Hailu K, Fechete R, Demco D E, Blümich B
Institut für Technische Chemie und Makromolekulare Chemie, Rheinisch-Westfalische, Technische Hochschule, Worringerweg 1, D-52056 Aachen, Germany.
Solid State Nucl Magn Reson. 2002 Sep-Nov;22(2-3):327-43. doi: 10.1006/snmr.2002.0067.
Single-side NMR is particularly suitable for measurements of segmental anisotropy induced in elastomers by uniaxial forces or local strain. Proton transverse nuclear magnetic relaxation was investigated with the NMR-MOUSE by recording the Hahn-echo decay in cross-linked natural rubber bands. This provided information on the dependence of the Hahn-echo decay on the angle between the direction of the uniaxial stretching force and the axis Z defined direction perpendicular to the magnet pole faces of the NMR-scanner. The anisotropy effect on the Hahn-echo decay is correlated with the extension ratio, and it is more evident in the liquid-like regime of the decay. A weaker segmental anisotropy is detected by 1H solid- and Hahn-echo decays recorded by multi-pulse sequences. A qualitative understanding of the angular dependence is obtained by an analytical theory of the Hahn-echo decay adapted to the case of stretched elastomers and to strongly inhomogeneous magnetic fields. Using angular-dependent 1H residual second van Vleck moments and correlation times reported previously [P.T. Callaghan and E.T. Samulski, Macromolecules 30, 113 (1997)] from stretched natural rubber bands the segmental anisotropy measured in inhomogeneous magnetic fields by the Hahn-echo decay was numerically simulated. As an example of a macroscopic distribution of local segmental anisotropy, 1H Hahn-echo decays were measured by the NMR-MOUSE sensor in a stretched cross-linked natural rubber plate with a circular cut in the center.
单侧核磁共振特别适用于测量单轴力或局部应变在弹性体中引起的链段各向异性。通过记录交联天然橡胶带中的哈恩回波衰减，利用核磁共振微成像仪研究了质子横向核磁弛豫。这提供了关于哈恩回波衰减与单轴拉伸力方向和垂直于核磁共振扫描仪磁极面定义的Z轴方向之间夹角的依赖关系的信息。哈恩回波衰减的各向异性效应与伸长率相关，并且在衰减的类液体区域中更为明显。通过多脉冲序列记录的1H固体和哈恩回波衰减检测到较弱的链段各向异性。通过适用于拉伸弹性体和强非均匀磁场情况的哈恩回波衰减解析理论，获得了对角度依赖性的定性理解。利用先前报道的[P.T.卡拉汉和E.T.萨穆尔斯基，《高分子》30，113（1997）]来自拉伸天然橡胶带的角度相关的1H剩余第二范弗莱克矩和相关时间，对通过哈恩回波衰减在非均匀磁场中测量的链段各向异性进行了数值模拟。作为局部链段各向异性宏观分布的一个例子，利用核磁共振微成像仪传感器在中心有圆形切口的拉伸交联天然橡胶板中测量了1H哈恩回波衰减。
