Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, Fribourg, CH-1700, Switzerland.
Pritzker School of Molecular Engineering, University of Chicago, 5640 S. Ellis Ave., Chicago, IL, 60637, USA.
Macromol Rapid Commun. 2020 Apr;41(7):e1900654. doi: 10.1002/marc.201900654. Epub 2020 Mar 5.
The development of polymers with built-in sensors that provide readily perceptible optical warning signs of mechanical events has received considerable interest. A simple and versatile concept to bestow polymers with mechanochromic behavior is the incorporation of dye-filled microcapsules. Such capsules release their cargo when their shell is damaged, and the dye is subsequently activated through a chemical or physical change that causes a chromogenic response. Here, we report the preparation of fluorescent poly(urea-formaldehyde) microcapsules containing solutions of a solvatochromic cyanostilbene dye and their integration in different polymers. When objects made from such composites are damaged, the dye solution is released from the containers, diffuses into the matrix, and the solvent evaporates. As a result, the polarity around the dye molecules changes, and this leads to a change of the fluorescence color. Alternatively, the dye is blended into the polymer matrix, microcapsules are loaded with a solvent, and the release of the latter triggers the color change. Both mechanisms afford ratiometric signals because the capsules that remain intact or dye molecules that are not exposed to the solvent can be used as a built-in reference; therefore, a quantitative assessment of the damage inflicted on the material is a priori possible.
具有内置传感器的聚合物的开发，这些传感器提供机械事件的明显光学警告信号，引起了相当大的关注。赋予聚合物机械变色行为的一种简单而通用的概念是掺入染料填充的微胶囊。当胶囊的外壳损坏时，这些胶囊会释放其货物，并且染料随后通过引起显色响应的化学或物理变化而被激活。在这里，我们报告了含有溶剂致变色氰基二苯乙烯染料溶液的荧光聚（脲-甲醛）微胶囊的制备及其在不同聚合物中的集成。当由这种复合材料制成的物体受到损坏时，染料溶液从容器中释放出来，扩散到基质中，并且溶剂蒸发。结果，染料分子周围的极性发生变化，这导致荧光颜色发生变化。或者，将染料混入聚合物基质中，将微胶囊装入溶剂中，并且后者的释放触发颜色变化。这两种机制都提供了比色信号，因为未损坏的胶囊或未暴露于溶剂的染料分子可以用作内置参考；因此，事先可以对施加于材料的损坏进行定量评估。
