Cholesteric Research Articles

Phototuning structural color and optical switching cholesteric textures in azobenzene-doped cholesteric liquid crystals

The first integration of structure modulation and phase modulation of CLCs has been accomplished. CLCs doped with azobenzene show rapid color shifts and phase modulation dependent on different intensity light source stimuli within a few seconds.

Smart beam via electrically addressing the dye-doped and polymer-stabilized cholesteric liquid crystals

Smart beam via electrically addressing the dye-doped and polymer-stabilized cholesteric liquid crystals

Handedness inversion of the Bragg reflection light of cholesteric liquid crystal polymer network film using a half-wave plate

Colourful cholesteric liquid crystal polymer network (CLCN) film can selectively reflect circularly polarized light whose handedness is consistent with that of the CLCN film. The CLCN patterns have been applied...

Polymerization-induced diffusion driven the formation of cholesteric liquid crystal network film with double helical pitches

Cholesteric liquid crystal polymer network (CLCN) films with a composite structural colour are attractive in decoration. Herein, CLCN films with double helical pitches were prepared using a non-reactive chiral dopant...

Significant anisotropic deformation and optical shifts in stretched cholesteric liquid crystal elastomers.

This study explores the opto-mechanical response of cholesteric liquid crystal elastomers (CLCEs) subjected to uniaxial stretching along the x-axis, perpendicular to their helical z-axis. A definitive crossover is observed in the strain (εx) dependencies of various optical and mechanical properties, such as the transmission spectra, degree of mesogen orientation, Poisson's ratios, and tensile stress. At low strains, CLCEs exhibit a blue shift in the selective reflection band due to a reduction in the helical pitch, accompanied by a decrease in reflection selectivity for circularly polarized light. Beyond a certain critical strain further pitch alterations halt. This strain regime is marked by substantial anisotropic lateral contractions without any z-axis contraction, as indicated by a Poisson's ratio (μxz) of zero. Within this intermediate strain regime, local directors predominantly reorient towards the x-direction within the xy-plane, resulting in a quasi-plateau of tensile stress. Approaching a higher critical strain a complete loss of reflective selectivity occurs. Past this threshold, while the mechanical responses resemble those of isotropic conventional rubber, they retain a periodic structure albeit without phase chirality. These observed features are accounted for by the Mao-Terentjev-Warner model, especially when the network anisotropy parameter is adjusted to match the critical strain magnitude associated with the cessation of selective reflection.

Unveiling the potential of polymer cholesteric liquid crystal interpenetrating networks as a label-free alcohol biochemical sensor.

In this study, an optical sensor is developed, incorporating hydrogen-bonded photonic array dots containing poly(acrylic acid) (PAA) within a polymer cholesteric liquid crystal interpenetrating polymer network (PCLCIPN) framework, thereby effectively controlling porosity. This methodology involves the fabrication of a porous photonic film, subsequent infusion with a hydrogel (PAA), and precise UV-curing to generate patterned array dots. The sensor exhibits exceptional discriminatory capability between methanol and ethanol, accurately discerning their varying concentrations within alcohol solutions. The optical sensing performance of the film is rigorously evaluated through continuous monitoring of wavelength shifts in the transmission spectrum across various alcohol concentrations. Notably, the observed wavelength shifts demonstrate a linear correlation with the concentration of alcohol, thereby enabling precise quantitative analysis of the alcohol solutions. The sensor exhibits a sensitivity of 0.44 nm/% for ethanol concentrations ranging from 5% to 60%, increasing to 2.1 nm/% for concentrations between 60% and 80%. Similarly, for methanol, sensitivities of 0.68 nm/% (5-60%) and 2.2 nm/% (60-80%) are recorded. Remarkably, this sensitivity trend extends seamlessly to 1 : 1 ethanol/methanol ratios, with values of 0.49 nm/% (5-60%) and 2.25 nm/% (60-80%). Furthermore, these sensors demonstrate colorimetric response to different alcohols, rendering them accessible and cost-effective biosensors for visual detection, thus obviating the necessity for complex analytical instruments.

Incorporating amidine groups into photonic cholesteric polymer networks for food quality sensing

Concerns about food safety and food quality have been the driving forces behind the development of smart packaging and food quality sensors. Cholesteric liquid crystal polymers make an excellent candidate...

An l-isosorbide-based reactive chiral dopant with high helical twisting power for cholesteric liquid crystal polymers reflecting left-handed circularly polarized light.

For visible light reflective cholesteric liquid crystal polymers, reactive chiral dopant enantiomers with high helical twisting power are attractive. However, a chiral dopant for reflecting left-handed circularly polarized light has been missing so far. Here, we report the synthesis of a reactive, left-handed, l-isosorbide-based chiral dopant with a high helical twisting power of -48 μm-1 that can be used in visible light reflective cholesteric liquid crystal polymers. The right handed dopant enantiomer was also synthesized, showing a helical twisting power of +63 μm-1.

Upconversion circularly polarized luminescence of cholesteric liquid crystal polymer networks with NaYF4:Yb,Tm UCNPs.

Upconversion circularly polarized luminescence (UC-CPL) exhibits promising potential for application for anti-counterfeiting and displays. Upconversion nanoparticles (UCNPs), NaYF4:Yb,Tm, with uniform morphology and high crystallinity, were prepared via a simple solvothermal method. These UCNPs were embedded into cholesteric liquid crystal polymer network (CLCN) films. The UC-CPL performance of these films was investigated using left- and right-handed circular polarizers. After calibration, the |gcallum| values (up to 0.33) were obtained for the free-standing CLCN-UCNPs films, while a |gcallum| value of 0.43 was achieved for the CLCN-UCNPs-coated PET film. Moreover, a combined system comprising a PMMA-UCNPs layer and a CLCN layer yielded an ultra-large |gcallum| value of up to 1.73. Flexible and colourful patterned CLCN films were fabricated using photomasks, offering potential applications in anti-counterfeiting. This study not only successfully prepared UC-CPL-active materials based on CLCNs and UCNPs, but also demonstrated the chiral filtering effect of CLCN films in upconversion luminescent materials.

Cholesteric liquid crystal doped with spiropyran and zinc ions for multi-state anti-counterfeiting

With the development of the information age, counterfeit products are rampant.

Optical anti-counterfeiting with cholesteric liquid crystal emulsions: preparation, properties, and applications

This review highlights recent advancements in cholesteric liquid crystal emulsions, focusing on their preparation, anti-counterfeiting applications, and future prospects. It also covers their role in information storage and encryption techniques.

Mechanochromic and ionic conductive cholesteric liquid crystal elastomers for biomechanical monitoring and human-machine interaction.

Cholesteric liquid crystal elastomers (CLCEs) that combine rubbery elasticity with structural colour from self-assembled helical nanostructures are of paramount importance for diverse applications such as biomimetic skins, adaptive optics and soft robotics. Despite great advances, it is challenging to integrate electrical sensing and colour-changing characteristics in a single CLCE system. Here, we report the design and synthesis of an ionic conductive cholesteric liquid crystal elastomer (iCLCE) through in situ Michael addition and free-radical photopolymerization of CLCE precursors on silane-functionalized polymer ionic liquid networks, in which robust covalent chemical bonding was formed at the interface. Thanks to superior mechanochromism and ionic conductivity, the resulting iCLCEs exhibit dynamic colour-changing and electrical sensing functions in a wide range upon mechanical stretching, and can be used for biomechanical monitoring during joint bending. Importantly, a capacitive elastomeric sensor can be constructed through facilely stacking iCLCEs, where the optical and electrical dual-signal reporting performance allows intuitive visual localization of pressure intensity and distribution. Moreover, proof-of-concept application of the iCLCEs has been demonstrated with human-interactive systems. The research disclosed herein can provide new insights into the development of bioinspired somatosensory materials for emerging applications in diverse fields such as human-machine interaction, prostheses and intelligent robots.

Dynamic regulation and application of cholesteric liquid crystal patterns

Dynamic regulation and application of cholesteric liquid crystal patterns

Self‐Assembled Multistable Scattering Mode for Versatile Energy‐Saving Smart Windows

AbstractSmart windows are crucial to dynamic control over light transmission to fulfill various demands in energy saving, privacy, and information display; however, most present technologies still perform a single function (often tint or haze adjustment) and require continuous electricity for operation. In this study, novel self‐assembled ionic liquid crystals (ILCs) doped with negative cholesteric liquid crystals (CLCs) to offer electrically switchable and stable scattering‐mode light modulators are presented. The novel smectic A phase based on the ILCs exhibits high solubility in the adopted nematics, enhancing the LC device's performance in several ways, including improved homogeneity, stable alignment quality, prolonged stability, and simplified fabrication. The LC device can potentially offer a dynamically rapid switching function between stable transparent (imperfect fingerprint textures) states and stable scattering (focal conic textures with small domains) states by using external stimuli and highly maintained multistable states for prolonged periods, even when the external stimuli are removed. The LC device also offers polarization‐independent scattering and transparent‐mode LC light modulators, low operating voltage, excellent contrast, and broad viewing angles. Its versatility and outstanding field‐off stability make it ideal for various applications such as smart lighting, building climate control, energy‐saving displays, and augmented reality (AR) glasses.

High-performance near-infrared narrowband circularly polarized light organic photodetectors

Efficient near-infrared (NIR) detection of circularly polarized light (CPL) provides a technologically attractive element for the next generation of quantum information, model encryption, remote sensing, and so on. However, conventional NIR CPL detectors typically require the installation of external optics, making it challenging to realize integrated and flexible devices. Despite considerable success in semiconductor-based chiroptical devices without optical elements, most of these devices only address one or a few aspects of the device quality. Here, we showcase a simple and facile strategy to achieve a high performance NIR narrowband CPL detector via combining cholesteric liquid crystal. films with a photodiode-type organic photodetector. Comprehensive performance is achieved with a super-high dissymmetry factor of 1.56, a high detectivity of 7.12 × 1012 Jones, a linear dynamic range. of 127.6 dB, a − 3 dB frequency of 279 Hz, and the rise and decay times of 0.65 ms and 5.7 ms, respectively. As a proof-of-concept, the device demonstrates excellent performance in the encrypted information using the principle of Morse code, exhibiting the potential for security communication applications.

Dynamic circularly polarized luminescence regulated by photosensitive achiral dichroic dyes in cholesteric liquid crystal medium

Herein, we have developed photosensitive ternary cholesteric liquid crystals (T-N*-LCs) by doping achiral dichroic dye PBCy and chiral inducer R/S-1 in 5CB. Under alternating UV and visible light treatment, different isomers of PBCy exhibited varying order parameter (SF) values in 5CB, resulting in T-N*-LCs showing a dynamic CPL switch from strong (SF = 0.18. glum = +0.45/-0.48) to weak (SF = 0.10. glum = +0.23/-0.21). This alteration allows for the regulation of the CPL signal of T-N*-LCs, while keeping the helical pitch and chiral spin of T-N*-LCs unchanged. Based on these phototunable CPL and fluorescence behaviors, a geminate mode device carrying different information could be prepared.

Research Progress of Electrically Driven Multi-Stable Cholesteric Liquid Crystals.

Electrically driven multi-stable cholesteric liquid crystals can be used to adjust the transmittance of incident light. Compared with the traditional liquid crystal optical devices, the multi-stable devices only apply an electric field during switching and do not require a continuous electric field to maintain the various optical states of the device. Therefore, the multi-stable devices have low energy consumption and have become a research focus for researchers. However, the multi-stable devices still have shortcomings before practical application, such as contrast, switching time, and mechanical strength. In this article, the latest research progress on electrically driven multi-stable cholesteric liquid crystals is reviewed, including electrically driven multi-stable modes, performance optimization, and applications. Finally, the challenges and opportunities of electrically driven multi-stable cholesteric liquid crystals are discussed in anticipation of contributing to the development of multi-stable liquid crystal devices.

Temperature Self-Adaptive and Color-Adjustable Smart Window Based on Templated Cholesteric Liquid Crystals.

Cholesteric liquid crystals (CLCs) exhibit selective reflection due to their self-assembled helical superstructures. Reconfigurable templates can achieve integration functions via inducing processes of molecular assemblies. Here we demonstrate temperature self-adaptive and color-adjustable smart windows using CLCs, which are fabricated via the templating method and exhibit simultaneous reflections in the visible and infrared spectra. Reflection bands formed by the refilled CLC materials can be adjusted reversibly both upon thermal and electrical actuation. In CLC with adjustable reflection in the infrared, the central wavelength of the infrared reflection band can be adjusted from 950 nm to 1305 nm via temperature, and from 1150 nm to 950 nm via electric field. A temperature variation of 10.3 °C within 55 s was induced by the single-layer templated CLC cell, and a comfortable temperature range could be effectively maintained by the CLC cell in a varied environment. In CLC with dynamic color in the visible spectrum, color shifts from 530 nm to 650 nm tuned by temperature and from 530 nm to 440 nm adjusted by electric field were obtained. Temperature-responsive reflection in the infrared spectrum contributes to automatic thermal management, and electric-field-induced band shift in the visible spectrum enables active dynamic color adjustment. The presented templated CLC smart windows show considerable potential in energy conservation and biological clock regulation fields.

Two‐Chromatic Printing Creates Skin‐Inspired Geminate Patterns Featuring Crosstalk‐Free Chemical and Physical Colors

AbstractSkin‐inspired optical materials that combine both chemical and physical colors provide enhanced information capacity for potential applications in optical multiplexing and anti‐counterfeiting technologies. However, the existing materials suffer from the limitations of an extremely narrow gamut and incompatibility with universal patterning methods to program dual‐mode images. Here, novel two‐chromatic printing technology is proposed to create full‐color, high‐resolution, and geminate patterns by newly designed fluorescent liquid crystal nanocomposites. Such nanocomposites consist of porous cholesteric liquid crystal networks embedded with core–shell CdSe/ZnS quantum dots to produce extended wide color palettes of both photoluminescence and Bragg reflection. The drop‐on‐demand two‐chromatic printing technology simultaneously enables the construction and patterning of the nanocomposites in a high‐precision way, orthogonally tuning the hues of two color palettes according to Grassmann's and Bragg's law. Therefore, the combination of different color generation mechanisms offers a versatile toolbox, which can be generalized to pigmentary, photonic, and even dynamic optical materials.

Electro-optical-coloration active polymers: Electrochemical polymerization in chiral liquid crystals supported by an α-tocopherol derivative

Electrochemical polymerization was performed in a cholesteric liquid crystal (CLC) with an α-tocopherol (vitamin E) derivative as a chiral inducer to yield electroactive polymers exhibiting dynamic electrochemical-driven changes in optical activity. Materials possessing multiple asymmetric centers with long alkyl chains can be conveniently obtained using vitamins as chiral substances. First, an α-tocopherol derivative was synthesized as a chiral dopant (chiral inducer) to induce a CLC from a nematic liquid crystal. Thereafter, π-conjugated polymers were electrochemically prepared in the CLC with the α-tocopherol derivative. The fingerprint texture derived from the CLC was successfully transcribed to the polymers, and molecular asymmetric imprinting polymerization was achieved. Furthermore, the oxidized (doped) and reduced (dedoped) forms of the polymers were subjected to ultraviolet–visible and circular dichroism analyses. Electrochemical polymerization in the helical CLC resulted in molecular aggregation–imprinted chirality in the polymers. The chiral information was transferred from vitamin E to the nematic liquid crystal and resulting polymers.