Brilliant Structural Colors Research Articles

Fluorescent Photonic Crystal (FPC) Films for Higher Dye-Sensitized Solar Cells (DSSCs)

A novel kind of fluorescent photonic crystal (FPC) films were prepared by co-assembly of monodispersed silica colloids and carbon dots (CDs), exhibiting brilliant structural color and excellent fluorescence simultaneously. The fluorescence spectra of FPC films have been showing a peak at 486 nm. By comparison, the dye-sensitized solar cells (DSSCs) with FPC film show higher power conversion efficiency (PCE) (4.28%) than those of DSSCs without PC film (4.08%). A relative efficiency enhancement of 4.9% was achieved, indicating that the carbon-based fluorescent photonic crystal film can be applied to enhance the efficiency of the dye-sensitized solar cell.

Large-Area and Water Rewriteable Photonic Crystal Films Obtained by the Thermal Assisted Air-Liquid Interface Self Assembly.

Compared with traditional paper, water rewritable photonic crystal (PC) paper is an environmentally friendly and low resource-consuming material for information storage. Although, recently reported PC papers have high-quality structure color showing promising prospect, the paper size, that is within several centimeters, still limits turning it from potential to reality. Here, we present a new water rewritable PC film as large as the A4 size (210 × 300 mm2) with a high-quality structure color. The material is prepared by thermal assisted self-assembly on the air-liquid interface. To fix such a large-area self-assembled PC film, we partially deform and coalesce the self-assembled nanoparticles, which have low glass transition temperature. This process causes the film to be transparent and structural colorless but still keeps the inner 3D-ordered structure. Then, utilizing the hydrophilic nature of the assembled block, the film can be switched to a structural color state by touching water. Diverse brilliant structural colors appear with different assembled particle (poly(butyl methacrylate- co-methylmethacrylate- co-butyl acrylate- co-diacetone acrylamide) named as PBMBD) sizes. The transparency-structural color transition can be performed multiple times reversibly in all or specific regions of the film. It provides a new solution for future applications of rewriteable PC paper.

Tough, structurally colored fabrics produced by photopolymerization

Structural coloration from photonic crystals (PCs) has attracted great interests owing to the chemical colorants-free process and highly brilliant color effects. However, the poor durability of the structural color severely restrains its practical applications. Based on this, a photopolymerization process to form polymer network structure was tactfully introduced in fabricating tough PCs on fabric substrates. The differences of surface morphology, tensile strength, binding strength and structural colors between poly(styrene-methacrylate) (P(St-MAA)) PCs and resultant P(St-MAA) PCs (named PHEA@P(St-MAA) PCs) were detailedly investigated and characterized. The results show that poly(hydroxyethyl acrylate) (PHEA) film is formed by photocross-linking reaction with diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide as initiator on the surface and interstices of P(St-MAA) PCs, which effectively improves the tensile strength and binding strength of P(St-MAA) PCs on fabric substrates. The PHEA@P(St-MAA) PCs display brilliant structural colors and obvious iridescence as well, although become red-shifted in accordance with Bragg’s law. It is concluded that this research will offer theoretical basis and practical guidance for the fabrication of the tough photonic crystals on fabric substrates.

Structural Coloration with Nonclose-Packed Array of Bidisperse Colloidal Particles.

Colloidal crystals and glasses have their own photonic effects. Colloidal crystals show high reflectivity at narrowband, whereas colloidal glasses show low reflectivity at broadband. To compromise the opposite optical properties, a simple means is suggested to control the colloidal arrangement between crystal and glass by employing two different sizes of silica particles with repulsive interparticle potential. Monodisperse silica particles with repulsive potential spontaneously form crystalline structure at volume fraction far below 0.74. When two different sizes of silica particles coexist, the arrangement of silica particles is significantly influenced by two parameters: size contrast and mixing ratio. When the size contrast is small, a long-range order is partially conserved in the entire mixing ratio, resulting in a pronounced reflectance peak and brilliant structural color. When the size contrast is large, the long-range order is rapidly reduced along with mixing ratio. Nevertheless, a short-range order survives, which causes low reflectivity at a broad wavelength, developing faint structural colors. These findings offer an insight into controlling the colloidal arrangements and provide a simple way to tune the optical property of colloidal arrays for structural coloration.

Visual sensors of an inverse opal hydrogel for the colorimetric detection of glucose

Possessing the combined advantages of a stable network structure, brilliant structural color, and high sensitivity, the three-dimensional inverse opal hydrogel film could be used as a colorimetric sensor for the precise detection of glucose.

A flexible and robust dual-network supramolecular elastic film with solvent resistance and brilliant structural colors

Structural color films were prepared by combining a Zn2+-crosslinked supramolecular elastic material with PS@SiO2 colloidal crystals.

Hollow silica opals/cellulose acetate nanocomposite films with structural colors for anti-counterfeiting of banknotes

We designed hollow silica opals/cellulose acetate nanocomposite films with brilliant structural colors for anti-counterfeiting applications of banknotes.

Cardiomyocytes-Actuated Morpho Butterfly Wings.

Morpho butterflies are famous for their wings' brilliant structural colors arising from periodic nanostructures, which show great potential value for fundamental research and practical applications. Here, a novel cellular mechanical visualizable biosensor formed by assembling engineered cardiac tissues on the Morpho butterfly wings is presented. The assembled cardiomyocytes benefit from the periodic parallel nanoridges of the wings and can recover their autonomic beating ability with guided cellular orientation and good contraction performance. As the beating processes are accompanied by the cardiomyocytes' elongation and contraction, the elastic butterfly wing substrate undergoes the same cycle of deformations, which causes corresponding synchronous shifts in their structural colors and photonic bandgaps for self-reporting of the cell mechanics. It is demonstrated that this self-reporting performance can be further improved by adding oriented carbon nanotubes in the nanoridges of the wings for the culture. In addition, taking advantage of the similar size of the cardiomyocyte and a single Morpho wing scale, the investigation of single-cell-level mechanics can be realized by detecting the optical performance of a single scale. These remarkable properties make these butterfly wings ideal platforms for biomedical research.

Facile Fabrication of Amorphous Photonic Structures with Non-Iridescent and Highly-Stable Structural Color on Textile Substrates.

Amorphous photonic structures with non-iridescent and highly-stable structural color were fabricated via a simple one-step spray-coating technique. With this strategy, the obtained films on textile substrates presented short-ordered and amorphous photonic structures (APSs) similar to the amorphous nanostructures of avian feathers. The structural color presented the same hue when viewed at different angles and could be well controlled by varying the diameters of the SiO2 nanospheres. The prepared fabrics with structural color exhibited high color stability due to stability in both the assembled physical structure and the refractive index. The high stability of the assembled physical structure was attributed to the cementing effect of Poly(methylmethacrylate-butylacrylate) P(MMA-BA) existing between textile substrate and SiO2 nanospheres and among SiO2 nanospheres, while the high stability in the refractive index was contributed by the liquid-resistance achieved by both the surface roughness and the low-surface-energy of the as-sprayed APSs. With the resistances to external forces and liquid invasion, the non-iridescent brilliant structural color of the as-prepared fabrics could be kept steady. In this study, an approach of fabricating APSs with non-iridescent and stable structural color was established to enhance its potential application in structural coloration of textiles, and other color-related smart textiles.

Designing the Iridescences of Biopolymers by Assembly of Photonic Crystal Superlattices

AbstractStructural color in naturally occurring systems is generally constituted by nanoscale lattices of biopolymers that generate beautiful iridescences through their regular structures, often interspersed with defects or period mismatch. Taking inspiration from both formats and materials found in Nature, a series of large‐scale, highly reflective biopolymer‐based photonic crystal superlattices constituted by stacking layers of 3D nanoscale lattices with different periodicity is presented. These silk photonic crystal superlattices (SPCSs) are fully composed of naturally derived structural proteins (silk fibroin) and exhibit brilliant structural color while being mechanically flexible. Multi‐stopbands over broad wavelength ranges or single‐stopbands with narrowband spectral responses can be readily realized and precisely controlled by manipulating the hierarchy of the lattice stacks or the repetition periods of the assembled colloidal monolayers. The unique ability to vary the silk protein conformation allows to vary the lattice and controllably “design” the iridescences of the SPCSs with water vapor adding versatility to this biopolymer‐based photonic structure.

Study on the fabrication of composite photonic crystals with high structural stability by co-sedimentation self-assembly on fabric substrates

The Silica/Poly(methylmethacrylate-butylacrylate)[SiO2/P(MMA-BA)] photonic crystals(PCs) with brilliant structural colors were fabricated on fabric substrates by co-sedimentation self-assembly, in which the relatively smaller P(MMA-BA) copolymer particles filled in the interstices among the larger SiO2 microspheres. The fabricated composite PCs were mechanically robust and strongly bonded to the substrate because of the cementing effect caused by the soft P(MMA-BA) copolymer particles filling in the interstices of the SiO2 microspheres like cement filling in the gap and tightly holding stones in a sturdy cement wall. The volume fraction and the size ratios of the two components significantly influenced the structural colors of the composite PCs, and the larger volume fraction could improve the structural stability of the composite PCs, while the smaller size ratios could enhance the brightness of the structural colors of the composite PCs. The composite PCs with both high structural stability and brilliant structural colors have great application prospect for structural coloration of textiles.

Robust and flexible thermal-plasticizing 3D shaped composite films with invariable and brilliant structural color

We present a novel flexible thermal-plasticizing 3D shaped composite film with invariable structural color through an organic–inorganic hybrid matrix design.

Magnetic light cloaking control in the marine planktonic copepod Sapphirina

We investigated the light cloaking behavior of the marine planktonic copepod Sapphirina under a magnetic field. Optical interferences in the multi-laminated guanine crystal layer beneath the dorsal body surface create a brilliant structural color, which can be almost entirely removed by changing the light reflection. In the investigation, we immersed segments of Sapphirina in seawater contained in an optical chamber. When the derived Sapphirina segments were attached to the container surface, they were inert to magnetic fields up to 300 mT. However, when the back plate segments were attached to the substrate at a point, with most of the plate floating in the seawater, the plate rotated oppositely to the applied magnetic field. In addition, the brilliant parts of the Sapphirina back plate rotated backward and forward by changing the magnetic field directions. Our experiment suggests a new model of an optical micro-electro-mechanical system that is controllable by magnetic fields.

Fabrication of patterned photonic crystals with brilliant structural colors on fabric substrates using ink-jet printing technology

In order to develop a fast, efficient and drop-on-demand method to produce structural colors, ink-jet printing technology was applied in fabricating photonic crystals on fabric substrates. The formulation of poly (styrene-methacrylic acid) (P(St-MAA)) colloidal inks, especially, the “coffee ring” effects on deposited droplets and the related suppression method were detailedly investigated through characterizing the morphology and color changes of the ink-jetted droplets, and different drop-on-demand ink-jet printers were used to print the photonic crystal patterns. The results showed that 10vol% P(St-MAA) colloidal microspheres and 4–6vol% Formamide (FA) were the main components of the colloidal inks, in which the addition of FA effectively suppressed the “coffee ring” effects by producing a surface tension gradient from the edge of the droplet to center and inducing an inward capillary flow from the edge to the center along the droplet surface due to its higher boiling point and lower surface tension. In addition, the resultant photonic crystal patterns exhibited vivid structural colors and distinct iridescent phenomenon.

Highly sensitive multiresponsive photonic hydrogels based on a crosslinked Acrylamide- N-isopropylacrylamide (AM-NIPAM) co-polymer containing Fe3O4@C crystalline colloidal arrays

Multiresponsive photonic hydrogels (MRPHs) were prepared by magnetically controlled self-assembly of Fe3O4@C nanoparticles and these are sensitive to temperature, humidity, compression, tension and ethanol. This exhibits brilliant structural color thanks to the combination of AM and NIPAM monomers. Along with the increase of compression and tension on the MRPHs, the reflection peak of the samples blue shifts. When exposed MRPHs in environments with different humidity, its structure color red shifts as the humidity increases from 33% RH to 95% RH. Besides, the reflection peak redshift was observed when the MRPHs was immersed in absolute ethyl alcohol. This work may provide a new way to prepare smart photonic hydrogel with integrated functions of mechano-, humidity-, temperature- and solvent- responses.

Colloidal Photonic Crystals Containing Silver Nanoparticles with Tunable Structural Colors

Polystyrene (PS) colloidal photonic crystals (CPhCs) containing silver nanoparticles (AgNPs) present tunable structural colors. PS CPhC color films containing a high concentration of AgNPs were prepared using self-assembly process through gravitational sedimentation method. High-concentration AgNPs were deposited on the bottom of the substrate and acted as black materials to absorb background and scattering light. Brilliant structural colors were enhanced because of the absorption of incoherent scattering light, and color saturation was increased by the distribution AgNPs on the PS CPhC surfaces. The vivid iridescent structural colors of AgNPs/PS hybrid CPhC films were based on Bragg diffraction and backward scattering absorption using AgNPs. The photonic stop band of PS CPhCs and AgNPs/PS hybrid CPhCs were measured by UV–visible reflection spectrometry and calculated based on the Bragg–Snell law. In addition, the tunable structural colors of AgNPs/PS hybrid CPhC films were evaluated using color measurements according to the Commission International d’Eclairage standard colorimetric system. This paper presents a simple and inexpensive method to produce tunable structural colors for numerous applications, such as textile fabrics, bionic colors, catalysis, and paints.

Bioinspired few‐layer graphene prepared by chemical vapor deposition on femtosecond laser‐structured Cu foil

AbstractInspired from butterfly wings that exhibit unique dewetting properties and brilliant structural color synchronously, we reported here the preparation of biomimetic few‐layer graphene films through a template‐directed chemical vapor deposition method using laser‐structured Cu foil as substrates. Hierarchical micronanostructures, including microscale stripes derived from the laser scanning and nanoscale laser‐induced periodic surface structures (LIPSS), formed on Cu foil after a simple femtosecond laser treatment. By tuning the laser power, the surface roughness of the resultant Cu foils can be well controlled. Using the laser structures Cu foil as templates, biomimetic few‐layer graphene films with both iridescence and superhydrophobicity have been successfully prepared. The present work may open up a new way to design and prepare structured graphene film in a biomimetic manner, and we deem that the bioinspired few‐layer graphene films may find broad applications in the near future. image

Synthesis of highly uniform Cu2O spheres by a two-step approach and their assembly to form photonic crystals with a brilliant color.

Monodisperse semiconductor colloidal spheres with a high refractive index hold great potential for building photonic crystals with a strong band gap, but the difficulty in separating the nucleation and growth processes makes it challenging to prepare highly uniform semiconductor colloidal spheres. Herein, real monodisperse Cu2O spheres were prepared via a hot-injection & heating-up two-step method using diethylene glycol as a milder reducing agent. The diameter of the as prepared Cu2O spheres can be tuned from 90 nm to 190 nm precisely. The SEM images reveal that the obtained Cu2O spheres have a narrow size distribution, which permits their self-assembly to form photonic crystals. The effects of precursor concentration and heating rates on the size and morphology of the Cu2O spheres were investigated in detail. The results indicate that the key points of the method include the burst nucleation to form seeds at a high temperature followed by rapid cooling to prevent agglomeration, and appropriate precursor concentration as well as a moderate growth rate during the further growth process. Importantly, photonic crystal films exhibiting a brilliant structural color were fabricated with the obtained monodisperse Cu2O spheres as building blocks, proving the possibility of making photonic crystals with a strong band gap. The developed method was also successfully applied to prepare monodisperse CdS spheres with diameters in the range from 110 nm to 210 nm.

Polymer opal with brilliant structural color under natural light and white environment

Abstract

Versatile hydrogel-based nanocrystal microreactors towards uniform fluorescent photonic crystal supraballs

Versatile hydrogel-based nanocrystal (NC) microreactors were designed in this work for the construction of uniform fluorescence colloidal photonic crystal (CPC) supraballs. The hydrogel-based microspheres with sizes ranging from 150 to 300 nm were prepared by seeded copolymerization of acrylic acid and 2-hydroxyethyl methacrylate with micrometer-sized PS seed particles. As an independent NC microreactor, the as-synthesized hydrogel microsphere can effectively capture the guest cadmium ions due to the abundant carboxyl groups inside. Followed by the introduction of chalcogenides, in situ generation of higher-uptake NCs with sizes less than 5 nm was finally realized. Additionally, with the aid of the microfluidic device, the as-obtained NC–latex hybrids can be further self-assembled to bi-functional CPC supraballs bearing brilliant structural colors and uniform fluorescence. This research offers an alternative way to finely bind CPCs with NCs, which will facilitate progress in fields of self-assembled functional colloids and photonic materials.