Preparation of Acrylic Yarns with Durable Structural Colors Based on Stable Photonic Crystals

Structural coloration of photonic crystals (PCs) is considered an ecological and environmental way to achieve colorful textiles. However, constructing PCs with obvious structural colors on traditional flexible yarns is still a great challenge. As a secondary structure that forms textiles, compared with fibers and fabrics, the yarns are rougher, hindering the construction of regular PCs. In this work, the flexible acrylic yarns with vivid structural colors, named PC-based structural color yarns, were prepared by constructing regular PCs via assembling poly(styrene-butyl acrylate-methacrylate) (P(St-BA-MAA)) colloidal microspheres on yarns. Specifically, the properties of P(St-BA-MAA) colloidal microspheres were investigated. The PCs with better structural stability and obvious structural colors were prepared by presetting the acrylic adhesive layer on yarns. Moreover, the color durability and color regulation methods of prepared PC-based structural color yarns were evaluated and discussed. The results showed that the P(St-BA-MAA) colloidal microspheres exhibited even particle sizes, excellent monodispersity, and a typical hard core-soft shell structure. And the glass-transition temperature (T _g) of the microspheres was tested to be about 65.6 °C. The cationic acrylate regarded as a pretreatment agent could not only improve the combination between the PC layers and the yarns by acting as a "bridge" but also enhance the structural color effect by smoothing the yarn surface. The results showed that when the mass fraction of cationic acrylate was 3 wt %, the microspheres were beneficial to access regular PCs with obvious structural colors. The PCs with bright structural colors could be constructed on black acrylic yarns, and the colors of yarns were still bright after rubbing and washing tests, indicating that the prepared PC-based structural color yarns have good color fastness. Moreover, the color hue of PC-based structural color yarns could be regulated by adjusting the particle sizes and viewing angles. This study provides strategic support for the structural coloration of flexible materials.

Thermally Responsive Photonic Fibers Consisting of Chained Nanoparticles

Fibers that can reversibly and passively change colors along with body temperatures are highly desired for potential applications including temperature sensors, smart wearables, and photonic devices. Here, we develop a facile strategy to fabricate thermochromic photonic fibers, which could exhibit tunable structural colors as a function of temperatures. The thermochromic fibers are prepared by aligning superparamagnetic, carbon-encapsulated Fe₃O₄ colloidal nanocrystal clusters (Fe₃O₄@C CNCs) in a thermoresponsive hydrogel, poly(N-isopropylacrylamide) (PNIPAM), forming chain-like structures under an external magnetic field before gelation. When the fiber is transferred from air to water at room temperature, it changes color from dark green to red as it swells. The red color can be reversibly changed back to green as the temperature is raised to 36 °C, while the fiber shrinks and the reflection peak shifts from 642 to 494 nm. The swelling of the fiber is anisotropic: by 60% in the diameter direction but 45% in the length direction. Therefore, the fiber can act as a thermochromic actuator.

Colloidal Crystals from Microfluidics

Colloidal crystals are of great interest to researchers because of their excellent optical properties and broad applications in barcodes, sensors, displays, drug delivery, and other fields. Therefore, the preparation of high quality colloidal crystals in large quantities with high speed is worth investigating. After decades of development, microfluidics have been developed that provide new choices for many fields, especially for the generation of functional materials in microscale. Through the design of microfluidic chips, colloidal crystals can be prepared controllably with the advantages of fast speed and low cost. In this Review, research progress on colloidal crystals from microfluidics is discussed. After summarizing the classifications, the generation of colloidal crystals from microfluidics is discussed, including basic colloidal particles preparation, and their assembly inside or outside of microfluidic devices. Then, applications of the achieved colloidal crystals from microfluidics are illustrated. Finally, the future development and prospects of microfluidic-based colloidal crystals are summarized.

Microfluidic spinning of editable polychromatic fibers

Chromatic fibers that change color in response to external stimuli are expected to be widely used in various applications such as anti-counterfeiting, military camouflage, and wearable displays. Advanced chromatic fibers with polychromatic and editable color properties behavior are strongly desired for practical applications but have not yet been realized using existing spinning technologies. Here, we present the low-cost, continuous microfluidic spinning of editable polychromatic polylactide (PLA) fibers. The structure and performance of the polychromatic PLA fibers were precisely controlled by adjusting the parameters used in microfluidic spinning. The structure of the as-spun products evolved through three different stages based on the editable encapsulation of functional materials into the PLA matrix. Fibers with versatile performance were achieved. A beaded polychromatic PLA fiber showed the possibility to delivery coded information through its editable chromatic behavior. A core-shell polychromatic PLA fiber showed good mechanical properties and knittability, which make it promising to fabricate smart color-changing textiles.

Structural Color Fibers Directly Drawn from Colloidal Suspensions with Controllable Optical Properties

Fibers with structural colors are of great interest due to their unique dye-free optical properties and show great potential in the textile industry. However, the preparation of structural color fibers with controllable optical properties in a simple way is still a challenge. In this paper, we prepared structural color fibers by simply drawing bare fibers from colloid suspensions. The obtained fibers displayed brilliant colors due to the assembled photonic crystal structures on the surface. The layer numbers of colloid coatings were tunable by varying the drawing speeds, concentration of colloid suspension, and diameters of core fibers. The optical properties of the obtained structural color fibers varied by layer numbers, viewing angles, and structure defects and were systematically studied both by experimental measurements and by computer simulations. Furthermore, noncrack blue fibers were demonstrated by coating "soft" poly[styrene- co-(butyl acrylate)- co-(acrylic acid)] (P(St-BA-AA)) polymer spheres on PET fibers. The coating was mechanically robust and made the fiber bendable with weaving ability, which means this method has versatile applicability and could be potentially used for green textile dyeing.

Review on Fabrication of Structurally Colored Fibers by Electrospinning

Structural color derived from the physical interactions of photons, with the specific chromatic mechanism differing from that of dyes and pigments, has brought considerable attention by the conducive virtue of being dye-free and fadeless. This has recently become a research hot-spot. Assemblies of colloidal nanoparticles enable the manufacture of periodic photonic nanostructures. In our review, the mechanism of nanoparticle assemblies into structurally colored structures by the electrospinning method was briefly introduced, followed by a comparatively comprehensive review summarizing the research related to photonic crystals with periodically aligned nanostructures constructed by the assembly of colloidal nanoparticles, and the concrete studies concerning the fabrication of well-aligned electrospun nanofibers incorporating with colloidal nanoparticles based on the investigation of relevant factors such as the sizes of colloidal nanoparticles, the weight ratio between colloidal nanoparticles, and the polymer matrix. Electrospinning is expected to be a deserving technique for the fabrication of structurally colored nanofibers while the colloidal nanoparticles can be well confined into aligned arrangement inside nanofibres during the electrospinning process after the achievement of resolving remaining challenges.

Polydopamine-Based 3D Colloidal Photonic Materials: Structural Color Balls and Fibers from Melanin-Like Particles with Polydopamine Shell Layers

Nature creates beautiful structural colors, and some of these colors are produced by nanostructural arrays of melanin. Polydopamine (PDA), an artificial black polymer produced by self-oxidative polymerization of dopamine, has attracted extensive attention because of its unique properties. PDA is a melanin-like material, and recent studies have reported that photonic materials based on PDA particles showed structural colors by enhancing color saturation through the absorption of scattered light. Herein, we describe the preparation of three-dimensional (3D) colloidal photonic materials, such as structural color balls and fibers, from biomimetic core-shell particles with melanin-like PDA shell layers. Structural color balls were prepared through the combined use of membrane emulsion and heating. We also demonstrated the use of microfluidic emulsification and solvent diffusion for the fabrication of structural color fibers. The obtained 3D colloidal materials, i.e., balls and fibers, exhibited angle-independent structural colors due to the amorphous assembly of PDA-containing particles. These findings provide new insight for the development of dye-free technology for the coloration of various 3D colloidal architectures.

The structural coloration of textile materials using self-assembled silica nanoparticles

The work presented investigates how to produce structural colours on textile materials by applying a surface coating of silica nanoparticles (SNPs). Uniform SNPs with particle diameters in a controlled micron size range (207-350 nm) were synthesized using a Stöber-based solvent varying (SV) method which has been reported previously. Photonic crystals (PCs) were formed on the surface of a piece of textile fabric through a process of natural sedimentation self-assembly of the colloidal suspension containing uniform SNPs. Due to the uniformity and a particular diameter range of the prepared SNPs, structural colours were observed from the fabric surface due to the Bragg diffraction of white light with the ordered structure of the silica PCs. By varying the mean particle diameter, a wide range of spectral colours from red to blue were obtained. The comparison of structural colours on fabrics and on glasses suggests that a smooth substrate is critical when producing materials with high colour intensity and spatial uniformity. This work suggested a promising approach to colour textile materials without the need for traditional dyes and/or pigments. Graphical abstract.

Approaches to self-assembly of colloidal monolayers: A guide for nanotechnologists

Self-assembly of quasi-spherical colloidal particles in two-dimensional (2D) arrangements is essential for a wide range of applications from optoelectronics to surface engineering, from chemical and biological sensing to light harvesting and environmental remediation. Several self-assembly approaches have flourished throughout the years, with specific features in terms of complexity of the implementation, sensitivity to process parameters, characteristics of the final colloidal assembly. Selecting the proper method for a given application amidst the vast literature in this field can be a challenging task. In this review, we present an extensive classification and comparison of the different techniques adopted for 2D self-assembly in order to provide useful guidelines for scientists approaching this field. After an overview of the main applications of 2D colloidal assemblies, we describe the main mechanisms underlying their formation and introduce the mathematical tools commonly used to analyse their final morphology. Subsequently, we examine in detail each class of self-assembly techniques, with an explanation of the physical processes intervening in crystallization and a thorough investigation of the technical peculiarities of the different practical implementations. We point out the specific characteristics of the set-ups and apparatuses developed for self-assembly in terms of complexity, requirements, reproducibility, robustness, sensitivity to process parameters and morphology of the final colloidal pattern. Such an analysis will help the reader to individuate more easily the approach more suitable for a given application and will draw the attention towards the importance of the details of each implementation for the final results.

Multiple Colors Output on Voile through 3D Colloidal Crystals with Robust Mechanical Properties

Distinguished from the chromatic mechanism of dyes and pigments, structural color is derived from physical interactions of visible light with structures that are periodic at the scale of the wavelength of light. Using colloidal crystals with coloring functions for fabrics has resulted in significant improvements compared with chemical colors because the structural color from colloidal crystals bears many unique and fascinating optical properties, such as vivid iridescence and nonphotobleaching. However, the poor mechanical performance of the structural color films cannot meet actual requirements because of the weak point contact of colloidal crystal particles. Herein, we demonstrate in this study the patterning on voile fabrics with high mechanical strength on account of the periodic array lock effect of polymers, and multiple structural color output was simultaneously achieved by a simple two-phase self-assembly method for printing voile fabrics with 3D colloidal crystals. The colored voile fabrics exhibit high color saturation, good mechanical stability, and multiple-color patterns printable. In addition, colloidal crystals are promising potential substitutes for organic dyes and pigments because colloidal crystals are environmentally friendly.

Facile fabrication of magnetically responsive PDMS fiber for camouflage

A new type of photonic crystal PDMS fiber which exhibits tunable structural color upon exposure to external magnetic field is described in this article. The novel magnetic field responsive fiber was prepared from embedding ethylene glycol droplets (containing Fe3O4@C nanoparticles) into PDMS. In the presence of an external magnetic field, Fe3O4@C nanoparticles which dispersed in ethylene glycol droplets formed one dimensional chain-like structures along the magnetic field. As a result, the color of the fiber changes to yellow green. By contrast, when the magnetic field was removed, the color of the fiber will disappear and display its original color. Moreover, this novel PDMS fiber has good mechanical properties and could keep its color under a fixed magnetic field no matter it was stretched or squeezed. This study is expected to have some important applications such as none-powered and functionalized fibers for camouflage.

Visibly vapor-responsive structurally colored carbon fibers prepared by an electrophoretic deposition method

A new type of photonic crystal carbon fiber exhibits tunable structural colors upon exposure to organic vapors.

Colorimetric sensing of melamine using colloidal magnetically assembled molecularly imprinted photonic crystals

A colorimetric colloidal MIPC sensor was constructed by the magnetic assembly of MMIP colloids, it could directly transmit the stimuli from the adsorption of MEL into visually perceptible optical signals.

Structural Coloration of Colloidal Fiber by Photonic Band Gap and Resonant Mie Scattering

Because structural color is fadeless and dye-free, structurally colored materials have attracted great attention in a wide variety of research fields. In this work, we report the use of a novel structural coloration strategy applied to the fabrication of colorful colloidal fibers. The nanostructured fibers with tunable structural colors were massively produced by colloidal electrospinning. Experimental results and theoretical modeling reveal that the homogeneous and noniridescent structural colors of the electrospun fibers are caused by two phenomena: reflection due to the band gap of photonic structure and Mie scattering of the colloidal spheres. Our unprecedented findings show promise in paving way for the development of revolutionary dye-free technology for the coloration of various fibers.

Facile fabrication of a magnetically assembled colloidal photonic crystal film via radical polymerization

A facile, economical and practical technique to fabricate a magnetically assembled colloidal photonic crystal in a polyacrylamide hydrogel matrix was demonstrated by an instant radical polymerization.

Red, green, blue (RGB) electrochromic fibers for the new smart color change fabrics

These fibers are prepared using stainless steel wires (SSWs) as a substrate. Three kinds of electrochromic materials (poly(3,4-ethylenedioxythiophene), poly(3-methylthiophene), and poly(2,5-dimethoxyaniline)) are quickly deposited on the surface of the SSWs by electrochemical polymerization. A polymer gel electrolyte is then coated onto the electrochromic layer, and another finer stainless steel wire is twisted on, in succession. The obvious RGB colors and gradient color phenomenon from gray to dark blue are observed by the naked eye besides color changes from oxidized to reduced states. Moreover, these electrochromic fibers have very short response times (millisecond scale), excellent flexibility, and good structural stability even though the bending and folding occurred. They also can be implanted into fabrics to achieve more color combinations through regulating the voltages and parallel connection of different circuits.

Structurally colored carbon fibers with controlled optical properties prepared by a fast and continuous electrophoretic deposition method

Structurally colored fiber was fabricated by an electrophoretic deposition method under a circinate electric field. These fibers exhibit structural color, based on the external field-assembly of charged PMMA microspheres on the surface of the electroconductive carbon fiber, with reflectance spectra stretch-tunable in the 430-608 nm, which are determined by the lattice constants of the photonic crystals. Also, the influence of applied voltage, deposition time and electroconductivity on the number of deposited layers and efficiency were studied. In addition, we further developed a horizontal and continuous process to fabricate a long range structurally colored fiber. And the method is a drastic acceleration in comparison with the gravity sedimentation technique that needs weeks or even months, and it would be fast and facile for the further study of structural color on the surface of the fiber. The process may be used to simulate the conventional fiber coloration process. Such elastically tuned structurally colored fibers are of interest for many applications.