In situ elastomer cutting: molecular insights from mechanophores.

In classic fracture mechanics, stress/strain concentration mediates the flow of energy toward the creation of new crack surfaces. However, the small scales and large deformations in this localized region make characterization challenging. Here, we visualize the deformation preceding a crack tip in an elastomeric material during fracture using the combination of reversible mechanophores and in situ cutting. Fluorescence intensity maps within tens of microns of the crack tip, which correlate to local deformation profiles, are made possible through Y-shaped cutting's ability to maintain fracture within the microscope's field of view. Comparison between these experimental intensity maps and deformation predictions from finite element analysis (FEA) highlight the importance of molecular probes in illustrating how continuum-level deformations translate to loads on molecular bonds in large deformation regions, such as those near the blade. FEA also highlights the presence of a previously unreported mechanophore deactivation zone within 2 µm of the blade tip.