Proton nuclear magnetic relaxation time measurements

The transition of polyethylene from the orthorhombic to the hexagonal phase was observed at very high pressures (3000-5000 bar) by proton NMR and nuclear magnetic relaxation time measurements the phase diagram derived from this spectroscopy is in substantial agreement with DSC data. According to these results (see Fig. 1), the hexagonal phase can be observed above the triple point at 490 K and 3000 bar [13,14]. 

B. D. Sykes, W. E. Hull, and G.H. Snyder, Biophys. /, 21, 137 (1978). Experimental Evidence for the Role of Cross-relaxation in Proton Nuclear Magnetic Resonance Spin Lattice Relaxation Time Measurements in Proteins. 

The first successful nuclear magnetic resonance (NMR) measurements were made by E. M. Purcell et al. at Harvard, and F. Bloch et al at Stanford, independently in 1946. They observed the proton ( H) signal of the hydrogen nucleus of samples of paraffin wax (solid) and water (liquid), respectively. Their success in observing the proton signal was based on using samples in which the relaxation time was short. 

The dilatometric method is time-consuming and subject to the bias introduced by the convention described. More recently pulsed Nuclear Magnetic Resonance (pNMR) has been used to measure the relative amounts of liquid and solid fat in a sample, based upon the difference in rates of relaxation of protons in the two phases after the sample has been pulsed (AOCS Method Cd 16-81). With proper calibration this gives a direct determination of the percentage of solid fat, and the results are termed sohd fat content (SFC). The analysis takes less time than dilato-metry, but the equipment is more expensive. 

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