent framework for the wet adhesion of soft solids. Here, we investigate theoretically the viscous adhesion emerging during the separation of a sphere from an elastic substrate. The suction pressure within the thin viscous film between the solids induces significant elastic displacements. Unexpectedly, the elastic substrate closely follows the motion of the sphere, leading to a sticking without contact. The initial dynamics is described using similarity solutions, resulting in a nonlinear adhesion force that grows in time as F ~ t^(2/3). When elastic displacements become large enough, another similarity solution emerges that leads to a violent snap-off of the adhesive contact through a finite-time singularity. The observed phenomenology bears a strong resemblance with JKR theory, and is relevant for a wide range of applications involving viscous adhesion.