Quantifying and mapping covalent bond scission during elastomer fracture

TL;DR

This study uses innovative fluorogenic mechanochemistry and microscopy to map covalent bond scission during elastomer fracture, revealing extensive, temperature- and rate-dependent damage that significantly contributes to fracture energy.

Contribution

It introduces a novel method combining mechanochemistry and microscopy to quantitatively and spatially map covalent bond scission in soft materials during fracture.

Findings

Bond scission can be delocalized over hundreds of micrometers.

Bond scission increases significantly with temperature and stretch rate.

Covalent bond scission accounts for a larger fraction of fracture energy than previously thought.

Abstract

Many new soft but tough rubbery materials have been recently discovered and new applications such as flexible prosthetics, stretchable electrodes or soft robotics continuously emerge. Yet, a credible multi-scale quantitative picture of damage and fracture of these materials has still not emerged, due to our fundamental inability to disentangle the irreversible scission of chemical bonds along the fracture path from dissipation by internal molecular friction. Here, by coupling new fluorogenic mechanochemistry with quantitative confocal microscopy mapping, we uncover how many and where covalent bonds are broken as an elastomer fractures. Our measurements reveal that bond scission near the crack plane can be delocalized over up to hundreds of micrometers and increase by a factor of 100 depending on temperature and stretch rate, pointing to an intricated coupling between strain rate dependent viscous dissipation and strain dependent irreversible network scission. These findings paint an entirely novel picture of fracture in soft materials, where energy dissipated by covalent bond scission accounts for a much larger fraction of the total fracture energy than previously believed. Our results pioneer the sensitive, quantitative and spatially-resolved detection of bond scission to assess material damage in a variety of soft materials and their applications.