The influence of molecular motion on cross-polarization in cross-linked elastomers

Towards quantitative measurements in solid-state CPMAS NMR: A Lee–Goldburg frequency modulated cross-polarization scheme

“…Clearly, this observation indicates that the direction of the 1 H spin-lock field has little effect on the cross-polarization time T NH , even if the 1 H offresonance spin-lock scales the heteronuclear 1 H-15 N dipolar coupling. In fact, the rate of the polarization buildup can be rationalized by [4,12] 1…”

“…On the other hand, for S spins that are not directly attached to protons (e.g., non-protonated 15 N spins) or whose structural group experiences significant motion (e.g., -CH 3 ), the I-S dipolar coupling becomes relatively weak resulting in a rather long T IS and thus a slow polarization buildup of the S spins. Other factors may also affect the polarization buildup, for instance, any Hartmann-Hahn mismatch D may slow the polarization buildup [10], and molecular motions may affect CP dynamics in various ways [12]. Within molecules, there usually exist different bonding structures for the dilute spins, such as protonated and non-protonated S spins.…”

An earth’s field nuclear magnetic resonance apparatus suitable for pulsed gradient spin echo measurements of self-diffusion under Antarctic conditions

“…One solution has been to use small permanent magnets housed in a compact probe, an approach that has been used with success in applications as diverse as oil-well logging 10 and for the detection of defects in car tires. 11 Although the sample volumes investigated with such probes are usually small the high field strength of currently available permanent magnets helps to compensate for any loss in overall NMR sensitivity.…”

Homonuclear Separated Local-Field Spectroscopy by Magnetization-Exchange NMR

“…The use of protons, for which the principal axes of the dipolar tensor can be easily established, represents an important advantage of this method. It can be correlated with the local segmental order, which can also be determined by alternative NMR methods [43,44]. The technique proposed in this work uses spin polarization which evolves independently of dephasing effects arising from magnetic inhomogeneities or chemical shift.…”