Electrically Responsive Photonic Crystals with Enhanced Suspension Stability and Color Saturation for Electrophoretic Displays and Smart Windows.

Electrophoretic displays (EPDs) based on photonic crystals show great potential due to their reduced eye fatigue and low power consumption. However, the current image quality and service life of this system still face great challenges. In this work, we fabricated a new kind of electrically responsive photonic crystal (ERPC) device based on PSMA@SiO2 liquid colloidal crystals (LCCs) for EPDs. By introduction of the PSMA core with lower density and higher refractive index, the suspension stability and color saturation of PSMA@SiO2 LCCs were greatly enhanced compared with those of bare SiO2 LCCs. The PSMA@SiO2 LCCs showed brilliant colors, wide color tuning range (∼200 nm), and good reversibility under low voltages (<4 V). Interestingly, the transparency of PSMA@SiO2 LCCs could also be obviously regulated by an electric field, which was different from the traditional ways that change the thickness of PCs or contrast of refractive index (Δn) between the nanospheres and matrix. This transparency modulation offered a novel idea for the transmittance control of smart windows. As a proof of concept, we fabricated a new type of patterned ERPC device to demonstrate their potential in electrophoretic displays and smart windows with controllable transmittance under an electric field.

Firefly-inspired bipolar information indication system actuated by white light.

The indication of information in materials is widely used in our daily life, and optical encoding materials are ideal for information loading due to their easily readable nature and adjustable optical properties. However, most of them could only indicate one type of information, either changing or unchanging due to the mutual interference. Inspired by firefly, we present a non-interfering bipolar information indication system capable of indicating both changing and unchanging information. A photochemical afterglow material is incorporated into the photonic crystal matrix through a high-throughput technique called shear-induced ordering technique, which can efficiently produce large-area photonic crystal films. The indication of changing and unchanging information is enabled by two different utilizations of white light by the afterglow material and photonic crystals, respectively, which overcome the limitations of mutual interference. As a proof of concept, this system is used to indicate the changing photodegradation level of mecobalamin (a photosensitive medicine) and unchanging intrinsic drug information with anti-counterfeiting functionality, which is a promising alternative to instantly ascertain the efficacy of medicine at home where conventional assays are impractical.

Butterfly-Inspired Tri-State Photonic Crystal Composite Film for Multilevel Information Encryption and Anti-Counterfeiting.

Counterfeiting is a worldwide issue and has long troubled legitimate businesses, while nowadays anti-counterfeiting materials and technology are still insufficient to combat the escalating counterfeit behaviors. Inspired by hindwing structure of Troides magellanus, a new kind of anti-counterfeiting material taking advantage of both physical and chemical structures to display multiple optical states is prepared. The chemical units (luminescent lanthanide) are blended with physical units (monodispersed colloidal particles) and mediating molecules, which are then assembled into a photonic crystal structure at room temperature in less than 10 s through a new assembly technique called molecule-mediated shear-induced assembly technique (MSAT). The as-prepared photonic crystal films feature three unique optical states, each displaying structural, fluorescent, and phosphorescent color under different lighting conditions, which integrates colors from both physical and chemical origins. Furthermore, by incorporating different luminescent materials into different parts of the photonic crystal pattern, a high-level information encryption system is designed to be capable of carrying three distinct types of information. Thanks to this powerful tool of MSAT, it is now possible to assemble different-sized, even irregular non-spherical units with monodispersed spherical units into high-quality photonic crystal films, which provides easy access to incorporating new features into photonic crystal systems.

Robust Large-Sized Photochromic Photonic Crystal Film for Smart Decoration and Anti-Counterfeiting.

Photochromic materials are widely investigated due to their vivid color transformation for many real applications. In this work, a new kind of multiangle photochromic photonic crystal (PC) material with high robustness and long durability for smart phone decoration and anticounterfeiting features is fabricated. After thermal mixing of spiropyran powder and monodisperse core-interlayer-shell (CIS) particles, a large-area and high-quality photochromic PC film has been prepared by the self-designed bending-induced ordering technique (BIOT). The spiropyran powder can be well dispersed in the order-structured PC system, so the perfect synergistic combination of photochromism and angle-dependent structure colors can be achieved. The color-switching test for the as-prepared photochromic PC film proved its excellent reversibility and stability. Because of the excellent flexibility of the photo-cross-linked PC films, they can be designed and cut into various shapes with high robustness and long durability. Interestingly, a temperature-controlled photochromic effect was found in this photochromic PC system. Therefore, the as-prepared photochromic PC films can play a significant role in the fields of smart decoration and anticounterfeiting by their unique color switching effects under different stimuli. More importantly, our work verified the feasibility of this route to prepare a series of large-sized advanced smart PC devices by adding versatile functional materials.

Scalable and Sensitive Humidity-Responsive Polymer Photonic Crystal Films for Anticounterfeiting Application.

In this study, we fabricate a new kind of ultrasensitive humidity-responsive photonic crystal (HPC) films based on emulsion polymerization and the open mill and bending-induced ordering technique (OM-BIOT) method, which is simple and scalable. The HPC film senses relative humidity (RH) from 9 to 98% for the polymer matrix swells up in high RH and shrinks in low RH, leading to a large reflectance shift (81 nm) and distinct color change. Based on the double-peak reflective spectra of the HPC film, we confirm the gradient swelling hypothesis and find that the thickness is another important factor for controlling the sensitivity and response rate of the HPC film. Except for static humidity, the HPC film can also respond to the dynamic humid flow of blowing and polar solvents, which broadens its application potential. This kind of HPC film shows a vivid structural color, and the humidity-responsive behavior is quick, distinct, energy-free, and reversible, having a great prospect for anticounterfeiting application.

Fabrication of industrial-level polymer photonic crystal films at ambient temperature Based on uniform core/shell colloidal particles.

HYPOTHESIS: Polymer photonic crystals have drawn a lot of interest due to cost-effective fabrication. Although tremendous efforts are tried, almost no large-size photonic crystal (PC) films can be obtained due to different kinds of reasons. The main issues are the tedious process and strict preparation conditions (like high temperature and solvents), sometimes the limitation of the machinery equipment, accordingly they are not conducive to preparation of subsequent large-scale PC films. Hence, there is an urgent desire to develop a technique that can assemble polymer PC films in a large scale at low temperature without solvent. EXPERIMENTS: Through semi-continuous emulsion polymerization, core-interlayer-shell (CIS) colloidal particles (PS@PEA@P2EHA) were synthesized with the output of 240 g/h. After the successful production of polymer PC films in the laboratory at room temperature, industrial roll-to-roll process was used for large-scale production of the PC films. FINDINGS: By introducing poly(2-ethylhexyl acrylate) which has quite low glass transition temperature (Tg) into the shell, we have successfully developed an energy-efficient technique for fabrication of large-area (over 100 m2) polymer PC films at ambient temperature for the first time. This technique has great potential to promote the industrial application of PC films, such as display, sensors, anti-counterfeiting and so on.