Soft‐Matter Relaxation by the NMR‐MOUSE

Mobile single-sided NMR

“…Nevertheless, one should be aware of the fact that the CPMG signals may differ for example for magnetization components from fluids experiencing restricted diffusion in different size pores, so that simple addition of echoes may lead to incorrect amplitudes. Schemes for rapid measurement of combined T 1 and T 2 have been published, which avoid long recovery delays and explore the inversion recovery scheme [61] and the saturation recovery scheme [61,62,184]. Also other relaxation times like T 1q (Fig.…”

“…18. For example, T 1 can be measured by inversion recovery (a) [60,65], saturation recovery (b) [61,62,184], and by hole-burning experiments (c) [311]. For detection, a single echo is sufficient, but a multi-echo train boosts the signal when all echoes are summed up [302].…”

“…If h is adjusted to different values, the echo contributions from the different coherence pathways are weighted differently and the signal decay is modified. This may be exploited to optimize the contrast to discriminate objects made from similar materials, like the same rubber formulation but differing in processing conditions [61,62]. As the flip angle of the refocusing pulse approaches 90°, solid echoes are obtained, and the CPMG sequence turns into a multi solid-echo sequence [62,292] with partial averaging of the homo-nuclear dipole-dipole interactions between the protons in solids.…”

“…This may be exploited to optimize the contrast to discriminate objects made from similar materials, like the same rubber formulation but differing in processing conditions [61,62]. As the flip angle of the refocusing pulse approaches 90°, solid echoes are obtained, and the CPMG sequence turns into a multi solid-echo sequence [62,292] with partial averaging of the homo-nuclear dipole-dipole interactions between the protons in solids. This concept can be generalized to search for different pulse sequences such as timesuspension sequences and others known from line-narrowing in solid-state NMR with stroboscopic observation of the transverse magnetization and an adequate description in terms of average Hamiltonians to move the observed magnetization decay into a time window where the contrast for discrimination of different materials is best [4,298].…”

“…In addition to T 2 measurements by single echoes [7,54] and echo trains [9,10,[55][56][57][58], the most important ones are measurements of other relaxation times [59] such as T 1 [60][61][62][63][64], diffusion coefficients D [7,9,[65][66][67][68][69], spin modes like double-quantum coherences and their relaxation times [70,71], velocities v [72], images [73][74][75][76] which assign signal to position r by Fourier techniques, velocity distributions [77] and velocity images [78], two-and multidimensional schemes that correlate distributions of different relaxation times [79] and diffusion coefficients [80], and last but not least even chemical-shift resolved spectra [81]. The latter is a fundamental turning point in the development of NMR, as inhomogeneous magnetic fields had been avoided in the previous 50 years because of the false understanding that chemical-shifts cannot be resolved in a polarization field B 0 that is inhomogeneous across the sample [82].…”