Magic-angle-spinning (MAS) enhances sensitivity and resolution in solid-state nuclear magnetic resonance (NMR) measurements. MAS is obtained by aerodynamic levitation and drive of a rotor, which results in large centrifugal pressures that may affect the physical state of soft materials, such as polymers, and subsequent solid-state NMR measurements. Here, we investigate the effects of MAS on the solid-state NMR measurements of a polymer electrolyte for lithium-ion battery applications, poly (ethylene oxide) (PEO) doped with the lithium salt LiTFSI. We show that stresses associated with MAS induce local chain ordering, which manifests itself as characteristic lineshapes with doublet-like splittings in subsequent solid-state 1 H, 7 Li, and 19 F static NMR spectra characterizing the PEO chains and solvated ions. MAS results in distributions of stresses that hence local chain orientations and extents of chain alignments, yielding distributions in the local magnetic susceptibility tensor that give rise to the observed NMR anisotropy and lineshapes. The effects of MAS were investigated on solid-state 7 Li, and 19 F pulsed-field-gradient (PFG) diffusion and 7 Li longitudinal relaxation NMR measurements. Activations energies for ion diffusion were affected modestly by MAS. 7 Li, longitudinal relaxation rates, which are sensitive to lithium ion dynamics in the nanosecond regime, were essentially unchanged by MAS. We recommend that NMR researchers studying soft polymeric materials use only the spin rates necessary to achieve the desired enhancements in sensitivity and resolution, as well as acquire static NMR spectra after MAS experiments to reveal any signs of MAS-induced local ordering.

中文翻译：

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高分子电解质中魔角自旋诱导的局部有序及其对固态扩散和弛豫核磁共振测量的影响

魔角自旋 (MAS) 提高了固态核磁共振 (NMR) 测量的灵敏度和分辨率。MAS 是通过空气动力悬浮和转子驱动获得的，这会产生很大的离心压力，这可能会影响软材料（如聚合物）的物理状态，以及随后的固态 NMR 测量。在这里，我们研究了 MAS 对锂离子电池应用聚合物电解质固态 NMR 测量的影响，聚（环氧乙烷）（PEO）掺杂锂盐 LiTFSI。我们表明，与 MAS 相关的应力会诱导局部链排序，这在表征 PEO 链和溶剂化离子的后续固态 1 H、7 Li 和 19 F 静态 NMR 光谱中表现为具有双峰状分裂的特征线形。MAS 导致应力分布，从而导致局部链取向和链排列范围，产生局部磁化率张量的分布，从而产生观察到的 NMR 各向异性和线形。研究了 MAS 对固态 7 Li 和 19 F 脉冲场梯度 (PFG) 扩散和 7 Li 纵向弛豫 NMR 测量的影响。离子扩散的活化能受 MAS 的影响不大。7 Li，纵向弛豫率对纳秒范围内的锂离子动力学敏感，但 MAS 基本上没有改变。我们建议研究软聚合物材料的 NMR 研究人员仅使用实现所需的灵敏度和分辨率增强所需的自旋速率，