Although soft materials are widely used in load-bearing engineering applications where lightweight and flexibility are essential, they are typically designed thicker than they need to be due to a poor prediction of their lifetime in use and of the onset of fracture occurring by localized covalent bond scission. At lower stretch bond scission is limited to a random scission of bonds in the bulk of the elastomer. However above a certain level of stretch the extent of bond scission localizes in specific spots and the rubber can break catastrophically by crack propagation. From a more fundamental standpoint, fracture of soft materials is a complex multi-scale process coupling macromolecular chemistry, statistical physics and non-linear mechanics1. Until recently the detection of damage ahead of a crack was limited to the detection of crystallization or cavitation, detectable by wide or small angle X-ray scattering2-3 or optical visualisation, but molecular bond scission was not directly detectable. However several new molecules responding to applied forces4 or bond scission5 by changing their light absorption or emission properties are providing opportunities for materials scientists to gain insight in molecular processes occurring during mechanical loading. We have incorporated mechanosensitive fluorophore molecules6 as crosslinkers in model transparent polyacrylate elastomers and studied how these bonds break during macroscopic fracture. In order to detect bond scission we incorporated 5% mole% of a Diels-Alder adduct of Pi-extended anthracene based fluorophore as a crosslinker. When the DA adduct breaks by mechanical force, the remaining fragment is photoactive. For an excitation at 405 nm, two maxima of emission are detected at 435 nm and 460 nm. This fluorescent signal is very resistant to photobleaching and can be used to obtain high resolution spatial information and the extent of damage can be quantified with suitable calibration samples.

From bond scission to macroscopic fracture in soft materials

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.