Jo Jun Young, Jang Han Gyeol, Jung Yong Chae, Lee Doh C, Kim Jaewoo
Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), 92 Chudong-ro, Bongdong-eup, Wanju-gun, Jeonbuk 55324, Korea.
Department of Chemical and Biomolecular Engineering, KAIST Institute for the NanoCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea.
ACS Macro Lett. 2019 Aug 20;8(8):882-887. doi: 10.1021/acsmacrolett.9b00373. Epub 2019 Jul 8.
The correlation between polymer architecture and molecular-level forces has long been a challenging research subject. Herein, spiropyran, a mechanophore that exhibits fluorescence change under force, was incorporated as a cross-linker between PMMA backbone segments. Using an in situ opto-mechanical setup to probe the molecular-level forces, the mechano-response of SP-linked PMMA as a function of the cross-link density was monitored during deformation. The dependence of the molecular-level force on cross-link density was quantitatively examined and revealed. First, a higher cross-link density shifted the fluorescence onset, that is, the onset of the spiropyran-to-merocyanine transition, to lower strains, eventually shifting the onset long before yield, without requiring sufficient chain mobility, owing to the higher efficiency of the force transfer. Under the same energy, the increase in cross-link density allowed for faster force transfer, but only to a certain level. Finally, the overall amount of spiropyran-to-merocyanine conversion linearly decreased with increasing cross-link density.
聚合物结构与分子水平力之间的相关性长期以来一直是一个具有挑战性的研究课题。在此，螺吡喃作为一种在受力时会发生荧光变化的机械响应基团，被引入到聚甲基丙烯酸甲酯（PMMA）主链段之间作为交联剂。利用原位光机械装置探测分子水平力，在变形过程中监测了螺吡喃连接的聚甲基丙烯酸甲酯（SP-linked PMMA）的机械响应与交联密度的函数关系。定量研究并揭示了分子水平力对交联密度的依赖性。首先，较高的交联密度将荧光起始点，即螺吡喃向部花青转变的起始点，移向更低的应变，最终在屈服前很久就发生了移动，这是由于力传递效率更高，无需足够的链迁移率。在相同能量下，交联密度的增加允许更快的力传递，但仅到一定程度。最后，螺吡喃向部花青转化的总量随交联密度的增加呈线性下降。
