Many organisms produce stunning optical displays based on structural color instead of pigmentation. This structural or photonic color is achieved through the interaction of light with intricate micro-/nano-structures, which are “grown” from strong, sustainable biological materials such as chitin, keratin, and cellulose. In contrast, current synthetic structural colored materials are usually brittle, inert, and produced via energy-intensive processes, posing significant challenges to their practical uses. Inspired by the brilliantly colored peacock feathers which selectively grow keratin-based photonic structures with different photonic bandgaps, we develop a self-growing photonic crystal system in which the photonic bandgaps and hence the coloration can be easily tuned. This is achieved via the selective growth of the polymer matrix with polymerizable compounds as feeding materials in a silica nanosphere-polymer composite system, thus effectively modulating the photonic bandgaps without compromising nanostructural order. Such strategy not only allows the material system to continuously vary its colors and patterns in an on-demand manner, but also endows it with many appealing properties including flexibility, toughness, self-healing ability, and reshaping capability. As this novel self-growing method is simple, inexpensive, versatile, and scalable, we foresee its significant potential in meeting many emerging requirements for various applications of structural color materials.
Article
Self-growing Photonic Composites with Programmable Colors and Mechanical Properties
https://doi.org/10.21203/rs.3.rs-1433654/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 19 Dec, 2022
Version 1
posted
You are reading this latest preprint version
Self-growth
Photonic composites
Self-healing
Flexible
Patterns
Structural coloration, which was first observed by Robert Hooke and Isaac Newton on peacock’s feathers more than 350 years ago, constitutes a class of fundamentally different mechanisms to generate color in contrast to chemical or pigment-based coloration1–3. Here the colors are produced by the microscopical structures or surfaces fine enough to interfere with light and thus show appealing features such as brilliant, stable, and non-toxic4. This phenomenon has initiated the field of artificial structural color materials and inspired many applications in optoelectronics5, anti-counterfeiting6, sensors7, etc. Essential to these applications is the fabrication of various sophisticated periodic photonic nanostructures8–11. To this end, both top-down and bottom-up technologies have been developed12,13. The former mainly depend on microfabrication processes14 that often suffer from high processing cost and low production efficiency, which hinders their scalable manufacture of structural color products. In contrast, bottom-up methods in which ordered nanostructures are made through the self-assembly of nano-/microscopic building blocks are simple, cheap, and scalable15. In self-assembly methods, building blocks with uniform sizes are required for achieving ordered nanostructures, which leads to single bandgaps and hence monochrome or iridescence16. To achieve multicolored images, several methods are developed recently, including confinement deposition17, regioselective removal18, post-modification of inverse opal19, etc. These methods involve elaborate fabrication techniques requiring superb synthetic skills and the obtained images are either ephemeral, low-resolution, or relatively dull. Moreover, artificial structural color materials are often fragile and not reprocessable20,21, in stark contrast to their glorious, durable, and lightweight natural counterparts. Therefore, it is highly desirable to develop facile approaches for fabricating bright, robust, and adaptive structure color images.
The intricate microstructures for structural colors of living creatures are produced via a natural growing process22–25. Take the brilliantly colored eye pattern of the peacock’s tail as an example (Fig. 1a). The barbules within this coloration pattern contain two-dimensional (2D) photonic crystals made up of melanin rods and air holes embedded in a keratin matrix26,27. By controlling the growth of keratin during feather development, peacocks can vary the spacing between adjacent melanin rods, which effectively adjust the lattice constant to modulate the photonic bandgaps for producing diversified colors (Fig. 1b and Figure S1). Such a sustainable approach not only allows living organisms to continuously and precisely evolve their colors and patterns on original coats, rather than to generate new substrates with a set of components with different sizes, but also mechanically robust matrices, implying a fundamentally new, efficient, sustainable method to synthesize or mediate structural color figures.
Inspired by the structural designs of peacock’s tail feathers, here we report a growing strategy for fabricating photonic crystal composites with controlled structural coloration, patterning capability, and versatile mechanical properties. As shown in Fig. 1c, this novel material system is composed of SiO2 nanospheres embedded in a “living” polymer matrix, which can undergo spatial-selective growth by introducing “nutrients” in the external environment. The growth-induced expansion of the lattice parameters allows the system to precisely and continuously vary its photonic bandgaps and thus color in an on-demand manner. More specifically, the growth is achieved via homogeneously swelling the crosslinked polymer matrices using a nutrient solution consisting of monomer, crosslinker, photoinitiator, and catalyst simultaneously, followed by light-induced polymerization. A new-old double network structure forms, in which the original network is stretched. Note that the stretched conformation would restrict the uptake of more nutrient solution for further growth. The catalyst in the nutrient solution is thus designed to remove such restriction by inducing chain exchange between new and old networks to homogenize the matrices, allowing the system to further grow. Under this growing mechanism, we can continuously change the photonic bandgap and composition of systems for modulating their colors and mechanical properties. Because of the spatial selectivity of the photopolymerization, it is facile to generate multicolor images.
System and synthesis
Acrylate-based polymers were selected as the growing matrices because of their widespread usage in various applications. The initial photonic crystal films were made from SiO2 nanospheres (Figures S2 & S3) and poly(ethylene glycol) diacrylate (PEGDA). Briefly, the suspending solutions of SiO2 nanoparticles and PEGDA in ethanol were allowed to evaporate to induce the self-assembly of SiO2 into colloidal crystals, followed by curing under UV irradiation (Scheme S1) in homemade containers. After annealing, vivid films were obtained. The formation mechanism and driving force of SiO2 forming an ordered structure were polymerization-induced colloidal assembly which had been carried out by Ge et al28. Scanning electron microscopy (SEM) study illustrates that the samples consisted of both ordered and disordered domains (Figure S4). In the ordered domain, SiO2 nanoparticles arranged into ordered structures with uniform photonic bandgaps. Due to such a short-range ordered structure, the obtained structural color is angle-independent (Figure S5)29. The wavelength (λ) of the reflected light to this class of structural color films could be estimated by the Bragg’s diffraction Eq. 30:
where \(d\) refers to the interplanar spacing of the photonic crystal lattice, \({n}_{eff}\) indicates the mean refractive index of the composites, and m is the order of reflection (m = 1, 2, ...). In our design, \(d\) could be modified by allowing the polymer matrices to grow.
The mixture of an acrylate monomer, 1,6-hexanediol diacrylate (HDDA, crosslinker), 2-hydroxy-2-methylpropiophenone (photoinitiator), and benzenesulfonic acid (BZSA, transesterification catalyst) was used as the nutrient solution. Here, three kinds of monomers were employed, including 4-hydroxybutyl acrylate (HBA), PEGDA, and 2-hydroxyethyl methacrylate (HEMA). HBA is a commonly used elastomer precursor, while PEGDA is the compound used to prepare the initiated sample and therefore would not vary the composition of the sample matrices during growth; compared to HBA and PEGDA, HEMA could form rigid polymer main chains and thus provided an approach to tune material mechanical properties. The nutrient solution containing HBA, PEGDA, or HEMA used for growth was defined as nutrient solution B, EG, or M, respectively. For growth, as-prepared purple films (typical mass percentage of the polymer matrix: 40 wt%) were selected as the initial samples. They were first immersed in a nutrient solution for swelling. During swelling, the samples increase in size and change their colors (Fig. 2a). The samples could swell the tested nutrient solutions with equilibrium swelling ratios of 9.1 wt% (B), 6.2 wt% (EG), and 7.1 wt% (M), respectively (Figure S6). The relatively low swelling ratios were attributed to the low polymer fraction in the photonic crystal films and their rigid nature. Despite low swelling ratios, obvious color changes were observed. The colors were unstable and would turn back to purple again if the samples were washed to remove the entrapped nutrient solution. Besides, the swelling significantly weakened the Young's modulus of the samples (Figure S7). By contrast, the samples that were subsequently irradiated by UV light (365 nm, 10 mW·cm-2) to trigger photopolymerization preserved their after-swelling weights and colors, as well as became tougher (Fig. 2a and Figure S8). The photopolymerization reaction was exothermic, which could heat the systems to 47.1oC in 50 s (Figure S9). Such thermal effects could trigger transesterification reactions to release any polymerization-induced mechanical tension in such dynamic networks31. The grown samples could swell nutrients again for further growing cycles (Fig. 2b). To illustrate the role of this homogeneous step in growth, a control sample without transesterification catalyst was treated under the same process aforementioned, and as expected, this catalyst-free sample was nearly non-swellable to the nutrient solution after the first growing cycle. We denoted the initial sample as \({EG}_{n}\) where n is the mass percentage of the polymer matrix, while the grown samples as \({EG}_{n}-B/EB/{M}_{m}\), where m is the increased mass of corresponding polymer matrices compared to the entire original sample. For example, specimen \({EG}_{40}-{B}_{9.7}\) was the grown sample of \({EG}_{40}\) obtained from nutrient B with a net increase of 9.7 wt% compared to initiated weight (total polymer fraction: (40 + 9.7)/(100 + 9.7) wt%). All the specimens, including both initiated and grown ones, were self-standing and macroscopically uniform.
Optical property
The homogeneous growth allowed for flexible modulation of sample colors in the full visible light spectrum from purple to red (Fig. 2c). During growth, SiO2 colloidal nanoparticles maintained their ordered arrangement in the polymer matrix but showed increasing interplanar lattices, as evidenced by the gradual change of the double interplanar spacing 2d from 313 to 473 nm collected from the SEM images (Fig. 2d). UV-Visible reflection spectroscopy was employed to characterize the optical properties of different grown samples (Fig. 2e). With the increase in polymer matrices (then lattice distances), the reflection peak (λ) shifts from 481 to 690 nm. These reflection peaks were surprisingly intensive and narrow, implying a highly ordered arrangement of SiO2 colloid crystals. In our self-growing photonic composites, the changes in both double interplanar spacing 2d and reflection peaks (the colors) were predictable. For a photonic composite with a homogeneous ordered structure, the double interplanar spacing 2d was proportional to the cube root of the volume fraction of SiO2 nanoparticles (\(1/\sqrt[3]{1-\text{\varnothing }}\), where \(\varnothing\) is the volume fraction of the polymer matrix). By using the experimental data obtained from the initial photonic composite to establish the linear relationship (See section 9 in supplementary information for calculation detail, Table S1), we found that the theoretic curve compared well with the experimental 2d values (Fig. 2f), suggesting that the 2d could be precisely controlled by growth. Furthermore, in our system, the monomer showed a similar refractive index n with that of SiO2 (SiO2: 1.45; monomer: 1.457 at 20oC), and therefore, the \({n}_{eff}\) could be considered as a constant during growth. It indicated a linear relationship between λ and 2d based on equation #1. When we plotted the experimental λ to 2d, they all well fit with the theoretic curve (obtained from equation #1 with a \({n}_{eff}\) of 1.453, Fig. 2g). All these results indicated that the optical properties of photonic crystal films could be precisely post-modulated by growth.
Mechanical properties
Growth allowed the samples to vary their compositions for modulating their mechanical properties. Two kinds of approaches could be applied, including changing the monomer types or the crosslinker concentration in the nutrient solution. For example, in the case of using crosslinker-free nutrient solutions, the sample would maintain its modulus when grown from nutrient EG but become softer or stiffer from nutrient B or M, respectively (Figs. 3a). On the other hand, increasing crosslinker concentration in the nutrient solution stiffens the samples regardless the monomer types (Figs. 3b).
Besides stiffness modulation, growth also significantly toughened the photonic composite structure. The as-prepared initial samples were brittle and would fracture upon bending (Fig. 3c). Such brittle samples could grow to be fully flexible by adding agents that could soften the matrices in the nutrient. In the current system, the composites were stiffened by both the highly crosslinking structure of polymer matrices and the covalent connection between SiO2 nanoparticles and polymer chains of matrices (Figure S10&S11, FTIR results indicated the existing of the transesterification between the ester polymer and the hydroxyl on the surface of SiO2 nanoparticles during the preparation of the initiated samples). Since both linkages were ester-based bonding, alcohol that could hydrolyze the ester connection was selected as the additive (Fig. 3d). As expected, the grown sample obtained from an alcohol-contained nutrient was very flexible. More than bending, the flexible grown sample can be rolled up, twisted, or folded (Fig. 3e) and shows fair elasticity. The sample became more stretchable without a tradeoff in strength (Fig. 3f). Here, the alcohol could either be used as an additive in normal nutrient solutions or an independent agent (a nutrient consisting of only alcohol) to make the sample flexible (Figure S12). The transesterification-based softening mechanism was confirmed by using a SiO2-free PEGDA film in which the contribution of SiO2 nanoparticles to material mechanical properties was absent. The film was grown in alcohol-free and alcohol-containing EG, respectively. The grown sample made from an alcohol-containing nutrient shows a nearly 50% increase in flexibility compared to the grown sample prepared by alcohol-free EG (Figure S13). To further prove the mechanism, hydroxyl-free agents like tetrahydrofuran were employed as the additive, and none of them could make the sample flexible (Figure S14). Traditional photonic crystal-based structural color materials are normally brittle and improving their mechanical properties thus constitutes one of the most critical aspects of current research32,33. Two strategies, i.e. softening photonic crystal materials by the use of flexibilizers or increasing polymer fractions34 and fabricating full organic-based inverse opal structures35, had been developed. In the former, increasing polymer/flexibililizer fraction would disturb the self-assembly of particles and thus destroy the ordered crystal microstructure. The materials with inverse opal structures show excellent flexibility, but their preparation normally required HF-based etching treatment and the materials display milky appearance and low color saturation due to the higher light scattering in inverse opal36. In contrast, the growth method allowed for post-modulation of the composition without compromising the ordered microstructure, implying a more efficient method to get mechanically robust photonic crystal materials.
Reshape
The alcohol-based transesterification reactions were reversible and the broken ester linkages could reform by removal of the absorbed alcohol (Fig. 3d). To elucidate this idea, the softened PEGDA film made from the alcohol-containing nutrient was annealed at 70oC for 4 h to remove the alcohol moieties. The grown sample became stiffer and showed a modulus similar to that of the grown sample directly obtained from the alcohol-free nutrient (Figure S13). Such reversible softening-stiffening process allowed for multiple-time reshaping of the samples. As shown in Fig. 3g, a rigid flat film was first softened by growth with alcohol and then deformed, followed by annealing treatment (to remove the alcohol moieties) to fix the obtained structures. The reshaping could be repeated to achieve different forms. Interestingly, the deformed sample maintained its new shape when it was turned into an elastic state. Compared to this processability, traditional structural color materials are either rigid (photonic crystal composite, would fracture) or elastic (inverse opal material, turn back to original shape), and do not show such reshaping capability.
Spatial-selective growth and multicolor patterning
Another significant advantage of this photonic composite system is its spatially selective growth capability by using patterned photoirradiation (Fig. 4a). As shown by the surface profile, the irradiated region grew up with a sharp boundary. A height drop of 9.5 µm (yellow-orange change) occurred in ⁓1 µm distance (aspect ratio: 9.5). Consequently, the grown region showed a significantly different structural color from the unirradiated region. Note that the modulation could be achieved without the removal of the unreacted nutrient solution. In a previous study31, we have proved that region-selective conversion of the monomer and crosslinker into polymer matrices by photopolymerization would induce a concentration gradient of the monomer and crosslinker. Such gradient would drive the nutrient to transport from unirradiated region to irradiated one, leading to the formation of convex surface textures at the irradiated region. The same mechanism was expected here. After growth, the residual nutrient entrapped in the composite was still active and could be transported to new irradiated regions for creating other surface textures and colors. The structure of the grown region was further probed by SEM. In the cross-section image of a grown sample, a sharp boundary was also observed. In the grown region, SiO2 nanoparticles distribute orderly as those in the unirradiated region but show a larger interplanar lattice, implying homogeneous expansion of the polymer matrices.
Localized growth of photonic crystal films indicated a novel approach for chromatic patterning. We fabricated a “Sichuan facebook” using a \({EG}_{48}\) substrate with single blue color to demonstrate the flexibility of this approach. As shown in Fig. 4b, the profile of the “Sichuan facebook” was outlined on the substrate swollen with nutrient EG after simple irradiation through a mask. Without any additional treatment, further selective irradiations through the masks could induce the formation of new structural colors and a clear multicolor image was created. This growth-based patterning approach differed from the reported methods based on either complicated instruments37,38 or sophisticated skills. Here the structural color was patterned by user-friendly photo-lithography to directly achieve complicated, high-resolution images. The obtained pictures were not only stable but also always permitted further modification, due to the “living” growing mechanism, implying a more facile and effective direction for batch manufactures.
Self-healing
The self-healing of mechanical damages on structure colored materials was extremely challenging because of their rigid nature39,40. Since growth allowed for selective formation of new matrices in the irradiated region, it opened up a novel approach for our composite photonic system to restore the damage. To demonstrate this self-healing capability, a photonic crystal structural color film was first scratched on its surface. Although the polymer matrix itself is self-healable at high temperatures due to the transesterification-based chain exchange reaction41, the scratch did not effectively repair upon heating treatment (Figure S15). In contrast, when we selectively induced growth on the damaged region by light irradiation, the scratch was completely repaired, and an intact photonic crystal film was achieved (Fig. 4c). The healed film maintained its vivid structural color through the whole body (color in the healed region might slightly shift due to the change in the photonic bandgap, Figure S16). This growth-based self-healing method differed from traditional intrinsic and extrinsic self-healing strategies. In the intrinsic self-healing, no new matrix would form and the polymer chains should be mobile enough to undergo reconfiguration42,43. It is difficult for a rigid substrate to self-heal through this mechanism. Extrinsic self-healing strategy allows for the formation of new matrices but no ordered structure forms in the healed matrices44. Moreover, an interface between original and healed matrices often appears, which is unfavorable for the recovery of the mechanical properties. Here, our method combined the merits of both intrinsic and extrinsic strategies, and the healed sample completely restored its color and mechanical properties. The healed region exhibits comparable mechanical strength as the original sample (the self-healing efficiency: 80.1%, evaluated by the work, Fig. 4d), therefore, when stretched, the sample may even break at the intact region, rather than the healed one. By contrast, the scratched sample without self-healing was easily broken (8.8%).
Inspired by the forming process of peacock’s tail feathers, we have proposed a fundamentally new strategy for fabricating photonic crystal structural color composites. This strategy involves the uniform expanding of the polymer matrices of the structural color composites by allowing the matrices to grow, in which the finely ordered microstructure is maintained. By varying the component in the nutrient used for the growth and the growing cycles, the samples can be selectively changed their sizes, color, and mechanical properties. Under this mechanism, the obtained materials not only show good flexibility, toughness, and self-healing/reshaping ability but also permit the fabrication of complicated, high-resolution patterns. Since this facile method can be applied to commonly used polymer systems and results in excellent performances, we foresee its great application potential in meeting many emerging challenges of structural color materials and broadening their commercial values.
Materials 4-Hydroxybutyl acrylate (HBA, refractive index n (20oC): 1.452), poly(ethylene glycol) diacrylate (PEGDA) (average Mn = 250 g·mol-1, n (20oC): 1.457), ammonia (28 vol%), 2-hydroxy-2-methylpropiophenone (photoinitiator), 1,6-hexanediol diacrylate (HDDA), and benzenesulfonic acid (BZSA, transesterification catalyst) were purchased from Aladdin Co. (Shanghai, China). Tetraethylorthosilicate (TEOS, 99.5%), 2-hydroxyethyl methacrylate (HEMA, 99%, n (20oC): 1.441), tetrahydrofuran (THF, 99.8%, anhydrous), and ethanol (AR, ≥ 99.8%) were purchased from J&K (Beijing, China) and Aladdin Reagent Co. (Shanghai, China). Ethyl decanoate (98%) was brought from Tansoole (Beijing, China). All reagents and solvents were used without further purification. Ultrapure water (18.25 MΩ·cm, 25°C) was used.
Synthesis of SiO 2 nanoparticles. SiO2 nanoparticles were prepared via a modified Stöber method involving the hydrolysis and condensation of TEOS in ethanol in the presence of ammonia (catalyst)45. Briefly, the mixture of 100 mL ethanol and 15 mL ammonia in a 250 mL flask containing was heated to 60oC under a stirring condition, followed by adding 6 mL TEOS. The mixture was stirred at 60oC for 8 h. Excess ammonia and unreacted reagents in the matrix were removed by washing with ethanol and the product was collected by high-speed centrifugation (a rate of 9000 r·min-1 for 5 minutes). The total washing times should not be less than 6.
SiO 2 /PEG precursors. Take \({EG}_{40}\) precursor as an example. Briefly, 60 µL PEGDA containing photoinitiator (5 wt%) was added into 0.132 g SiO2 ethanol suspensions (6 wt%). The solution was treated with vortex mixing and sonication, followed by annealing in an oven at 90oC for 2 h to allow for solvent evaporation. When the ethanol solvent was evaporated, a supersaturated acrylate solution of SiO2 was obtained. The precursor solution was nearly transparent and kept in dark for 5 h before use. The same protocol was used to prepare the other precursor solutions with different ratios of SiO2 nanoparticles and PEGDA28.
Fabrication of photonic crystal films. For example, 50 µL precursor solution was sandwiched between a glass slide (18 \(\times\) 18 mm) and a hydrophobic cover silicon wafer (18 \(\times\) 18 mm) (Scheme S1). The sample was irradiated by UV light (365 nm, 10 mW·cm-2) for 2 min. After illumination, a vivid film formed and it was peeled off from the substrate for further study. This method could be applied to prepare large-scale films and the thickness of the films was controlled by the amount of the precursor solution and the area of the substrate.
The authors declare that the main data supporting the findings of this study are available within the article and its Supplementary Information files. Extra data are available from the corresponding author upon reasonable request.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51973023 and 52003035), Sichuan Science and Technology Program (2021JDRC0014 and 2021JDRC0106) and China Postdoctoral Science Foundation (W03019023601004133). We also thank Ms. Songzi Xu and Junchang Guo at University of Electronic Science and Technology of China for their help on experiments and discussion.
Author contributions
J.C. and J.X. conceived the concept. J.C. supervised the project. J.C. and J. X. designed the experiment. J.X., X.Y., and C.Z. conducted the experiments. J.X., J.C., and L.L. wrote the manuscript. All authors contributed to the analysis and discussion of the data.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at https://xxxxxxxxx.
- Kinoshita, S., Yoshioka, S. & Miyazaki, J. Physics of structural colors. Rep. Prog. Phys. 71, 076401 (2008).
- Zhao, Y., Xie, Z., Gu, H., Zhu, C. & Gu, Z. Bio-inspired variable structural color materials. Chem. Soc. Rev. 41, 3297–3317 (2012).
- He, L., Wang, M., Ge, J. & Yin, Y. Magnetic Assembly Route to Colloidal Responsive Photonic Nanostructures. Acc. Chem. Res. 45, 1431–1440 (2012).
- Vatankhah-Varnosfaderani, M. et al. Chameleon-like elastomers with molecularly encoded strain-adaptive stiffening and coloration. Science 359, 1509–1513 (2018).
- Liu, C., Fan, Z., Tan, Y., Fan, F. & Xu, H. Tunable Structural Color Patterns Based on the Visible-Light-Responsive Dynamic Diselenide Metathesis. Adv. Mater. 32, 1907569 (2020).
- Hong, W., Yuan, Z. & Chen, X. Structural Color Materials for Optical Anticounterfeiting. Small 16, e1907626 (2020).
- Wang, Y., Cui, H., Zhao, Q. & Du, X. Chameleon-inspired structural-color actuators. Matter 1, 626–638 (2019).
- Joannopoulos, J. D., Villeneuve, P. R. & Fan, S. Photonic crystals: putting a new twist on light. Nature 386, 143–149 (1997).
- Ge, J. & Yin, Y. Responsive photonic crystals. Angew. Chem. Int. Ed. 50, 1492–1522 (2011).
- Fenzl, C., Hirsch, T. & Wolfbeis, O. S. Photonic crystals for chemical sensing and biosensing. Angew. Chem. Int. Ed. 53, 3318–3335 (2014).
- Aguirre, C. I., Reguera, E. & Stein, A. Tunable colors in opals and inverse opal photonic crystals. Adv. Funct. Mater. 20, 2565–2578 (2010).
- von Freymann, G., Kitaev, V., Lotsch, B. V. & Ozin, G. A. Bottom-up assembly of photonic crystals. Chem. Soc. Rev. 42, 2528–2554 (2013).
- Cheng, J. Y., Ross, C. A., Smith, H. I. & Thomas, E. L. Templated self-assembly of block copolymers: top‐down helps bottom‐up. Adv. Mater. 18, 2505–2521 (2006).
- Takahashi, S. et al. Direct creation of three-dimensional photonic crystals by a top-down approach. Nat. Mater. 8, 721–725 (2009).
- Li, K., Li, C., Li, H., Li, M. & Song, Y. Designable structural coloration by colloidal particle assembly: from nature to artificial manufacturing. Iscience 24, 102121 (2021).
- Kim, J. B., Lee, S. Y., Lee, J. M. & Kim, S.-H. Designing structural-color patterns composed of colloidal arrays. ACS Appl. Mater. Interfaces 11, 14485–14509 (2019).
- Shiu, J.-Y., Kuo, C.-W. & Chen, P. Actively Controlled Self-Assembly of Colloidal Crystals in Microfluidic. J. Am. Chem. Soc. 126, 8096–8097 (2004).
- Gu, Z.-Z., Fujishima, A. & Sato, O. Patterning of a Colloidal Crystal Film on a Modified Hydrophilic and Hydrophobic surface. Angew. Chem. Int. Ed 114, 2172–2174 (2002).
- Burgess, I. B. et al. Wetting in color: colorimetric differentiation of organic liquids with high selectivity. ACS nano 6, 1427–1437 (2012).
- Clough, J. M., Weder, C. & Schrettl, S. Mechanochromism in Structurally Colored Polymeric Materials. Macromol. Rapid. Commun. 42, 2000528–2000558 (2021).
- Shi, X., He, J., Xie, X., Dou, R. & Lu, X. Photonic crystals with vivid structure color and robust mechanical strength. Dyes Pigm. 165, 137–143 (2019).
- Kim, H. et al. Structural colour printing using a magnetically tunable and lithographically fixable photonic crystal. Nat. Photonics 3, 534–540 (2009).
- Forster, J. D. et al. Biomimetic Isotropic Nanostructures for Structural Coloration. Adv. Mater. 22, 2939–2944 (2010).
- Osotsi, M. I. et al. Butterfly wing architectures inspire sensor and energy applications. Natl. Sci. Rev. 8, 1–22 (2020).
- Saranathan, V. et al. Structural Diversity of Arthropod Biophotonic Nanostructures Spans Amphiphilic Phase-Space. Nano Lett. 15, 3735–3742 (2015).
- Zi, J. et al. Coloration strategies in peacock feathers. Proc. Natl. Acad. Sci. U.S.A. 100, 12576–12578 (2003).
- Freyer, P., Wilts, B. D. & Stavenga, D. G. Reflections on iridescent neck and breast feathers of the peacock, <i > Pavo cristatus. Interface Focus 9, 20180043, doi:doi:10.1098/rsfs.2018.0043 (2019).
- Yang, D., Qin, Y., Ye, S. & Ge, J. Polymerization-Induced Colloidal Assembly and Photonic Crystal Multilayer for Coding and Decoding. Adv. Funct. Mater. 24, 817–825 (2014).
- Shi, L. et al. Amorphous Photonic Crystals with Only Short-Range Order. Adv. Mater. 25, 5314–5320 (2013).
- Kim, S.-H., Lee, S. Y., Yang, S.-M. & Yi, G.-R. Self-assembled colloidal structures for photonics. NPG Asia Materials 3, 25–33 (2011).
- Xue, L. et al. Light-regulated growth from dynamic swollen substrates for making rough surfaces. Nat. Commun. 11, 1–9 (2020).
- Wu, X. et al. Hydrophobic Poly(tert-butyl acrylate) Photonic Crystals towards Robust Energy-Saving Performance. Angew. Chem. Int. Ed. 58, 13556–13564 (2019).
- Zhang, R., Wang, Q. & Zheng, X. Flexible mechanochromic photonic crystals: routes to visual sensors and their mechanical properties. J. Mater. Chem. C 6, 3182–3199 (2018).
- Paquet, C. & Kumacheva, E. Nanostructured polymers for photonics. Mater. Today 11, 48–56 (2008).
- Hatton, B., Mishchenko, L., Davis, S., Sandhage, K. H. & Aizenberg, J. Assembly of large-area, highly ordered, crack-free inverse opal films. Proc. Natl. Acad. Sci. U. S. A. 107, 10354–10359 (2010).
- Shen, Z., Shi, L., You, B., Wu, L. & Zhao, D. Large-scale fabrication of three-dimensional ordered polymer films with strong structure colors and robust mechanical properties. J. Mater. Chem. 22, 8069–8075 (2012).
- Lee, J. H., Kim, Y. S., Constant, K. & Ho, K. M. Woodpile Metallic Photonic Crystals Fabricated by Using Soft Lithography for Tailored Thermal Emission. Adv. Mater. 19, 791–794 (2007).
- Schaffner, M., England, G., Kolle, M., Aizenberg, J. & Vogel, N. Combining Bottom-Up Self‐Assembly with Top‐Down Microfabrication to Create Hierarchical Inverse Opals with High Structural Order. Small 11, 4334–4340 (2015).
- Zhou, J. et al. Self-Healable Organogel Nanocomposite with Angle-Independent Structural Colors. Angew. Chem. Int. Ed. 56, 10462–10466 (2017).
- Niu, W. et al. Photonic Vitrimer Elastomer with Self-Healing, High Toughness, Mechanochromism, and Excellent Durability based on Dynamic Covalent Bond. Adv. Funct. Mater. 31, 2009017 (2021).
- Wang, S. et al. Nonequilibrium Transesterification for Programming a Material’s Stiffening. ACS Appl. Polym. Mater. 1, 3227–3232 (2019).
- Li, C. H. & Zuo, J. L. Self-Healing Polymers Based on Coordination Bonds. Adv. Mater. 32, 1903762–1903765 (2020).
- Chen, Y., Kushner, A. M., Williams, G. A. & Guan, Z. Multiphase design of autonomic self-healing thermoplastic elastomers. Nat. Chem. 4, 467–472 (2012).
- Blaiszik, B. J. et al. Self-healing polymers and composites. Annu. Rev. Mater. Res. 40, 179–211 (2010).
- Xie, J. et al. Self-Assembly of Colloidal Nanoparticles into Well‐Ordered Centimeter‐Long Rods via Crack Engineering. Adv. Mater. Interfaces 8, 2000222 (2021).
There is NO Competing Interest.
- SupportingInformation20220307.docx
Supplementary Information