Structural colors in nature: the role of regularity and irregularity in the structure.

Coloring in nature mostly comes from the inherent colors of materials, but it sometimes has a purely physical origin, such as diffraction or interference of light. The latter, called structural color or iridescence, has long been a problem of scientific interest. Recently, structural colors have attracted great interest because their applications have been rapidly progressing in many fields related to vision, such as the paint, automobile, cosmetics, and textile industries. As the research progresses, however, it has become clear that these colors are due to the presence of surprisingly minute microstructures, which are hardly attainable even by ultramodern nanotechnology. Fundamentally, most of the structural colors originate from basic optical processes represented by thin-film interference, multilayer interference, a diffraction grating effect, photonic crystals, light scattering, and so on. However, to enhance the perception of the eyes, natural creatures have produced various designs, in the course of evolution, to fulfill simultaneously high reflectivity in a specific wavelength range and the generation of diffusive light in a wide angular range. At a glance, these two characteristics seem to contradict each other in the usual optical sense, but these seemingly conflicting requirements are realized by combining appropriate amounts of regularity and irregularity of the structure. In this Review, we first explain the fundamental optical properties underlying the structural colors, and then survey these mysteries of nature from the viewpoint of regularity and irregularity of the structure. Finally, we propose a general principle of structural colors based on structural hierarchy and show their up-to-date applications.     

Full‐Spectrum Photonic Pigments with Non‐iridescent Structural Colors through Colloidal Assembly

Structurally colored materials could potentially replace dyes and pigments in many applications, but it is challenging to fabricate structural colors that mimic the appearance of absorbing pigments. We demonstrate the microfluidic fabrication of “photonic pigments” consisting of microcapsules containing dense amorphous packings of core–shell colloidal particles. These microcapsules show non‐iridescent structural colors that are independent of viewing angle, a critical requirement for applications such as displays or coatings. We show that the design of the microcapsules facilitates the suppression of incoherent and multiple scattering, enabling the fabrication of photonic pigments with colors spanning the visible spectrum. Our findings should provide new insights into the design and synthesis of materials with structural colors.     

Biomimetic Chiral Photonic Crystals

Although it is well known that the amazing iridescent colors of the cuticle of beetles reflect the intricate nanoscale organization of bio‐fibers, artificial inorganic materials with comparable optical responses have not yet been synthesized from abiotic nanoscale building blocks. Such materials could find broad applications, including in circular polarizers, to generate circularly polarized luminescence, or in lasers. Herein, we describe a general method for the fabrication of biomimetic chiral photonic crystals by Langmuir–Schaefer assembly of colloidal inorganic nanowires. We not only reproduced the intricate helical structure and circularly polarized color reflection observed in beetles, but also achieved the highest chiroptical activity with a dissymmetry factor of ?1.6 ever reported for chiral inorganic nanostructures. More importantly, the programmable structural control based on the precise interlayer arrangement endows us with unprecedented freedom to manipulate the optical activity of as‐fabricated chiral photonic crystals.     

Recent Progress of Bio-inspired Camouflage Materials: From Visible to Infrared Range

The adaptability of biological organisms to the environment is reflected in many aspects, especially in their camouflage of appearance. Inspired by biological camouflage strategies, a number of adaptive camouflage materials and devices have been developed to protect soldiers, vehicles, or equipment in the military. Today, the need for adaptive camouflage extends into people’s lives, whose privacy and information security need to be protected in the era of big data. Herein, a review is provided on the recent advancements of adaptive camouflage from the perspective of biological organisms and bio-inspired materials. Firstly, according to different biological mechanisms, we review the typical organisms that use pigmentary color, structural color, and morphological variation for adaptive camouflage, as well as those combine these strategies. Then, we provide an up-to-date review on recent developments in bio-inspired adaptive camouflage materials and devices with an emphasis on visible, infrared, and multispectral camouflage. At last, this review concludes the challenges and prospects for the future development of adaptive camouflage materials. It is noteworthy that there is never the best camouflage. To counter advanced detection techniques, it is necessary to unremittingly develop new materials and technologies to meet the increasing need for adaptive camouflage.     

Recent advances in spherical photonic crystals: Generation and applications in optics

Spherical photonic crystals (PCs), generated by assembly of monodisperse colloidal nanospheres in a spherical confined geometry, attract great attention recently owing to their potential applications in the fields of displays, sensors, optoelectronic devices, and others. Compared to their conventional film or bulk counterparts, the optical stop band of the spherical PCs is independent of the rotation under illumination of the surface of a fixed incident angle of the light, broadening their applications. In this paper, we will review recent advances in the field of spherical PCs including design, preparation and potential applications. Various preparation strategies for spherical PCs, including solvent-evaporation induced crystallization method, microfluidic-assisted approach, and others are outlined. Their applications based on the unique optical properties (such as photonic band gaps and structural colors) for sensing and displaying are then presented, followed by the perspective of this emerging field.     

Structural colored gels for tunable soft photonic crystals

A periodically ordered interconnecting porous structure can be embodied in chemical gels by using closest‐packed colloidal crystals as templates. The interconnecting porosity not only provides a quick response but also endows the porous gels with structural color arising from coherent Bragg optical diffraction. The structural colors revealed by porous gels can be regulated by several techniques, and thus, it is feasible to obtain desirable, smart, soft materials. A well‐known thermosensitive monomer, N‐isopropylacrylamide (NIPA), and other minor monomers were used to fabricate various structural colored gels. The selection of minor monomers depended on the targeted properties. This review focuses on the synthesis of templates, structural colored porous gels, and the applications of structural colored gel as smart soft materials for tunable photonic crystals. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 87–105; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20169     

Self‐Healable Organogel Nanocomposite with Angle‐Independent Structural Colors

Structural colors have profound implications in the fields of pigments, displays and sensors, but none of the current non‐iridescent photonic materials can restore their functions after mechanical damage. Herein, we report the first self‐healable organogel nanocomposites with angle‐independent structural colors. The organogel nanocomposites were prepared through the co‐assembly of oleophilic silica nanoparticles, silicone‐based supramolecular gels, and carbon black. The organogel system enables amorphous aggregation of silica nanoparticles and the angle‐independent structural colors in the nanocomposites. Moreover, the hydrogen bonding in the supramolecular gel provides self‐healing ability to the system, and the structural colored films obtained could heal themselves in tens of seconds to restore storage modulus, structural color, and surface slipperiness from mechanical cuts or shear failure repeatedly.     

水凝胶的制备及仿生设计在能源领域应用的研究进展

能源与环境问题是当前时代面临的一大课题,有效利用并储存能源,缓解一系列严峻的环境污染问题也是当前研究的热点,电化学储能、光催化、光热界面蒸发和水汽收集这些能源利用措施已经作为环保手段深入人类的生活.大自然作为一位天然的设计师为我们能够提供诸多灵感,自然界诸多生物、生命体系中特性、机制和结构均暗含着十分巧妙的奥秘.本文重...     

TiO2掺杂调控聚苯乙烯微球折射率及胶体光子晶体结构色

胶体光子晶体由于其可调变的结构色在绿色印刷、印染等领域备受关注,而其光子带隙的宽度和位置由光子晶体的晶格参数(晶面间距,通常受胶体微球尺寸影响)和介质的折射率决定。现有人工胶体光子晶体主要基于SiO_2和高分子(如聚苯乙烯(PS)等)微球的组装制备,由于胶体微球材质种类有限,折射率调控受限,因而目前调控胶体光子晶体结构色主要靠改变胶体微球的尺寸来实现。本文首先制备高折射率(2.6)的TiO_2纳米晶,在乳液聚合制备单分散的PS(折射率1.6)微球过程中,将所制备的TiO_2纳米晶掺杂于PS微球中,通过TiO_2的掺杂量有效调控胶体微球的折射率,进而实现胶体光子晶体的结构色调控。以多色胶体光子晶体微球的水溶液为墨水,采用彩色喷墨打印技术打印了电脑设计的光子晶体彩画。本文发展的光子晶体结构色调控新技术拓展了胶体光子晶体的应用。     

纤维素纳米晶体手性复合材料:结构色的调控与应用

结构色在自然界中扮演了重要的角色,在昆虫外骨骼、鸟类羽毛以及植物果实中广泛分布.纤维素纳米晶体(CNCs)的水悬浮液达到一定浓度时会自组装形成左旋的手性向列液晶结构,这种手性向列结构在水分挥发后仍能保持并形成光子晶体虹彩薄膜,具有极强的手性和光子晶体的双重性质.膜内的周期性层状结构与光线产生干涉、衍射作用,表现出复杂的...     

仿生器官芯片研究进展

自然界在漫长的进化过程中创造了大量具备优异特性的天然材料,为人工材料的设计和制备以及相关学科的发展提供了源源不断的灵感来源.得益于材料科学和微加工制造工艺的飞速发展,受自然界天然材料启发而构建的仿生材料受到科研界的广泛关注并随之蓬勃发展.基于精细的形貌加工和组分设计,仿生材料已经被赋予自适应、自修复、自清洁以及雾收集等...     

Hierarchical assembly of micro-/nano-building blocks: bio-inspired rigid structural functional materials

The huge diversity of hierarchical micro-/nano-rigid structures existing in biological systems is increasingly becoming a source of inspiration of materials scientists and engineers to create next-generation advanced functional materials. In the past decades, these multiscale hierarchical structures have been intensively investigated to show their contributions to high performance in mechanical properties. Recently, accompanied with the development of nanotechnology, some biologically hierarchical rigid structures have been duplicated and mimicked in artificial materials through hierarchical organization of micro-/nano-building blocks. In this critical review, we will present biological rigid structural models, functional micro-/nano-building blocks, and hierarchical assembly techniques for the manufacture of bio-inspired rigid structural functional materials (177 references).     

胶体晶体微球及其生物医学应用

光子晶体(PhCs)是由单分散纳米粒子周期性排列形成的材料,具有光子禁带,频率落在光子禁带内的光被禁止传播,这个特性激起了研究者对其制备和应用的研究热情。然而,一般的光子晶体材料都具有角度有偏性质,限制了其在宽视角光学材料和设备上的应用。近几年有一系列围绕球形胶体光子晶体材料的研究成果问世,由于球形的对称性,球形胶体晶体的衍射峰不会随着光的入射角变化而发生变化,从而拓宽了胶体晶体的应用范围。随着微流控技术被用于制备液滴模板,球形胶体晶体的制备取得了巨大的进步。微流控技术不仅保证了液滴模板的单分散性,还增加了胶体晶体微球的结构与功能的多样性。胶体晶体微球这些特有的性质,可以很好地将光子晶体材料与编码、非标记检测、细胞培养以及载药等生物医学领域连接起来,为其应用提供了广阔的前景。本文总结了球形光子晶体的研究进展,包括球形光子晶体的设计、制备及其生物医学应用,最后,对球形光子晶体未来的发展方向作了展望。     

Cellulose Nanocrystal Elastomers with Reversible Visible Color

Responsive photonic crystals have potential applications in mechanical sensors and soft displays; however, new materials are constantly desired to provide new innovations and improve on existing technologies. To address this, we report stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible color upon the application of mechanical stress. When stretched (or compressed) the colorless materials maintain their chiral nematic structure but the helical pitch is reduced into the visible region, resulting in coloration of the CNC‐elastomer composite. By increasing the percentage elongation of the material (ca. 50–300 %), the structural color can be tuned from red to blue. The color of the materials was characterized by reflectance optical microscopy and reflectance circular dichroism to confirm the wavelength and polarization of the reflected light. We also probed the mechanism of the structural color using 2D‐X‐ray diffraction. Finally, by either water‐patterning the starting CNC film, or by forming a CNC film with gradient color, through masked evaporation, we were able to prepare encoded stretchable chiral nematic CNC‐elastomers.     

Mechanochromic Fibers with Structural Color

Responsive photonic crystals have been widely developed to realize tunable structural colors by manipulating the flow of light. Among them, mechanochromic photonic crystals attract increasing attention due to the easy operation, high safety and broad applications. Recently, mechanochromic photonic crystal fibers were proposed to satisfy the booming wearable smart textile market. In this Concept, the fundamental mechanism, fabrication, and recent progress on mechanochromic photonic crystals, especially in fiber shape, are summarized to represent a new direction in sensing and displaying.     

Reconfigurable Photonic Crystal Reversibly Exhibiting Single and Double Structural Colors

Unlike absorption-based colors of dyes and pigments, reflection-based colors of photonic crystals, so called “structural colors”, are responsive to external stimuli, but can remain unfaded for over ten million years, and therefore regarded as a next-generation coloring mechanism. However, it is a challenge to rationally design the spectra of structural colors, where one structure gives only one reflection peak defined by Bragg's law, unlike those of absorption-based colors. Here, we report a reconfigurable photonic crystal that exhibits single-peak and double-peak structural colors. This photonic crystal is composed of a colloidal nanosheet in water, which spontaneously adopts a layered structure with single periodicity (407 nm). After a temperature-gradient treatment, the photonic crystal segregates into two regions with shrunken (385 nm) and expanded (448 nm) periodicities, and thus exhibits double reflection peaks that are blue- and red-shifted from the original one, respectively. Notably, the transition between the single-peak and double-peak states is reversible.     

Mechanochromic Photonic‐Crystal Fibers Based on Continuous Sheets of Aligned Carbon Nanotubes

A new family of mechanochromic photonic‐crystal fibers exhibits tunable structural colors under stretching. This novel mechanochromic fiber is prepared by depositing polymer microspheres onto a continuous aligned‐carbon‐nanotube sheet that has been wound on an elastic poly(dimethylsiloxane) fiber, followed by further embedding in poly(dimethylsiloxane). The color of the fiber can be tuned by varying the size and the center‐to‐center distance of the polymer spheres. It further experiences reversible and rapid multicolor changes during the stretch and release processes, for example, between red, green, and blue. Both the high sensitivity and stability were maintained after 1000 deformation cycles. These elastic photonic‐crystal fibers were woven into patterns and smart fabrics for various display and sensing applications.     

Assembly and photonic properties of superparamagnetic colloids in complex magnetic fields

Interparticle magnetic dipole force has been found to drive the formation of dynamic superparamagnetic colloidal particle chains that can lead to the creation of photonic nanostructures with rapidly and reversibly tunable structural colors in the visible and near-infrared spectrum. Although most studies on magnetic assembly utilize simple permanent magnets or electromagnets, magnetic fields, in principle, can be more complex, allowing the localized modulation of assembly and subsequent creation of complex superstructures. To explore the potential applications of a magnetically tunable photonic system, we study the assembly of magnetic colloidal particles in the complex magnetic field produced by a nonideal linear Halbach array. We demonstrate that a horizontal magnetic field sandwiched between two vertical fields would allow one to change the orientation of the particle chains, producing a high contrast in color patterns. A phase transition of Fe(3)O(4)@SiO(2) particles from linear particle chains to three-dimensional crystals is found to be determined by the interplay of the magnetic dipole force and packing force, as well as the strong electrostatic force. While a color pattern with tunable structures and diffractions can be instantly created when the particles are assembled in the form of linear chains in the regions with vertical fields, the large field gradient in the horizontal orientation may destabilize the chain structures and produces a pattern of 3D crystals that compliments that of initial chain assemblies. Our study not only demonstrates the great potential of magnetically responsive photonic structures in the visual graphic applications such as signage and security documents but also points out the potential challenge in pattern stability when the particle assemblies are subjected to complex magnetic fields that often involve large field gradients.     

Bio-inspired special wetting surfaces via self-assembly

Self-assembly is the fundamental principle, which can occur spontaneously in nature. Through billions of years of evolution, nature has learned what is optimal. The optimized biological solution provides some inspiration for scientists and engineers. In the past decade, under the multi-disciplinary collaboration, bio-inspired special wetting surfaces have attracted much attention for both fundamental research and practical applications. In this review, we focus on recent research progress in bio-inspired special wetting surfaces via self-assembly, such as low adhesive superhydrophobic surfaces, high adhesive superhydrophobic surfaces, superamphiphobic surfaces, and stimuli-responsive surfaces. The challenges and perspectives of this research field in the future are also briefly addressed.     

Electrochromic photonic crystal displays with versatile color tunability

An electrochromic photonic crystal (EPC) display device that combines chemical (electrochromic) and physical (photonic) coloring mechanisms is reported for the first time. This EPC exhibits superior and versatile color tunability. The TiO₂ inverse opals fabricated by atomic layer deposition are adopted as EPC material. Results show that the photonic band gaps selectively modified the optical properties of the EPC and enabled facile tuning of electrochromic colors. In addition, the reversible photonic and photonic modified electrochromic coloring states with insertion/extraction of lithium ions enable novel and promising approaches for future display applications.