Nuclear magnetic resonance oriented systems

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

The potential of nuclear magnetic resonance spectroscopy for studying liquid crystalline systems is discussed. Typical spectra of nematic, smectic, and cholesteric mesophases were obtained under high resolution conditions. The observed line shape in the cholesteric phase agrees with that proposed on the basis of the preferred orientation of this phase in the magnetic field. The line shapes observed in lyotropic smectic phases appear to be the result of a distribution of correlation times in the hydrocarbon portions of the surfactant molecules. Thermotropic and lyotropic phase transitions are easily detected by NMR and agree well with those reported by other methods. The NMR parameters of the neat and middle lyotropic phases allow these phases to be distinguished and are consistent ivith their proposed structures. 

Various improvements have broadened the research in the field of zeolite membranes and films, such as the development of new synthesis procednres, the use of new supports with specific characteristics (monoliths, foams, etc.), or the use of modified supports by means of masking or grafting techniques, the application of new analytical techniques (isotopic-transient experiments, permporometry, pulsed field gradient nuclear magnetic resonance [NMR], interference microscopy, IR microscopy, etc.), the control of the orientation of the crystals (by means of covalent linkages, synthesis conditions, etc.) and of the thickness of the membranes, and the preparation of new zeolites as membranes or new zeolite-related materials. In addition, a variety of zeolites can now be prepared as colloidal systems with particle dimensions ranging from tens to a few hnndred nanometers. 

Nuclear magnetic resonance (NMR) is a technique of considerable versatility in polymer science. It is used universally as a probe of chemical configurations, it provides information on the dynamics and relaxation times of a polymer system and it offers a route to the determination of orientation parameters, the exact route depending on the particular nuclei employed. In principle quadrupolar, dipolar, shielding tensor and indirect spin coupling interactions can all be employed " however, in practice only the first two have any universal appeal. Dipolar coupling using proton NMR offers the simplest approach in terms of material preparation and will be considered first. 

Stator orientation at each stage of the rotary cycle. A and B can be remote (stage I), in close proximity with M helicity (stage II), or in close proximity with P helicity (stage III). As a consequence, the cooperative effect of A and B and the preferred chiral sense induced in a transformation catalyzed by the system is modulated by the rotary cycle. Unidirectional clockwise rotation of the rotor with respect to the stator in the motor was confirmed by a combination of UV-vis, CD, and proton nuclear magnetic resonance ( H-NMR) spectroscopy—see Figure 44. 

K.V.R.M. Murali, N. Sinha, T.S. Mahesh, M.H. Levitt, K.V. Ramanatham, A. Kumar, Quantum-information processing by nuclear magnetic resonance experimental implementation of half-adder and subtractor operations using an oriented spin-7/2 system, Phys. Rev. A 66 (2002) 022313. 

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