Molecular Dynamics Study for Experimental Design Guideline of Dimeric Anthracene-based Mechanophore in the Thermoset Polymer Matrix

This paper presents a molecular level trade-off analysis on mechanophore embedded thermoset polymer matrix between its self-sensing capability and critical mechanical properties affecting performance. Dimeric 9-anthracene carboxylic acid (Di-AC), a mechanophore, was synthesized in epoxy polymer, and with the application of mechanical load, fluorescence was observed under ultraviolet (UV) excitation prior to the yield point. Experimental results, conducted with 5% Di-AC weight fraction, showed successful early damage detection capability; however, it was also observed that the inclusion of Di-AC reduced the material yield strength. To mimic this experimentally observed phenomenon and understand the complex mechanochemistry of this novel material, the molecular dynamic (MD) methodology simulates mechanophore synthesis, epoxy curing, and the mechanical loading test. Mechanophore sensitivity is investigated with different Di-AC weight fractions and the corresponding effects on the yield strength are analyzed. An initial degradation and subsequent recovery in yield strength over a certain range of weight fraction is observed. The possibility of early damage detection capability using higher Di-AC weight fractions is also investigated. Results indicate that the sensitivity to external stress is an inherent mechanophore property and is independent of the weight fraction. However, visible fluorescence (intensity), which is essential to damage detection, is highly dependent on the amount of Di-AC in the polymer.