Scaling laws to predict humidity-induced swelling and stiffness in hydrogels

TL;DR

This paper develops a power-law model based on semi-dilute polymer theory to predict how hydrogels' stiffness and swelling change with humidity, aiding material design in variable environments.

Contribution

It introduces a universal scaling law linking hydrogel elastic modulus and swelling, validated across multiple polymer types and conditions.

Findings

Accurately predicts hydrogel properties across different polymers and humidities.

Demonstrates the model's generality and predictive power.

Facilitates rapid hydrogel material discovery for diverse applications.

Abstract

From pasta to biological tissues to contact lenses, gel and gel-like materials inherently soften as they swell with water. In dry, low-relative-humidity environments, these materials stiffen as they de-swell with water. Here, we use semi-dilute polymer theory to develop a simple power-law relationship between hydrogel elastic modulus and swelling. From this relationship, we predict hydrogel stiffness or swelling at arbitrary relative humidities. Our close predictions of properties of hydrogels across three different polymer mesh families at varying crosslinking densities and relative humidities demonstrate the validity and generality of our understanding. This predictive capability enables more rapid material discovery and selection for hydrogel applications in varying humidity environments.