Thermal fluctuations of director orientation in nematic liquid crystals with inclusions

We investigate thermal fluctuations of order parameters (director for mesomorphic subsystem and density for isomorphic liquid) in filled liquid crystal. We consider finite-size system with geometry of plane-parallel layer with zero boundary condition. We use a special model that takes into account the interaction of mesomorphic and isotropic subsystems and find general expressions for pair correlators. Based on these expressions we calculate the shift of critical temperature of isotropic liquid due to the interaction with the mesomorphic subsystem and space limitation.Досліджуються теплові флуктуації параметрів порядку (директор для рідкокристалічної підсистеми та густина для ізотропної рідини) в рідкому кристалі з домішками. Розглядається просторово обмежена система з геометрією плоского паралельного прошарку з нульовими граничними умовами. Запропоновано модель, що враховує взаємодію рідкокристалічної та ізотропної підсистем та знаходяться загальні вирази для парних кореляторів. На основі цих виразів розраховується зсув критичної температури ізотропної підсистеми, що виникає внаслідок взаємодії з рідким кристалом та через просторове обмеження

Light scattering by filled liquid crystals in anomalous-diffraction approach

The differential and total light scattering cross sections by LCs which contain hard macroscopic spherical and cylindrical particles are theoretically studied using the anomalous-diffraction approach. The influence of form and size of particles, the type and strength of director anchoring on the particle surface as well as light wave polarization on the light scattering is analysed.Проведено теоретичне вивчення диференційного та повного поперечних перерізів розсіяння світла на рідких кристалах, що містять тверді макроскопічні сферичні та ціліндричні частинки, у підході аномальної дифракції. Проаналізовано вплив форми і розміру частинок, типу і сили закріплення директора на поверхні частинок, а також поляризації світлових хвиль на розсіяння світла

Correlation properties of thermal orientation fluctuations in nematic liquid crystals with macroscopic inclusions

Influence of the director interaction with small macroscopic impurity particle surface as well as the cell surface on thermal director fluctuations in the nematic liquid crystal cell has been considered. The interaction with the impurity particle surface has been shown to have a stabilizing effect similar to that of the external field. In the liquid crystal isotropic phase, the interaction mentioned above results in a shift of the nematic phase absolute stability temperature, two existing shift mechanisms may compete with each other.Рассмотрено влияние взаимодействия директора с поверхностью малых макроскопических примесных частиц и поверхностью ячейки на тепловые флуктуации директора в ячейке нематического жидкого кристалла. Показано, что взаимодействие с поверхностью примесных частиц имеет стабилизирующий эффект, подобный тому, который имеет место во внешнем поле. В изотропной фазе жидкого кристалла указанное взаимодействие приводит к сдвигу температуры абсолютной стабильности нематической фазы, при этом существующие два механизма сдвига могут конкурировать

Correlations in the director-orientation fluctuations in the presence of microscopic impurities in a nematic liquid crystal

The model of a spatially restricted liquid-crystal system with microscopic impurities homogeneously distributed in the system is considered. The thermodynamic correlations of the director-orientation fluctuations and the correlations of the scalar order parameter characterizing impurities in the system are investigated for this system. It is shown that the impurity correlations are weaker than in a pure isotropic liquid. The correlations in the director deviations depend essentially on the wavevector and can be substantially weakened in the presence of impurities

Magnetic field induced orientational bistability in a ferronematic cell

The equilibrium states of a suspension of single-domain ferroparticles in a nematic liquid-crystalline homeotropic cell subject to an external magnetic field are studied. We predict the existence of magnetic field induced orientational bistability in such a system in a magnetic field ?102 Oe. The existence of the bistability phenomenon is governed by conditions on the cell thickness and on the director anchoring energy. The effect can be controlled using a small bias magnetic field normal to the unperturbed director. The director reorientation in a magnetic field causes an effective change in refraction index, which enables the orientational bistability to be exploited in optical devices

Light scattering by liquid crystals in anomalous-diffraction approach

The differential and total light scattering cross sections by LCs which contain hard macroscopic spherical and cylindrical particles are theoretically studied using the anomalous-diffraction approach. The influence of form and size of particles, the type and strength of director anchoring on the particle surface as well as light wave polarization on the light scattering is analyse

Rayleigh-Gans theory of light scattering by liquid crystals filled with cylindrical particles

Light scattering cross-sections by the director inhomogeneity near small cylindrical particles in a nematic cell are calculated in the Rayleigh-Gans approximation. We use the Percus-Yevick approximation to account for interference effects and study the influence of the boundary conditions on the particle surface as well as the effect of an external electric field on the angular dependence and on the magnitude of the light scattering cross-section

Adsorption phenomena and macroscopic properties of ferronematics caused by orientational interactions

We have studied the effect of adsorption and desorption of rod-like magnetic grains on the macroscopic properties of ferronematics in a ferronematic cell. An external magnetic field controls the equilibrium between ferroparticles in the bulk and those adsorbed on the cell surfaces. The magnetic field can thus influence the anchoring and the nematic orientational texture. In the presence of ferroparticle adsorption, the segregation effect is diminished, and the system becomes less susceptible to bulk ferroparticle coagulation