Spiropyran (SP) is a mechanophore that undergoes changes in chemical structure and thus in optical character when subjected to a force. Incorporation of SP into polymer chains enables optical detection of stress/strain and damage in the material under load. However, the mechano-sensitivity of SP-linked polymers is in general insufficient for many applications. Attempts have been made to enhance the mechano-sensitivity of SP-linked polymers via modification of the chemical structure of the SP mechanophore or the mesostructure of the polymer matrix. In the present study, we explore how the mechano-sensitivity of SP incorporated in a poly(dimethylsiloxane) (PDMS) network is influenced by the pre-swelling of PDMS with an organic solvent (xylene). The effect of PDMS swelling on the optical property of the mechanophore was investigated by measuring the fluorescence intensity from the SP-linked PDMS in situ during uniaxial deformation using a custom-built opto-mechanical measurement setup. The results suggest that a longer swelling time causes a decrease in the initial fluorescence, a decrease in the activation onset strain, and an increase in the activation slope, resulting in enhanced apparent mechano-sensitivity. For instance, the 15 min pre-swollen SP-linked PDMS showed an 8.3-fold increase in mechano-sensitivity relative to the unswollen reference. Such effect is not limited to uniaxial extension but also observed in other modes of deformation, such as compression and bending. When corrected against the variation in sample thickness during uniaxial extension, and pre-strain and initial fluorescence intensity due to solvent swelling, the SP fluorescence intensity vs true strain (or chain entropy) curves obtained at various degrees of initial swelling collapse into a single curve, which suggests that the swelling-enhanced mechano-sensitivity is due to the pre-strain of the network and a decrease in initial fluorescence intensity caused by the pre-swelling.

中文翻译：

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通过溶剂溶胀增强螺吡喃连接的聚二甲基硅氧烷的机械敏感性

螺吡喃（SP）是一种机械体，当受到力时其化学结构发生变化，因此光学特性发生变化。将SP掺入聚合物链中可以对负载下的材料进行应力/应变和损坏的光学检测。然而，SP连接的聚合物的机械敏感性通常不足以用于许多应用。已经尝试通过改变SP机制的化学结构或聚合物基质的介观结构来增强SP连接的聚合物的机械敏感性。在本研究中，我们探讨了聚二甲基硅氧烷（PDMS）网络中掺入的SP的机械敏感性如何受到PDMS与有机溶剂（二甲苯）的预溶胀的影响。原位在单轴变形过程中使用定制的光机械测量装置。结果表明，更长的溶胀时间会导致初始荧光的减少，激活起始菌株的减少以及激活斜率的增加，从而导致表观机械敏感性增强。例如，与未溶胀的参比相比，预溶胀15分钟的SP-连接的PDMS的机械敏感性提高了8.3倍。这种效果不仅限于单轴延伸，而且还可以在其他变形模式（例如压缩和弯曲）中观察到。如果针对单轴延伸过程中样品厚度的变化以及由于溶剂溶胀引起的预应变和初始荧光强度进行了校正，