Rapid activation of non-oriented mechanophores via shock loading and spallation

BW Hamilton and A Strachan, PHYSICAL REVIEW MATERIALS, 7, 045601 (2023).

DOI: 10.1103/PhysRevMaterials.7.045601

Mechanophores (MPs), stimuli-responsive molecules that respond chromatically to mechanochemical reactions, are important for understanding the coupling between mechanics and chemistry as well as in engineering applications. However, the atomic-level understanding of their activation originates from gas phase studies or under simple linear elongation forces directly on molecules or polymer chains containing MPs. The effect of many-body distortions, pervasive in condensed-phase applications, is not understood. Therefore, we performed large-scale molecular dynamics (MD) simulations of a poly(methyl methacrylate)-spiropyran copolymer under dynamic mechanical loading and studied the activation of the MP under various conditions from dynamical compression to tension during unloading. Detailed analysis of the all- atom MD trajectories shows that the MP blocks experience significant many-body intramolecular distortion that can significantly decrease the activation barrier as compared with when deformation rates are slow relative to molecular relaxation time scales. We find that the reactivity of MPs under material compression states is governed by many- body effects of intramolecular torsions, whereas under tension, the reactions are governed by tensile stresses.

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