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Интеллектуальная Система Тематического Исследования НАукометрических данных 

Spin probe techniques are widely used for studying of structure and dynamics of various media including partially ordered matrixes such as liquid crystals, stretched polymers, biological membranes, etc. In such studies the parameters characterizing rotational and translational diffusion as well as orientational ordering of paramagnetic molecules are obtained. Further basing on these parameters values the conclusions about matrix properties are made. For successful realization of spin probe methods it is necessary to have the answers for some questions. What radical would be most appropriate for studying the matrix under consideration? What is the correlation between the properties of the probe and the properties of the matrix? To answer these questions it is necessary to have the detailed information about localization of admixture molecules in the media and their interaction with the host molecules. The guesthost interaction of nitroxide radicals in liquid crystalline matrixes was analyzed at present work. The molecular orientation distribution functions of different nitroxides were determined in different macroscopically ordered super cooled liquid crystals by numerical analysis. The used procedure is modelfree and allows finding of order parameters up to rank 10, as well as estimating of direction of the orientational axis of the admixture molecule. By means of analysis of EPR spectra, recorded at the temperatures of existing of the mesophases, the rotational diffusion coefficients and the directions of rotational axes of the probe molecules were obtained. In general, it was concluded that the dominant factor determining localization of the guest molecules in the liquid crystal is not their shape, but specific interactions with the molecules of the matrix. It was found also that some guest molecules have at least two ways of ordering in the aligned nematic and smectic liquid crystals. As an illustration the orientation distribution function of stable nitroxide radical in smectic 8CB liquid crystal is represented in Figure 1. It can be seen that there are two kind of orientation of paramagmetic molecules in the liquid crystal in this case. In Figure 2 the possible orientational axes of this radical are shown.