Mechanochemical Systems
Mechanochemically active polymers undergo a chemical reaction (fluorescence, healing, etc.) in response to mechanical stress. Until now, the widespread use of polymers and composites has been hampered by the inability to autonomously detect and repair matrix damage before catastrophic failure. One way to overcome this limitation is mechanochemically triggered adaptation to mechanical stress in which changes in color and fluorescence or cross-link density are achieved in polymers. In our group, we have developed mechanochemically active polymers with the intrinsic ability to detect and repair damage.
Mechanochemistry employs mechanophores (force-sensitive molecules) to produce chemical changes in a material in response to an applied mechanical force. Mechanophores can be linked into the polymer backbone or as crosslinks in a polymer network. When mechanical force is applied to the polymer, the force is transferred to the mechanophore which responds by altering its chemical structure. Mechanophores can be designed to produce favorable chemical reactions in engineering polymers; imparting novel capabilities such as damage sensing, cross-linking, stress redistribution and catalysis promotion.
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| Cylinderical test specimen of cross-linked PMMA with spiropyran crosslinker subject to torsion testing. The color change to purple indicates activation of the electrocyclic ring opening reaction of spiropyran to merocyanine. Ref. Kingsbury et al. J. Mater. Chem., 2011. 1. Kingsbury, C.M.; May, P.A.; Davis, D.A.; White, S.R.; Moore, J.S.; Sottos, N.R. Shear activation of mechanophore-crosslinked polymers. J. Mater. Chem. 2011, 21, 8381-8388. |
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Sequence of fluorescence images acquired during Mode I fracture testing of a single edge-notch fracture specimen of cross-linked PMMA with spiropyran crosslinker. Fluorescence is shown to correlate with the plastic zone ahead of the crack tip during propagation of the crack tip. Ref: Celestine et al. Polymer, 2014 (in review). |