Structural coloration with colloidal photonic crystals (CPCs) is a physical coloration technology producing colorful materials without using chemical colorants (dyes/pigments). It is an environmentally friendly process enabling tunable and charming structural colors, high colorfastness to light, and many other attractive characteristics. However, its application in textile industry faces two bottlenecks: the insufficient stability of self-assembled structures for textiles and the difficulty in achieving large-scale and uniform assemblies on flexible and rough textile substrates. This review provides a brief introduction into the fundamental concepts and principles of structural color originating from CPCs, as well as the commonly used assembly materials of CPCs for structural coloration of textiles (monodisperse colloidal nanospheres, and liquid colloidal photonic crystals (LCPCs)). Special attention is paid to the efficient technical means employed for large-scale assembly of CPCs on textile substrates, including shear-induced assembly, inkjet printing, screen printing, spray coating, transfer printing, and photonic nanopigment dyeing. The stabilization strategies of CPC structures (chemical bonding, "spot welding" bonding, polymer encapsulation, shell fusion of hard-core/soft-shell nanospheres, interfacial molecule migration-resolidification, and overall curing of photocurable LCPCs) are described as well. Finally, the application potential and prospects of CPC-based structural coloration technology in sustainable coloration of textiles, fashion textiles, and smart textiles are discussed.

The conductive hydrogels have emerged as the promising bioelectronics in various applications. To address the persistent challenge of reconciling extreme mechanical robustness with outstanding electrical properties during the long-term use, we propose a synergistic strategy to develop a strong and highly conductive hydrogel with hierarchical network through sequential Dimethyl sulfoxide (DMSO) crystal-templating, solvent replacement, multi-amine-mediated crystal reorganization and co-polymerization. Taking the merits of the aligned microstructure, adaptive non-covalent interactions, and the re-organized Poly(vinyl alcohol) (PVA) crystalline domains, the resultant hydrogel could effectively dissipate the impact energy, demonstrating excellent tensile strength as high as 4.26 MPa with a satisfactory fracture strain of 206%. Besides, this reliable conductive hydrogel displays a tissue-like self-strengthening behavior upon cyclic mechanical training, where the respective tensile strength and strain could be further increased up to 8.5 MPa and 221%. Notably, the conductive particles could be firmly immobilized into the outer layer of hydrogel via in-situ co-polymerization between the multi-amine molecules (i.e., 2,4,6-Triaminopyrimidine) and aniline monomers. Due to the existence of anisotropic transport channels, the ductile hydrogel possesses high electrical conductivity up to 13 S.m(-1), and exhibits consistent sensitivity to external strains. The high-performances make the hydrogel as an efficient electronic device for real-time motion sensing.

The preparation of anti-counterfeiting textiles is usually associated with laborious processes, high cost and environmental risks. In this work, the core-shell colloidal nanospheres composed of the polystyrene (PS) core with embedded aggregation-induced emission (AIE) molecules of tetraphenylethene (TPE) and the shell of densely crosslinked PS ((PS-TPE)@CPS) were designed and synthesized via emulsion polymerization. The patterned fluorescence-responsive photonic crystals (FRPCs) were then constructed using the (PS-TPE)@CPS nanospheres as building blocks on textile substrates via screen printing. Thanks to the compatibility and affinity of TPE with PS and its own AIE property, the TPE molecules enriched in the PS core and then aggregated and embedded within (PS-TPE)@CPS colloidal nanospheres. Confined by the polymer chains, the TPE molecules formed π-π stacking and exhibited AIE effect, while maintaining a stable conjugated structure. The FRPC anti-counterfeiting patterns constructed with the (PS-TPE)@CPS nanospheres exhibited angle-dependent structural colors under visible light and sensitive responsive fluorescence characteristic under ultraviolet light, realizing the double anti-counterfeiting effect. This approach to achieve anti-counterfeiting textile is simple, cost-effective, and environmentally friendly. The obtained FRPC patterns possess excellent optical properties and anti-counterfeiting functions, meeting the requirements for the sustainable structural coloration of textiles, and also promoting the practical application of responsive photonic crystal anti-counterfeiting textiles.

Biomimetic structural coloration with photonic crystals (PCs) possesses the advantages of eco-friendly coloration, brilliant structural colors, and high colorfastness to light, etc. It is appealing for advanced coloration of various substrate surfaces. However, the fabrication of PCs with iridescent effect and high colorfastness on three-dimensional (3D) irregular substrate surfaces is still challenging. In this work, liquid photonic crystals (LPCs) with high mass fraction (40wt.%) of colloidal nanospheres were used as the spraying solution to assemble long-range ordered PCs with iridescent effect. Thanks to the fluidity and dynamic reversibility, the pre-crystallized LPCs could disassemble under the applied spraying pressure, which promoted smooth spraying and enabled the formation of atomized micro-droplets. The colloidal nanospheres present in these micro-droplets were able to quickly reassemble and restore their pre-crystallized state. This allowed micro-droplets to connect with each other on the curved or 3D irregulated substrate surface into orderly assembled solid PCs upon the water evaporation, exhibiting brilliant structural colors with iridescent effect. Meanwhile, the use of the spraying solution with high mass fraction of colloidal nanospheres was shown to be effective against the slipping problem of the micro-droplets on 3D substrate surfaces, enabling the fabrication of PCs with pronounced iridescent structural colors on various 3D substrate surfaces (metal, ceramic, rubber, glass and so on). In addition, pre-spraying a specific polymer slurry to form a bearing layer on the 3D substrate prior to spraying the LPC allows improving the stability of the assembled PC structure under external forces (rubbing, washing, etc.), while retaining the refractive index contrast of PCs and thus achieving the consistency between their structural stability and color saturation.

Photonic crystals (PCs) as eco-friendly structural coloring materials have great application potential in the textile coloration. However, the difficulties in scale production of structurally colored fabrics with PCs, as well as in achieving the balance between the structural stability and optical properties of PCs, limit the widespread use of such textiles. Herein, inspired by chameleon skin, the structural coloration of textiles with non-close-packed PCs was designed and prepared. The soft-shell and hard-core PS@P(MMA-BA) nanospheres were designed and prepared via stepwise emulsion polymerization for constructing soft non-close-packed PCs. The liquid photonic crystals (LPCs) were controllably prepared using a rotary evaporation/surfactant method. Therewith, the designed step by step self-assembly method enabled one to realize the controllable assembly of the nanospheres on the fabric surface, whereby the non-close-packed PCs with the cross-linked hard core as the skeleton and the fused soft shell as the filling medium were obtained. On the basis of step by step self-assembly, large-scale structurally colored fabric with non-close-packed PCs was prepared by continuous pilot equipment. The prepared structurally colored textiles possess high structural stability and color saturation, as well as the mechanochromic properties, and has the potential as a smart textile.

Responsive photonic crystals (RPCs) have the advantages of visual response, controllable response speed, and reasonable response sensitivity, enabling them attractive in sensing detection, intelligent displays, anti-counterfeiting identification and other fields. At present, the rapid development of anti-counterfeiting technology ensures product quality and brand influence, as well as human health, placing an important economic value and bringing social benefits. This review introduces the research status of visual responsive photonic crystals, and the special attention is paid to the preparation principle, classification and preparation methods of RPCs, and their application progress in the anti-counterfeiting systems for the textile industry.

Rapid preparation of structurally colored fabric with PMMA photonic crystals.

The structural coloration of textiles with bionic photonic crystals (PCs) is expected to become a critical approach to the ecological coloration of textiles. Rapid and large-area preparation of PC structurally colored textiles can be achieved via self-assembly of high mass fractions of liquid photonic crystals (LPCs). However, the rapid and large-scale manufacturing of LPCs remains a challenge. In this work, the pH regulator is added in the process of emulsion polymerization to solve the problem of phase transformation caused by the thermal decomposition of the initiator to produce H+ , directly achieving 40 wt.% PS nanospheres in the dispersion. Then oligomers and small-molecule salts are removed from the system via dialysis, and the pre-crystallized LPC system is efficiently prepared. Adjusting the particle size and the mass fraction of nanospheres is shown to be an efficient way to control the optical properties of LPCs. The rapid and large-area preparation of PC structural color fabric and the patterned PC structural color fabric with an iridescent effect is implemented by using LPCs as the assembly intermediate. By constructing the encapsulation layer on the surface of the PC structural color fabric, the consistency of high structural stability and high color saturation of the PC is realized.

针对目前光子晶体结构生色织物难以大面积连续化制备以及光子晶体的结构稳定性与光学性质难以兼顾的问题,以旋蒸法制备具有预结晶形态的液态光子晶体(LPC),并以LPC为组装中间体,在经特殊高分子预处理的纺织基材上快速大面积制备具有高结构稳定性、高颜色饱和度的光子晶体.结果表明:所制备的LPC呈现鲜艳的结构色且具有优异的动态恢复性;通过外力剪切诱导作用将LPC施加到经特殊高分子预处理改性的织物表面,LPC快速重构显色并向固态光子晶体转变(1 min),再经适当的加热后处理(60℃,5 min),织物表面高分子层界面分子发生弛豫和迁移,以稳固光子晶体结构;以LPC为工作液,应用自行研制的中试设备,实现了光子晶体结构生色织物的快速连续化制备.

In this study, a poly(vinyl alcohol) (PVA) based thermo-sensitive polymer was prepared by cationic and acetalization of PVA (CAPVA), which showed the lowest critical solution temperature (LCST).The polymer is characterized by the fact that below LCST, the CAPVA hydrogel is transparent; when the temperature is higher than LCST, CAPVA becomes precipitated and turbid.The advancement of this study is that by combining the thermosensitive polymer CAPVA with a photonic crystal (PC) having the optical property of structural color, the phase change phenomenon of thermally induced CAPVA can be observed with the naked eye.Then, the CAPVA was combined with photonic crystal (PC) to reveal the thermally induced phase transition phenomenons relying on the structural color rendering of PC.Fourier transforms infrared (FTIR) spectroscopy and UV spectrophotometer were utilized to characterize the structure and LCST of CAPVA.The optical-fiber spectrometer was utilized to capture the diffraction properties of PC and CAPVA/PC.The results showed that the CAPVA/PC combined hydrogel can visually detect the temperature change, which further provides ideas for the design of thermo-switch, controlled drug release, and temperature sensor materials.

为解决光子晶体结构生色墨水在喷印过程中易造成喷头堵塞的问题,从喷印设备和光子晶体结构生色墨水2方面进行研究,以提高喷印流畅性,实现高质量图案化光子晶体结构生色纺织品的制备和工业化应用.结果表明:使用15％的PS纳米微球分散液作为喷印墨水,在墨水体系中引入分散剂,可以保证墨水的分散稳定性,当加入0.2％分散剂3B时,墨水分散性良好,放置24h后无聚集;通过加入较高浓度的保湿剂丙三醇,并在喷印设备上附加水封装置,可以减缓墨水中的纳米微球在喷印间隙以及喷印结束后喷头处因为水分蒸发而自发结晶,避免出现因为微球结晶而引起喷头堵塞现象;当保湿剂用量为5％时,墨水具有优异的保湿性能,连续喷印2h后喷嘴仍然无堵塞问题;以15％的纳米微球分散液作为墨水进行喷印时,所印制的光子晶体结构生色图案颜色鲜艳明亮,具有明显的虹彩效应;通过在纺织基材表面涂覆特殊高分子层,所制备的图案化光子晶体具有优异的结构稳定性,为结构生色技术在纺织染整领域的实际应用开辟了新途径.

Photonic crystals (PCs) constructed by colloidal self-assembly have attracted increasing attention in textile field because of their brilliant structural colors produced without using chemical colorants (dyes and pigment). And, the rapid and large-scale production of PC structurally colored textiles could be achieved via self-assembly of high-mass fractions of liquid photonic crystals (LPCs). However, the extensive and efficient preparation of LPCs still remains a challenge. In this work, the rotary evaporation method is applied for rapid preparation of LPCs, and a three-dimensional barrier based on charge repulsion and space obstruction was constructed by the synergistic effect of anionic/nonionic surfactants. As a result, the key issue that, the colloidal nanospheres aggregate and sediment more and more seriously with increasing the mass fraction of nanospheres during rotary evaporation, was resolved, and the LPC system with pre-crystallized form was efficiently prepared from the monodispersed nanosphere system with low mass fraction of 30 wt% or lower. The mass fraction of nanospheres in the prepared LPC system enriched 55%, and the optical properties of LPCs could be controlled by the mass fraction and/or the particle size of nanospheres. With the increase of the nanosphere mass fraction in the system, the pre-crystallization region increased, and the structural color became much brighter. The prepared LPCs exhibited excellent dynamic reversibility of the assembled structure. Under the applied external force, the LPCs disassembled, as it could be concluded from the vanishing structural color. After removing the external force, the structure was quickly reconstructed into a pre-crystallized LPC in around 10 s, and the structural color reappeared, showing a fast response performance of the LPC. Finally, the prepared LPC was applied onto a flexible textile substrate under external shear force. Due to the characteristics of LPC, it quickly reconstructed to form a uniform LPC film on the substrate surface, which rapidly transformed into a solid PC film with brilliant structural colors, realizing a rapid large-scale preparation of PC structural color fabrics.

针对常规喷涂法制备的光子晶体通常存在无虹彩效应的短程有序、长程无序非晶态结构问题,以液态光子晶体作为喷涂工作液,在经特殊高分子预处理的纺织基材上制备具有高结构稳定性和高颜色饱和度的光子晶体.结果表明:防膜裂剂的引入可以使喷涂工作液在基材表面铺展均匀,在组装过程中不发生收缩现象,避免组装后光子晶体出现龟裂问题;由于喷涂工作液自身具有准结晶状态的特性,纳米微球在组装过程中避免了复杂的自组装历程,易于快速组装为规整的面心立方结构;在加热组装过程中,织物表面高分子层的界面分子发生弛豫和迁移,起到稳固光子晶体的作用;通过调控PS微球粒径,可以制备不同颜色且具备虹彩效应的光子晶体结构生色织物;结合掩膜的使用,可以在纺织基材表面制备轮廓清晰的图案化光子晶体,为结构生色技术在纺织染整领域的实际应用开辟新途径.

The development of bio-based polymers will be beneficial to reducing carbon emissions. The biobased fiber-reinforced biobased epoxy resin can prepare fully-biobased polymer composites. However, their flame retardation will become a challenging issue. Here, fire-retardant ramie fabrics surface-modified by ammonium polyphosphate (APP) and polyethyleneimine were integrated into an epoxy system followed by fabricating high-performance composites. Notably, the epoxy resin composite with 8.9 % flame retardant displays a UL-94 V-0 rating. Besides, EP/(MF-2) exhibits a remarkably decreased peak of heat release rate (285 kW/m2) in contrast to pristine fabric-reinforced epoxy resin composite (608 kW/m2) from the cone calorimeter test. The improved flame-retardant performance follows the mechanism of the catalytic dehydration and charring effect by phosphorus-containing acids from the degradation of APP. Furthermore, flexural strength of EP/(MF-2) increases by 29 %, compared with neat EP, indicating obvious reinforcement of ramie fabric.

Patterned photonic crystals (PCs) have great application potential in the textile field owing to their attractive high-saturation iridescent effect. Herein, based on the idea of resist printing, a novel approach to constructing patterned photonic crystals via screen printing was designed and achieved. A colorless pattern with hydrophilic and hydrophobic difference was firstly prepared by screen printing using a hydrophilic polymer paste printed on a hydrophobic fabric, and then the PC structurally colored pattern was obtained through scrapping liquid photonic crystals (LPCs) on the fabric because the LPCs were spread and assembled in the hydrophilic pattern but resisted in the hydrophobic areas, so that to realize the rapid preparation of patterned PCs on the fabric surface. Once the contact angle difference (ΔCA) between the hydrophilic and hydrophobic areas exceeded 80, the "color paste" (that is, LPCs) did not stain the hydrophobic area at all after scrapping, and the assembled PCs pattern showed good contour sharpness and high-saturation iridescence effect. The complex multistructural color patterns on the fabrics were achieved by adjusting the size of nanospheres and using multistep printing and scrapping. The preparation of the protective layer on the PC surface effectively improved the structural stability of the patterned PCs while retaining the optical properties of the pattern. This patterned PCs preparation method was combined with a conventional responsive substance (rhodamine B) to obtain double anti-counterfeiting patterned PCs with the iridescence effect. The results suggested a promising future in both the highly efficient preparation of patterned PCs and the application of PCs in the anti-counterfeiting field.

Patterned photonic crystals (PCs) have great development potential in the textile field because of their unique high-saturation iridescent pattern displays. Herein, PC-produced patterns were printed on the fabric surface via screen printing technology. The nanosphere dispersion has reached the required level of viscosity for printing (2435 mPa s) and possessed obvious shear thinning after adding 2.5 wt% of synthetic thickener with strong thickening ability. The interference of the thickener to the self-assembly of nanospheres was weakened as the synthetic thickener accounted for a small proportion in the printing precursor, so the regularity of the microstructure evolution of the assembled PCs was in quasi-ordered arrangement that is short-range order/long-range quasi-order. Therefore, the structurally colored PC pattern exhibited a visual "flicker" effect with certain angular dependence. In addition, the polymer-bearing layer pretreated on the fabric surface enabled to improve the structural stability of the PC pattern. Thus, the patterned PCs obtained via screen printing have promising applications in textile coloration industry.

An ion-imprinted photonic crystal (IIPC) sensor for visual detection of copper ions was prepared by the combination of ion-imprinting polymer and colloidal photonic crystal (CPC) structure. Monodisperse polystyrene (PS) colloidal nanospheres synthesized by the boiling soap-free emulsion polymerization method were used to prepare the CPC template by the solvent evaporation method. An ion-imprinted polymer based on poly(vinyl alcohol) and chitosan (PVA/CS) is infiltrated therein. The IIPC sensor film was then prepared by solvent-assisted freeze-thaw method while the CPC template was strengthened as the air pores of the template were replaced by PVA/CS hydrogel. The shift of the diffraction wavelength can be directly observed by the naked eye through the color change of the IIPCS according to the concentration change of copper ion. Such sensor film showed good selectivity and sensitivity with a lower detection limit of 10(-4) M.

针对光子晶体材料结构稳定性较差的问题,以光固化型单体取代常规组装介质水制备液态光子晶体,通过紫外光聚合固化构建纳米微球嵌入弹性体式的非密堆积阵列光子晶体,制备结构稳定的柔性光子晶体结构生色膜,并对其结构和性能进行分析.结果表明:液态光子晶体的光学性质可通过胶体体系中SiO2纳米微球的体积分数及其粒径进行调控,随SiO2体积分数由22％增大至40％,其微球间的平均间距逐渐减小,液态光子晶体结构色蓝移;固定SiO2微球体积分数,当其粒径由123 nm增加至178 nm时,液态光子晶体结构色红移;液态光子晶体色彩鲜艳、饱和度高,经紫外光辐照后,所构建的固态光子晶体膜具有明显的虹彩效应和优异的柔韧性,并表现出显著的力致变色性能,展示了其在智能可穿戴纺织材料领域良好的应用潜能.

Responsive photonic crystals (PCs) with a nano-scale band gap assembled by colloidal nanospheres have been increasingly utilized in detection and sensing devices owing to their attractive ability to change color in response to external conditions. However, most of the reported works have been dedicated to single-functional PCs, which can only be used as sensors or detectors in a specific situation. Thus, producing a multi-functional PC for various industrial applications remains a challenge. In this work, multi-functional soft PC films (SPCFs) with a brilliant structural color and a robust structure are fabricated by using polystyrene@poly(methyl methacrylate-butyl acrylate) [PS@P(MMA-BA)] nanospheres with size in the range of 200-350 nm as building blocks. The SPCFs possess both the mechanochromic and solvatochromic properties owing to the adjustable photonic band gap under stress and polar solvent conditions. The mechanochromic effect of the SPCF under stretching results in a blue shift of the structural color due to the decrease in lattice spacing. In contrast, the solvatochromic mechanism of the SPCF is that it can be swollen by polar solvents, resulting in the increase in the lattice spacing of PCs and a red shift of the structural color. Meanwhile, the SPCF can keep its original structural color while stretched for 20 cycles or when the organic solvent is completely evaporated. Therefore, robust multi-functional SPCFs fabricated by the self-assembly of PS@P(MMA-BA) nanospheres under gravity sedimentation can respond to stress and organic solvents, showing great potential for use in sensors and detectors.