Entropy maximization underlies topology and mechanical properties in dynamic covalent hydrogels

TL;DR

This paper demonstrates that entropy maximization due to bond exchange in dynamic covalent hydrogels governs their topology and mechanical properties, enabling better predictions and control of their behavior.

Contribution

It introduces a model considering entropy-driven topology changes in dynamic networks, improving understanding and prediction of gelation and elasticity.

Findings

Bond exchange enables network rearrangement and higher entropy states.

Predicted gel point and elasticity match experimental observations.

Controlling bond exchange alters mechanical properties without bond loss.

Abstract

Adding dynamic bonds in polymer networks enables reprocessing and recycling; however the full impact of reversible bonds on dynamic network mechanics remains unclear. We build model dynamic networks and observe substantial deviations from classic theory. We rationalize these findings by considering that bond exchange enables the networks to rearrange and adopt a topology with a higher entropy. This allows us to accurately predict the gel point and elasticity of the dynamic networks. Further, we show by controlling bond exchange that network rearrangement can dramatically alter the mechanical properties, even without loss of bonds.