Enhancement of Mechano-Sensitivity for Spiropyran-Linked Poly(dimethylsiloxane) via Solvent Swelling
Enhancement of Mechano-Sensitivity for Spiropyran-Linked Poly(dimethylsiloxane) via Solvent Swelling
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DOI：
10.1021/acs.macromol.0c00985
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发表时间：
2020-09-22
期刊：
影响因子：
5.5
通讯作者：
Kim, Jaewoo
中科院分区：
文献类型：
--
作者：
Kim, Dong Woo;Medvedev, Grigori A.;Kim, Jaewoo
螺吡喃（SP）是一种机械载体，当受到力时，其化学结构发生变化，从而光学特性发生变化。将SP结合到聚合物链中使得能够光学检测负载下材料中的应力/应变和损伤。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。已经尝试通过修饰SP机械基团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，我们探讨了机械敏感性的SP纳入聚（二甲基硅氧烷）（PDMS）网络的影响与有机溶剂（二甲苯）的PDMS的预溶胀。PDMS溶胀对机械基团的光学性质的影响进行了研究，通过测量荧光强度从SP连接的PDMS原位单轴变形过程中使用定制的光机械测量装置。结果表明，较长的溶胀时间会导致初始荧光降低，活化起始应变降低，活化斜率增加，导致表观机械敏感性增强。例如，相对于未溶胀的参照，15分钟预溶胀的SP连接的PDMS显示出机械敏感性的8.3倍增加。这种效应不仅限于单轴拉伸，而且在其他变形模式中也可以观察到，例如压缩和弯曲。当针对单轴拉伸过程中样品厚度的变化以及预应变和由于溶剂溶胀引起的初始荧光强度进行校正时，SP荧光强度与真实应变的关系为：（或链熵）曲线在不同程度的初始溶胀下塌陷成单一曲线，这表明膨胀增强的机械敏感性是由于预-网络的应变和由预溶胀引起的初始荧光强度的降低。
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 swellingenhanced mechano-sensitivity is due to the pre-strain of the network and a decrease in initial fluorescence intensity caused by the pre-swelling.