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Suppressing depolarization by tail substitution in an organic supramolecular ferroelectric
摘要： Despite being very well established in the field of electro-optics, ferroelectric liquid crystals so far lacked interest from a ferroelectric device perspective due to a typically high operating temperature, a modest remnant polarization and/or poor polarization retention. Here, we experimentally demonstrate how simple structural modification of a prototypical ferroelectric liquid-crystal benzene-1,3,5-trisamide (BTA) – introduction of branched-tail substituents – results in materials with a wide operating temperature range and a data retention time of more than 10 years in thin-film solution-processed capacitor devices at room temperature. The observed differences between linear- and branched-tail compounds are analyzed using density functional theory (DFT) and molecular dynamics (MD) simulations. We conclude that morphological factors like improved packing quality and reduced disorder, rather than electrostatic interactions or intra/inter-columnar steric hindrance, underlay the superior properties of the branched-tailed BTAs. Synergistic effects upon blending of compounds with branched and linear side-chains can be used to further improve the materials’ characteristics.
关键词： liquid crystal,BTA,DFT,molecular dynamics,supramolecular,ferroelectric,polarization retention
更新于2025-09-19 17:15:36
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Electrically Tunable Liquid-Crystala??Polymer Composite Laser with Symmetric Sandwich Structure
摘要： This study investigates and develops for the first time an electrically tunable liquid-crystal?polymer composite laser with a symmetric sandwich structure. This structure includes two identical polymer-stablized cholesteric liquid-crystal (PSCLC) layers, and a dye-doped nematic LC (DDNLC) layer is sandwiched between them. The PSCLC and DDNLC layers act as distributed Bragg reflectors and half-wave plate with a gain medium, respectively. The entire cell behaves as an optical cavity, where the resonant modes occur at the maxima of the cell’s transmission spectrum. Through the competition among the resonant modes by considering the gain and loss, the resonant mode with the lowest lasing threshold can be sieved out for lasing occurrence. When the same voltage is applied to the two PSCLC layers, the pitch gradients are simultaneously formed through the two layers because of the electrically induced ion-concentration gradients. When the voltage increases, the pitch gradients increase, thereby leading to the expansion of the cell photonic band gap (PBG) and blue shift of the lasing wavelength. The sandwich cell PBG can expand from 55 nm to over 170 nm, and the tuning range of the lasing wavelength is as high as 70 nm, which is the widest ever achieved in LC-related sandwich systems. The proposed configuration of the sandwich sample presents new insights into tunable LC PBG and laser devices, thereby providing potential applications in the form of sensors, medical imaging, displays and lighting, among others.
关键词： distributed Bragg reflectors,electrically tunable,dye-doped nematic LC,photonic band gap,liquid-crystal?polymer composite laser,optical cavity,symmetric sandwich structure,half-wave plate,lasing wavelength,polymer-stablized cholesteric liquid-crystal
更新于2025-09-19 17:13:59
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High-quality tuning of cholesteric liquid crystal lasers based on polymer composite system
摘要： Electrically fine tuning is demonstrated in a cholesteric liquid crystal (ChLC) laser based on the polymer composite system. Photo-polymerization in the mixture of LC monomer and LC hardly causes phase separation due to miscibility, forming a microscopically well-mixed polymer-LC composite structure like gel. Light scattering in the polymer-LC composite system decreases with increasing the polymer component, and the composite of equal parts of the polymer and LC exhibits high transparency in electric modulation of the selective reflection band, resulting in high-quality tuning of lasing wavelength in ChLC laser. In tuning operation, the ChLC laser retains a high slope efficiency greater than 19%, a low threshold smaller than 3 nJ/pulse, and a spectral linewidth narrower than 0.13 nm, while the change in lasing wavelength is fully continuous and reaches 13 nm.
关键词： selective reflection band,laser,polymer composite,cholesteric liquid crystal,electrically fine tuning
更新于2025-09-19 17:13:59
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Preparation and Characterization of Semi-Alicyclic Polyimide Resins and the Derived Alignment Layers for Liquid Crystal Display Technology
摘要： Uniform alignment of rigid-rod liquid crystal (LC) molecules under applied voltage is critical for achievement of high-quality display for thin-film transistor-driven liquid crystal display devices (TFT-LCDs). The polymeric components that can induce the alignment of randomly aligned LC molecules are called alignment layers (ALs). In the current work, a series of organo-soluble polyimide (SPI) ALs were designed and prepared from an alicyclic dianhydride, hydrogenated 3,3',4,4'-biphenyltetracarboxylic dianhydride (HBPDA), and various aromatic diamines, including 4,4'-methylenedianiline (MDA) for SPI-1, 4,4',5,5'-aminodianiline (NDA) for SPI-2, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane (TMMDA) for SPI-3, and 3,3',5,5'-diethyl-4,4'-diaminodiphenylmethane (DMDEDA) for SPI-4. The derived SPI resins were all soluble in N-methyl-2-pyrrolidone (NMP). Four SPI alignment agents with the solid content of 6 wt.% were prepared by dissolving the SPI resins in the mixed solvent of NMP and butyl cellulose (BC) (NMP/BC = 80:20, weight ratio). Liquid crystal minicells were successfully fabricated using the developed SPI varnishes as the LC molecule alignment components. The SPI ALs showed good alignment ability for the LC molecules with the pretilt angles in the range of 1.58°–1.97°. The LC minicells exhibited good optoelectronic characteristics with voltage holding ratio (VHR) values higher than 96%. The good alignment ability of the SPI ALs is mainly attributed to the good comprehensive properties of the SPI layers, including high volume resistivity, high degree of imidization at the processing temperature (230 °C), good rubbing resistance, good thermal stability with glass transition temperatures (Tgs) higher than 260 °C, and excellent optical transparency with the transmittance higher than 97% at the wavelength of 550 nm.
关键词： alignment layer,semi-alicyclic polyimide,thin-film transistor-driven liquid crystal display device (TFT-LCD),residual direct circuit voltage,voltage holding ratio
更新于2025-09-19 17:13:59
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Liquid Crystal-Based Enclosed Coplanar Waveguide Phase Shifter for 54a??66 GHz Applications
摘要： A 0–10 V bias voltage-driven liquid crystal (LC) based 0–180? continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than ?4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed coplanar waveguide (ECPW) with LC as tunable dielectrics encapsulated by a unified ground plate in the design, which significantly reduced the instability due to floating effects and losses due to stray modes. By competing for spatial volume distribution of the millimeter-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics, the ECPW’s geometry and materials are optimized to minimize the total of dielectric volumetric loss and metallic surface loss for a fixed phase-tuning range. The optimized LC-based ECPW was impedance matched with 1.85 mm connectors by the time domain reflectometry (TDR) method. Device fabrication featured the use of rolled annealed copper foil of lowest surface roughness with nickel-free gold-plating of optimal thickness. Measured from 54 GHz to 66 GHz, the phase shifter prototype presented a tangible improvement in phase shift effectiveness and signal-to-noise ratio, while exhibiting lower insertion and return losses, more ease of control, and high linearity as well as lower-cost fabrication as compared with up-to-date documentations targeting 60 GHz applications.
关键词： tunable circuits and devices,true time delay,millimeter-wave,60 GHz,liquid crystal,phase shifter,enclosed coplanar waveguide
更新于2025-09-19 17:13:59
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[IEEE 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Guangzhou, China (2019.5.19-2019.5.22)] 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Microwave CSIW Filter Based on The High Anisotropy Electro-Optic Nematic Liquid Crystal
摘要： In this work, for the research of novel waveguide filters, we propose a microwave corrugated substrate integrated waveguide CSIW filter based on the high anisotropy electro-optic nematic liquid crystal. Metallic vias of the substrate integrated waveguide (SIW) is replaced by quarter microstrip stubs of the CSIW, which solves the problem of shorting the upper and lower planes of the waveguide due to metalized vias when the SIW is biased. Using the electromagnetic scattering complementary open-loop resonance type anisotropic medium structure, the enhanced scattering characteristics can amplify the cutoff mode. In combination with the dielectric anisotropy of the liquid crystal and the high modulation efficiency of the inverted microstrip line, the waveguide filter has advantages such as high modulation efficiency, high Q value, and low transmission loss.
关键词： nematic liquid crystal,CSRR,CSIW,tunable,microwave
更新于2025-09-19 17:13:59
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Temperature and voltage sensing based on a tapered optical fiber device with the liquid crystal cladding
摘要： This paper presents the results of light transmission in a tapered optical ?ber surrounded by the cladding formed by a nematic liquid crystal (LC) E7 mixture in a classical LC cell con?guration where embedded optical ?ber axis is perpendicular, parallel or twist with regard to rubbing directory of the LC orienting layers. The LC cladding e?ective refractive index is modulated by the electric ?eld. Observations were done for di?erent modulation frequencies of the driving electric ?eld in a temperature range of T = 20–50 °C. Light transmission through the device while driving an LC medium was measured in a broad wavelength range of λ = 500–1000 nm. Spectral characteristics of the transmission, as well as response times (switching on and o?), were estimated.
关键词： Tapered ?ber,Liquid crystal,Temperature sensing,Voltage sensing,Optical ?ber device
更新于2025-09-19 17:13:59
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Fluoro-substitution in hydrogen bonding liquid crystal benzoic acid: dielectric, electro-optic and optical proprieties and inducing polar nematic phase
摘要： Dielectric and electro-optic properties have been studied in order to understand the effect of the fluoro-substitution on hydrogen bonded liquid crystal proprieties. The fluoro-substitution alters the characteristics of pure LC structure and changes its physical parameters. In the present paper, variation in physical parameters like dielectric permittivity, response time, elastic constant, rotational viscosity etc. has been explained based on many factors. In addition, the fluorine substitution has lead to the appearance of the polar nematic phase.
关键词： dielectric anisotropy,polar nematic,Hydrogen bonded liquid crystal,electro-optical properties,fluoro-substitution
更新于2025-09-19 17:13:59
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Influences of nickel plated multi-walled carbon-nanotube on the electro-optical properties of nematic liquid crystal
摘要： Some enhanced performances can be obtained by doping multi-walled carbon-nanotube (MWCNT) into self-organized nematic liquid crystal (NLC). However, the dispersion of MWCNT in NLC is very few, thus the enhancement is restricted. In this work, a nickel plated MWCNT (MWCNT@Ni) is synthesized to obtain a relatively high dispersion. The morphology, element and chemical bond differences between MWCNT and MWCNT@Ni are characterized. For MWCNT@Ni, there is a layer of coaxial nickel coated on the surface of MWCNT, which weakens the interaction energy between the adjacent MWCNTs and further results in a relatively high dispersion. Moreover, MWCNT@Ni has a more orderly arrangement in NLC compared with MWCNT. The results suggest that the dielectric anisotropy of MWCNT@Ni/NLC with mass fraction of 0.01 wt% is increased by ～3.6%, and the saturation voltage is reduced by ～7.3%. Besides, the rise time is decreased by ～9.5% at 5 V and 1 kHz. These performances have been improved compared with MWCNT/NLC under the same mass fraction. The effect of mass fraction of MWCNT@Ni on rise time is further investigated. As a result, the rise time is decreased by ～16.7% as MWCNT@Ni with mass fraction of 0.10 wt% is added into NLC. In general, the method to increase dispersion of dopant in NLC is proposed, which can serve as a reference to improve the performances of NLC composites.
关键词： dispersion,nematic liquid crystal,nickel plated multi-walled carbon-nanotube
更新于2025-09-19 17:13:59
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Simulation analysis of the optical properties of a liquid crystal-filled microstructured optical fiber
摘要： The optical properties of a liquid crystal-?lled microstructured optical ?ber (LC-MOF) were investigated using the ?nite element method. Liquid crystal E7 was designed to be in?ltrated into six small air holes at the neighbourhood of silica core. Simulation results showed that the designed LC-MOF supported a continuous transmission in the silica core over a wide wavelength range. The optical properties of core modes such as refractive index, birefringence, con?nement loss, model area, group refractive index, group birefringence, and zero dispersion wavelength, were illustrated. The structure parameters of LC-MOF and temperature could be used to adjusted the optical properties. The designed LC-MOF, providing a way for ?lling high refractive index materials in MOF air holes, has potential applications in optical ?ber modulators and sensors.
关键词： optical property,liquid crystal,microstructured optical ?ber
更新于2025-09-19 17:13:59