Dynamic Mechanochemical Memory for Imaging Stress History and Heterogeneity in Elastomers

Mechanosensitive chemical reactions are well suited for imparting stress response to common polymer materials for failure analysis and early damage detection. In this work we report on the unexpected behaviour of common spiropyran mechanophores in polydimethylsiloxane elastomer networks. While the majority of techniques employing spiropyrans make use of fluorescence imaging or absorption spectroscopy, we demonstrate that tracking mechanophore activation and interconversion kinetics can reveal mechanical stress history and qualitatively map the deformation type and intensity, post-impact. Surprisingly this mechanochemical memory manifests in elastomers far above their glass transition temperature. We demonstrate that observed changes in kinetics are well correlated with global mechanical stress and spectroscopic footprint of activated spiropyran. The large scale of mechanically induced perturbations to mechanophore interconversion kinetics, make the underlying chemistry particularly suitable for wide field imaging in a simple experimental setting.