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Topologically non-equivalent textures generated by the nematic electrohydrodynamics
摘要： Some classes of nematic liquid crystals can be driven through turbulent regimes when forced by an external electric field. In contrast to isotropic fluids, a turbulent nematic exhibits a transition to a stochastic regime that is characterised by a network of topological defects. We study the deformations arising after the electric field has been switched-off. In contrast to the turbulent regime, the relaxation of this topological-defect regime involves the annihilation of an interlacement of defect lines. We show that these defect lines separate regions of the nematic having topologically non-equivalent textures.
关键词： Nematic liquid crystals,electrohydrodynamics,twist deformation,topological defects
更新于2025-09-23 15:22:29
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Simulations of some physical parameters of homologous series of nBT and nCHBT at 0.3–20.0 THz
摘要： In this work, the terahertz (THz) absorption of homologous series of isothiocyanobiphenyls (nBT) and 4-(trans-4?-n-alkylcyclohexyl)isothiocyanato-benzene (nCHBT) are simulated by using the density functional theory (DFT) method. Numerical results show that absorption of the tested nematic liquid crystals (NLCs) varies up to 0.04 in the broad range of 0.3–20.0 THz and takes maximum value in the range of 9–14 THz. In addition, the values of molecular polarisabilities (αo, αe) increase with the increase in the number of carbon atoms in the alkyl chain, while refractive indices (no, ne) decreases. The calculated birefringence (Δn) values for nCHBT are approximately twice as large as the birefringence value for nBT. It is crucial to examine these series of nematic liquid crystals at THz frequencies due to the role of soft matter in various switchable THz components.
关键词： Numerical calculations,refractive index,terahertz radiation,birefringence,nematic liquid crystals
更新于2025-09-23 15:22:29
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Electro-optical switching in twisted nematic samples doped with gold nanorods
摘要： The present study is devoted to the investigation of reorientation properties of 8CB liquid crystal samples doped with gold nanorods with distinct aspect ratios. By using an optical experimental setup to probe the electro-optic response of twist cells under an AC electric field, we measure the characteristic switch times and Freedericksz threshold of doped nematic liquid crystals. The effects associated with the surface plasmon resonance and disorder induced by the metallic guest particles are analyzed. Further, we exploit the Gooch-Tarry conditions and Mauguin minima to account the thermal dependence of nematic birefringence in pristine and doped samples. Our results show that the electro-optical and thermal parameters of twisted nematic cells are strongly affected by the addition of gold nanorods.
关键词： Nematic liquid crystals,Gold nanorods,Reorientation
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Self-Written Y-Junctions using Spatial Solitons
摘要： The self-focusing and the formation of spatial solitons attracted a great deal of attention since the early days of nonlinear optics. Essentially a high-power beam changes the refractive index, writing a waveguide capable to con?ne the beam itself. Accordingly, spatial solitons behave like optical waveguides for beams at different wavelength and low power, thus enabling the generation of integrated optical devices written by the light itself. Several all-optical devices have been demonstrated based on this principle, with particular attention devoted in the last two decades to nematic liquid crystals (NLCs) due to their huge nonlinear response. The main nonlinear mechanism in NLC for CW excitations is reorientational, that is, the extraordinary (e-) wave rotates the optical axis of the material, providing a focusing effect. Nonetheless, NLCs are also subject to a strong thermo-optical effect, typically yielding a defocusing effect for the e-wave. Here we demonstrate the excitation of couples of solitons with a single-humped beam caused by the interaction between reorientational and thermal nonlinearity.
关键词： thermal nonlinearity,nematic liquid crystals,reorientational nonlinearity,spatial solitons,nonlinear optics
更新于2025-09-16 10:30:52
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Palladium-induced transformation of nematic liquid crystals to robust metallogel comprising self-assembled nanowires
摘要： The formation of a nematic liquid-crystalline phase in the bulk along with gelation of a novel asymmetric bolaamphiphilic NDI sca?old has been demonstrated. Further, a discrete metal NDI complex that is capable of forming a robust metallogel through wrapping of the NDI core with the oxyethylene chains of the neighboring molecules has been synthesized.
关键词： nematic liquid crystals,Palladium,metallogel,self-assembled nanowires
更新于2025-09-16 10:30:52
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Electro-Optical and Dielectric Responses of ZnO Nanoparticles Doped Nematic Liquid Crystal in In-Plane Switching (IPS) Mode
摘要： In present work, electro-optical and dielectric characteristics of ZnO nanoparticles (NPs) doped nematic liquid crystal mixture are studied in In-Plane Switching (IPS) mode. Effect of doping of ZnO nanoparticles on phase transition behaviour, threshold and operating voltage were studied. Polarising Optical Microscope (POM) study confirms a reduction in nematic to isotropic (N-I) phase transition temperature after doping of ZnO NPs. A decrease in threshold and operating voltages with better contrast ratio was observed. Further, a significant change in dielectric behaviour of NLC was also perceived in doped sample.
关键词： ZnO nanoparticles,threshold voltage,nematic liquid crystals,In-plane switching,inter-digital electrodes
更新于2025-09-12 10:27:22
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Monte Carlo Study of Slot-waveguide Liquid Crystal Phase Shifters
摘要： We present detailed Monte Carlo simulations of a simple model of a nematic liquid crystal slot waveguide shifter, investigating the effect of an applied electric external field. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the planar alignment as in Silicon Organic Hybrid waveguides anchoring appropriate for Polydimethylsiloxane polymer walls. The external field is modeled by adding a term to the Hamiltonian which describes its coupling to the mesogenic molecules. We have investigated the effect of the external field on the optical transmission and the ordering across the cell.
关键词： Monte Carlo,confined nematic liquid crystals,anchoring,waveguide shifters
更新于2025-09-12 10:27:22
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Thermal and Electro-optical Properties of Graphene Oxide/Dye-Doped Nematic Liquid Crystal
摘要： In this paper, the liquid crystalline complex systems were obtained by dispersing graphene oxide (GO) and methyl blue (MB) dye to liquid crystal mixture E7. The phase transitions and microstructural properties of the prepared liquid crystalline complex systems were investigated by differential scanning calorimeter (DSC) and polarised optical microscopy (POM). DSC and POM results showed that there was no change in the molecular structures of the complexes and they exhibited completely liquid crystalline properties during continuous heating. Also, the voltage-dependent optical transmissions of the complex systems were measured by the voltage transmittance experiments. It was found that the optical transmissions of the complex systems were not very different from the each other, but threshold voltage of the complex decreased by GO doping and increased for MB/GO doping. Furthermore, the dielectric properties of the complex systems were investigated by using impedance analyser. Dielectrically, measurements showed that the dielectric constant decreased with the dispersion of GO and GO/MB, and the critical frequency of E7 increased with doping.
关键词： POM,Graphene oxide,Electro-optic,Nematic liquid crystals
更新于2025-09-11 14:15:04
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Electro-optical, dielectric and optical properties of graphene oxide dispersed nematic liquid crystal composites
摘要： Graphene oxide (GO) in various concentrations (0.04 wt.%, 0.1 wt.% and 0.3 wt.%) was dispersed into nematic liquid crystal (LC) 5CB and studied for electro-optical, dielectric and optical responses. The textural and phase transition studies were investigated by optical polarising microscopy in the nematic phase. The effect of GO concentration on the micro-texture, phase transition temperatures, birefringence, threshold voltage, contrast ratio, dielectric permittivity, dielectric loss and conductivity was also investigated. The nematic–isotropic transition temperature slight increases (~3%) in the 0.04 wt.% and 0.1 wt.% GO dispersed 5CB composites as compared to 5CB. Threshold voltage decreases in the GO–5CB composites with the increase of GO concentration. Additionally, the effect of GO concentration on the optical absorbance of UV–visible light and energy bandgap is also considered.
关键词： graphene oxide,phase transitions,birefringence,threshold voltage,Nematic liquid crystals
更新于2025-09-11 14:15:04
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Topological defect enabled formation of nematic domains
摘要： We study numerically curvature and electric field driven domain formation and reorientations in two-dimensional nematic liquid crystals within square confinement. We use the Landau-de Gennes description in terms of the nematic tensor order parameter. We show that on increasing the amplitude of a sinusoidally shaped confining wall, pairs {defect, antidefect} are formed, which enable insertion of domains displaying significantly different average orientational order with respect to the surrounding nematic body. Furthermore, we study E-driven transformation between two competing degenerate domain-type structures. We show that transformations could be mediated via qualitatively different intermediate structures possessing topological defects.
关键词： Nematic liquid crystals,topological defects,order reconstruction,phenomenological modelling
更新于2025-09-11 14:15:04