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1H nuclear magnetic resonance (NMR) spectra and birefringence of noncubic plastic single crystals (CH3)2CCl2–CCl4 have been measured. The investigation has demonstrated that in these crystals weak preferred orientations of molecules were observed. Concentration dependence of orientational ordering matrix of (CH3)2CCl2 molecules has been obtained from computer simulations of NMR line shape and birefringence data. It has been found that all ordering matrix elements become zero at mole fraction of 2,2-dichloropropane 0.5.

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A simple method to study di †usion with the help of NMR has been suggested, based on the measurement of the rate of establishment of equilibrium in a sample with initial non-equilibrium distribution of labelled species. The distribution of components in the sample during the process of di †usion was determined with the use of a standard NMR spectrometer or relaxometer. Di †usion coefficients, D, measured in water and the plastic phase of sulfolane agreed well with the data obtained by other methods. D values for dioxane in cross-linked polyurethane and for water in the lamellar phase of waterÈammonium per-Ñuorononanoate (APFN) mixtures were also measured, to demonstrate the application of the method. The technique, being a tracer method, can be applied in a number of cases where the application of spin-echo is difficult (e.g. low concentration of solvent in polymers, in conditions of incomplete averaging of internal Ðelds, large chemical shifts etc.) ; for the study of mutual di †usion and dissolution kinetics of complex phase mixtures ; and for the measurement of D in systems with physical hindrances to di †usion where the method allows one to determine D corresponding to " inÐnite Ï time of observation.The proposed method has its origin in the property of NMR phenomena, that the integral intensity of the detected signal is proportional to the number of resonating nuclei in the volume of the rf coil of the spectrometer. Thus it is possible to determine the absolute or the relative concentration of a substance in any part of the cylindrical tube used in the NMR investigation. In the presented method, two chemically identical substances (or mixtures in the case of multicomponent systems) but with di †erent isotopic content are put into contact directly in the NMR tube and the change in concentration of one (or both) components with time is observed along the NMR tube. The integral intensity of the NMR spectrum or the maximum amplitude of the free precession signal is measured. D is calculated from the time dependence of the NMR signal. Previously, NMR has been applied to monitor the change in concentration of a labelled species.1h4 However, in this study, for the Ðrst time, the initial, non-equilibrium distribution of isotopic species was used, allowing one, in principle, to Ðnd the self-di †usion coefficient. Since the chemical potentials of both samples are very close, the measured value in many cases reÑects the " true Ï translational mobility (selfdi †usion, intradi †usion), which is di †erent from mutual di †usion. The driving force of the latter is the di †erence in chemical potentials of the two samples.5h9The method was applied to the determination of D in water and polycrystalline sulfolane in the plastic state and gave results which were in a good agreement with those determined by other methods.10,11 It was supposed that this method could be applied to other systems including liquids, liquid crystals, polymer solutions etc., in which the widely used spinecho technique might have difficulties due to non-...