Determining the elasto-adhesion length by void collapse in ultra-soft materials.

Fu, Hongbo; Crosby, Alfred J · Soft Matter · 2023

basic_science · Level V

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Abstract

The elasto-adhesion length (<i>l</i><sub>EA</sub>) is a materials property that describes the size scale where the relative importance of adhesion and elastic forces transitions for defined structures and functions. Conventional approaches for determining <i>l</i><sub>EA</sub> require independent measurements of the critical energy release rate (<i>G</i><sub>c</sub>) and Young's modulus (<i>E</i>). Herein, we introduce a new method to obtain <i>l</i><sub>EA</sub>, only relying upon visual inspection. This method relies upon the introduction of a controlled void within a soft material, for example an ultra-soft hydrogel as studied here. The geometry of the void within the hydrogel is tuned to control the relative strength of adhesion and elastic energy, and a relationship between the observed equilibrium configuration of the void and <i>l</i><sub>EA</sub> is derived. We validate this new method with independent force-based contact adhesion tests. This method allows for the easy measurement of <i>l</i><sub>EA</sub> for difficult-to-handle soft materials and can be amended for various chemistries and materials.