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      Autonomous Indication of Mechanical Damage in Polymeric Coatings

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          Abstract

          High-resolution in situ autonomous visual indication of mechanical damage is achieved through a microcapsule-based polymeric material system. Upon mechanical damage, ruptured microcapsules release a liquid indicator molecule. A sharp color change from light yellow to bright red is triggered when the liberated indicator 2',7'-dichlorofluorescein reacts with the polymeric coating matrix.

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          Most cited references 46

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          Force-induced activation of covalent bonds in mechanoresponsive polymeric materials.

          Mechanochemical transduction enables an extraordinary range of physiological processes such as the sense of touch, hearing, balance, muscle contraction, and the growth and remodelling of tissue and bone. Although biology is replete with materials systems that actively and functionally respond to mechanical stimuli, the default mechanochemical reaction of bulk polymers to large external stress is the unselective scission of covalent bonds, resulting in damage or failure. An alternative to this degradation process is the rational molecular design of synthetic materials such that mechanical stress favourably alters material properties. A few mechanosensitive polymers with this property have been developed; but their active response is mediated through non-covalent processes, which may limit the extent to which properties can be modified and the long-term stability in structural materials. Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups-so-called mechanophores-that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. We anticipate that force activation of covalent bonds can serve as a general strategy for the development of new mechanophore building blocks that impart polymeric materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing.
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            Mechanically-induced chemical changes in polymeric materials.

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              Polymorphism and reversible mechanochromic luminescence for solid-state difluoroboron avobenzone.

              Difluoroboron avobenzone (BF(2)AVB), a simple boron complex of a commercial sunscreen product, exhibits morphology-dependent emission and mechanochromic luminescence in the solid state. When scratched, smeared, or even gently touched, the emission color of BF(2)AVB films is significantly red-shifted under UV excitation. In the rubbed regions, the fluorescence recovers slowly at room temperature or much faster with heating, resulting in a simple rewritable "scratch the surface" ink of potential commercial use.
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                Author and article information

                Journal
                Advanced Materials
                Adv. Mater.
                Wiley
                09359648
                March 2016
                March 2016
                January 11 2016
                : 28
                : 11
                : 2189-2194
                Affiliations
                [1 ]Department of Materials Science and Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
                [2 ]Department of Mechanical Science and Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
                [3 ]Department of Aerospace Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
                Article
                10.1002/adma.201505214
                26754020
                © 2016

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