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Armenian Journal of Physics=Ֆիզիկայի հայկական հանդես
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The possible transitions between smectic A (SmA), Sm C, Sm C* and the nematic phases (N), viscosity and orientation processes were studied in liquid crystals (LC) and LC’ systems during and in the vicinity of the N LC ↔ Sm LC phase transition. Iinvestigation of structural and dynamic aspects of liquid crystalline mesophases were carried out by ESR relaxation induced by spin probes. The values of the viscosity coefficient in the mesophase were estimated. The dependence of the viscosity coefficient on the structural features of molecules of the components of the studied systems was established. Based on the obtained experimental and theoretically calculated data, as well as on the conducted explanatory theoretical analyses, it was shown that in the studied LC systems the N^* LC→IL phase transition was apparently best described as a combined phase transition, close to the Lifshitz’ tricritical point, which occurs in the systems with short-range interactions of molecules.