Fast detection of early-stage damage in soft elastomers*

In order to investigate the fracture mechanism of soft polymer networks, it is necessary to cover a wide range of length scales: from the molecular scale with bond breaking in stretched chains to the macroscopic scale with the crack propagation and rupture of the material. In this work, we developed time- and space-resolved multi-speckle diffusing wave spectroscopy (MSDWS) coupled with molecular scale measurement of bond breaking, to provide a new approach to studying fracture mechanics in multiple length scales.

Based on a single-edge notched PDMS elastomer with the additional mechanophore and probe particles, strain rate distribution over the whole sample and bond breaking around the crack can be simultaneously mapped until macroscopic fracture. During induction period of macroscopic fracture, we discovered a large scale strain rate localization (~1 cm²), which is related to local damage in the scales of tens of microns. Applying the results, we developed a detection method of microscopic damage long time before macroscopically observable. Our insight of the coupling between ongoing molecule damage and dynamic mechanical response will also provide us complete vision to the research of fracture mechanism and advanced molecular design for soft material development.