Abstract
Self-reporting polymers, which can indicate damage with perceptible optical signals in a tailored force range, are useful as stress-sensitive sensors. We demonstrate a simple approach to realize this function by embedding two distinct mechanophores — rhodamine (Rh) and bis(adamantyl)-1,2-dioxetane (Ad), in polyurethane/polylactic acid blends. The deformed blends generate red coloration and red chemiluminescence. Such a unique dual-responsive behavior was evaluated by solid-state UV-vis spectroscopy, macroscopic tensile tests with in situ RGB and light intensity analyses, which supported a stress-correlated occurrence of the ring-opening of Rh, the scission of Ad and the fluorescence resonance energy transfer process between the respective mechanochemical species. Complementarity stemming from the difference in properties and manifestations of the two mechanophores is essential. That is, the more labile Rh allows shifting the appreciable optical changes to a much lower force threshold; the transient nature and high dynamic range of mechanochemiluminescence from Ad map in real time where and when many of the covalently incorporated dioxetane bonds break; besides, the disrupted yet non-scissile structure of Rh acts as a fluorescent acceptor to effectively harvest chemiluminescence from ruptured Ad. The current strategy is thus empowering multi-functional mechano-responsive polymers with greatly improved sensitivity and resolution for multimodal stress reporting.
Highlights
Stress induced covalent bond scission underlies the macroscopic failure of polymeric materials.[1]
We demonstrate a simple approach to realize this function by embedding two distinct mechanophores — rhodamine (Rh) and bis(adamantyl)-1,2-dioxetane (Ad), in polyurethane/polylactic acid blends
The past few decades have witnessed great progress on polymer mechanochemistry, which opens a new avenue for the design of selfreporting polymers with functional mechanophores as stress probes.[6,7,8,9]
Summary
Stress induced covalent bond scission underlies the macroscopic failure of polymeric materials.[1]. Rhodamine (Rh) and bis(adamantyl)-1,2-dioxetane (Ad) have been demonstrated as versatile self-reporting mechanophores (Fig. 1a).[17,19] When covalently coupled with polyurethane chains or networks, Rh experiences ring-opening transition under stress.[19,26] Discoloration and uorescence arise for highcontrast stress detection, since the ring opened Rh exhibits excellent optical properties including a high absorption coefficient and quantum efficiency with long-wavelength absorption and emission. Exhibiting a more or less persistent mechanochromic response, the non-scissile, reversible Rh delivers limited temporal resolution in recording chain scission events.[26,27] In this sense, real-time monitoring of bond breakage is possible when bis(adamantyl)-1,2-dioxetane is integrated as a chemiluminescent stress probe.[17] Mechanical dissociation of the dioxetane ring leads to the excited adamantanone that relaxes to the ground state with blue auto-luminescence The two mechanophores have been well studied individually, they as well as other chromic mechanophores can only respond under speci c loading force either under daylight or in darkness.[30,31,32,33,34,35,36] Using this strategy, limitations derived from the large force threshold of Ad and limited resolution of Rh have been overcome, empowering the polymer blends with abilities to report whether, where and when mechanical events take place, which can work as a full-day stress sensor responsive in an expanded force region
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
