In recent decades, more than 100 different mechanophores with a broad range of activation forces have been developed. For various applications of mechanophores in polymer materials, it is crucial to selectively activate the mechanophores with high efficiency, avoiding nonspecific bond scission of the material. In this study, we embedded cyclobutane-based mechanophore cross-linkers (I and II) with varied activation forces (f_a) in the first network of the double network hydrogels and quantitively investigated the activation selectivity and efficiency of these mechanophores. Our findings revealed that cross-linker I, with a lower activation force relative to the bonds in the polymer main chain (f_a-I/f_a-chain = 0.8 nN/3.4 nN), achieved efficient activation with 100% selectivity. Conversely, an increase of the activation force of mechanophore II (f_a-II/f_a-chain = 2.5 nN/3.4 nN) led to a significant decrease of its activation efficiency, accompanied by a substantial number of nonspecific bond scission events. Furthermore, with the coexistence of two cross-linkers, significantly different activation forces resulted in the almost complete suppression of the higher-force one (i.e., I and III, f_a-I/f_a-III = 0.8 nN/3.4 nN), while similar activation forces led to simultaneous activations with moderate efficiencies (i.e., I and IV, f_a-I/f_a-IV = 0.8 nN/1.6 nN). These findings provide insights into the prevention of nonspecific bond rupture during mechanophore activation and enhance our understanding of the damage mechanism within polymer networks when using mechanophores as detectors. Besides, it establishes a principle for combining different mechanophores to design multiple mechanoresponsive functional materials.

中文翻译：

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聚合物网络中力团的活化力对其活化选择性和效率的影响


近几十年来，已经开发出 100 多种具有广泛激活力的不同机械载体。对于力团在聚合物材料中的各种应用来说，高效选择性地激活力团、避免材料的非特异性键断裂至关重要。在本研究中，我们将具有不同活化力（f _a ）的环丁烷基机械载体交联剂（I和II）嵌入双网络水凝胶的第一个网络中，并定量研究了双网络水凝胶的活化选择性和效率。这些机械载体。我们的研究结果表明，交联剂 I 相对于聚合物主链中的键具有较低的活化力 (f _a-I /f _a-chain = 0.8 nN/3.4 nN)，实现了高效活化，选择性 100%。相反，机械基团II激活力的增加（f _a-II /f _a-chain = 2.5 nN/3.4 nN）导致其激活效率显着下降，同时伴随着显着的降低。非特异性键断裂事件的数量。此外，当两种交联剂共存时，显着不同的活化力导致几乎完全抑制较高力的交联剂（即 I 和 III，f _a-I /f _a-III = 0.8 nN/3.4 nN)，而相似的激活力导致同时激活，效率适中（即 I 和 IV，f _a-I /f _a-IV = 0.8 nN/1.6 nN ）。这些发现为防止机械载体激活过程中非特异性键断裂提供了见解，并增强了我们对使用机械载体作为检测器时聚合物网络内损伤机制的理解。此外，它还建立了结合不同力团来设计多种力响应功能材料的原则。