Pattern Formation in Crumpled Hydrogel upon Rapid Dehydration with Acetone

TL;DR

This study investigates the pattern formation caused by rapid dehydration of hydrogel sheets in acetone, revealing a transient crumpling instability and how pattern wavelength depends on hydration duration.

Contribution

It introduces experimental insights into dehydration-induced pattern formation in hydrogels, highlighting the dependence of pattern wavelength on hydration time and drawing parallels to crumpling instability.

Findings

Pattern formation occurs during dehydration, independent of total hydration extent.

Pattern wavelength scales with hydration duration following a power law.

Dehydration induces a crumpling-like instability on hydrogel surfaces.

Abstract

From microactuators to biological tissues, non-porous materials with the ability to strongly expand when in contact with a solvent are ubiquitous. Consequently, the swelling of polymer systems such as hydrogel has received recently much research attention. However, the related dehydration of these systems has received much less attention. Here, we present experiments investigating the rapid dehydration of a swollen hydrogel sheet whose surface exhibits a transient crumpling instability characterised by line segments of cusps patterning the surface of the gel into an array of bumps. We perform this dehydration through immersion in acetone, which is highly miscible in water, but poorly miscible in the hydrogel. We report the onset of a fascinating pattern formation where regions of the hydrogel sheet turn turbid. We find that the emerging pattern is independent of the overall extent of the hydrated swollen surface. The pattern wavelength only depends on the duration of hydration before immersion in acetone, growing temporally with a power law behaviour. We conclude through drawing comparisons between features of this dehydration induced pattern and the original crumpling instability in the water swollen hydrogel sheet.