We have recently developed a method to report quantitatively for bond scission in soft polymer networks by using mechanofluorescent probes. By incorporating methacrylate terminated π-extended anthracene-maleimide adducts as crosslinkers in poly(ethyl-acrylate) elastomers, we were able to visualize where molecular damage occurred upon mechanical loading to fracture. These probes yield a strong and stable fluorescent signal when the crosslinker breaks enabling non-destructive detection of covalent bond damage via confocal fluorescence microscopy. We have determined that the signal can be quantitatively related to the concentration of broken Diels-Alder bonds and that, for dilute concentrations of fluorophores, the signal is representative of the failure of covalent bonds. This important result will be used to address different problems of polymer mechanics.<br/><br/>1) When an elastomer is saturated with gas and then rapidly decompressed, small cavities may nucleate, inflate, and deflate inside the material. This cavity growth process, causes invisible but important molecular damage and influences the lifetime of elastomer parts. Cavities nucleated by rapid decompression from hydrogen gas in a polyacrylate elastomer were examined post-mortem with confocal microscopy with the present methodology. We observe that cavity growth in elastomers occurs through a localized fracture process with irreversible bond breakage and subsequent deformation of the initially planar damaged area into a cavity.<br/><br/>2) Although elastomers often experience 10-100 million cycles prior to failure, there is a limited understanding of their resistance to fatigue crack propagation. Here, we use soft and tough double-network elastomers tagged with mechanofluorescent probes to understand the role of sacrificial bond scission on mechanical durability by reconstructing 3-D maps of damage by sacrificial bond scission near the crack surface.

Using mechanochemistry to learn about bond scission near a fracture locus

ACS Spring Meeting 2021

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