Dimeric anthracene-based mechanophore for damage precursor detection in epoxy-based thermoset polymer matrix: Characterization and atomistic modeling

The mechanochemical response of a dimeric anthracene-based mechanophore (force-sensitive molecule), embedded within a thermoset polymer matrix, is studied through characterization and atomistic modeling. The dimeric anthracene-based mechanophore (dimeric 9-anthracene carboxylic acid, Di-AC) synthesized through ultraviolet dimerization was successfully incorporated into an epoxy-based thermoset polymer matrix to detect damage precursors. Mechanical loading tests showed that the Di-AC embedded epoxy polymer is capable of detecting damage precursors via fluorescence emission that occurs immediately before the yield point. The sensitivity of the Di-AC to external stress, which enables the damage precursor detection, is verified through a comparative study of bond dissociation energies of mechanophores using atomistic simulations. A hybrid molecular dynamics (MD) simulation methodology, integrating a classical force-field and a bond-order based force-field, is used to simulate epoxy curing, investigate elastic moduli and yield strength/strain, and capture mechanophore activation. Local work analysis within the hybrid MD simulation methodology is conducted to capture the critical strain representing the initiation of mechanophore activation due to the deformation of Di-AC embedded epoxy polymer. The capability to detect damage precursor is observed through MD simulations by comparing the yield strain and the critical strain. Furthermore, the experimentally observed variation in yield strength due to the inclusion of Di-AC is accurately reproduced by the comparative study between two systems: neat epoxy and 5 wt% Di-AC epoxy polymer, thus, validating the computational framework.