Spin-diffusion curve

Fig. 10.3.9 Spin diffusion in LDPE. (a) Spin-diffusion curves showing the decay of magnetization in the mobile chain segments as a function of distance across the sample. The symbols I and II mark the regions unaffected and affected by the electrical ageing process, respectively, (b) Representative magnetization decays from regions I and II. Their different shapes indicate different morphologies. Dots experimental values. Solid lines Simulations.

The initial part of this Ti-corrected spin diffusion curve is linear, as described elsewhere [9,11]. Extrapolation of this linear decay for intensity = 0 leads to the value (tm ) that is needed to determine the domain size according to Eq. 1. 

H NMR spin diffusion curve for sanqile PAioPDMSn (Ti-corrected). 

Taking the values from the corrected spin diffusion curves, the Deft values and e =3 for... 

FIGURE 20.17. (a) Series of spin-diffusion Hetcor data for poiycarbonateatmixingtimesof(top)0 ms, (middle) 0.1 ms, and (bottom) 2.0 ms. (b) Representative spin-diffusion curves extracted from Hector spin-diffusion data, like that in (a), for two different poly( -caprolactone)/poiy-(L-lactic acid) biends. Note the ciear distinction between intramolecular and interchain/interdomain equilibration, the latter occurring at longer times for one blend versus the other. [Adapted with permission from Refs. [62] and [63]. 

In conclusion, if temperature can be chosen freely, the best one is around the high-temperature maximum of a". Then, the NOESY spectrum has the highest possible sensitivity but is still free of spin diffusion. Low-temperature spectroscopy can increase sensitivity immensely, but quantitative data analysis requires either the full matrix or the buildup curve analysis. 

When the spin-diffusion rate is comparable to the values, the relaxation decay curves become non-single exponential, and when the spin-diffusion rate is less than 10% of the values, the relaxation decay curve can be described by a single exponential with an intrinsic relaxation rate. 

In the modified ISPA approach,166 16 the distances are calculated from the NOE intensities using special calibration curves, which take into account that short distances are typically overestimated and long distances underestimated in the classical ISPA due to the spin diffusion, but ignores individual differences between specific pairs of protons. The curves are calibrated based on NOE data for interproton distances with fixed values. Model calculations for a short DNA duplex showed that this approach produces good results,166 however, it is expected that the errors should increase for larger molecules with more prominent spin diffusion. 

The magnetization-decay curves have been analysed for each position in space. The spin-diffusion constants were obtained from the H linewidths of the broad and the narrow components according to [Demi],... 

Fig. 5.16. Imaging polymer morphology by spin-diffusion contrast on a sample of electrically aged polyethylene, (a) Sample for electrical aging in needle-plate geometry and region cut out for spin diffusion imaging with one-dimensional spatial resolution, (b) Spatially resolved distribution of the domain sizes derived from fitting theoretical diffusion curves of a sandwich layer model to the experimental data. Pronounced changes in the thickness for crystalline, interfacial and amorphous layers are obtained [58].

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