Droplet absorption and spreading into thin layers of polymer hydrogels

TL;DR

This study investigates the absorption and spreading behavior of water droplets on thin polymer hydrogel layers, combining experimental observations with a theoretical poroelastic model to understand blister formation.

Contribution

It introduces a linear poroelastic framework and a non-linear diffusion model to describe droplet-induced blister formation in hydrogels, validated by experiments.

Findings

Fast absorption causes radially spreading blisters.

The theoretical model accurately predicts blister height evolution.

Experimental data confirms the model's validity.

Abstract

From biological tissues to layers of paint, macroscopic non-porous materials with the capacity to swell when brought in contact with an appropriate solvent are ubiquitous. Here, we study experimentally and theoretically one of the conceptually simplest of such systems, the swelling of a thin hydrogel layer by a single water drop. Using a bespoke experimental setup, we observe fast absorption leading to a radially spreading axisymmetric blister. Employing a linear poroelastic framework and thin-layer scalings, we develop a non-linear one-dimensional diffusion equation for the evolution of the blister height profile, which agrees well with experimental observations.