Department Technical Physics II, Technische Universität Ilmenau, 98684 Ilmenau, Germany.
Institute of Physics, Kazan Federal University, Kazan 420008, Tatarstan, Russia.
J Chem Phys. 2017 Aug 21;147(7):074904. doi: 10.1063/1.4998184.
A thorough theoretical description of the recently suggested method [A. Lozovoi et al. J. Chem. Phys. 144, 241101 (2016)] based on the proton NMR dipolar-correlation effect allowing for the investigation of segmental diffusion in polymer melts is presented. It is shown that the initial rise of the proton dipolar-correlation build-up function, constructed from Hahn Echo signals measured at times t and t/2, contains additive contributions from both inter- and intramolecular magnetic dipole-dipole interactions. The intermolecular contribution depends on the relative mean-squared displacement of polymer segments from different macromolecules, which provides an opportunity for an experimental study of segmental translational motions at the millisecond range that falls outside the typical range accessible by other methods, i.e., neutron scattering or NMR spin echo with the magnetic field gradients. A comparison with the other two proton NMR methods based on transverse spin relaxation phenomena, i.e., solid echo and double quantum resonance, shows that the initial rise of the build-up functions in all the discussed methods is essentially identical and differs only in numerical coefficients. In addition, it is argued that correlation functions constructed in the same manner as the dipolar-correlation build-up function can be applied for an experimental determination of a mean relaxation rate in the case of systems possessing multi-exponential magnetization decay.
本文对最近提出的一种基于质子 NMR 偶极相关效应的方法[A. Lozovoi 等人，J. Chem. Phys. 144, 241101 (2016)]进行了深入的理论描述，该方法可用于研究聚合物熔体中的链段扩散。结果表明，由在时间 t 和 t/2 测量的 Hahn Echo 信号构建的质子偶极相关积累函数的初始上升包含来自分子内和分子间磁偶极-偶极相互作用的附加贡献。分子间贡献取决于来自不同大分子的聚合物链段的相对均方根位移，这为实验研究毫秒范围内的链段平移运动提供了机会，而这些运动超出了其他方法（例如中子散射或带有磁场梯度的 NMR 自旋回波）通常可达到的范围。与基于横向自旋弛豫现象的另外两种质子 NMR 方法（即固体回波和双量子共振）的比较表明，在所有讨论的方法中，积累函数的初始上升本质上是相同的，仅在数值系数上有所不同。此外，还认为可以以与偶极相关积累函数相同的方式构造相关函数，以便在具有多指数磁化衰减的系统中实验确定平均弛豫率。
