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Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell
摘要： We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f1 and, subsequently, f2, which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 Vrms at f1 = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 Vrms and f1 = 55 kHz, our results indicate that switching of the voltage frequency from f1 to f2 enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f2 = 1 kHz or by the electrohydrodynamic effect at f2 = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.
关键词： cholesteric liquid crystals,uniform lying helix,dielectric heating
更新于2025-11-14 17:28:48
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Phototuning Energy Transfer in Self-Organized Luminescent Helical Superstructures for Photonic Applications
摘要： Stimuli-triggered changes in the emission color of functional materials are in demand for a variety of potential applications. Herein, a strategy to reversibly phototune fluorescence color in cholesteric liquid crystal (CLC) with self-organized luminescent helical superstructure via fluorescence resonance energy transfer (FRET) is developed. This dynamic FRET system is constructed by doping with 1,2-dithienyldicyanoethene-based chiral fluorescent photoswitch (switch 7) as an acceptor and a conventional coumarin dye C6 as a donor into a nematic liquid crystal (LC) host. The efficient energy transfer from C6 to switch 7 in the LC media, which is evidenced by both of emission color shift and enhanced circularly polarized luminescence, can be modulated on the basis of reversible trans–cis photoisomerization of switch 7 upon visible/UV light irradiations, leading to the emission color change from orange to green. Noteworthily, the FRET efficiency can be significantly improved when CLCs are confined in the polymer microtubes. Preliminary demonstrations of the LC film and LC microtubes array for information display and encryption with ease of electrical operation between planar, homeotropic, and focal conic states or light manipulation are described.
关键词： cholesteric liquid crystals,optically and electrically tunable fluorescence patterns,displaying and encrypting,phototuning energy transfer,polymer microtubes
更新于2025-09-23 15:21:01
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Study on the morphologies and electro-optical properties of cyano-phenyl-ester liquid crystals/polymer composite films prepared by a stepwise polymerisation
摘要： In this work, a series of liquid crystal molecules containing cyano-phenyl-ester was designed and synthesised. Subsequently, a novel cyano-phenyl-ester liquid crystals (CPE-LCs) with a wide temperature range from ?30°C to 96.4°C were developed by mixturing these liquid crystal compositions. Then as the host materials, the CPE-LCs were used for preparing polymer-dispersed and polymer-stabilised cholesteric liquid crystals (PD&SCLC) composite ?lms by a stepwise polymerisation. The morphologies and electro-optical properties of the as-made composite ?lms were systematically investigated through varying the acrylate liquid crystalline polymerisable monomers content, chiral doping R1011 content, applied electric ?eld intensity and polymerisation time. Indeed, the formation of homeotropically aligned anisotropic polymer networks (HAAPNs) enabled to reduce the driving voltage of PD&SCLC from 86.6 V to 22.2 V with a reasonable contrast ratio. This work provides a new method to optimise PD&SCLC composite ?lms in terms of the host liquid crystals.
关键词： electro-optical properties,polymer-dispersed and polymer-stabilised cholesteric liquid crystals,network morphologies,Cyano-phenyl-ester liquid crystals,stepwise polymerisation
更新于2025-09-23 15:19:57
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Tunable Microlasers Modulated by Intracavity Spherical Confinement with Chiral Liquid Crystal
摘要： Manipulation of laser emission offers promising opportunities for the generation of new spatial dimensions and applications, particularly in nanophotonics, super-resolution imaging, and data transfer devices. However, the ability to control laser modes and wavelength in a microcavity remains challenging. Here, a novel approach is demonstrated to control laser modes by manipulating the 3D-optical confinement, chirality, and orientations in a Fabry?Pérot microcavity with cholesteric liquid crystal droplets. Different configurations of intracavity micro-/nanostructures generate versatile dimensions of laser modes, while the significantly reduced laser mode volume further leads to single-mode lasing. Theoretical analysis is carried out to support this interesting discovery. Finally, switchable lasing wavelength with various surface anchoring forces and pH interactions is demonstrated. This novel concept not only provides a simple yet highly versatile method to manipulate laser emissions, but deepens insight into how molecules interact with and modulate laser light, laying the foundation for the development of tunable photonic devices at the molecular level. Promising applications include highly selective laser devices, laser-emission imaging, and bioinspired sensing.
关键词： tunable lasing,high-order laser mode,cholesteric liquid crystals,spherical confinement,intracavity interactions
更新于2025-09-23 15:19:57
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Effect of Cell Thickness on the Electro-optic Response of Polymer Stabilized Cholesteric Liquid Crystals with Negative Dielectric Anisotropy
摘要： It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective re?ection notch can be controlled by a direct-current (DC) electric ?eld. The ?eld-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin ?lms (≤5 μm). Increasing the DC ?eld strength redshifts the re?ection notch to longer wavelength until the re?ection disappears at high DC ?elds. The extent of the tuning range is dependent on the cell thickness. The transition from the re?ective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the ?eld-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC ?eld strength, various re?ection wavelengths can be addressed from either a di?erent re?ective (colored) state at 0 V or a transparent state at a high DC ?eld. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.
关键词： polymer stabilization,cholesteric liquid crystals,red tuning,switching responses
更新于2025-09-19 17:13:59
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Acid mediated tunability of stimulated laser emission from dye doped chiral microdroplets
摘要： In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60 nm. This effect could find applications for the development of spectroscopy based sensors.
关键词： Microdroplets,dyes,cholesteric liquid crystals,laser tuning,solvatochromism
更新于2025-09-12 10:27:22
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Reversible LED controlled optical activity of a cholesteric liquid crystal layer
摘要： A thin layer of the photosensitive cholesteric liquid crystal possessing a high value of the optical activity is studied. Reversible change in the optical activity controlled by two light emission diodes (LEDs) with different emission wavelengths is applied for information recording. The behavior of this structure under exposure to UV and blue light is investigated. A smooth decrease in optical activity caused by the UV light resulting in a change in the color of the structure between crossed polarizers is obtained. The reverse process occurs under exposure to the blue light. On the basis of the obtained results, two methods of optical information recording in such a layer have been demonstrated.
关键词： information recording,optical activity,cholesteric liquid crystals
更新于2025-09-12 10:27:22
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Thermally tunable and electrically switchable solid sphere shell three-layer 3D Bragg microcavity laser based on cholesteric-liquid-crystals
摘要： This letter reports a thermally tunable and electrically switchable three-layer 3D Bragg resonance cavity consisting of dye-doped cholesteric-liquid-crystal (DDCLC) microdroplet, polyglycerol-2 and hollow-glass-microsphere (HGM). The whispering-gallery-mode and photonic bandgap mode can be controlled by varying the CLC refractive indices in HGM. The effects of the temperature and electric field on the peaks wavelengths were studied. The study results present the prospect of thermally and electrically controlled the output mode of the microlaser and such solid shell tunable DDCLC microsphere lasers have an outstanding potential applications in integrated microlasers, tunable optical devices and highly sensitive sensor.
关键词： thermally tunable,cholesteric-liquid-crystals,electrically switchable,3D Bragg microcavity,microlaser
更新于2025-09-11 14:15:04
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Disappearance of Reflection Color by Photopolymerization of Lyotropic Cholesteric Liquid Crystals from Cellulose Derivatives
摘要： In this communication, we report on the disappearance of reflection color by photopolymerization of an acrylate monomer in lyotropic cholesteric liquid crystals from a cellulose derivative for color image applications. When a hydroxypropyl cellulose (HPC) derivative possessing propionyl side chains (HPC-Pr) was homogeneously dissolved in a liquid monomer of 4-hydroxybutyl acrylate (4HBA), we obtained lyotropic cholesteric liquid crystals (HPC-Pr_4HBA) with a Bragg reflection peak in the visible wavelength range. Such reflection wavelength was controllable by not only temperature, but also concentration of HPC-Pr in 4HBA. We found that Bragg reflection peak of lyotropic HPC-Pr_4HBA mixture disappears by photopolymerization of 4HBA, thereby leading to the fabrication of a photolithographic color image. This report provides promising clues to fabricate intriguing photonic devices adopted with cellulose derivatives by utilizing such Bragg reflection characteristics.
关键词： Color image,Cholesteric liquid crystals,Lyotropic liquid crystals,Cellulose,Bragg reflection,Photopolymerization
更新于2025-09-09 09:28:46
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Thermal and electrical wavelength tuning of Bragg reflection with ultraviolet light absorbers in polymer-stabilized cholesteric liquid crystals
摘要： Autonomous stimulus-responsive polymer-stabilized cholesteric liquid crystals (PSCLCs) are promising materials for various applications. In this work, a PSCLC cell whose wavelength of selective reflection changes autonomously according to the temperature or can be controlled by applying an electric field was fabricated by using ultraviolet (UV) light absorbers. The UV light absorbers in the PSCLC cell are used not only for preventing the degradation of the substrate but also for stabilizing the polymeric network by converting the harmful UV radiation into harmless heat. To achieve the optimum conditions, different types of UV light absorbers were examined at various concentrations and UV light intensities. The results revealed that the benzophenone-type UV absorbers provide an extensive blue-shift tuning of the Bragg reflection in the PSCLC. By determining the molar extinction coefficient (e) values, which provide a measure of UV light absorption at a given wavelength, at three important wavelengths—the maximum absorption wavelength (lmax) of the UV absorbers, lmax of the photoinitiator (345 nm), and the UV lamp wavelength (365 nm)—the UV light intensity gradient throughout the cell was defined. Reduction of the e value indicates a sharp drop in the UV light intensity within a PSCLC cell. This phenomenon leads to the diffusion of reactive mesogens towards the UV lamp side of the cell to achieve a tight pitch gradient and extensive blue-shift tuning of the selective reflection.
关键词： thermal tuning,blue-shift tuning,electrical tuning,UV light absorbers,polymer-stabilized cholesteric liquid crystals
更新于2025-09-09 09:28:46