Electrostatically Powered Multimode Liquid Crystalline Elastomer Actuators.

Soft actuators based on liquid crystalline elastomers (LCEs) are captivating significant interest because of their unique properties combining the programmable liquid crystalline molecular order and elasticity of polymeric materials. For practical applications, the ability to perform multimodal shape changes in a single LCE actuator at a subsecond level is a bottleneck. Here, we fabricate a monodomain LCE powered by electrostatic force, which enables fast multidirectional bending, oscillation, rotation, and complex actuation with a high degree of freedom. By tuning the dielectric constant and resistivity in LCE gels, a complete cycle of oscillation and rotation only takes 0.1 s. In addition, monodomain actuators exhibit anisotropic actuation behaviors that promise a more complex deployment in a potential electromechanical system. The presented study will pave the way for electrostatically controllable isothermal manipulation for a fast and multimode soft actuator.

Voxelated opto-physically unclonable functions via irreplicable wrinkles.

The increased prevalence of the Internet of Things (IoT) and the integration of digital technology into our daily lives have given rise to heightened security risks and the need for more robust security measures. In response to these challenges, physical unclonable functions (PUFs) have emerged as promising solution, offering a highly secure method to generate unpredictable and unique random digital values by leveraging inherent physical characteristics. However, traditional PUFs implementations often require complex hardware and circuitry, which can add to the cost and complexity of the system. We present a novel approach using a random wrinkles PUF (rw-PUF) based on an optically anisotropic, facile, simple, and cost-effective material. These wrinkles contain randomly oriented liquid crystal molecules, resulting in a two-dimensional retardation map corresponding to a complex birefringence pattern. Additionally, our proposed technique allows for customization based on specific requirements using a spatial light modulator, enabling fast fabrication. The random wrinkles PUF has the capability to store multiple data sets within a single PUF without the need for physical alterations. Furthermore, we introduce a concept called 'polyhedron authentication,' which utilizes three-dimensional information storage in a voxelated random wrinkles PUF. This approach demonstrates the feasibility of implementing high-level security technology by leveraging the unique properties of the rw-PUF.

Versatile Mechanochromic Sensor based on Highly Stretchable Chiral Liquid Crystalline Elastomer.

A mechanochromic strain sensor that is capable of distinguishing the orientation, the location, and the degree of deformation based on the highly stretchable membrane of main-chain chiral liquid crystalline elastomer (MCLCE) is proposed. The MCLCE film is designed to exhibit uniform and significant color shift upon the small strain by using step-growth polymerization of liquid crystal (LC) oligomer and its phase-stabilization in solvent mesogen. As conformally placed on the bottom elastomer sheet, the MCLCE film shows multimodal, instantaneous color change for sensing arbitrary in-plane deformation, out-of-plane bending, and nonzero Gaussian deformation. Based on high freedom in the device design, it is also demonstrated that this sensor can display color patterns or encrypted images in response to the localized weight or strain. The simple and straightforward concept proposed here can be applicable in the fields of wearable devices, displays, and soft robotics.

Broadband and pixelated camouflage in inflating chiral nematic liquid crystalline elastomers.

Living organisms such as fishes1, cephalopods2 and clams3 are cryptically coloured with a wide range of hues and patterns for camouflage, signalling or energy regulation. Despite extensive efforts to create colour-changing materials and devices4, it is challenging to achieve pixelated structural coloration with broadband spectral shifts in a compact space. Here, we describe pneumatically inflating thin membranes of main-chain chiral nematic liquid crystalline elastomers that have such properties. By taking advantage of the large elasticity anisotropy and Poisson's ratio (>0.5) of these materials, we geometrically program the size and the layout of the encapsulated air channels to achieve colour shifting from near-infrared to ultraviolet wavelengths with less than 20% equi-biaxial transverse strain. Each channel can be individually controlled as a colour 'pixel' to match with surroundings, whether periodically or irregularly patterned. These soft materials may find uses in distinct applications such as cryptography, adaptive optics and soft robotics.

Deformable Photonic Crystals Based on Chiral Liquid Crystals with Thermal-Mediative Shape Memory Effect.

We propose a deformable photonic crystal that exhibits the thermal-mediative shape memory effect. The chiral liquid crystalline polymeric scaffold, which produces the structural colors from a helical twist of the liquid crystal director, is prepared through phase-stabilization of a reactive mesogen in a small molecular chiral liquid crystal (CLC), polymerization, and removal of the CLC. The prepolymer of polyurethane acrylate (PUA) is then infiltrated in the prepared scaffold and subsequently photo-polymerized to form a CLC-PUA composite film. Upon compression, this film shows the blue shift of the structural color and retains this color-shift as released from compression. As the temperature increases, the color is recovered to a pristine state. The concept proposed in this study will be useful for designing mechanochromic soft materials.

Printable Nanocomposite Metalens for High-Contrast Near-Infrared Imaging.

Printable metalenses composed of a silicon nanocomposite are developed to overcome the manufacturing limitations of conventional metalenses. The nanocomposite is synthesized by dispersing silicon nanoparticles in a thermally printable resin, which not only achieves a high refractive index for high-efficiency metalenses but also printing compatibility for inexpensive manufacturing of metalenses. The synthesized nanocomposite exhibits high refractive index >2.2 in the near-infrared regime, and only 10% uniform volume shrinkage after thermal annealing, so the nanocomposite is appropriate for elaborate nanofabrication compared to commercial high-index printable materials. A 4 mm-diameter metalens operating at the wavelength of 940 nm is fabricated using the nanocomposite and one-step printing without any secondary operations. The fabricated metalens verifies a high focusing efficiency of 47%, which can be further increased by optimizing the composition of the nanocomposite. The printing mold is reusable, so the large-scale metalenses can be printed rapidly and repeatedly. A compact near-infrared camera combined with the nanocomposite metalens is also demonstrated, and an image of the veins underneath human skin is captured to confirm the applicability of the nanocomposite metalens for biomedical imaging.

High-Definition Optophysical Image Construction Using Mosaics of Pixelated Wrinkles.

Despite many efforts in structuring surfaces using mechanical instabilities, the practical application of these structures to advanced devices remains a challenging task due to the limited capability to control the local morphology. A platform that programs the orientation of mechanically anisotropic molecules is demonstrated; thus, the surface wrinkles, promoted by such instabilities, can be patterned in the desired manner. The optics based on a spatial light modulator assembles wrinkle pixels of a notably small dimension over a large area at fast fabrication speed. Furthermore, these pixelated wrinkles can be formed on curved geometries. The pixelated wrinkles can record images, which are naturally invisible, by mapping the gray level to the orientation of wrinkles. They can retrieve those images using the patterned optical phase retardation generated under the crossed polarizers. As a result, it is shown that the pixelated wrinkles enable new applications in optics such as image storage, informative labeling, and anti-counterfeiting.

Programming emergent symmetries with saddle-splay elasticity.

The director field adopted by a confined liquid crystal is controlled by a balance between the externally imposed interactions and the liquid's internal orientational elasticity. While the latter is usually considered to resist all deformations, liquid crystals actually have an intrinsic propensity to adopt saddle-splay arrangements, characterised by the elastic constant [Formula: see text]. In most realisations, dominant surface anchoring treatments suppress such deformations, rendering [Formula: see text] immeasurable. Here we identify regimes where more subtle, patterned surfaces enable saddle-splay effects to be both observed and exploited. Utilising theory and continuum calculations, we determine experimental regimes where generic, achiral liquid crystals exhibit spontaneously broken surface symmetries. These provide a new route to measuring [Formula: see text]. We further demonstrate a multistable device in which weak, but directional, fields switch between saddle-splay-motivated, spontaneously-polar surface states. Generalising beyond simple confinement, our highly scalable approach offers exciting opportunities for low-field, fast-switching optoelectronic devices which go beyond current technologies.

Selective photonic printing based on anisotropic Fabry-Perot resonators for dual-image holography and anti-counterfeiting.

We present the photonic printing that can display different color images depending on the optical polarization of incident light. The dynamic selection among different images becomes possible by using anisotropic Fabry-Perot resonators that incorporate a layer of liquid crystal molecules aligned by directional molecular registration (DMR) as polarization-dependent color pixels. Using the new device platform, we demonstrate a prototype of an anticounterfeiting label with inherent anti-replicability that results from the molecular-level origin of security images. In addition, this concept is extended to polarization-selective holography. Our molecular-level approach enables to develop a new class of security labels and holographic storage media.

Concept of chiral image storage and selection based on liquid crystals by circular polarization.

We demonstrate a liquid crystal (LC)-based optical device with the polarization switching capability, which can store two different chiral images to be selected according to the polarization state of the viewing polarizer. The chiral dual-image device consists of chiral surface patterns for image storage and the LC layer as a tunable phase retarder. Each chiral surface pattern behaves as a helical photonic crystal that reflects circularly polarized light at a specific wavelength. Depending on the applied voltage across the LC layer, either a right-handed or a left-handed circular polarization image appears, and thus one of the two stored images can be selectively read by the polarization state. Our concept of the LC-based chiral image storage and selection provides simplicity in fabrication, flexibility in design, and high optical efficiency. It will be directly applicable for reflective-type 3D displays, color filters, and anti-counterfeiting devices.

Generation of intensity-tunable structural color from helical photonic crystals for full color reflective-type display.

A new concept of intensity-tunable structural coloration is proposed on the basis of a helical photonic crystal (HPC). The HPCs are constructed from a mixture of chiral reactive mesogens by spin-coating, followed by the photo-polymerization. A liquid crystal (LC) layer, being homogeneously aligned, is prepared on the HPCs to serve as a tunable waveplate. The electrical modulation of the phase retardation through the LC layer directly leads to the intensity-tunable Bragg reflection from the HPCs upon the incidence of the polarized light. The bandwidths of the structural colors are found to be well preserved regardless of the applied voltage. A prototype of a full color reflective-type display, incorporated with three primary color units, is demonstrated. Our concept of decoupling two mutually independent functions, the intensity modulation by the tunable waveplate and the color reflection by the HPCs provides a simple and powerful way of producing a full color reflective-type display which possesses high color purity, high optical efficiency, the cycling durability, and the design flexibility.

Concept of active parallax barrier on polarizing interlayer for near-viewing autostereoscopic displays.

We proposed a concept of an active parallax barrier using a liquid crystal-on-polarizing interlayer (LPI) for near-viewing autostereoscopic displays. In contrast to a conventional two-panel configuration where two independent panels are stacked together for displaying and parallaxing purposes, a monolithic one-panel architecture was demonstrated with the help of the LPI. The LPI was constructed using a polarizer sheet, one side of which provided the support for the active parallax barrier and the other served as the substrate for the image panel. For the active parallax barrier, an array of periodically patterned indium-tin-oxide electrodes was first prepared on the LPI and bi-level structures were subsequently fabricated for the cell gap and the liquid crystal alignment. Our monolithic one-panel architecture allows the near-viewing distance property which is essential for mobile applications.

Optically switchable grating based on dye-doped ferroelectric liquid crystal with high efficiency.

We demonstrate an all-optically switchable ferroelectric liquid crystal (FLC) grating constructed in an alternating binary configuration with different optical properties from domain to domain. A dye-doped FLC is uniformly aligned in one type of domains whereas it is infiltrated into the photo-polymerized networks of reactive mesogens in the other. Compared to conventional nematic LC cases, our FLC grating allows more efficient all-optical modulation and faster diffraction switching between the 0th and the 1st orders in subsecond since the optical response associated with the dye molecules in the layered state is less hindered than in the orientationally ordered state. Our dye-doped FLC grating with periodically infiltrated structures will be useful for designing a new class of all-optically switching systems.

Self-organized wrinkling patterns of a liquid crystalline polymer in surface wetting confinement.

Self-organized wrinkling patterns of a liquid crystalline polymer, dictated by the chemico-physically anisotropic nature of surface wettability, are demonstrated in confined geometries. The symmetry of the geometrical constraints of the confinement primarily governs the periodic wrinkling patterns of such a polymer in the wetting region. In a circular geometry, the number of the radial domains with multi-fold symmetries is linearly proportional to the radius of the confinement. The physical origin of the wrinkling process comes from the periodic bend-splay distortions through the relaxation of the curvature elasticity.

Combinatorial color arrays based on optical micro-resonators in monolithic architecture.

We demonstrate two types of combinatorial color arrays based on the Fabry-Perot (FP) micro-resonators in monolithic architecture. Optical micro-resonators corresponding to color elements are constructed using a soluble dielectric material between two transreflective layers by transfer-printing in either a pattern-by-pattern or a pattern-on-pattern fashion. The color palette depends primarily on the thickness and the refractive index of a dielectric material embedded in the micro-resonator. A self-defined lateral gap between two adjacent color elements provides the functionality of light-blocking by the underlying background layer. A prototype of a liquid crystal display incorporated with our combinatorial color array is also demonstrated. This monolithic integration of different FP micro-resonators leads to a versatile platform to build up a new class of color arrays for a variety of visual applications including displays and coloration devices.

Array of solid-state dye-sensitized solar cells with micropatterned TiO2 nanoparticles for a high-voltage power source.

We demonstrate an array of solid-state dye-sensitized solar cells (SS-DSSCs) for a high-voltage power source based on micropatterned titanium dioxide nanoparticles (TNPs) as photoanodes connected in series. The underlying concept of patterning the TNP of a few micrometers thick lies on the combination of the lift-off process of transfer-printed patterns of a sacrificial layer and the soft-cure treatment of the TNP for fixation. This sacrificial layer approach allows for high pattern fidelity and stability, and it enables to construct stable, micrometer-thick, and contamination-free TNP patterns for developing the SS-DSSC array for miniature high-voltage applications. The array of 20 SS-DSSCs integrated in series is found to show a voltage output of around 7 V.

Physical mechanism for flat-to-lenticular lens conversion in homogeneous liquid crystal cell with periodically undulated electrode.

A convertible lenticular liquid crystal (LC) lens architecture is demonstrated using an index-matched planarization layer on a periodically undulated electrode for the homogeneous alignment of an LC. It is found that the in-plane component of the electric field by the undulated electrode plays a primary role in the flat-to-lens effect while the out-of-plane component contributes to the anchoring enhancement of the LC molecules in the surface layer. Our LC device having an index-matched planarization layer on the undulated electrode is capable of achieving the electrical tunability from the flat surface to the lenticular lens suitable for 2D/3D convertible displays.