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a) Schematic illustration to show lateral diffusion and transverse diffusion of an LC droplet on the surface of the CLCNs. b) Theoretical model to show the variation in surface height of the CLCNs printed by one LC droplet. The increased surface height (Δh) is calculated as 2.4 µm. c,d) Schematic illustration to show the translation of the fluorescent image c) and reflective image d) to print files. The fluorescent image is translated to bitmaps that illustrate the colors of the QD inks. The reflective image is translated to bitmaps that illustrate the printing layers of the LC inks. All the bitmaps are divided into a pixel array and the expanded view of the partial pixel array (10 × 10) in the print files is shown as an example. The black squares present the areas (pixels) that should be printed by a 20 pL droplet of the QD or LC inks. The size of the fluorescent Chinese opera mask is 214 × 290 pixels. The size of the reflective Chinese opera mask is 158 × 214 pixels. The spot‐to‐spot spacing is set as 80 µm. e) Schematic illustration to show four areas distributed over the CLCNs. I, original area; II, fluorescent area; III, reflective area; IV, geminate area.
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Skin‐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 t...
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Citations
... For universal patterning of program dual-mode images, Liu et al. designed fluorescent LC polymer coatings to create geminate patterns using two-chromatic inkjet printing technique (Figure 8b) [106]. Nanocomposites as a novel paradigm of fluorescent LC materials integrate colloidal quantum dots with CLC polymer networks for producing extensive color palettes of photoluminescence and Bragg reflection. ...
... Optical response to mechanical deformation; Path-dependent tilt of the cholesteric domains Low saturation; Low pattern resolution [90] PDMS-b-PLA BBCP inks PS particles in mixture of deionized water and ethylene glycol with fluorescence Angle independent structural colors; Enhanced brightness (˃40 times); Wide viewing-angle (from 0° to 180°) 2D patterns only [101] Silica nanoparticles in ATPS of PEG and DEX Dual-color domes for nonuniform selfassembly 2D pattern only [103] PS nanoparticles in a binary solvent (ethylene glycol and formamide) with fluorescence Unclonable multiplex encryption pattern; Rapid (≈2 s) and accurate (0 false alarm rate) authentication 2D pattern only [104] Aqueous CNC suspension Angle-dependent color and polarizationselective reflection; Ability to be printed in full-color dotmatrix patterns and bespoke images 2D pattern only [106] colloidal quantum dots/CLC networks inks Fluorescent LC polymer coatings; Full-color, high-resolution geminate patterns Limited material selection [108] BPLC inks Erasable high-resolution "live" pattern Limited material selection [110] Fluorinated monomer in 1 wt% Pluronic F-127 in water ...
Structural color is ubiquitous in nature and biological systems, and synthetic structural-color materials have been considered as a more durable substitute for traditional pigments. Recent advancements in the additive manufacturing of exquisite photonic objects have enabled the preparation of structurally colored materials with customized properties. Herein, an up-to-date review about additive manufacturing of bioinspired structural-color materials is presented. This review begins with an overview of the direct ink writing of colloidal crystals, chiral liquid crystals, cellulose nanocrystals, and block copolymers. Then, significant advances in inkjet printing strategy are showcased, including inkjet printing of colloidal crystals and cellulose nanocrystals, inkjet printing inks on photonic polymer coatings, and inkjet printing based on total internal reflections. The third section focuses on the recent advances in other additive manufacturing methods, including digital light processing, two-photon lithography, and fused deposition modeling. This review summarizes a perspective on potential opportunities, challenges, and future prospects encountered by advanced printing technology and functional structural-color materials.
With the rise in environmental awareness, the development of smart polymer materials is gradually becoming environmentally friendly and sustainable. Fluorescent liquid crystal elastomers (LCE) can change their shape or optical properties in response to external stimuli, showing great potential for applications in sensing, information storage, and encryption. However, their life cycle is often unsustainable and not in line with the circular economy model. Based on the principle of green chemistry, a fluorescent LCE was developed through the co-polymerization of multiple monomers with 1,2-dithiolane end groups, which exhibited excellent self-healing, reprocessing, and closed-loop recyclability. In addition, by tailoring the phase transition temperature of the LCE, the transparency and fluorescence intensity of the resulting material can change at a low temperature of 8.0 °C. By further integrating light or acid/base-triggered fluorescence information, a proof-of-concept for temperature monitoring during short-time vaccine transportation using the reusable fluorescent LCE film is demonstrated. This study establishes a new environmentally friendly manufacturing strategy for multifunctional LCE materials.
Cholesteric liquid crystals (CLCs) exhibit unique helical superstructures that selectively reflect circularly polarized light, enabling them to dynamically respond to environmental changes with tunable structural colors. This dynamic color-changing capability is crucial for applications that require adaptable optical properties, positioning CLCs as key materials in advanced photonic technologies. This review focuses on the mechanisms of dynamic color tuning in CLCs across various forms, including small molecules, cholesteric liquid crystal elastomers (CLCEs), and cholesteric liquid crystal networks (CLCNs), and emphasizes the distinct responsive coloration each structure provides. Key developments in photochromic mechanisms based on azobenzene, dithienylethene, and molecular motor switches, are discussed for their roles in enhancing the stability and tuning range of CLCs. We examine the color-changing behaviors of CLCEs under mechanical stimuli and CLCNs under swelling, highlighting the advantages of each form. Following this, applications of dynamic color-tuning CLCs in information encryption, adaptive camouflage, and smart sensing technologies are explored. The review concludes with an outlook on current challenges and future directions in CLC research, particularly in biomimetic systems and dynamic photonic devices, aiming to broaden their functional applications and impact.
Blue phase liquid crystals (BPLCs) have exhibited promising applications in 3D flexible displays due to their molecular‐level self‐assembled chiral structures, fast response, and tunable polarized colors. However, there remain challenges for spatiotemporal programming of 3D chiral color units for BPLC dynamic patterning. Herein, the programmable temporal evolution of micrometer‐scale color units and spatial configuration switch of chiral modes are achieved by spontaneous ink diffusion‐driven asymmetric lattice deformation in dual‐chiral polymer‐templated blue phases. Custom‐printed colorful patterns are designed by machine learning‐assisted parameter optimization, which displays programmable multidimensional encrypted information that incorporates temporal evolving colors (wavelength), spatial distribution (depth), chiral modes (L/R). The quantitative relationship between ink diffusion kinetics and blue‐phase dynamic 3D structural optics is established by in situ characterization, finite element analysis, and mathematical geometry modeling. This work provides insights into the microgeometric manipulation of 3D chiral color of BPLCs in the application of information security and self‐adaptive indicators.
Circularly polarized luminescence (CPL) of chiral luminescent materials has gained increasing attention because of their significant applications in 3D displays, chiral optoelectronics, anti‐counterfeiting, and encryption. A strongly emissive chiral dye BAcT is synthesized using (R)‐BINOL as the chiral source and a tetraphenylethene group as the fluorophore. Upon the addition of BAcT to the nematic liquid crystal, a left‐handed cholesteric structure is induced. Different concentrations of R/S5011 as chiral co‐dopants are added to prepare a series of structurally colored cholesteric liquid crystal polymer network (CLCN) films. CPL bands are detected for these green emissive CLCN films, and relatively high |glum| values (up to 0.48) are obtained. Furthermore, a fluorescent PMMA‐BAcT layer is prepared by embedding the dye in the PMMA matrix and stacked with a CLCN layer to construct a composite film. Because of the chiral filtering effect of the CLCN film, a high |glum| value up to 1.41 is successfully achieved. Colorful CLCN patterns are prepared, and clear pictures are observed in both reflective and fluorescent modes, contributing to optical anti‐counterfeiting with enhanced security. This work not only provides a deeper understanding of CPL, but also establishes a practical strategy to prepare colorful CLCN patterns for anti‐counterfeiting using inkjet printing technology.
