Dynamics of swelling and drying in a spherical gel

TL;DR

This paper develops a dynamic poromechanical model to understand the complex, transient internal processes during swelling and drying of hydrogel spheres, validated through experiments with polyacrylamide.

Contribution

It introduces a large-deformation poromechanical model for spherical hydrogel swelling and drying, providing new insights into transient behaviors and fracture risks.

Findings

Model accurately predicts swelling and drying dynamics.

Transient internal patterns form and vanish during processes.

Drying poses a fracture risk due to internal stresses.

Abstract

Swelling is a volumetric-growth process in which a porous material expands by spontaneous imbibition of additional pore fluid. Swelling is distinct from other growth processes in that it is inherently poromechanical: Local expansion of the pore structure requires that additional fluid be drawn from elsewhere in the material, or into the material from across the boundaries. Here, we study the swelling and subsequent drying of a sphere of hydrogel. We develop a dynamic model based on large-deformation poromechanics and the theory of ideal elastomeric gels, and we compare the predictions of this model with a series of experiments performed with polyacrylamide spheres. We use the model and the experiments to study the complex internal dynamics of swelling and drying, and to highlight the fundamentally transient nature of these strikingly different processes. Although we assume spherical symmetry, the model also provides insight into the transient patterns that form and then vanish during swelling as well as the risk of fracture during drying.