Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611, Japan.
Graduate School of Science and Engineering, Kagoshima University, Korimoto, Kagoshima 890-0065, Japan.
Phys Chem Chem Phys. 2020 Mar 11;22(10):5561-5567. doi: 10.1039/c9cp06717e.
We report the structure of poly(ethylene glycol) (PEG) in a imidazolium-based ionic liquid (IL) electrolyte containing lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) salt, as determined using Raman spectroscopy, high-energy X-ray total scattering (HEXTS), and molecular dynamics (MD) simulations. The Raman spectral study indicated that the TFSA anions bound to Li ions are desolvated when PEG is added to the LiTFSA/IL solution to form stable Li+-PEG complexes. Via quantitative analysis of the obtained Raman spectra, the desolvation number of the TFSA [nd, per one oxygen atom of the ethylene glycol unit (Opeg)] was determined to be ∼0.4, irrespective of the shape (star or linear) and molecular weight of the polymer. On the basis of radial distribution functions obtained from the HEXTS experiments and MD simulations, we demonstrated that the Li+-PEG complexation induces a conformational change of the PEG chain from gauche/anti-conformers to a syn conformer. This Li+-coordination-induced conformation resulted in a decrease in the radius of gyration (Rg) of the PEG chain, implying a folding behavior of polymer chains through multiple OpegLi+Opeg interactions.
我们使用拉曼光谱、高能 X 射线全散射（HEXTS）和分子动力学（MD）模拟研究了含锂双（三氟甲烷磺酰基）酰胺（LiTFSA）盐的咪唑基离子液体（IL）电解质中聚乙二醇（PEG）的结构。拉曼光谱研究表明，当 PEG 加入到 LiTFSA/IL 溶液中形成稳定的 Li+-PEG 配合物时，与 Li 离子结合的 TFSA 阴离子被去溶剂化。通过对获得的拉曼光谱进行定量分析，确定 TFSA 的去溶剂化数（nd，每一个乙二醇单元的氧原子（Opeg））约为 0.4，与聚合物的形状（星形或线性）和分子量无关。基于 HEXTS 实验和 MD 模拟得到的径向分布函数，我们证明了 Li+-PEG 配合物诱导 PEG 链从 gauche/反构象到 syn 构象的构象变化。这种 Li+-配位诱导的构象导致 PEG 链的回转半径（Rg）减小，这意味着通过多个 OpegLi+Opeg 相互作用，聚合物链发生折叠行为。
