In this work, light and temperature responsive, brush‐painted photonic coatings exhibiting three different colored and surface topographical states are reported. The different states arise from the ...use of cholesteric liquid‐crystalline micrometer‐sized polymer particles as shape‐memory photonic pigments that are dispersed in a shape‐memory binder. The first temporal state is induced by compressing the photonic particles at high temperature, resulting in blueshift of the structural color. The second temporal state is obtained by embossing a diffractive grating on the surface at an intermediate temperature leading to a relief topography and a rainbow optical effect. Both optical and surface topographical changes coexist and are stable at room temperature until they are reverted independently either by heating or locally by light illumination. Multicolored paints that reflect selectively left‐handed or right‐handed polarized light are developed to create arbitrary polarization‐dependent multicolor and topographical brush‐painted patterns. These temperature and light responsive triple shape‐memory photonic paints have potential applications as battery‐free optical sensors, responsive decoration, and smart adhesives.
Brush‐paintable, light and temperature responsive triple shape‐memory photonic coatings are fabricated by using cholesteric liquid‐crystalline particles as shape‐memory pigments dispersed in a shape‐memory binder. These easy‐to‐apply coatings exhibit irreversible optical and surface topographical changes that can be reverted independently either by direct heating or locally by light illumination. Such coatings find applications in battery‐free optical sensors and responsive decoration.
Cholesteric liquid crystal elastomers (CLCEs) are soft and dynamic photonic elements that couple the circularly polarized structural color from the cholesteric helix to the viscoelasticity of ...rubbers: the reflection color is mechanically tunable (mechanochromic response) over a broad range. This requires uniform helix orientation, previously realized by long‐term centrifugation to ensure anisotropic deswelling, or using sacrificial substrates or external fields. The present paper presents a simple, reproducible, and scalable method to fabricate highly elastic, large‐area, millimeters thick CLCE sheets with intense uniform reflection color that is repeatably, rapidly, and continuously tunable across the full visible spectrum by stretching or compressing. A precursor solution is poured onto a substrate and allowed to polymerize into a 3D network during solvent evaporation. Pinning to the substrate prevents in‐plane shrinkage, thereby realizing anisotropic deswelling in an unprecedentedly simple manner. Quantitative stress–strain–reflection wavelength characterization reveals behavior in line with theoretical predictions: two linear regimes are identified for strains below and above the helix unwinding threshold, respectively. Up to a doubling of the sample length, the continuous color variation across the full visible spectrum repeatedly follows a volume conserving function of the strain, allowing the CLCE to be used as optical high‐resolution strain sensor.
A facile preparation strategy based on anisotropic deswelling is developed to achieve uniformly colored large‐area cholesteric liquid crystal (CLCE) films. The CLCE exhibits rapid and reversible color changes to any mechanical deformation locally or globally. This easily scalable approach for fabricating CLCE films opens up possibilities for numerous applications.
Over the past decade, solid‐state cholesteric liquid crystals (CLCsolid) have emerged as a promising photonic material, heralding new opportunities for the advancement of optical photonic biosensors ...and actuators. The periodic helical structure of CLCsolids gives rise to their distinctive capability of selectively reflecting incident radiation, rendering them highly promising contenders for a wide spectrum of photonic applications. Extensive research is conducted on utilizing CLCsolid’s optical characteristics to create optical sensors for bioassays, diagnostics, and environmental monitoring. This review provides an overview of emerging technologies in the field of interpenetrating polymeric network‐CLCsolid (IPN) and CLCsolid‐based optical sensors, including their structural designs, processing, essential materials, working principles, and fabrication methodologies. The review concludes with a forward‐looking perspective, addressing current challenges and potential trajectories for future research.
This review provides an overview of emerging technologies in the field of IPN‐CLCsolid and CLCsolid‐based optical sensors, including their structural designs, processing, essential materials, working principles, and fabrication methodologies. The review concludes with a forward‐looking perspective, addressing current challenges and potential trajectories for future research.
The responsive and dynamic character of liquid crystals (LCs), arising from their ability to self‐organize into long‐range ordered structures while maintaining fluidity, has given them a role as key ...enabling materials in the information technology that surrounds us today. Ongoing research hints at future LC‐based technologies of entirely different types, for instance by taking advantage of the peculiar behavior of cholesteric liquid crystals (CLCs) subject to curvature. Spherical shells of CLC reflect light omnidirectionally with specific polarization and wavelength, tunable from the UV to the infrared (IR) range, with complex patterns arising when many of them are brought together. Here, these properties are analyzed and explained, and future application opportunities from an interdisciplinary standpoint are discussed. By incorporating arrangements of CLC shells in smart facades or vehicle coatings, or in objects of high value subject to counterfeiting, game‐changing future uses might arise in fields spanning information security, design, and architecture. The focus here is on the challenges of a digitized and information‐rich future society where humans increasingly rely on technology and share their space with autonomous vehicles, drones, and robots.
The omnidirectional selective reflection of cholesteric liquid crystal shells opens surprising application opportunities in future emerging technologies, such as autonomous vehicle navigation, object‐based secure authentication, and infrastructure for augmented reality. A review of the optics of cholesteric shells is presented, leading into a visionary discussion of how they may fill critical needs in our future.
A mechanochromic, programmable, cholesteric liquid crystalline elastomer (CLCE) is fabricated, and after straining, resulting in a blue shift through the visible spectrum, is returned to its initial ...shape and color upon heating through its isotropic phase transition. Light initiated, radical‐mediated, addition fragmentation chain transfer (AFT), facilitate permanent programming or erasure of thermoreversible shape and color by relaxing stress imparted on the strained network through reversible bond exchange. Thermoreversible strain is coupled with reversible color change and can be made permanent at any desired strain by light exposure and corresponding AFT activation, temporarily restoring nearly initial shape and color upon heating. The optical characteristics and photonic structure, inherently linked to the network, are measured as a function of strain, to confirm the reflection notch narrowing indicating that prepolymerization alignment via shearing is poor thereby causing a broad spectrum of reflected light that narrows when the material is stretched. Beyond programming a new shape and color, the reflection notch is erased and separately, photopatterned to achieve dynamic color schemes that are toggled with heating and cooling, similar to that of a chameleon's camouflaging technique that has the ability to manipulate multiple colors in a single material, also with use for strain mapping.
A mechanochromic, programmable, cholesteric liquid crystal elastomer (CLCE) is fabricated that initially, is visibly red reflective, and upon straining, blue shifts. Furthermore, the thermoreversible CLCE is capable of undergoing light initiated addition fragmentation chain transfer, to permanently program the material to a new color and strained shape, or erase color, for strain mapping or camouflaging applications.
Halide perovskites have received tremendous attention due to their fantastic optical and electrical properties. Here, circularly polarized light emission is successfully demonstrated using a simple ...configuration consisting of inorganic perovskite nanocrystals embedded within a predefined handedness cholesteric superstructure stack. The helical structured cholesteric liquid crystal film acts as a selective filter to transform the unpolarized light emission from perovskite nanocrystals into circularly polarized luminescence. The transformation is accompanied by an extraordinary dissymmetry factor (|glum|) up to 1.6, well‐defined handedness, high photoluminescence quantum yield, and full‐color availability. Furthermore, the circularly polarized luminescence is angular dependent and can easily be modulated by shifting the overlap of the reflection band and the emission band. The proposed method is more straightforward and powerful than the previous approaches, offering new opportunities in optoelectronic and photonic devices.
Circularly polarized luminescence is successfully demonstrated from CsPbX3 perovskite nanocrystals enabled by cholestericsuperstructure stacks. Using the cholesteric liquid crystal films with opposite handedness, high dissymmetry factor values of 1.5–1.6 can easily be achieved for the red, green, and blue emission.
Creating a security label that carries entirely distinct information in reflective and fluorescent states would enhance anti-counterfeiting levels to deter counterfeits ranging from currencies to ...pharmaceuticals, but has proven extremely challenging. Efforts to tune the reflection color of luminescent materials by modifying inherent chemical structures remain outweighed by substantial trade-offs in fluorescence properties, and vice versa, which destroys the information integrity of labels in either reflection or fluorescent color. Here, a strategy is reported to design geminate labels by programming fluorescent cholesteric liquid crystal microdroplets (two-tone inks), where the luminescent material is 'coated' with the structural color from helical superstructures. These structurally defined microdroplets fabricated by a capillary microfluidic technique contribute to different but intact messages of both reflective and fluorescent patterns in the geminate labels. Such two-tone inks have enormous potential to provide a platform for encryption and protection of valuable authentic information in anti-counterfeiting technology.
A light shutter, which consists of a dye-doped cholesteric liquid crystal (ChLC) layer and a polymer-dispersed liquid crystal (PDLC) film, for simultaneous control of haze and transmittance is ...demonstrated. In the opaque state, it can not only provide a black color by using the dye-doped ChLCs but also hide the objects behind the display panel by using the PDLC film. The proposed light shutter shows a high haze value of 90.7% with a low specular transmittance of 1.20%. By switching the proposed light shutter placed at the back of a see-through display, we can choose between the see-through mode and the high-visibility mode in a see-through display.
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•We propose a light shutter consisting of a dye-doped ChLC layer and a PDLC film.•We can simultaneously control haze and transmittance.•It can provide the black color and hide the objects behind the display panel.
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