Orientation Distribution of Molecules in a Smectic Liquid Crystal with a Distorted Director Geometryстатья
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Дата последнего поиска статьи во внешних источниках: 25 мая 2022 г.
Аннотация:Quantitative determination of the molecular orientation distributionfunction in samples of liquid crystals with a complex director geometry was performedusing the numerical simulation of electron paramagnetic resonance (EPR) spectra of thespin probes in a liquid-crystalline medium. To achieve the quantitative agreement ofexperimental and simulated EPR spectra, the hierarchy of the orientation order wasexplicitly taken into account, namely, the local ordering of liquid crystal molecules by themean-field potential of surrounding molecules, and the partial disordering of local directorswithin the sample. The samples under study are planar and twist LC cells with liquid crystal8CB cooled from the nematic into the smectic A phase in the magnetic field. The presenceof the magnetic field perpendicular to the cell director leads to distortion of the orientation of the liquid crystal in the cell. The spinprobe technique was successfully employed for the reliable measurement of orientation distribution functions of the lownonorthorhombic symmetry. Orientation order parameters up to 12th rank were measured, including nonaxial andnonorthorhombic order parameters. It is shown that the presence of several contradicting aligning forces leads to the tilt of thepreferential director toward the direction, which is a compromise between the orienting forces.