Understanding crack versus cavitation in pressure-sensitive adhesives: the role of kinetics

TL;DR

This study investigates the mechanisms of crack and cavitation in pressure-sensitive adhesives during traction tests, revealing the interplay of these phenomena in viscous liquids and proposing a theoretical model to describe different regimes.

Contribution

It introduces a theoretical model capturing crack and cavitation regimes in viscous liquids during adhesion tests, highlighting the coexistence of these mechanisms in liquid adhesives.

Findings

Cracks and cavitation occur simultaneously at certain velocities.

A phase diagram maps different force peak regimes.

Model predictions align with experimental data.

Abstract

We perform traction experiments on viscous liquids highly confined between parallel plates, a geometry known as the probe-tack test in the adhesion community. Direct observation during the experiment coupled to force measurement shows the existence of several mechanisms for releasing the stress. Bubble nucleation and instantaneous growth had been observed in a previous work. Upon increasing further the traction velocity or the viscosity, the bubble growth is progressively delayed. At high velocities, cracks at the interface between the plate and the liquid appear before the bubbles have grown to their full size. Bubbles and cracks are thus observed concomitantly. At even higher velocities, cracks develop fully so early that the bubbles are not even visible. We present a theoretical model that describes these regimes, using a Maxwell fluid as a model for the actual fluid, a highly viscous silicon oil. We present the resulting phase diagramme for the different force peak regimes. The predictions are compatible with the data. Our results show that in addition to cavitation, interfacial cracks are encountered in a probe-tack traction test with viscoelastic, \emph{liquid} materials and not solely with viscoelastic solids like adhesives.