Li Yahui, Yang Junsheng, Cheng Hong, Cai Linkun, Ye Ke, Xia Zhijie, Zhang Qianlei, Wang Daoliang, Chen Wei
National Synchrotron Radiation Laboratory, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei 230026, China.
South China Advanced Institute for Soft Matter Science and Technology, School of Molecular Science and Engineering, Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, and State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China.
Soft Matter. 2021 Oct 13;17(39):8973-8981. doi: 10.1039/d1sm00988e.
The network structure in the amorphous domain of swollen iodine-doped poly(vinyl alcohol) (PVA) was systematically investigated by low-field (LF) NMR techniques to reveal the PVA-iodine complex formation mechanism. Three PVA-iodine complexes were obtained under different iodine concentrations () of KI/I solution: (i) < 0.1 M: PVA-I/I complex only exists in the non-crystalline region, (ii) 0.1 M < < 1 M: formation of PVA-I complex I, and (iii) > 1 M: formation of PVA-I complex II. It was found that there is no intermediate-magnitude chain motion of PVA under dyeing conditions to induce the substance exchange, as evidenced by the unchanged second moment (∼1.2 × 10 m s) at elevated temperature (<380 K). The introduction of iodine ions can affect the chain mobility of the interphase and mobile regions. With increasing , the chain dynamics become more restricted, as detected by the faster decay of the relaxometry results, which further accelerates the complexation process. The residual dipolar coupling strength, , obtained by the more quantitative double-quantum (DQ) NMR, increases abruptly at > 1 M. This suggests more constraints form in the amorphous network for the PVA-I complex II system. The constant defects fraction further reveals that the complexation prefers to happen along the tie chains. These results supply a possible formation pathway for the PVA-iodine complexes.
通过低场（LF）核磁共振技术系统研究了溶胀碘掺杂聚乙烯醇（PVA）非晶区的网络结构，以揭示PVA - 碘络合物的形成机制。在不同KI/I溶液碘浓度（）下获得了三种PVA - 碘络合物：（i）<0.1 M：PVA - I/I络合物仅存在于非晶区；（ii）0.1 M <<1 M：形成PVA - I络合物I；（iii）>1 M：形成PVA - I络合物II。结果发现，在染色条件下PVA不存在中等程度的链运动来诱导物质交换，这由高温（<380 K）下不变的二阶矩（~1.2×10 m s）证明。碘离子的引入会影响相间和可移动区域的链流动性。随着增加，链动力学变得更加受限，这通过弛豫测量结果更快的衰减检测到，这进一步加速了络合过程。通过更定量的双量子（DQ）核磁共振获得的剩余偶极耦合强度在>1 M时突然增加。这表明在PVA - I络合物II系统的非晶网络中形成了更多的约束。恒定的缺陷分数进一步表明络合作用更倾向于沿着系链发生。这些结果为PVA - 碘络合物提供了一种可能的形成途径。
