This work reports on the implementation of an an iterative procedure to solve the non-linear problem of wave propagation in homeotropic Nematic Liquid Crystals (N-LC). The nematic structure of the ...crystal molecules is strongly dependent on the applied external electromagnetic field. In our case, a monochromatic plane wave is normally incident on the liquid crystal, which is sandwiched between two glass layers. The orientation of these molecules, called the directors, determine the dielectric tensor properties of the medium. A Mode-Matching Technique (MMT) was used to accurately solve for the governing fields in each of the subdivided layers composing the crystal, whereas an explicit finite-difference scheme with relaxation was implemented to solve for the directors' orientation. The non-linear problem was also solved using a more efficient implicit finite difference scheme characterized by a faster convergence rate. Obtained computational results were compared to published data indicating good agreement.
In a liquid crystal cell, under a given boundary condition and an externally applied field, the liquid crystal is in director field configuration that minimizes the total free energy of the system. ...When an external electric field is applied to the liquid crystal, it will reorient because of the dielectric interaction between the liquid crystal and the applied field. This field‐induced reorientation of the liquid crystal is referred to as the Fréedericksz transition. Anchoring strength of alignment layers in liquid crystal devices has profound effects on the electro‐optical properties of the devices. This chapter considers how to measure anchoring strengths. In liquid crystal devices it is highly desirable that the alignment layer has a pretilt angle such that the reorientation of the liquid crystal is well controlled and uniform. Large pretilt angles can be measured by using the magnetic ‘null’ method.
We measure, under stationary conditions, the power spectrum of the transmitted and scattered light intensity in a planar nematic liquid crystal cell as a function of the applied voltage in the ...neighbourhood of the electrically-induced splay Fréedericksz transition. The Fréedericksz threshold is independently determined using a standard interferometric technique. The low-frequency noise spectral density of the transmitted light displays a well defined peak at the critical voltage; this feature is instead hidden in the scattering noise. We critically examine the performances of these different experimental techniques and show that noise measurements are an adequate tool to study orientation transitions in nematic liquid crystals.
Prewavy Pattern: A Director-Modulation Structure in Nematic Liquid Crystals Huh, Jong-Hoon; Hidaka, Yoshiki; Yusuf, Yusril ...
Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals,
08/2001, Letnik:
364, Številka:
1
Journal Article, Conference Proceeding
A periodic structure (the prewavy pattern) found below the onset of electroconvection in a homeotropically aligned nematic liquid crystal is reported. It is characterized by a periodic modulation of ...the director in the xy-plane, which can be distinguished from electroconvection patterns with modulation in the xz-plane. The prewavy instability is investigated in detail; a phase diagram in the frequency-voltage plane, the voltage dependence of the azimuthal rotation angle, the voltage and frequency dependence of the wavelength of the prewavy pattern, and the director field in the prewavy pattern are provided. This prewavy pattern always evolves into the so-called chevrons above onset of convection. The wavelength of the chevrons and the orientation of their alternating zig and zag rolls depend on the director structure of the prewavy pattern.
LIGHT-INDUCED PATTERN FORMATION IN NEMATIC LIQUID CRYSTALS Demeter, Gábor; Kramer, Lorenz
Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals,
20/8/1/, Letnik:
366, Številka:
1
Journal Article, Conference Proceeding
We present a theoretical study of the Light-Induced Fréedricksz transition in two geometries where dynamical phenomena induced by the laser light have been observed. We consider a spatially extended ...system, i.e. we assume the laser beam to be much wider than the thickness of the cell. We suggest that pattern formation phenomena in the plane of the cell entirely due to the light-director interaction should be possible to observe.
In this paper, the complete theoretical and experimental studies of electrically and magnetically induced orientational transitions in suspensions of goethite nanorods in a nematic liquid crystal ...4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT), known as ferronematics are presented. Two types of samples with different magnetic properties are prepared and observed. A compensated ferronematic with zero initial magnetization is obtained after cooling of the sample from isotropic to nematic phase in the absence of a magnetic field. A magnetized ferronematic with nonzero initial magnetization is prepared during application of magnetic field. The magnetically induced transitions demonstrated two different types of orientational behavior of the samples. The Fréedericksz transition in the compensated ferronematic occurred in higher magnetic field in comparison with pure nematic while the magnetized ferronematic shown well measurable response in capacitance to the applied magnetic field, even much below the Fréedericksz threshold in usual 6CHBT. Full theoretical descriptions of such behaviours of compensated and magnetized ferronematic samples are presented and all observed dependencies of the cells capacitance on magnetic field are numerically calculated. A comparative analysis shows very well qualitative and quantitative agreement between theoretical results and experimental data. Due to this, the material parameters of the investigated ferronematic system with goethite nanoparticles are estimated.
•Liquid crystal suspensions of goethite particles are synthesized.•Ferromagnetic and antiferromagnetic suspensions are prepared.•Electric and magnetic orientational responses of the suspension are studied.•A remarkable agreement between theory and experiment is obtained.
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