Tri-branched gels: Rubbery materials with the lowest branching factor approach the ideal elastic limit

TL;DR

This paper demonstrates that tri-branched rubbery materials with the lowest branching factor achieve near-ideal elastic limits through reversible strain-induced crystallization, challenging traditional tetra-branched designs.

Contribution

It reveals that tri-branching enhances elastic deformation and crystallization, providing a new design paradigm for rubbery materials with superior mechanical properties.

Findings

Tri-branched networks reach the theoretical elastic limit.

Reversible strain-induced crystallization is enhanced in tri-branched networks.

Mathematical theory explains the increased chain orientation in tri-branched polymers.

Abstract

Unlike hard materials such as metals and ceramics, rubbery materials can endure large deformations due to the large conformational degree of freedom of the crosslinked three-dimensional polymer network. However, the effect of the branching factor of the network on the ultimate mechanical properties of rubbery materials has not yet been clarified. This study shows that tri-branching, which entails the lowest branching factor, results in a large elastic deformation near the theoretical upper bound. This ideal elastic limit is realized by reversible strain-induced crystallization, providing on-demand reinforcement. The findings indicate that the polymer chain is highly orientated along the stretching axis, whereat enhanced reversible strain-induced crystallization is observed in the tri-branched and not in the tetra-branched network. A mathematical theory of structural rigidity is used to explain the difference in the chain orientation. Although tetra-branched polymers have been preferred since the development of vulcanization, these findings highlighting the merits of tri-branching will prompt a paradigm shift in the development of rubbery materials.