Designing Structural-Color Patterns Composed of Colloidal Arrays

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Designing Structural-Color Patterns composed of Colloidal Arrays Jong Bin Kim, Seung Yeol Lee, Jung-Min Lee, and Shin-Hyun Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 03 Apr 2019 Downloaded from http://pubs.acs.org on April 3, 2019

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ACS Applied Materials & Interfaces

Designing Structural-Color Patterns composed of Colloidal Arrays Jong Bin Kim†, Seung Yeol Lee†, Jung-Min Lee‡, and Shin-Hyun Kim*,† †Department of Chemical and Biomolecular Engineering (BK21+ Program), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea ‡The 4th R&D Institute, Agency for Defense Development, Daejeon 34060, Republic of Korea KEYWORDS Structural colors, colloidal crystals, colloidal glasses, photonic crystals, micropatterns

ABSTRACT: Structural coloration provides a great potential for various applications due to unique optical properties distinguished from conventional pigment colors. Structural colors are nonfading, iridescent, and tunable, which are difficult to achieve with pigments. In addition, structural color is potentially less toxic than pigments. However, it is challenging to develop structural colors because elaborate nanostructures are a prerequisite for the coloration. Furthermore, it is highly suggested to pattern the nanostructures at various length scales on a large area to provide practical formats. There have been intensive studies to develop pragmatic methods for producing structural-color patterns in a controlled manner using either colloidal crystals or glasses. This article reviews the current state of the art in the 1 ACS Paragon Plus Environment

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structural-color patterning based on the colloidal arrays. We first discuss common and different features between colloidal crystals and glasses. Then, we categorize colloidal arrays into six distinct structures of 3D opals, inverse opals, non-close-packed arrays, 2D colloidal crystals, 1D colloidal strings, and 3D amorphous arrays and study various methods to make them patterned with recent key contributions. Finally, we outline the current challenges and future perspectives of the structural-color patterns.

1. INTRODUCTION Colors are usually developed by chemical pigments which strongly absorb certain wavelengths in the visible. For example, chlorophyll strongly absorbs blue and red bands for photosynthesis while weakly absorbing green, rendering leaves green. Therefore, the colors are determined by the constituting materials and fade out as the chemicals are transformed or decomposed. Unlike the pigments, regular nanostructures with a dimension of wavelength scale can develop colors through constructive interference. For example, opals are composed of a close-packed array of silica nanoparticles in random-stacking hexagonal close-packed (rhcp) crystal, which develop a brilliant reflection colors.1 A Morpho butterfly has tree-like multi-layered branches made of nonlight-absorbing chitin on the scales, which also develop a pronounced blue reflection color.2 A beetle A. graafi uses randomly-packed structures of uniformly-sized chitin nanoparticles to develop colors.3, 4 The colors developed by regular nanostructures, so-called structural color, varies according to structural dimension and refractive index so that various colors can be obtained using a single set of materials. In addition, the structural colors never fade as long as the structures persist; structural color developed by inorganic materials can survive at high 2 ACS Paragon Plus Environment

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temperature where conventional pigments die out. As the colors can be purely developed by structures without the use of chemical pigments, low toxicity can be achieved by selecting a biocompatible set of dielectric materials.5-7 These features render the structural coloration promising rather than pigment-based coloration for various applications, including longlasting decorative paints,8 anti-counterfeiting patches,9, 10 colorimetric sensors on skins and eyes,11,

12

color-encoded microcarriers for bioassays,13-16 reflection-mode displays,17-20 and

many others.21-25 To develop structural colors, regular dielectric nanostructures with a modulation of the refractive index at the length scale of half the wavelength are required. The regular optical structures can be prepared by various top-down and bottom-up approaches. For example, a Bragg stack which is the one-dimensional (1D) periodic structure can be prepared by alternately depositing two different materials with controlled thicknesses.26,

27

Two-

dimensional (2D) structures composed of a regular hole array have been prepared by an ebeam lithography technique.28 Three-dimensional (3D) structures can be prepared by the interference lithography.29 However, the approaches mentioned above usually are far from low-cost and large-scale fabrication. Bottom-up approaches based on the self-assembly of building blocks are cost-effective and can be applied on a large area. Although self-assembly usually leads to the formation of defects, there is no significant reduction of structural colors as long as the density of defects is low; defects are critical for photonic devices such as waveguides or laser resonators.30-33 Three different building blocks have been widely utilized, which are colloids,34 liquid crystal molecules,35-37 and block copolymers.38 Liquid crystal molecules form cholesteric or blue phases in the presence of dopants that have a pitch at wavelength scale. Block copolymers form various regular nanostructures through microphase separation. However, the liquid 3 ACS Paragon Plus Environment


crystals are difficult to stabilize and block copolymers have a relatively small periodicity, restricting practical uses. Colloidal particles can form either crystalline lattices with longrange order or glassy arrays with short-range order through self-assembly, which provides stable structures with high controllability over a relatively wide range of length scales that cover ultraviolet, visible, and infrared. In addition, the colloidal assembly provides the most economical way to develop structural colors, rendering it promising for practical applications. To utilize structural colors in many applications, it is highly required to make patterns or graphics rather than uniform coatings as we do with pigments. The patterns deliver more information and attract users. However, it is very difficult to directly use normal printers for chemical inks or toners to create structural-color patterns as an elaborate control over the nanostructures is necessary to develop the colors. There have been intensive studies to develop versatile and reproducible methods for structural-color patterning based on colloidal structures. This review article summarizes and discusses key contributions to this field of structural-color patterning and the applications of the patterns. There have been many reviews on colloidal self-assembly and structural coloration for colloidal photonic crystals and glasses.1, 34, 39-41 Recently, patterning of colloidal photonic crystals has been reviewed.42 However, there is no systematic and well-organized review for the colloidal structures including 3D, 2D, and 1D crystalline arrays and 3D amorphous arrays and a variety of patterning methods. In the following second section, we first discuss the features of structural colors developed by colloidal crystals with long-range order and colloidal glasses with short-range order, respectively. Afterward, we categorize the structures into the four groups of 3D colloidal crystals, 2D colloidal crystals, 1D colloidal strings, and 3D colloidal glasses. The 3D colloidal crystals are further classified into three: Close-packed opal structures, inverse-opal 4 ACS Paragon Plus Environment

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structures, and nonclose-packed structures. For the six distinct structures, four different approaches have been used to make photonic patterns, as summarized in Figure 1. The four approaches include 1) regioselective deposition, 2) regioselective removal, 3) regioselective post-modification, and 4) regioselective in-situ modification. The post-modification indicates the local deformation of solid photonic structures, whereas in-situ modification indicates a repeatable control over interparticle distance and localized fixation of fluidic photonic structures. We discuss the patterning methods for the six distinct colloidal structures respectively in the third to sixth section. A few important contributions are described in detail. In the seventh section, we discuss the photonic patterns that show dynamic color changes with external stimuli; mechanisms of the color changes or stimuli are summarized in the bottom part of Figure 1. Finally, we outline the current challenges and outlook on the structural-color patterning and applications in the eighth section.

2. STRUCTURAL COLORS DEVELOPED BY COLLOIDAL CRYSTALS AND GLASSES The structural colors developed by colloidal crystals and glasses have common features of no fading, color tunability, and potentially low toxicity as we discussed in the introduction. At the same time, there are distinct features. Colloidal crystals usually show reflective and glittering colors which are strongly iridescent, thereby being clearly distinguished from pigment-based colors. By contrast, colloidal glasses show relatively faint and diffuse colors which are less iridescent, being more comparable to pigment colors.39,

40

This contrast in

optical properties originates from the difference in interference of light for highly-ordered and less-ordered structures.

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2.1. Structural coloration for 3D and 1D colloidal crystals. Colloidal crystals have spatially-alternating refractive indices in a periodic manner at the characteristic length scale of half the wavelength. The periodic structures have photonic stopbands at which photon density of state is extremely low. As a light in the stopbands is forbidden in the structure, it cannot propagate, thereby being selectively reflected. When the stopband is located in the visible range of 400 – 700 nm in wavelength, the reflection results in striking reflection colors. The selective reflection at the stopbands can be also described by Bragg’s diffraction. When light impinges on multi-slab structures in a normal direction, each slab partially reflects the light.43 If the reflected beams from the multiple slabs are in-phase, they constructively interfere to strengthen the amplitude of wave (Figure 2a-i). Overall, the sum of the beams results in a light with a large amplitude outside the multi-slabs and no light beyond a certain thickness of the slabs (Figure 2a-ii); the thickness is referred to as optical penetration depth or Bragg attenuation length.44,

45

The geometric path difference between

two beams reflected from two neighboring slabs is double the periodicity, 2d, which corresponds to the central wavelength responsible for constructive interference. When the refractive index of the structure is neff, the wavelength for normal incident light is modified as follows: 𝑚𝜆 = 2𝑑𝑛𝑒𝑓𝑓

(m=1, 2, ...) ,

[1]

where m is a diffraction order. Therefore, the diffraction wavelength can be controlled by adjusting the periodicity and refractive index. In addition, we can notice that the color varies with the angle of the incident beam on the crystal plane for specular reflection. The width of the bandgap, Δλ, increases so does the difference of refractive indices for two alternating materials, Δn, which roughly follows the relation:


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∆𝜆 Δ𝑛 𝜆 ~𝑛𝑒𝑓𝑓

.

[2]

The Bragg attenuation length is inversely proportional to Δn/neff. Monodisperse colloidal particles usually form crystalline structures with lattices of either face-centered cubic (fcc), hexagonal close-packed (hcp), or rhcp; a body-centered cubic (bcc) lattice can be formed in a limited condition. The fcc, hcp, and rhcp lattices are all composed of a stack of hexagonal arrays and only stacking sequences are different. When the colloidal crystals have a close-packed array with the lattices, the structures are referred to as opal structures as the natural opals have similar rhcp lattice.1 The wavelength for Bragg’s diffraction from stacked hexagonal arrays which corresponds to (111) plane of fcc or (0002) plane of hcp is determined by the diameter, D, and the refractive index of particles, np:34

𝑚𝜆 = 2𝑑𝑛𝑒𝑓𝑓 =

1/2

(83)

𝐷(𝑛2𝑝𝜙 + 𝑛2𝑚(1 ― 𝜙))

1/2

(m=1, 2, ...)

, [3]

where ϕ is the volume fraction of particles which is 0.7405 for close-packed fcc or hcp structures and nm is the refractive index of the matrix which is 1 for air. When particles repel each other, they form nonclose-packed fcc or hcp structures at which the volume fraction of particles influences interparticle separation. Therefore, the wavelength for the diffraction is determined by a volume fraction as well as particle diameter:

𝑚𝜆 = 2𝑑𝑛𝑒𝑓𝑓 =

1/3 8 1/2 𝜋 𝐷 3 3 2𝜙

( ) ()

(𝑛2𝑝𝜙 + 𝑛2𝑚(1 ― 𝜙))1/2

(m=1, 2, ...).

[4]

The wavelength for the diffraction is readily controllable by adjusting the volume fraction with the same size of particles in nonclose-packed crystalline arrays. The wavelength for 1D colloidal strings is also determined by equation [1], where d is simply a distance between two adjacent particles. 7 ACS Paragon Plus Environment


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2.2. Structural coloration for 2D colloidal crystals. 2D colloidal crystals show structural colors through two different mechanisms—thin-film interference and grating diffraction—, which are different from 3D or 1D structures. The 2D colloidal crystals can serve as a thin film with an effective refractive index averaged from the colloids and matrix. The beams reflected from the top surface and the bottom surface of the thin film can make a constructive interference when the beams are in-phase (Figure 2b). The wavelength of the interference is simply expressed as: 𝑚𝜆 = 2𝐷𝑛𝑒𝑓𝑓cos 𝜃𝑏 (𝑚 = 1, 2, …) ,

[5]

where θb is the refraction angle of light.46 The thin-film interference usually results in low reflectivity and faint colors. The other mechanism, grating diffraction, uses the ordered 2D array for constructive interference (Figure 2c). The incident beams are scattered to all directions by colloidal particles in the 2D array. When the scattered beams by two adjacent particles are in-phase, they show structural colors through constructive interference. The wavelength of the interference is influenced by angles of incident beam and reflection, θi and θm:47 𝑚𝜆 = 𝑑𝑛(sin 𝜃𝑖 + sin 𝜃𝑚) (𝑚 = 1, 2, …) ,

[6]

where d is the distance between two adjacent particles which is D for a close-packed array and n is the refractive index of the surrounding medium which is 1 for 2D colloidal crystals in the air. The grating diffraction is unable to develop structural colors for normal observation for the normal incident beam (θi = θm = 0), unlike 3D and 1D colloidal crystals and the thinfilm mechanism for 2D colloidal crystals. The grating diffraction has been dominantly utilized for coloration with 2D colloidal crystals. As noticed in equation [6], the color can be observed at various angles and the color is strongly angle-dependent; the 3D and 1D crystals 8 ACS Paragon Plus Environment

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show a brilliant structural color only for specular reflection. As the beams are omnidirectionally scattered, the color brightness is very low. The wavelength of the diffraction can be dynamically modulated for a nonclose-packed array partially embedded in a volume-changeable substrate.48-52 2.3. Structural coloration for colloidal glasses. Amorphous arrays of monodisperse or bidisperse colloids are lack of long-range order. However, they still have short-range order as the interparticle distance is consistent throughout the structures. The short-range order also makes the colloidal glasses show structural colors through constructive interference.53, 54 As the scattered lights from colloidal particles in amorphous arrays are not perfectly in-phase, the interference occurs at a relatively wide range of wavelength, resulting in weak reflection at a broad range of wavelength.55, 56 The central wavelength of the reflection is approximately located in 2davgneff, where davg is average interparticle distance. As the reflection by the amorphous array is not strong, the structural color is sometimes overwhelmed by multiple scattering or incoherent scattering.57 The multiple scattering makes the colloidal glasses white.58 The thin film of amorphous arrays formed on a black substrate can reduce the multiple scattering.59-61 For thick films, the multiple scattering can be reduced by adding absorptive materials in the amorphous array, such as carbon black,62-65 polydopamine,66-68 Cuttlefish ink,69 graphene nanosheet,70 polypyrrole,71 and iron oxide nanoparticles.18 In addition to the broadband-absorbing materials, plasmonic metal nanoparticles have been used to suppress the multiple scattering. As the metal nanoparticles, such as titania-silver composite72 and gold nanoparticles,73

strongly absorb a selected

narrow band through plasmonic resonance, they reduce the multiple scattering while minimizing the loss of color brightness; the plasmonic nanoparticles have been also used for colloidal crystals and inverse opals to improve color saturation.74 The incoherent scattering 9 ACS Paragon Plus Environment


by individual particles, or cavity resonance, leads to a backscattering peak at a short wavelength.57 The resonant wavelength of this scattering is proportional to the refractive index and the diameter of particles. The incoherent scattering by individual particles is suppressed by using core-shell particles whose shell is index-matched with medium,75, 76 or making air cavities in a solid matrix,75,

77

thereby pushing the resonant wavelength to

ultraviolet. Despite the relatively low reflectivity, colloidal glasses are still attractive for structural coloration as they are less iridescent in a comparison with colloidal crystals. The low angular dependence is important for many applications such as displays and sensors. The angle dependence is usually analyzed by three different configurations with directional illumination, which correspond to near-backward scattering, specular reflection, and diffusive scattering (Figure 3a).78 As colloidal glasses are isotropic, the rotation of the glass does not cause any change in structural colors in the near-backward scattering when the directions of the incident beam and observation are fixed (Figure 3a-i). Therefore, the colloidal glasses show consistent structural colors regardless of the rotation. By contrast, the rotation of colloidal crystals leads to variation in the angle of incident light on a certain crystal plane and therefore change in the angle of reflection. Therefore, it is difficult to observe strong structural colors for sample rotation when there is no change in the observation direction. For specular reflection at which the angle of the incident beam and that of observation are simultaneously varied in the same magnitude yet opposite direction (Figure 3a-ii), structural colors blue-shift with the angle for both colloidal glasses and crystals. This color change is inevitable as optical path difference for scattered beams from two neighboring particles changes with the angle. It is known that structural colors by colloidal glasses are slightly less shifted than those by colloidal crystals.77


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In the diffusive scattering (Figure 3a-iii), there is also an angle-dependence for colloidal glasses and crystals, though the dependence is weak. Although glass structures also have the angle dependence for specular reflection and diffusive scattering, some beetles and birds show almost angle-independent structural colors. In nature, light is omnidirectional rather than unidirectional, which further renders the structural colors angle-independent. Because the incident beam has all the angles in the range of 0-90° in the omnidirectional illumination, the reflectance spectra are broader than the directional illumination. In addition, with the same reason, the resonant wavelength of glass structures under the omnidirectional illumination is blue-shifted from the directional illumination normal to the surface; it turns out that the wavelength is comparable to the specular reflection wavelength with an incident angle of 30-35°.78 The common and different features of structural colors from colloidal crystals and glasses are summarized in Figure 3b.

3.

STRUCTURAL-COLOR

PATTERNS

COMPOSED

OF

3D

COLLOIDAL

CRYSTALS 3.1. Opal structures. When monodisperse colloidal particles are slowly concentrated to have a final volume fraction of 0.7405, they form a close-packed array with a lattice of fcc, hcp, or rhcp, referred to as opal structures. To produce structural-color patterns with the opal structure, either local deposition or regioselective removal is required. The colloidal dispersions can be confined and slowly concentrated to deposit close-packed colloidal crystals in local areas. The confinement can be achieved by either solid walls or free interfaces. For the solid-wall confinement, colloidal dispersions are infiltrated into capillary channels with open ends. The evaporation of solvent at the open end results in a 11 ACS Paragon Plus Environment


unidirectional flow of dispersions toward the end, which concentrates and crystallizes colloidal particles (Figure 4a); the capillary channels are usually prepared by affixing a softlithographically-featured elastomeric mold on a solid support.79-81 To achieve higher controllability, the colloidal particles can be concentrated by centrifugal forces,82 instead of evaporation-driven convective flow (Figure 4b). The colloidal crystals are only formed in the microchannels so that the structural colors are patterned. These patterns can serve as sensors for measuring the refractive index of fluids as the reflectance spectrum varies with the effective refractive index. The microchannel geometries facilitate the injection and replacement of fluids. Higher complexity of color patterns can be prepared by local deposition of opal structures using electrocapillary force.83,

84

An aqueous dispersion of colloidal particles is precisely

injected by electrocapillary force to selected microchambers in 2D arrays with an electrode pattern (Figure 4c). Water slowly evaporates from the chambers, producing opal structures. It is also possible to produce multicolor patterns using this method by consecutively using two or more different sizes of particles. This electrocapillary-based colloidal assembly can produce multicolor patterns including color pixels which can be used as a color panel for a backlight-free reflection-mode display by using a liquid-crystal layer to control light transmission on the surface of the panel. With open microchannels, localized deposition can be also achieved.85, 86 When a substrate with open microchannels is vertically pulled off from the colloidal dispersions, the dispersions are confined by trenches with solid walls and air-dispersion interface, in which opal structures are selectively grown during the evaporation of dispersion medium (Figure 4d);86-89 this coating process is generally known as a vertical deposition method or dipcoating. As the dispersions are not fully confined by solid walls, a delicate control is a 12 ACS Paragon Plus Environment

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prerequisite to guide the colloidal crystallization only in the trenches: Particle-to-wall interactions should be carefully controlled and experimental conditions of particle concentration and pulling speed should be optimized depending on the depth and width of the trenches. However, both closed and open microchannels only provide a restricted degree of freedom in pattern design. The regioselective formation of opal structures can be achieved with chemical patterns in the absence of solid walls.90-94 When the planar substrate is chemically patterned to have the hydrophilic and hydrophobic areas, colloidal crystals can be formed only on the hydrophilic area when the substrate is subjected to dip-coating with an aqueous dispersion of colloids. During the dip-coating, a concave meniscus is formed on the hydrophilic area due to small contact angle, whereas a convex or less-concave meniscus is formed on the hydrophobic area. The contrast in the shape of meniscus results in the selective concentration of particles and the formation of colloidal crystals only on the hydrophilic surfaces. The regioselective chemical patterning can be done by various methods: silanization of the photoresist-patterned silicon wafer and subsequent removal of photoresist,91 or removal of the hydrophobic moiety on the surface of a titania substrate by localized ultraviolet (UV) exposure through a photocatalytic reaction (Figure 4e).90 Although the localized deposition of opal structures using the chemical pattern provides an enhanced degree of freedom in pattern design, it is difficult to create a high-resolution pattern, as free interfaces do not provide a sufficient confinement effect on the small dimension of the hydrophilic areas. Localized deposition of colloidal crystals can be done by droplets sitting on a substrate or sessile drops. As droplets are precisely formed and patterned in a facile and cost-effective inkjet printing, so are the colloidal crystals.95-98 During the inkjet printing, a droplet of colloidal dispersions is ejected from a nozzle and then deposited on a substrate. Upon drying 13 ACS Paragon Plus Environment


of the droplet, colloidal particles form a close-packed colloidal array in the local area (Figure 5a).99 The shape of the colloidal structures varies among spherical dome, ring, and circular disk depending on the contact angle of drop, contact-angle hysteresis, particle volume fraction, and evaporation rate.100, 101 Liquid substrates that are immiscible to the drop can be used, which produces a relatively thick disk as contact line is not pinned.102 The evaporation rate also influences the particle arrangement: slower evaporation usually leads to a higher degree of ordering. The inkjet printing provides high-resolution patterns in a large area.99, 101, 103, 104

In addition, the multi-color patterning is also accomplished through repeated printing

with distinct colloidal dispersions (Figure 5a). However, the colloidal structures do not fully cover the entire substrate so that reflectivity is limited. Spherical shape95, 97 and thinness of the colloidal layer further reduce the reflectivity. Nevertheless, the inkjet method is promising for the production of customized color patterns as it provides a high resolution and fast deposition. The inkjet-printed patterns are useful as decorative coatings and anticounterfeiting tags. One simple way to make a color pattern with a continuous film of opal structures is to use spray coating methods. An aqueous dispersion of colloidal particles is sprayed on the target substrate. The aerosol droplets are formed at the nozzle, which travel through air and arrive at the surface before complete consolidation. Therefore, the droplets spread on the surface to form a film of dispersion. Water evaporates from the film, which finally consolidates the particles. The evaporation results in a film of opal structures; the amorphous structures as well as crystalline structures are also formed due to fast evaporation.105-107 The opal film can be patterned by spraying the dispersions through a mask with a hole pattern (Figure 5b).108 Repeated spray-deposition with different dispersions and masks creates multicolor patterns. Once the mask is prepared, one can reproduce the patterns by hand fast. 14 ACS Paragon Plus Environment

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Micropatterns of opal structures can be prepared by regioselective post-treatment of continuous opal films formed by a normal dip-coating process. The regioselective removal of an opal film with a sacrificial pattern or stamp 109, 110 and stamp-assisted local compression 110 have been used. In the regioselective lifting-off process, micropatterns of a positive photoresist prepared by photolithography are used as a substrate (Figure 5c).109 The patterns are first coated with chromium and copper by sputtering and treated by oxygen plasma, which are then subjected to dip-coating for the preparation of opal layer. When the entire substrate is immersed in acetone and ultrasonicated, the positive photoresist pattern dissolves into acetone, selectively lifting-off the opals on the photoresist. Therefore, the opal structures on the photoresist-free regions remain on the substrate, forming color patterns. In addition, dual-color patterns can be obtained by depositing different size of silica particles on the asbuilt pattern by dip-coating process. For the dual colors, the first opal film is pretreated to render the surface hydrophobic, which is then subjected to ultrasonication with acetone. The resulting hydrophobic opal pattern enables the selective growth of the second opal only in the voids during the second dip-coating. In the stamping method, two different approaches have been used for patterning.110 For opal films composed of polymer particles that are thermally annealed above the glass transition temperature, the stamping leads to the local compression of structures (Figure 5d). Therefore, dual-color patterns are prepared, which is composed of intact opal and compressed opal. For opal films without thermal treatment, the stamping leads to the adhesion of the opal into the stamp. Therefore, void patterns are formed in the opal film as the stamp is detached. In addition, the opal on the stamp can be further transferred to another substrate (Figure 5e). Although these post-treatment methods of opal films are able to produce various designs,



they are difficult to be applied to a large area and usually result in the uncontrolled shape of pattern boundaries. 3.2. Inverse opal structures. Although opal structures are directly prepared by one-step self-assembly, they have many limitations. First of all, the structures are mechanically unstable as physical contacts among particles only support their integrity. Second, materials for the synthesis of monodisperse colloids are restricted to polystyrene (PS), poly(methyl methacrylate) (PMMA), silica, and few others, which makes the functionalization or patterning processes difficult. To overcome the limitation, phase-inverted structures from opals, so-called inverse opals, have been prepared. The inverse opals are prepared by three consecutive steps of opal formation, infiltration of matrix materials into interstitial voids, and removal of the opal template; the composites, opals whose voids are filled with matrix materials, are sometimes directly formed in one step by co-assembly.111-113 There is no limit in choosing the matrix materials as long as they are fluidic during the infiltration and changed to a solid during consolidation for the three-step method. In an opal removal step, calcination is used for polymer particles in an inorganic matrix and wet etching with hydrofluoric acid is used for silica particles in a polymeric matrix. Inverse opal structures have a monolithic matrix as the voids of opals are continuously connected so that they usually have enhanced mechanical stability. In addition, high freedom in the selection of matrix materials enables the enhanced control over property, providing advanced functionality. For example, the inverse opals show flexibility,114 shape-memory property,115 or responsiveness to external stimuli.116,

117

The wavelength responsible for

diffraction in inverse opal can be estimated with the equation [3], where np is 1 for air and nm is the refractive index of the selected matrix material.


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Micropatterns of inverse opals can be photolithographically-featured by using a negative photoresist as a matrix material.118, 119 For a controlled formation of a composite composed of silica opal and photoresist matrix, the opal is formed on the surface of photoresist by dipcoating, which is then embedded into the photoresist by the capillary action above the glass transition temperature of the photoresist. The composite is subjected to photolithography to make micropatterns; localized UV exposure through a photomask and removal of uncrosslinked parts are performed. Finally, the silica opals are etched out from the patterned composite (Figure 6a).119 Multi-color patterns can be prepared by sequentially employing different sizes of silica particles. For example, red, green, and blue (RGB) tiles are pixelated through the method, which is potentially useful as a color panel for a display operated at the reflection mode (Figure 6a-iv). As an alternative to using negative photoresist as a matrix material, a positive photoresist can be used to form an etching mask for silica inverse opal.120 Silica inverse opal is prepared by co-assembly of polymer particles and silica precursor and subsequent calcination of the particles. A positive photoresist is infiltrated into the pores of the inverse opal film, which is then micropatterned by photolithography. The resulting structure is further subjected to reactive-ion beam etching, which completely removes unprotected inverse opals while maintaining the photoresist-filled inverse opals. After dissolving out the photoresist from the inverse opals, single-color micropatterns are obtained. These photolithography-based approaches provide high-resolution patterns with high reflectivity. The inverse opal film can be locally collapsed by a stamping process to make a singlecolor pattern.114 Using silica opal template, inverse opal is made of a flexible and mechanically-stable polymer. The polymer inverse opal structure experiences a plastic deformation under stamping, being permanently losing structural colors. As the regions 17 ACS Paragon Plus Environment


uncompressed persist, single-color patterns are created. To make multicolor patterns, opal templates with different particle diameters are sequentially deposited through the dip-coating process, from which inverse opals with multiple domains of different structural-colors are prepared. The stamping on the inverse opal results in multicolor patterns (Figure 6b); this approach has a limited degree of freedom in designing multicolor patterns as the single-color domains are always aligned parallel. The resulting flexible inverse opal patterns are potentially useful for an anti-counterfeiting patch applicable on a banknote. In another approach, inverse opals are made of the shape-memory polymer using a silica opal template (Figure 6c).115 The inverse opal structure wet by water is collapsed when the water dries; this is caused by capillary force. The original structure can be recovered by mechanically stimulating the inverse opals due to the memory effect of the matrix. Therefore, it is possible to make color patterns using stamps. Only the parts under contact pressure recover the original structural color, whereas the parts without contact to the stamp remain discolored. With this principle of regioselective structure recovery, various designs of singlecolor patterns can be prepared. For example, a clear color image of the fingerprint can be prepared by pressing the collapsed film with a finger (Figure 6c-iv). Inverse opals can be micropatterned in a high resolution through various distinct approaches as we discussed. This pressure-sensitive film and pattern are promising for 2D mapping of mechanical stress, which is otherwise difficult to achieve. However, it is still difficult to prepare a multi-color pattern from the single inverse-opal template. As the size of templating particles determines the resonant wavelength of inverse opals, different sizes of particles are separately but consequently employed to make multi-color patterns. However, the dip-coating process or other opal-forming processes are delicate and time-consuming. It is possible to produce multi-color patterns from single inverse opal film 18 ACS Paragon Plus Environment

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through the local modulation of a void fraction or lattice constant. The void fraction of inverse opal can be locally varied by the photolithography technique (Figure 7a).121 All the voids of inverse opals are filled with a negative photoresist, which is then locally irradiated by UV using a photomask. The photoresist unexposed to UV is removed during development, recovering original structures, whereas that exposed to UV is crosslinked, filling the pores. As the photoresist is cured from the pore walls, longer exposure time makes smaller pores after the development. Therefore, the reflection color red-shifts as UV exposure time increases in a certain range as the reduction of void fraction from 0.7405 increases the effective refractive index. Multicolor patterns can be prepared from single inverse opals by locally controlling UV doses. For example, the photoresist-filled inverse opal that is exposed to UV using a linepatterned photomask twice with two orthogonal directions of photomask alignment turns to RGB pixels. There are three regions with no UV, one-time UV exposure, two-time UV exposure, which correspond to blue, green, and red squares, respectively. The RGB pixels are useful as a color panel for reflection-mode displays, as we discussed above. This method is beneficial for making multiple colors in a single film. However, it is difficult to completely fill the pores of inverse opals with viscous photoresist without air trapping. In addition, the range of color shift is relatively limited as the lattice constant remains unchanged. A simpler way to modulate the resonant wavelength of inverse opal is the thermal compression of the lattice. As the inverse opal structure has a large surface area on the pores, pores are closed to reduce surface energy when the matrix is molten. When the inverse opals formed on the solid substrate, the spherical pores deform to disk shape as a lateral retraction is restricted due to the substrate.113, 122 The deformation reduces interlayer distance along the thickness direction, which causes a blue-shift of structural colors. The rate of the lattice 19 ACS Paragon Plus Environment


compression depends on applied temperature relative to the glass transition or melting temperature of matrix materials. When the matrix of inverse opal is made of photoresist, the glass transition temperature can be controlled by UV dose. Therefore, the rate of compression can be spatially varied by region-selectively controlling UV dose even if the temperature is uniformly applied in the whole area of the inverse opal. To make the inverse opal made of negative photoresist, silica opal is formed on the surface of the photoresist, which is then thermally embedded. On the composite, UV is locally irradiated using a photomask. After the removal of the opal, the inverse opal is subjected to thermal treatment. The inverse opal exposed to UV remains intact, whereas that unexposed experiences vertical compression. The degree of deformation or equivalently degree of color shift can be controlled by temperature and thermal treatment time. Therefore, dual- or multiple-color patterns can be prepared depending on the number of different UV doses (Figure 7b). The color patterns can be permanently stabilized by sufficient UV dose after the thermal treatment. The resolution of the resulting pattern is as small as several micrometers. In a similar manner, inverse opal whose matrix is made of silk is used to locally compress the lattice.117 As water leads to the formation of beta-sheet of silk proteins and causes shrinkage, a localized compression occurs when the inverse opal is exposed to water vapor through a protection layer. Alternatively, the silk inverse opals can be locally compressed by UV exposure through a photomask. UV induces scission of peptide chains and degradation of silk fibroin, leading to the compression of the lattice. The lattice of inverse opal can be increased by light-induced local swelling (Figure 7c).116 For this, the inverse opal is made of a hydrogel containing azobenzene compound. When the 20 ACS Paragon Plus Environment

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azobenzene has a trans configuration, the matrix is not highly polar so that the degree of swelling is low in the water. The configuration can be changed from trans to cis by UV irradiation, which leads to an increase of polarity, making the matrix highly swollen by water. Therefore, the reflection color red-shifts with UV exposure. Local UV exposure through a photomask yields dual-color pattern. Interestingly, the color pattern can be removed by the irradiation of visible light which turns back the cis configuration to trans. This swelling-based reversible change requires a water environment. This mechanism resembles how the iridophores in a special fish change their color, and opens up the possibility for designing color-tunable smart gels. It will be possible to make photonic layers for protecting aquatic organisms from harmful light and improving photosynthetic efficiency.123, 124 Another way to make a dual-color pattern from a single inverse opal is to utilize surface plasmon resonance as well as photonic stopbands. Inverse opals with open pores on the top surface are subjected to metal deposition, which makes metal nanostructures on the top of inverse opal. As the metal nanostructures show a plasmonic color, it is possible to create a dual-color pattern by regioselectively depositing the metal (Figure 7d).125 The regioselective deposition can be done with a shadow mask formed on the top surface of inverse opal. The shadow mask is made of positive photoresist and the graphic can be featured by photolithography. After metal deposition, the shadow mask is lifted off to make two distinct regions of metal-free inverse opal and metal-deposited inverse opal. The metal-free inverse opals show structural color from photonic stopbands and the metal-deposited inverse opals show plasmonic color. This dual-color pattern shows unique color recovery behavior when a liquid infiltrated in the pores is evaporated as two different origins of coloration are utilized. The uniqueness in the color recovery behavior renders the patterns valuable as anticounterfeiting tags for advanced security. 21 ACS Paragon Plus Environment


3.3. Nonclose-packed structures. To produce opal structures, a slow concentration of particles is a prerequisite. However, most approaches including dip-coating methods are delicate and time-consuming. Particles rapidly form nonclose-packed crystalline structures in a liquid dispersion when they repel each other; the structures formed by repulsive interparticle potential are referred to as crystalline colloidal arrays (CCAs). When particles are dispersed in water, they form CCA through electrostatic repulsion as they are charged. The nonclose-packed array can be captured in a hydrogel matrix to form a polymerized CCA (PCCA) as the hydrogel precursors are soluble in water.126 Although PCCAs have been widely studied for colorimetric sensing,127 they are inadequate for many applications of color patterns as water environment is required and mechanical property of hydrogel is not good enough. The particles dispersed in carefully-selected monomer can experience a repulsive force due to the formation of the solvation layer or another mechanism. When the functional groups on the surface of particles form hydrogen bonds with monomers, the solvation layer is firmly formed, which renders the particles repulsive when the interparticle separation is small; for silica particles dispersed in an acrylate-based monomer, a silanol group on the particle forms a hydrogen bond with an acrylate group or other groups in the monomer. Therefore, the particles spontaneously form nonclose-packed crystals when the volume fraction of particles is high enough. The colloidal crystals can be stabilized by polymerization of the monomer, forming a liquid-free PCCA. Photocurable colloidal dispersions that spontaneously form nonclose-packed crystal structures can be patterned by localized photo-polymerization. The various methods used for the opal patterning are applicable to the photocurable dispersions. As solvent evaporation is not required, the process is much simple, fast, and reproducible. For example, the capillary channels can be infiltrated with the photocurable dispersions by the capillary action or 22 ACS Paragon Plus Environment

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negative pressure applied, which are then irradiated by UV. After the release of the channel mold, color patterns are formed; all the channel space is fully occupied by the colloidal photonic structure without voids as there is no evaporation or concentration process. The multi-color pattern can be prepared by infiltrating distinct dispersions into separated channels. For example, 20 photonic stripes whose central wavelengths are in the entire visible range with almost equal interval are prepared using 20 different dispersions and 20 separated microchannels.128 The stripes can be used as a miniaturized spectrometer. The photocurable dispersions can be patterned into a spherical dome array by depositing the drops on a substrate by the dispenser.129 In addition, multi-compartment spherical domes can be prepared by merging two or more distinct drops during the deposition.130 Instead of one-byone drop deposition, a substrate with a chemical pattern of hydrophobic dot array is used for one-step selective adhesion of monodisperse emulsion drops of the photocurable dispersions onto the hydrophobic dots in a water environment. A photolithographic technique can be used for the photocurable dispersions, which is not applicable for opal structures. The dispersions are infiltrated into the gap between a photomask and a substrate, which is then irradiated by UV through the photomask. As the dispersions are polymerized under UV exposure, micropatterns with the design same to the photomask are formed after washing unpolymerized dispersions (Figure 8a).9 The resulting patterns are useful as anti-forgery tags. The resolution of the method is approximately tens of micrometers which is lower than photoresist-based photolithography. The wavelength of diffraction is given by the equation [4] for nonclose-packed fcc or hcp. The wavelength can be further tuned by expanding or compressing the matrix. For example, the PCCA film can be swollen by photocurable monomer to increase lattice constant. The swollen film can be locally irradiated by UV to polymerize the monomer and fix the swollen 23 ACS Paragon Plus Environment


state.131 The subsequent washing of unpolymerized monomer makes the film recover the original structures. Therefore, two different colors can be patterned from the regioselective permanent swelling of the single-color film. Alternatively, nonclose-packed array embedded in an elastomeric matrix can be subjected to local compression with a stamp.11 As the lattice is compressed on relief regions of the stamp, the color blue-shifts. On the other hand, the color red-shifts on engraved regions due to the expansion of the matrix; the expansion is accompanied by the compression as the volume of the composite is conserved during elastic deformation. Therefore, dual-color patterns are formed by the stamping (Figure 8b). The pattern disappears when the stamp is released because the deformation is elastic. This mechanochromic behavior is useful for mapping mechanical strain and stress. In addition, the elastic films and patterns can be used as sound-to-vision transformers and active military camouflages. The enhanced controllability over color can be achieved by using the electric field on colloidal dispersion. When the particles are charged in the dispersion, they experience electrophoretic force under direct-current electric field. Therefore, the nonclose-packed array of particles is compressed by the electric field and the degree of compression increases along with the intensity of the field. As the dispersion medium is a photocurable monomer, the lattice can be permanently fixed by UV irradiation. The combination of electric-field application and local UV exposure through a photomask enables the fixation of the lattice with a controlled color in the UV-exposed area.132 Therefore, the multi-step process makes complex designs of multicolor patterns with a high degree of freedom (Figure 8c). This technique is competitive as it provides fast and economical ways to make multicolor patterns. The resulting patterns are useful especially for anti-counterfeiting tags and decorative coatings. 24 ACS Paragon Plus Environment

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4.

STRUCTURAL-COLOR

PATTERNS

COMPOSED

OF

2D

COLLOIDAL

CRYSTALS Monodisperse colloidal particles confined in 2D spaces can form a monolayer composed of an ordered array.133 To confine colloids or colloidal dispersions in 2D space, various approaches— vertical deposition,134 horizontal deposition,135, mechanical rubbing,138 and interfacial trapping139,

140—have

136

inkjet printing,137

been utilized. In a vertical

deposition, colloidal dispersions with a low concentration are dip-coated as the solid substrate is pulled out from the dispersion. Although the vertical deposition usually produces 3D colloidal crystals during the evaporation of dispersion medium as we discussed in Figure 4d, it can produce 2D crystals when the colloidal concentration is carefully lowered.141,

142

However, the vertical deposition frequently results in strip patterns with uncontrolled widths due to the stick-slip motion of the triple line.143

A horizontal deposition is suggested as an

alternative to the vertical deposition, which coats a thin film of colloidal dispersions on a solid substrate by blading with a knife or rod.144, 145 In a similar manner to vertical deposition, a monolayer film can be prepared by carefully adjusting the concentration of particles. This coating process is much faster than the vertical deposition and the dispersions can be saved. However, the stick-slip motion is difficult to avoid so that strip patterns are frequently formed.146 For both methods, the substrate should be highly wettable for the dispersion medium so that the film of dispersions should be as thin as the particle diameter near the triple line. Inkjet printing provides precise droplet deposition as we discussed in Figure 5a. When the droplet spreads on a solid substrate and contains a low concentration of particles, a monolayer composed of 2D colloidal crystals can also be prepared.



Aforementioned three methods use colloidal dispersions to form a 2D array. Mechanical rubbing employs dry powders rather than dispersions to make the 2D array. By carefully controlling the adhesion between particle and substrate stronger than that between particles, dry particles can be coated to form a monolayer on an elastomer substrate by simply rubbing the powders.138 Colloidal particles can be trapped at fluid-fluid interfaces and assembled to form a monolayer without a solid substrate. The particles interact with their neighbors through various mechanisms such as van der Waals attraction, hydrophobic attraction, and electrostatic repulsion. In most cases, the particles form a close-packed 2D hexagonal array. But, it is also reported that nonclose-packed array can be formed when the repulsion dominates the attraction.147,

148

The interfacial assembly is a unique way to produce 2D

colloidal crystals composed of only a monolayer and it is possible to transfer the colloidal array onto solid substrates.149-153 There are other ways to produce 2D colloidal crystals. Charged colloids are assembled on an oppositely-charged substrate through the electrostatic attraction.154 Particles can be concentrated on the substrate to form a 2D array through electrophoresis or dielectrophoresis.155, 156 The assembly of colloids at the air-water can be regioselectively transferred on the substrate with a chemical pattern (Figure 9a).157 The substrate is prepared by locally treating a glass slide with hydrophobic molecules. When the substrate is first coated with a thin film of water and then inserted into water, the colloidal monolayer spontaneously climbs along the thin film on the unmodified part of the glass due to slightly higher interfacial tension of free water interface than the monolayer-anchored interface. The hydrophobic pattern remains dried, resulting in the selective deposition of 2D colloidal crystals. The area of 2D crystal shows iridescent colors for various viewing angles yet not highly striking as much as 3D crystals. This wetting-based patterning method can be used for patterning on curved surfaces. 26 ACS Paragon Plus Environment

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Inkjet printing is one of the simplest methods to make patterns of not only 3D colloidal crystals but also 2D colloidal crystals. When the particle concentration is low and the dispersions spread on the substrate with a low contact angle, dots composed of a monolayer can be deposited using the inkjet droplets (Figure 9b).47 To make droplet spreads, the dispersion medium should be properly selected depending on the surface property of the substrate, while retaining the dispersion stability of the particles. A mixture of water and formamide is a good candidate of the medium for silica particles on a glass substrate to form a monolayer.137 The inkjet printing provides precise patterns in a wide area with a high degree of freedom for pattern design. For example, it is possible to produce monolayercontained dots with a diameter of 70 μm that are arranged in a square array with a separation of 100 μm (Figure 9b). The collection of dots can constitute any graphic in a centimeter-scale. The macroscopic graphics show a dramatic color change with the viewing angle and incidentbeam angle. In addition, as the reflection intensity is very low, the pattern can be hidden under the low intensity of illumination, while disclosed under high intensity. These features distinguished from 3D colloidal crystals render the patterns appealing for anti-counterfeiting tags. The inkjet-printed patterns can be densely packed by transferring them at the air-water interface (Figure 9c).158 Even if the particles are sparsely deposited in each dot, they can be closely-packed at the interface; the sparsely arranged particles are formed by the electrostatic attraction between negatively-charged particles and a positively-charged substrate from dilute dispersions. Particles anchored at the air-water interface interact with their neighbors, which leads to spontaneous 2D packing and ordering, as we discussed above. With this interfacial assembly, multicolor patterns with a minimum void can be prepared. For example, strips



containing sparsely-deposited colloids are prepared on a solid substrate using the inkjet printing, on which those with colloids with a different diameter are additionally prepared. When the pattern of strips without any colloidal order is transferred at the interface, the colloidal particles are assembled to form a close-packed hexagonal array, where the strips are brought into contact with adjacent ones, resulting in a color pattern (Figure 9c). The colloidal array can be transferred onto either a hydrophilic substrate by spreading and evaporation of water or hydrophobic substrate through the hydrophobic attraction.151 However, it is challenging to transfer the pattern without deformation due to the undesired pinning of the triple line on the hydrophilic substrate. Furthermore, the resulting patterns have a limited resolution as the patterns designed by inkjet experience the compression not in a highly controlled manner. The simplest and fastest process for producing 2D colloidal crystals is to rub dry particles on substrates without the use of any liquid medium. Using a substrate with a square or hexagonal array of shallow indents, it is possible to produce the corresponding array of colloids by rubbing as a result of the deposition of particles in the indents.159 Without a predefined pattern, a hexagonal array can be simply produced by rubbing. For this, two conditions should be satisfied. First, the adhesion energy between the particle and substrate is required to be larger than that between two particles so that the particles prefer to stick to the substrate; a set of PS particles and polydimethylsiloxane (PDMS) elastomer substrate satisfies this. With this condition, the substrate can be fully covered by particles when a sufficient amount of particles are applied. Second, particle aggregates should disassemble and spread on the substrate by shear force during the rubbing; this condition requires the size of particles larger than 100 nm.138 Therefore, PS particles with a diameter larger than 100 nm


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are simply assembled to form 2D dense packing of a hexagonal array on PDMS substrate by rubbing. The orientation of the hexagonal lattice follows the direction of rubbing (Figure 10a).160 With this rubbing method, 2D colloidal crystals can be patterned. For example, a graphic composed of 2D colloidal crystals can be manually drawn by hand using a PDMS-coated pen (Figure 10b). In the other approach, a PDMS substrate is regioselectively pretreated with ultraviolet-ozone (UVO) through a metal mask, which renders the surface have ultralow adhesion energy between particles and the substrate (Figure 10c). Therefore, particles slip on the treated area during the rubbing so that 2D colloidal crystals are formed only on the untreated surface. Moreover, the orientation of hexagonal lattice can be locally adjusted by controlling the rubbing direction. Therefore, a dual-color pattern can be formed from a single size of particles (Figure 10c-ii). Patterns of 2D colloidal crystals can be prepared by a stamp-assisted transfer,161 in a similar manner to Figure 5e. When an elastomer stamp is compressed on the top surface of 3D colloidal crystals and released, a monolayer of colloids in the top layer is selectively transferred on the surface of the stamp. The transfer of 2D arrays is caused by a stronger adhesion between the elastomer and particles than the interparticle adhesion. The monolayer on the stamp is further transferred on the polymer-coated substrate by contacting and heating above the glass transition temperature. By repeating this process, multicolor patterns can be prepared. Nonclose-packed 2D colloidal crystals can be prepared by spin-coating colloidal dispersions composed of silica particles in a photocurable resin (Figure 10d).162 For a monolayer coating, the angular speed is gradually increased and maintained at each step of spinning, where 29 ACS Paragon Plus Environment


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multiple steps are used. The nonclose-packed array is attributed to compression along the thickness direction during the spin-coating and solvation layers formed on the surface of particles.163 The 2D colloidal crystals are stabilized by photopolymerizing the resin. The resulting films are further subjected to oxygen plasma etching through a metal mask. As the etching removes the polymer matrix and the masked regions retain 2D crystals, a single-color pattern can be produced.

5.

STRUCTURAL-COLOR

PATTERNS

COMPOSED

OF

1D

COLLOIDAL

STRINGS Magnetic particles can be assembled to form chains under an external magnetic field even at low volume fraction.164 Under a magnetic field, magnetic particles align with the field direction and opposite poles attract one another. In addition to the dipole-dipole attraction, a dipole-field force originated from the gradient of the field assembles the particles into chains. While being kept in chains, particles hardly come into contact because a disjoining pressure by solvation layers or an electrostatic repulsions by the surface charges render the particles repulsive. As dipole-dipole interaction is repulsive among chains, the chains stay away from one another. The 1D arrangement of particles in the chains enables the diffraction at the wavelength determined by interparticle separation. As the interparticle separation decreases along with the intensity of magnetic field, the wavelength is readily controllable.165 Using a photocurable dispersion medium for magnetic particles, multicolor patterns can be prepared with a high degree of freedom in design and color. Under an external magnetic field, particles form chains, which can be permanently captured by local UV exposure. The unpolymerized dispersions are further available for a chain formation and structural fixation. 30 ACS Paragon Plus Environment

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Therefore, the repeated combination of field-intensity control and local UV exposure produces various color patterns (Figure 11a).165 As the local UV exposure can be dynamically controlled by a digital micromirror array (DMD) without the use of photomasks, the complex multicolor patterns can be easily produced in high resolution. This technique also enables the production of microdisks with complex color patterns which are useful as barcoded carriers for biological assays.14 The color patterns can be also produced by adjusting the direction of the external magnetic field. As the magnetic particles form chains along the field direction, the orientation of the chains can be varied from the vertical by controlling the field direction. Therefore, two or more distinct domains with different directors of chains can be prepared in a single film using the repeated combination of field-direction control and local UV exposure (Figure 11b).166 The resulting pattern shows an inversion of colors in the pattern depending on the direction of view. Such an observation-angle dependence is appealing for anti-forgery applications. The patterning technique based on the 1D colloidal structure provides high-resolution patterns with complex designs and various colors. Moreover, the delicate process for a crystal formation is not required, which makes the technique simpler and more reproducible. However, it is difficult to make high reflection intensity as 1D chains do not fully occupy the space.

6.

STRUCTURAL-COLOR

PATTERNS

COMPOSED

OF

3D

COLLOIDAL

GLASSES The structural colors developed by crystalline arrays are highly angle-dependent. The iridescence predominantly originates from the anisotropic nature of crystalline colloidal 31 ACS Paragon Plus Environment


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structures. Therefore, the angle-dependency can be reduced by making isotropic structures with short-range order, which are amorphous colloidal arrays or colloidal glasses. To suppress colloidal crystallization and produce colloidal glasses in a controlled manner, three different approaches have been made. The fast concentration of colloidal particles kinetically captures the random dispersions in a fluid state, which is done by centrifugation,167,

168

electrophoresis,169 spray drying,170 or inkjet printing on an absorptive substrate.61 Two different sizes of particles68, 171 or polydisperse particles18 form amorphous arrays as they are unable to form close-packed crystalline structures. The fine control over interparticle potential has enabled the formation of glasses. For example, the aqueous dispersions of colloids forms random aggregates in the presence of salts as electrostatic repulsion is reduced.65 Meanwhile, particles with weakly repulsive interparticle potential behave like hard spheres with large effective diameter. The particles form nonclose-packed amorphous array when the volume fraction is low enough for particles to behave like hard sphere yet high enough to induce interparticle interaction. This is observed for colloids dispersed in ionic liquid172-175 or in monomers77; solvation layer-induced repulsion is dominant over other interactions in both dispersion media. Inkjet printing is a facile way to make amorphous colloidal structures in a high-resolution as well as crystalline structures. To rapidly concentrate particles, the dispersion drops are deposited on a liquid-absorptive porous substrate such as anodic aluminum oxide membrane or photopaper (Figure 12a).61 Due to fast downward flux, the particles are randomly stacked on the surface, making glassy packing. The low contact angle of the dispersion medium on the substrate is required to make the drops thin so that the dispersion medium is fully absorbed.

Using

a

home

inkjet

printer,

three

distinct

dispersions

of

polystyrene@polydopamine (PS@PDA), PS, and silica with different sizes are patterned on a 32 ACS Paragon Plus Environment

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black photopaper to develop three primary colors of magenta, yellow, and cyan, respectively; the black background reduces the undesired multiple scattering. As the size of colloidal structures from a single drop is as small as 100 μm, a color mixing from two or more neighboring structures is also possible to develop secondary color. Spray-drying method provides a simple means to create glass structures as drying of a dispersion medium in the tiny aerosol is fast. In particular, a highly volatile medium such as methanol further accelerates the drying process. When the particles are consolidated in the aerosol drops before being deposited on a target surface, the resulting structures are spherical granules composed of glassy packing of particles (Figure 12b).64 Although the spherical granules show white appearance, incorporation of carbon black nanoparticles reduces multiple scattering and enhances the color contrast. The spray-drying of colloidal particles usually results in spherical granules. However, when the size of aerosol drops is very small so that only a few particles are contained, fast evaporation leads to nonspherical clusters; a polymer binder can be included in the droplet to increase the stability of resulting assemblies. The clusters form amorphous arrays in a film format when deposited on a target surface (Figure 12c).8 In the presence of carbon black, the amorphous arrays show pronounced colors. Using masks with a hole pattern, multicolor patterns can be prepared, where consecutive deposition of two different sizes of particles in the same position results in color mixing from two distinct layers. This method produces angle-independent color patterns that can be formed even on the surface of fabrics. The spray coating can be used to deposit the dispersions of bidisperse colloidal particles. The aerosol droplets are not fully consolidated so that the droplets spread on a target surface to form a film. As two different sizes of particles are concentrated during the drying from the film, they form amorphous arrays (Figure 12d).70 The structural colors are vivid in the 33 ACS Paragon Plus Environment


presence of graphene nanosheets as the nanosheets reduce multiple scattering. As bidisperse colloidal particles form amorphous arrays without fast concentration, a simple drying can be used to develop non-iridescent colors.68,

171

For example, monodisperse PS particles and

light-absorbing particles obtained from a cuttlefish ink are simultaneously dispersed in water, which is dried in patterned trenches (Figure 12e); the particles from the cuttlefish ink are monodisperse and has an average diameter of 110 nm.69 The particles from the cuttlefish ink whose diameter is different from PS particles suppress the crystallization of PS particles and at the same time, reduce multiple scattering, developing non-iridesecent structural colors. In the amorphous colloidal arrays, a cavity resonance usually causes a back-scattering which makes the structural resonance less predominant. To exclude the cavity resonance out of visible range, inverted glass structures composed of an amorphous array of air cavities have been prepared. Particles dispersed in a certain photocurable monomer have a solvation layer on the surface, which renders the particles weakly repulsive. The particles form crystalline structures when they are highly concentrated, whereas they form a fluidic phase when diluted. At an intermediate concentration, the particles form a nonclose-packed amorphous array with short-range order, which can be captured by photopolymerization. The selective removal of the particles from the polymerized matrix yields inverse glass structures. As the inverse glass has the cavity resonance in the UV region, the structural resonance develops a pronounced color. In addition, the photocurable dispersions can be easily patterned by photolithography (Figure 12f).77

7. DYNAMIC CHANGE OF STRUCTURAL-COLOR PATTERNS BY EXTERNAL STIMULI 34 ACS Paragon Plus Environment

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There have been many reports on the dynamic change of color patterns caused by controlled external stimuli. The advanced property is highly demanded in various applications including anti-counterfeiting, colorimetric sensing, and color-tunable painting. The dynamic change is somewhat restricted in chemical colors. As structural colors are tunable by adjusting lattice constant or refractive index, dynamic change can be achieved through the elaborate design of materials and structures. In the following sections, we categorize dynamic changes of the color pattern according to the mechanisms of the change. 7.1. Swelling. Polymeric colloidal structures can be swollen by solvent with high affinity to the polymer. Water is a good solvent to swell a hydrogel and organic solvents are appropriate for crosslinked hydrophobic polymers. The swelling leads to a red-shift of reflective color because it increases the lattice constant.21-25 As the swollen matrix recovers the original structure when the solvent fully evaporates, the structural color is also reversibly recovered. If the photonic film is designed to have different degrees of swelling depending on the region, the hidden pattern can be disclosed when it is immersed in an appropriate solvent.176 For example, 1D colloidal chains of magnetic particles are embedded in a hydrogel containing trimethoxysilyl groups. The photonic film is treated by NaOH using a protection mask, which locally crosslinks trimethoxysilyl groups. The film shows no pattern in the dry state. However, the film discloses a hidden pattern when it is immersed in water. The parts crosslinked by trimethoxysilyl groups are slightly swollen, while those untreated are highly swollen, thereby revealing the hidden pattern with two different colors (Figure 13a). The film hides the pattern again when water is fully dried. 7.2. Liquid infiltration. The refractive index influences the diffraction wavelength so that infiltration of liquid into inverse opals causes a red-shift of structural color. If the inverse opal is regioselectively treated to allow spontaneous infiltration of specific liquid in local regions, 35 ACS Paragon Plus Environment


a hidden pattern is disclosed only when the specific liquid is dropped on the inverse opal. To implement the local modification of surface property, silica inverse opals are used.177 The entire surfaces of pores are treated by a first hydrophobic silane, which is then treated by oxygen plasma with a shadow mask. The plasma treatment removes the hydrophobic silane on the surfaces unprotected by the mask. The bare silica surfaces are further subjected to chemical treatment with a second hydrophobic silane. With a shadow mask, the second silane is also regioselectively removed. The resulting inverse opals have three different regions of bare silica surfaces, the first-silane-coated surfaces, and the second-silane-coated surfaces (Figure 13b); the number of domains with different surface properties can be further increased by repeating the coating and etching processes. The different surface properties result in different threshold contact angles for spontaneous liquid infiltration. Therefore, a hidden pattern can be partially or fully disclosed depending on the selection of an infiltration liquid. The number of domains with different surface properties determines the steps of partial disclosing. This material can be used for a multi-level encryption and an optical test paper that measures surface tension. The regioselective surface treatment using a common shadow mask has a limited resolution of patterning. To improve the resolution, a photoresist is micropatterned by photolithography on the surface of the composite composed of silica opals and crosslinked-polymer matrix. Silica opal is removed and the inverse opal is treated by reactive ion etching with oxygen gas. As the micropatterned photoresist serves as a shadow mask, unprotected regions are selectively rendered to be hydrophilic. As the shadow mask has a conformal contact on the inverse opal, the feature size of the resulting pattern can be as small as 10 μm.178 7.3. Vapor adsorption. Instead of liquid, vapor can be also used to modulate the refractive index. When ethanol vapor is exposed to mesoporous structure, the vapor is adsorbed on the 36 ACS Paragon Plus Environment

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surfaces of pores by capillary condensation. Therefore, opal structures composed of coreshell particles with a dense silica core and mesoporous silica shell show a red-shift of structural color when exposed to the vapor.179 In particular, the degree of condensation or equivalently degree of color change is controlled by adjusting the relative volume ratio of the mesoporous shell in the particles. To show a graphical color change, three different particles of dense silica only, thin mesoporous shell, and thick mesoporous shell are respectively printed by inkjet to form a complex pattern of an apple tree (Figure 13c). The trunk, leaves, and apples are made of dense silica particles, thin-shelled particles, and thick-shelled particles, respectively. As the diameters of three different particles are the same, all parts show the same color. Upon exposure to ethanol vapor, the apples turn from green to red and the leaves turn to yellow, whereas the trunk maintains green. The original single-color graphic is recovered when the condensed ethanol is evaporated. 7.4. Deformation. To make the color change in photonic patterns discussed above, liquid or vapor is required. The stimulus easily applicable without the additional supply of materials is mechanical stress. The photonic film can be designed to show a hidden color pattern when subjected to compression or stretching.180 For example, crystallites composed of the closepacked array can be captured in an elastomeric film and the film can be locally hardened by an additionally crosslinking monomer that forms a rigid polymer. The film shows a blue-shift of color in the elastic regions and no change in the hardened regions when stretched; the blueshift is caused by the reduction of interlayer distance along thickness direction upon the stretching along the lateral direction. When the film is compressed, the elastic regions turn from green to red as lattice expands along the thickness direction. The color change by stretching and compression is fully reversible as the deformation is elastic.



Deformation can be used to switch on and off structural colors.181 Amorphous arrays of silica particles are prepared by a spray coating, whose interstitial voids are fully occupied by index-matched elastomer. Therefore, the composite is highly transparent. However, when the composite film is stretched, the contact between silica particles and the elastomer fails, forming voids around the particles along the stretching direction (Figure 14a). As the refractive index of void is 1 which is much smaller than silica and elastomer, a structural color is developed from the amorphous arrays.

When the amorphous arrays are

regioselectively deposited, only the areas with the arrays turn from transparent to colored, revealing the hidden pattern. 7.5. Electric field. The 2D colloidal crystals can be dynamically assembled by electrohydrodynamic (EHD) flow under an alternating electric field (AEF) and disassembled by thermal energy without the field for charged particles dispersed in an aqueous solution of salt.182-184 To make patterns of 2D colloidal crystals, two different strategies have been used. One is an electrode whose surface is regioselectively covered with a micropatterned photoresist. Under an AEF, the particles are gathered and assembled in the photoresist-free regions.185 The interparticle distance in the hexagonal array is controlled with the field strength and the frequency. The colloidal array is disassembled when the field is turned off. In addition, the pattern can be permanently fixed by applying a direct electric field. The other is an electrode at which 1D colloidal string is pre-formed by dewetting-assisted deposition.186 Under an AEF, particles are assembled to a 2D hexagonal array around the string, which results in structural colors through grating diffraction (Figure 14b).187 The array disassembles by thermal energy when the field is off, losing the color pattern. This method provides a very well-defined hexagonal array with a very low density of defects or dislocations. In addition, this dynamic switching of the structural color on and off is promising for displays. 38 ACS Paragon Plus Environment

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7.6. Magnetic field. The magnetic particles show a brown absorption color in the absence of an external magnetic field. When the particles form 1D chains under a magnetic field, the structural colors are developed. Therefore, structural color is able to be easily switched on and off. Using this principle, the color patterns are designed to be disclosed only when an external magnetic field is applied. For example, two different dispersions of magnetic particles in ethylene glycol with different sizes are respectively emulsified into elastomer precursors. The two emulsions are then used to make macroscopic patterns manually.188, 189 The pattern is not discernable in the absence of a magnetic field as both dispersion drops show a brown color. When the magnetic field is applied, the drops show two different colors due to different sizes of particles, thereby disclosing the color pattern. The color developed by 1D chains is restricted to one from the rainbow. When two different sizes of magnetic nanoparticles are dispersed in the same medium, they can form two distinct chains one of which is composed of large particles and the other composed of small particles (Figure 14c).189 The simultaneous formation of two distinct chains causes the diffraction at two different wavelengths, which results in color mixing. Therefore, an enhanced variety of color can be formulated. The magneto-responsive color pattern can be prepared in a more controlled manner. The elastomer film containing the drops of magnetic particle dispersions is first prepared, which is then regioselectively irradiated by UV through a photomask.190 The elastomer exposed to UV degrades, which leads to the formation of the macroporous structure as drops leak out. As magnetic particles are adsorbed on the surfaces of pores during the leaking, the UV-exposed region shows an invariable brownish absorption color. The intact drops in the regions without UV exposure turn from brown to a structural color upon the magnetic field applied. Therefore,



the film only shows the color pattern on a brown background when the magnetic field is applied. This approach improves the resolution of color patterns.

8. CONCLUSIONS Structural colors are nonfading, tunable, and potentially non-toxic. These unique features distinguished from pigment colors render the structural colors promising for various applications. In particular, the patterning of structural colors provides additional values to the materials. There are intense demands on the structural-color patterns in various industries including cosmetics, apparels, security, bioanalysis, sensors, electrical appliances, automobiles, and many others. For example, unique impression makes the structural-color patterns appealing as the aesthetic tags on cosmetic containers, apparels, and electrical appliances. The color patterns are promising as anti-counterfeiting patches as they are uncopiable, iridescent, and tunable. The unique shape of reflectance or transmittance spectra can serve as invisible optical barcodes to enhance authenticity. As the color patterns can be designed to show a dynamic change of colors or graphics depending on the external stimuli of environmental conditions or concentration of specific molecules, they are valuable as intuitive standalone colorimetric sensors. Quantitative measurement is also possible with spectral analysis. There have been intense studies on enhancing optical performance and patterning structural colors in a controlled and reproducible manner. The study and development have improved the level of technologies for structural coloration and pattern formation. There are various materials, structures, production methods, optical properties for structural-color patterns as we have discussed throughout the paper. Therefore, we can select one combination among 40 ACS Paragon Plus Environment

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available sets according to requirements for the target applications. However, there remain important challenges for the pragmatic uses of structural-color patterns. First, the production cost is expected to be very high. Although colloidal self-assembly is relatively inexpensive and scalable, it is a prerequisite to devise and optimize manufacturing processes for producing the color patterns with affordable cost. Second, the structural stability should be improved according to the target applications even if optical properties and production costs are satisfactory. As the colors originate from elaborate colloidal structures or their derivatives, they disappear during the use under mechanical stress or high temperature unless sufficient stability is secured. For uses in a thermal condition, the photonic structures should be made of materials with high thermal resistance. To use patterns under mechanical stresses, durable materials should be selected to compose the photonic structures. If the photonic patterns are used on flexible substrates, the photonic structures should also be made of flexible materials. For example, anti-counterfeiting patches for a banknote should be made of flexible polymers such as polyvinylidene fluoride.114 Third, color saturation and brightness should be further improved. Multiple scattering and incoherent scattering are not negligible for many crystalline colloidal structures as well as amorphous structures, lowering a color saturation. Although the use of a black background or low contrast of refractive index between particles and matrix reduces the undesired scattering, these restrict the applications. Recently, lightabsorptive nanoparticles have been incorporated to colloidal structures to increase color saturation and exhibit consistent color regardless of backgrounds, as we discussed in section 2.3. Structural coloration for colloidal glasses. Fourth, the response time of the dynamic color change is required to be further reduced for many applications. Although stretching-, magnetic-field-, and liquid-infiltration-induced color changes are fast enough to use them for most applications except active displays, color change based on the swelling and deswelling of the matrix is usually slow. Another issue is the angle dependence of structural color. All 41 ACS Paragon Plus Environment


colloidal structures show a color change depending on angles for specular reflection even for amorphous structures and spherical geometries although the dependence is slightly weaker. Although the strong iridescence is beneficial for some applications, such as aesthetic coatings and anti-counterfeitings, it is not preferred in many others such as sensors and displays. The principles of structural coloration and patterning methods have been well-established. We believe that the aforementioned remaining issues will be successfully addressed by additional research and development and structural-color patterns will be commercialized in the future.


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Figure 1. Patterning methods of colloidal arrays with six photonic structures



Figure 2. Principles of coloration by colloidal crystals. (a) Bragg’s diffraction by periodic dielectric slabs which is a model for 3D colloidal crystals. (b) Thin-film interference by a 2D colloidal crystals in a monolayer. (c) Grating diffraction by 2D colloidal crystals.


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Figure 3. (a) Three different configurations for evaluating angle-dependence of structural colors: (i) near-backward scattering, (ii) specular reflection, and (iii) diffusive scattering. (b) Common and different features of colloidal crystals and colloidal glasses.



Figure 4. Patterning of opal structures using confinement by solid walls or free interfaces. (a) Colloidal crystallization in microchannel by evaporation-induced concentration at open end: (i) Schematic illustration and (ii, iii) scanning electron microscopy (SEM) images of patterned opal structure. (b) Colloidal crystallization in microchannel by centrifugal forceinduced concentration: (i) Schematic of microchannel design and (ii, iii) optical microscope (OM) and SEM images of patterned opal structure. (c) Localized deposition of opal structures using electrocapillary force: (i, ii) Designs of an electrode pattern and microchamber array, (iii) OM image of dual-color pattern, (iv) SEM image of opal structures formed in one chamber. (d) Colloidal crystallization in open microchannels by dip-coating: (i) Schematic illustration and (ii, iii) OM and SEM images of opal structures formed in trenches. (e) Selective formation of opal on hydrophilic regions in a chemically-patterned substrate: (i) Schematic illustration showing the procedure for regioselective hydrophilic treatment by UVinduced photocatalytic degradation of hydrophobic moiety on a titania substrate and (ii) image of a fish-shaped opal pattern. Reproduced with permission from ref. 79 (a-ii, iii), 82 (b), 84 (c), 86 (d-ii, iii), and 90 (e). Copyright WILEY-VCH (a-ii, iii, c, d-ii, iii, and e), The Royal Society of Chemistry (b).


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Figure 5. Patterning of opal structures using local deposition or regioselective removal. (a) Inkjet printing: (i) Scheme of drop deposition and evaporation-induced colloidal assembly, (ii) SEM image of disk-shaped colloidal structure formed from a single drop, and (iii) image of a complex pattern formed on a silicon wafer. (b) Spray coating with a mask: (i) Scheme of the spray coating, (ii,iii) images of multi-color patterns, and (iv) SEM image of colloidal crystals. (c) Regioselective removal of first opal and consecutive deposition of second opal: (i) Scheme of the procedure and (ii) SEM image of the boundary between two distinct opal structures made of two different sizes of particles. Inset of (ii) is OM image of the dual-color pattern. (d) Regioselective compression of pre-annealed opal structures by stamping: (i) Scheme of stamping, (ii,iii) SEM images of the pattern and the boundary, and (iv,v) crosssectional SEM images of the uncompressed and compressed regions. Inset of (ii) is an OM image of the pattern. (e) Regioselective lifting-off of pristine opal by stamping: (i) Scheme of the procedure, (iii) OM image of opal film with a hole pattern and transferred opal dots, and (iv) SEM image of the boundary of pattern. Reproduced with permission from ref. 99 (a), 108 (b), 109 (c), and 110 (d and e). Copyright WILEY-VCH (a), Elsevier (b), The Royal Society of Chemistry (c, d, and e).



Figure 6. Patterning of inverse opal structures. (a) Photolithography-featured micropatterns obtained by using a negative photoresist as a matrix of inverse opal: (i) Schemes for the procedure and (ii-iv) OM images of micropatterns composed of red squares, green squares, and RGB pixels. Insets of (ii) and (iii) are SEM images of top surfaces of the inverse opals. (b) Regioselective collapse of polymeric inverse opal by stamping: (i) Schemes for the procedure, (ii) SEM images showing the boundary between intact and collapsed inverse opals and the cross-section of the collapsed region, and (iii) series of images showing angledependent color change for the patterns. (c) Regioselective recovery of collapsed inverse opal made of shape-memory polymer by stamping: (i) Scheme showing capillarity-induced collapse of inverse opal during drying and recovery of the original structure by contact pressure, (ii, iii) SEM images of recovered and collapsed structures, and (iv) image of a fingerprint pattern formed by the regioselective recovery. Reproduced with permission from ref. 119 (a), 114 (b), and 115 (c). Copyright WILEY-VCH (a, b), and Nature Publishing Group (c). 48 ACS Paragon Plus Environment

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Figure 7. Multicolor patterning through regioselective modulation of single-colored inverse opal. (a) Controlled pore filling with a negative photoresist by controlled UV exposure: (i) Scheme of the procedure for the preparation of RGB pixels, (ii) SEM images of empty pores (A), partially-filled pores (B), and mostly-filled pores (C), and (iii) OM image of pixelated RGB pattern. (b) Regioselective compression of inverse opal made of a negative photoresist: (i) Scheme of the procedure to produce dual-color patterns, (ii) cross-sectional SEM image showing uncompressed (red arrow) and compressed (green arrow) regions, (iii, iv) OM images of dual-color line pattern and RGB pixels, and (v) image of a macroscopic pattern with a design of 2016 Olympic logo. (c) UV-induced swelling of inverse opal hydrogel and visible light-induced recovery: (i) Conformational change of azobenzene groups from trans to cis by UV and from cis to trans by visible light, (ii) scheme of localized light exposure through a photomask, and (iii) OM images of the recovered (left) and patterned (right) inverse opal by visible and UV, respectively. (d) Regioselective deposition of metal to make dual-color pattern with photonic stopband and surface plasmon resonance: (i) Scheme of procedure, (ii,iii) cross-sectional SEM images of metal-free inverse opal and metal-deposited inverse opal, and (iv) OM image of the dot pattern. Arrows in (iii) indicate the metal deposited. Reproduced with permission from ref. 121 (a), 122 (b), 116 (c), and 125 (d). Copyright WILEY-VCH (a, b, c, and d).



Figure 8. Patterning of nonclose-packed colloidal arrays. (a) Photolithograpically-featured pattern: (i) Scheme of the procedure, (ii) images of micropatterns observed at two different angles, and (iii) cross-sectional SEM image showing nonclose-packed array. (b) Regioselective compression of the elastomeric photonic film by stamping: (i) Scheme showing compression of lattice under relief regions and expansion under engraved regions, (ii) OM image of dual-color pattern formed by the stamping, and (iii) cross-sectional SEM image showing nonclose-packed array embedded in elastomer. (c) Electric-field-induced lattice compression and fixation by UV exposure: (i) Scheme showing multicolor pattering through three steps, (ii) image of a flower prepared by repeated steps, and (iii, iv) crosssectional SEM images of the lattice formed by voltages of 0 V and 3.3 V. Reproduced with permission from ref. 9 (a), 11 (b), and 132 (c). Copyright American Chemical Society (a, b), and WILEY-VCH (c).


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Figure 9. Patterning of 2D colloidal arrays. (a) Regioselective transfer of colloidal monolayer at air-water interface to chemically-patterned substrate by self-driven climbing: (i-ii) Schemes for the procedure of patterning and self-driven climbing, (iii) a pattern of 2D colloidal crystals transferred on the glass slide, and (iv) SEM image of the hexagonal array on the slide. (b) Inkjet printing: (i) Scheme showing the formation of a colloidal monolayer from the droplet deposited on a solid substrate, (ii, iii) SEM images showing the dot pattern and cross-section of a monolayer, and (iv) image of the inkjet-printed pattern. (c) Interfacial assembly of inkjet-printed particles at low density: (i) Scheme showing the formation of close-packed array for the particles at air-water interface that are transferred from solid substrate, (ii) image of inkjete-printed stripe patterns composed of different sizes of particles, (iii) SEM image of sparcely-deposited particles in the stripe (ii), (iv) image of the stripe pattern transferred on a hydrophilic substrate from air-water interface after forming closepacked array of particles, (v) SEM image showing the boundary between two different domains. Reproduced with permission from ref. 157 (a), 47 (b), and 158 (c). Copyright The Royal Society of Chemistry (a-iii, iv, c) and Nature Publishing Group (b).



Figure 10. Patterning of 2D colloidal arrays. (a-c) Mechanical rubbing: (a) (i) Scheme for rubbing process with elastomer block on elastomer substrate, and (ii) otical and SEM image showing the rubbing-direction dependent change of lattice orientation. (b) (i) Scheme for a handwriting with an elastomer-coated pen, and (ii) images of a structural-color painting under two different direction of light illumination. (c) (i) Scheme for the regioselective treatment of an elastomer substrate with ultraviolet-ozone (UVO) using a metal mask and subseqent deposition of 2D colloidal crytsals by rubbing, (ii) image of a pattern with two differnet orientation of hexagonal lattice, and (iii) OM image of the pattern. (d) Patterning of nonclosepacked 2D crystals formed by spin-coating through regioselective oxygen plasma etcihng: (i) Images of a film and pattern containing 2D crystals, (ii, iii) SEM images showing the crosssection of spin-coated monolayer and top surface of the pattern. Reproduced with permission from ref. 160 (a), and 162 (b). Copyright Nature Publishing Group (a-ii, iv, v, vi, vii), and American Institute of Physics (b).


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Figure 11. Patterning of 1D colloidal arrays of magnetic particles. (a) Control of structural color with the intensity of magnetic field and UV-induced fixation: (i) Scheme showing the procedure for multicolor patterning, (ii, iii) images of multicolor patterns with designs of a tree and a butterfly, and (iv) cross-sectional SEM image of 1D chains. (b) Control of chain orientation by adjusting the direction of magnetic field: (i) Scheme of the procedure for production of a photonic pattern with two different orientations of chains and (ii) images of a pattern showing color inversion depending on the observation angle. Reproduced with permission from ref. 165 (a), and 166 (b). Copyright Nature Publishing Group (a), and American Chemical Society (b).



Figure 12. Patterning of colloidal glass structures. (a) Inkjet printing on a liquid-absorptive substrate: (i) Scheme showing liquid infiltration-driven colloidal assembly, (ii) image of a multi-color painting, and (iii, iv) SEM images of colloidal structure formed from single droplet and amorphous colloidal arrays in the structure. (b) Spray drying of dispersions and subsequent deposition: (i) Scheme of spray-drying printing, (ii) image of a dark color pattern, and (iii, iv) SEM images of spherical assemblies and the surface morphology. Inset of (iv) is 2D Fourier power spectra. (c) Spray drying with microdroplets: (i,ii) Schemes of microdroplet formation and deposition of clusters on fabric through a mask, (iii,iv) images of silk fabric with a color pattern which are free from stress and stretched, and (v) SEM image of amorphous structures. (d) Spray-coating of bidisperse colloids: (i) Scheme of spraycoating, (ii) images of spray-coated patterns, and (iii) SEM of amorphous colloidal arrays containing graphene nanosheets. (e) Drying of bidisperse colloids of PS particles and lightabsorbing particles obtained from a cuttlefish ink: (i,ii) Images of a pattern taken at two different observation directions and (iii) SEM image of the structures where red-marked particles are the ink particles. (f) Patterning of polymeric inverse glasses by photolithography: (i,ii) Images of a pattern observed at two different angles of 30° and 60° under diffusive light condition and (iii) SEM image of inverse glass structure. Reproduced 54 ACS Paragon Plus Environment

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with permission from ref. 61 (a), and 64 (b), 8 (c), 70 (d), 69 (e), and 77 (f). Copyright WILEY-VCH (a, b, d, and e), and American Chemical Society (c and f).



Figure 13. Dynamic change of structural-color patterns by liquid or vapor. (a) Disclosure of a hidden pattern by local swelling of a film containing 1D chains: (i) Scheme of the procedure for production of a pattern with two different crosslinking densities and (ii, iii) images of a pattern before and after immersion in water. (b) Step-wise disclosure of hidden patterns by regioselective infiltration of liquids into chemically-modified silica inverse opal: (i) Scheme of the procedure for regioselective chemical treatment of inverse opal, (ii, iii) SEM images showing top and cross-section of silica inverse opal, and (iv) images of inverse opal chemically patterned which is in air or submerged in liquids as denoted in each panel, where mixtures of ethanol and water are used. (c) Color change of opal composed of mesoporous particles by condensation of ethanol vapor: (i) Scheme of inkjet printing, (ii) transmission electron microscopy (TEM) images of dense silica particles (A), core-shell particles with thin mesoporous shell (B), and thick mesoporous shell (C), and (iii, iv) images of a pattern with a design of apple tree before and after exposure to ethanol vapor, where trunk, leaves, and apples are composed of particles A, B, and C, respectively. Reproduced with permission from ref. 176 (a), 177 (b), and 179 (c). Copyright The Royal Society of Chemistry (a), American Chemical Society (b, and c).


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Figure 14. Dynamic change of structural-color patterns by stretching or magnetic field. (a) Stretching-induced coloration: (i) Scheme showing the stretching-induced formation of voids, (ii-iii) image of an elastomeric film free from strain and stretched, at which amorpous arrays of index-matched particles is embedded in the surrounding area of “PENN”, and (iv) crosssectional SEM images of pristine and stretched film. (b) Electric field-induced structural coloration: (i, ii) optical image and OM image of a pattern of 2D colloidal crystals assembled by an alternating electric field and (iii) OM images showing the formation of 2D crystals along pre-deposited 1D string. (c) Magnetic field-induced coloration: (i,ii) Schemes of the procedure for making a pattern and magnetic field-induced formation of two distinct chains of two different sizes of magnetic particles, and (iii,iv) images of the pattern without and with the magnetic field. Reproduced with permission from ref. 181 (a), 187 (b) and 189 (c). Copyright WILEY-VCH (a), American Chemical Society (b), The Royal Society of Chemistry (c).



AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (S.-H.K.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by the National Research Foundation (NRF) (NRF2017R1A2A2A05001156, NRF-2018M3A7B8060189) funded by the Ministry of Science, ICT and Future Planning (MSIP) and the Agency for Defense Development of Korea (17113-706-011).

References (1) Marlow, F.; Muldarisnur; Sharifi, P.; Brinkmann, R.; Mendive, C. Opals: Status and Prospects. Angew. Chem. Int. Ed. 2009, 48, 6212-6233. (2) Smith, G. S. Structural Color of Morpho Butterflies. Am. J. Phys. 2009, 77, 1010-1019. (3) Dong, B. Q.; Liu, X. H.; Zhan, T. R.; Jiang, L. P.; Yin, H. W.; Liu, F.; Zi, J. Structural Coloration and Photonic Pseudogap in Natural Random Close-Packing Photonic Structures. Opt. Express 2010, 18, 14430-14438. 58 ACS Paragon Plus Environment

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(4) Shi, L.; Zhang, Y. F.; Dong, B. Q.; Zhan, T. R.; Liu, X. H.; Zi, J. Amorphous Photonic Crystals with Only Short-Range Order. Adv. Mater. 2013, 25, 5314-5320. (5) Andreeva, Y. I.; Drozdov, A. S.; Fakhardo, A. F.; Cheplagin, N. A.; Shtil, A. A.; Vinogradov, V. V. The Controllable Destabilization Route for Synthesis of Low Cytotoxic Magnetic Nanospheres with Photonic Response. Sci. Rep. 2017, 7, 11343. (6) Kamita, G.; Frka-Petesic, B.; Allard, A.; Dargaud, M.; King, K.; Dumanli, A. G.; Vignolini, S. Biocompatible and Sustainable Optical Strain Sensors for Large-Area Applications. Adv. Opt. Mater. 2016, 4, 1950-1954. (7) Kim, J.-W.; Lee, J.-S.; Kim, S.-H. Biodegradable Inverse Opals with Controlled Discoloration. Adv. Mater. Interfaces 2018, 5, 1701658. (8) Li, Q. S.; Zhang, Y. F.; Shi, L.; Qiu, H. H.; Zhang, S. M.; Qi, N.; Hu, J. C.; Yuan, W.; Zhang, X. H.; Zhang, K. Q. Additive Mixing and Conformal Coating of Noniridescent Structural Colors with Robust Mechanical Properties Fabricated by Atomization Deposition. ACS Nano 2018, 12, 3095-3102. (9) Lee, H. S.; Shim, T. S.; Hwang, H.; Yang, S.-M.; Kim, S.-H. Colloidal Photonic Crystals toward Structural Color Palettes for Security Materials. Chem. Mater. 2013, 25, 2684-2690. (10) Heo, Y.; Lee, S. Y.; Kim, J. W.; Jeon, T. Y.; Kim, S.-H. Controlled Insertion of Planar Defect in Inverse Opals for Anticounterfeiting Applications. ACS Appl. Mater. Interfaces 2017, 9, 43098-43104. (11) Lee, G. H.; Choi, T. M.; Kim, B.; Han, S. H.; Lee, J. M.; Kim, S.-H. ChameleonInspired Mechanochromic Photonic Films Composed of Non-Close-Packed Colloidal Arrays. ACS Nano 2017, 11, 11350-11357. (12) Alexeev, V. L. Photonic Crystal Glucose-Sensing Material for Noninvasive Monitoring of Glucose in Tear Fluid. Clin. Chem. 2004, 50, 2353-2360.



(13) Zhao, Y. J.; Zhao, X. W.; Sun, C.; Li, J.; Zhu, R.; Gu, Z. Z. Encoded Silica Colloidal Crystal Beads as Supports for Potential Multiplex Immunoassay. Anal. Chem. 2008, 80, 1598-1605. (14) Lee, H.; Kim, J.; Kim, H.; Kim, J.; Kwon, S. Colour-Barcoded Magnetic Microparticles for Multiplexed Bioassays. Nat. Mater. 2010, 9, 745-749. (15) Zhao, Y. J.; Zhao, X. W.; Gu, Z. Z. Photonic Crystals in Bioassays. Adv. Funct. Mater. 2010, 20, 2970-2988. (16) Zhao, Y. J.; Zhao, X. W.; Hu, J.; Xu, M.; Zhao, W. J.; Sun, L. G.; Zhu, C.; Xu, H.; Gu, Z. Z. Encoded Porous Beads for Label-Free Multiplex Detection of Tumor Markers. Adv. Mater. 2009, 21, 569-572. (17) Puzzo, D. P.; Arsenault, A. C.; Manners, I.; Ozin, G. A. Electroactive Inverse Opal: A Single Material for All Colors. Angew. Chem. Int. Ed. 2009, 48, 943-947. (18) Lee, I.; Kim, D.; Kal, J.; Baek, H.; Kwak, D.; Go, D.; Kim, E.; Kang, C.; Chung, J.; Jang, Y.; Ji, S.; Joo, J.; Kang, Y. Quasi-Amorphous Colloidal Structures for Electrically Tunable Full-Color Photonic Pixels with Angle-Independency. Adv. Mater. 2010, 22, 4973-4977. (19) Shim, T. S.; Kim, S.-H.; Sim, J. Y.; Lim, J.-M.; Yang, S.-M. Dynamic Modulation of Photonic Bandgaps in Crystalline Colloidal Arrays Under Electric Field. Adv. Mater. 2010, 22, 4494-4498. (20) Arsenault, A. C.; Puzzo, D. P.; Manners, I.; Ozin, G. A. Photonic-Crystal Full-Colour Displays. Nat. Photon. 2007, 1, 468-472. (21) Ge, J.; Goebl, J.; He, L.; Lu, Z.; Yin, Y. Rewritable Photonic Paper with Hygroscopic Salt Solution as Ink. Adv. Mater. 2009, 21, 4259-4264. (22) Hu, H.; Chen, Q.-W.; Wang, H.; Li, R.; Zhong, W. Reusable Photonic Wordpad with Water as Ink Prepared by Radical Polymerization. J. Mater. Chem. 2011, 21, 13062-13067.


Page 60 of 80

Page 61 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Fudouzi, H.; Xia, Y. Photonic Papers and Inks: Color Writing with Colorless Materials. Adv. Mater. 2003, 15, 892-896. (24) Fudouzi, H.; Xia, Y. Colloidal Crystals with Tunable Colors and Their Use as Photonic Papers. Langmuir 2003, 19, 9653-9660. (25) Gu, H.; Zhao, Y.; Cheng, Y.; Xie, Z.; Rong, F.; Li, J.; Wang, B.; Fu, D.; Gu, Z. Tailoring Colloidal Photonic Crystals with Wide Viewing Angles. Small 2013, 9, 2266-2271. (26) Choi, S. Y.; Mamak, M.; von Freymann, G.; Chopra, N.; Ozin, G. A. Mesoporous Bragg stack color tunable sensors. Nano Lett. 2006, 6, 2456-2461. (27) Wang, Z.; Zhang, J.; Xie, J.; Wang, Z.; Yin, Y.; Li, J.; Li, Y.; Liang, S.; Zhang, L.; Cui, L.; Zhang, H.; Yang, B. Polymer Bragg Stack as Color Tunable Photonic Paper. J. Mater. Chem. 2012, 22, 7887-7893. (28) Peng, Y.-S.; Xu, B.; Ye, X.-L.; Niu, J.-B.; Jia, R.; Wang, Z.-G. Fabrication of High Quality Two-Dimensional Photonic Crystal Mask Layer Patterns. Opt. Quant. Electron. 2009, 41, 151-158. (29) Campbell, M.; Sharp, D. N.; Harrison, M. T.; Denning, R. G.; Turberfield, A. J. Fabrication of Photonic Crystals for the Visible Spectrum by Holographic Lithography. Nature 2000, 404, 53-56. (30) Dutta, H. S.; Goyal, A. K.; Srivastava, V.; Pal, S. Coupling Light in Photonic Crystal Waveguides: A review. Photonics and Nanostruct. 2016, 20, 41-58. (31) Melati, D.; Melloni, A.; Morichetti, F. Real Photonic Waveguides: Guiding Light Through Imperfections. Adv. Opt. Photonics 2014, 6, 156-224. (32) Painter, O. Two-Dimensional Photonic Band-Gap Defect Mode Laser. Science 1999, 284, 1819-1821.



(33) Park, H. G.; Kim, S.-H.; Kwon, S. H.; Ju, Y. G.; Yang, J. K.; Baek, J. H.; Kim, S. B.; Lee, Y. H. Electrically Driven Single-Cell Photonic Crystal Laser. Science 2004, 305, 14441447. (34) Kim, S.-H.; Lee, S. Y.; Yang, S.-M.; Yi, G. R. Self-Assembled Colloidal Structures for Photonics. NPG Asia Mater. 2011, 3, 25-33. (35) Broer, D. J.; Lub, J.; Mol, G. N. Wide-Band Reflective Polarizers from Cholesteric Polymer Networks with a Pitch Gradient. Nature 1995, 378, 467-469. (36) Qin, L.; Gu, W.; Wei, J.; Yu, Y. Piecewise Phototuning of Self-Organized Helical Superstructures. Adv. Mater. 2018, 30, 1704941. (37) Moirangthem, M.; Schenning, A. P. H. J. Full Color Camouflage in a Printable Photonic Blue-Colored Polymer. ACS Appl. Mater. Interfaces 2018, 10, 4168-4172. (38) Kang, Y.; Walish, J. J.; Gorishnyy, T.; Thomas, E. L. Broad-Wavelength-Range Chemically Tunable Block-Copolymer Photonic Gels. Nat. Mater. 2007, 6, 957-960. (39) Takeoka, Y. Angle-Independent Structural Coloured Amorphous Arrays. J. Mater. Chem. 2012, 22, 23299-23309. (40) Wiersma, D. S. Disordered Photonics. Nat. Photon. 2013, 7, 188-196. (41) Galisteo-Lopez, J. F.; Ibisate, M.; Sapienza, R.; Froufe-Perez, L. S.; Blanco, A.; Lopez, C. Self-Assembled Photonic Structures. Adv. Mater. 2011, 23, 30-69. (42) Hou, J.; Li, M. Z.; Song, Y. L. Patterned Colloidal Photonic Crystals. Angew. Chem. Int. Ed. 2018, 57, 2544-2553. (43) Yablonovitch, E. Photonic Crystals: Semiconductors of Light. Sci. Am. 2001, 285, 47-51. (44) Koenderink, A. F.; Vos, W. L. Optical Properties of Real Photonic Crystals: Anomalous Diffuse Transmission. J. Opt. Soc. Am. B 2005, 22, 1075-1084. (45) Neve-Oz, Y.; Golosovsky, M.; Davidov, D.; Frenkel, A. Bragg Attenuation Length in Metallo-Dielectric Photonic Band Gap Materials. J. Appl. Phys. 2004, 95, 5989-5993. 62 ACS Paragon Plus Environment

Page 62 of 80

Page 63 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46) Kinoshita, S.; Yoshioka, S. Structural Colors in Nature: the Role of Regularity and Irregularity in the Structure. ChemPhysChem 2005, 6, 1442-1459. (47) Nam, H.; Song, K.; Ha, D.; Kim, T. Inkjet Printing Based Mono-layered Photonic Crystal Patterning for Anti-counterfeiting Structural Colors. Sci. Rep. 2016, 6, 30885. (48) Zhang, J.-T.; Smith, N.; Asher, S. A. Two-Dimensional Photonic Crystal Surfactant Detection. Anal. Chem. 2012, 84, 6416-6420. (49) Zhang, J.-T.; Cai, Z.; Kwak, D. H.; Liu, X.; Asher, S. A. Two-Dimensional Photonic Crystal Sensors for Visual Detection of Lectin Concanavalin A. Anal. Chem. 2014, 86, 90369041. (50) Cai, Z.; Smith, N. L.; Zhang, J.-T.; Asher, S. A. Two-Dimensional Photonic Crystal Chemical and Biomolecular Sensors. Anal. Chem. 2015, 87, 5013-5025. (51) Chen, C.; Dong, Z.-Q.; Shen, J.-H.; Chen, H.-W.; Zhu, Y.-H.; Zhu, Z.-G. 2D Photonic Crystal Hydrogel Sensor for Tear Glucose Monitoring. ACS Omega 2018, 3, 3211-3217. (52) Qi, F.; Lan, Y.; Meng, Z.; Yan, C.; Li, S.; Xue, M.; Wang, Y.; Qiu, L.; He, X.; Liu, X. Acetylcholinesterase-Functionalized Two-Dimensional Photonic Crystals for the Detection of Organophosphates. RSC Adv. 2018, 8, 29385-29391. (53) Prum, R. O.; Torres, R. H.; Williamson, S.; Dyck, J. Coherent Light Scattering by Blue Feather Barbs. Nature 1998, 396, 28-29. (54) Prum, R. O.; Torres, R. H. Structural Colouration of Mammalian Skin: Convergent Evolution of Coherently Scattering Dermal Collagen Arrays. J. Exp. Biol. 2004, 207, 21572172. (55) Garcia, P. D.; Sapienza, R.; Blanco, A.; Lopez, C. Photonic Glass: A Novel Random Material for Light. Adv. Mater. 2007, 19, 2597-2602.



(56) Garcia, P. D.; Sapienza, R.; Bertolotti, J.; Martin, M. D.; Blanco, A.; Altube, A.; Vina, L.; Wiersma, D. S.; Lopez, C. Resonant Light Transport Through Mie Modes in Photonic Glasses. Phys. Rev. A 2008, 78, 023823. (57) Magkiriadou, S.; Park, J. G.; Kim, Y. S.; Manoharan, V. N. Absence of Red Structural Color in Photonic Glasses, Bird Feathers, and Certain Beetles. Phys. Rev. E 2014, 90, 062302. (58) Garcia, P. D.; Sapienza, R.; Lopez, C. Photonic Glasses: A Step Beyond White Paint. Adv. Mater. 2010, 22, 12-19. (59) Osorio, D.; Ham, A. D. Spectral Reflectance and Directional Properties of Structural Coloration in Bird Plumage. J. Exp. Biol. 2002, 205, 2017-2027. (60) Iwata, M.; Teshima, M.; Seki, T.; Yoshioka, S.; Takeoka, Y. Bio-Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background. Adv. Mater. 2017, 29, 1605050. (61) Bai, L.; Mai, V.; Lim, Y.; Hou, S.; Mohwald, H.; Duan, H. W. Large-Scale Noniridescent Structural Color Printing Enabled by Infiltration-Driven Nonequilibrium Colloidal Assembly. Adv. Mater. 2018, 30, 1705667. (62) Aguirre, C. I.; Reguera, E.; Stein, A. Colloidal Photonic Crystal Pigments with Low Angle Dependence. ACS Appl. Mater. Interfaces 2010, 2, 3257-3262. (63) Forster, J. D.; Noh, H.; Liew, S. F.; Saranathan, V.; Schreck, C. F.; Yang, L.; Park, J. G.; Prum, R. O.; Mochrie, S. G. J.; O'Hern, C. S.; Cao, H.; Dufresne, E. R. Biomimetic Isotropic Nanostructures for Structural Coloration. Adv. Mater. 2010, 22, 2939-2944. (64) Takeoka, Y.; Yoshioka, S.; Takano, A.; Arai, S.; Nueangnoraj, K.; Nishihara, H.; Teshima, M.; Ohtsuka, Y.; Seki, T. Production of Colored Pigments with Amorphous Arrays of Black and White Colloidal Particles. Angew. Chem. Int. Ed. 2013, 52, 7261-7265.


Page 64 of 80

Page 65 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(65) Takeoka, Y.; Yoshioka, S.; Teshima, M.; Takano, A.; Harun-Ur-Rashid, M.; Seki, T. Structurally Coloured Secondary Particles Composed of Black and White Colloidal Particles. Sci. Rep. 2013, 3, 2371. (66) Xiao, M.; Li, Y. W.; Allen, M. C.; Deheyn, D. D.; Yue, X. J.; Zhao, J. Z.; Gianneschi, N. C.; Shawkey, M. D.; Dhinojwala, A. Bio-Inspired Structural Colors Produced via SelfAssembly of Synthetic Melanin Nanoparticles. ACS Nano 2015, 9, 5454-5460. (67) Kohri, M.; Nannichi, Y.; Taniguchi, T.; Kishikawa, K. Biomimetic Non-Iridescent Structural Color Materials from Polydopamine Black Particles that Mimic Melanin Granules. J. Mater. Chem. C 2015, 3, 720-724. (68) Kawamura, A.; Kohri, M.; Yoshioka, S.; Taniguchi, T.; Kishikawa, K. Structural Color Tuning: Mixing Melanin-Like Particles with Different Diameters to Create Neutral Colors. Langmuir 2017, 33, 3824-3830. (69) Zhang, Y. F.; Dong, B. Q.; Chen, A.; Liu, X. H.; Shi, L.; Zi, J. Using Cuttlefish Ink as an Additive to Produce Non-iridescent Structural Colors of High Color Visibility. Adv. Mater. 2015, 27, 4719-4724. (70) Zhang, Y. X.; Han, P.; Zhou, H. Y.; Wu, N.; Wei, Y.; Yao, X.; Zhou, J. M.; Song, Y. L. Highly Brilliant Noniridescent Structural Colors Enabled by Graphene Nanosheets Containing Graphene Quantum Dots. Adv. Funct. Mater. 2018, 28, 1802585. (71) Yang, X. M.; Ge, D. T.; Wu, G. X.; Liao, Z. W.; Yang, S. Production of Structural Colors with High Contrast and Wide Viewing Angles from Assemblies of Polypyrrole Black Coated Polystyrene Nanoparticles. ACS Appl. Mater. Interfaces 2016, 8, 16289-16295. (72) Hirashima, R.; Seki, T.; Katagiri, K.; Akuzawa, Y.; Torimotoa, T.; Takeoka, Y. LightInduced Saturation Change in the Angle-Independent Structural Coloration of Colloidal Amorphous Arrays. J. Mater. Chem. C 2014, 2, 344-348.



(73) Vogel, N.; Utech, S.; England, G. T.; Shirman, T.; Phillips, K. R.; Koay, N.; Burgess, I. B.; Kolle, M.; Weitz, D. A.; Aizenberg, J. Color from Herarchy: Diverse Optical Properties of Micron-Sized Spherical Colloidal Assemblies. Proc. Natl. Acad. Sci. U.S.A 2015, 112, 10845-10850. (74) Koay, N.; Burgess, I. B.; Kay, T. M.; Nerger, B. A.; Miles-Rossouw, M.; Shirman, T.; Vu, T. L.; England, G.; Phillips, K. R.; Utech, S.; Vogel, N.; Kolle, M.; Aizenberg, J. Hierarchical Structural Control of Visual Properties in Self-Assembled Photonic-Plasmonic Pigments. Opt. Express 2014, 22, 27750-27768. (75) Kim, S.-H.; Magkiriadou, S.; Rhee, D. K.; Lee, D. S.; Yoo, P. J.; Manoharan, V. N.; Yi, G. R. Inverse Photonic Glasses by Packing Bidisperse Hollow Microspheres with Uniform Cores. ACS Appl. Mater. Interfaces 2017, 9, 24155-24160. (76) Park, J. G.; Kim, S.-H.; Magkiriadou, S.; Choi, T. M.; Kim, Y. S.; Manoharan, V. N. Full-Spectrum Photonic Pigments with Non-iridescent Structural Colors through Colloidal Assembly. Angew. Chem. Int. Ed. 2014, 53, 2899-2903. (77) Lee, G. H.; Sim, J. Y.; Kim, S.-H. Polymeric Inverse Glasses for Development of Noniridescent Structural Colors in Full Visible Range. ACS Appl. Mater. Interfaces 2016, 8, 12473-12480. (78) Noh, H.; Liew, S. F.; Saranathan, V.; Mochrie, S. G. J.; Prum, R. O.; Dufresne, E. R.; Cao, H. How Noniridescent Colors Are Generated by Quasi-ordered Structures of Bird Feathers. Adv. Mater. 2010, 22, 2871-2880. (79) Kim, E.; Xia, Y.; Whitesides, G. M. Two- and Three-Dimensional Crystallization of Polymeric Microspheres by Micromolding in Capillaries. Adv. Mater. 1996, 8, 245-247. (80) Mı́guez, H.; Yang, S.-M.; Ozin, G. A. Colloidal Photonic Crystal Microchannel Array with Periodically Modulated Thickness. Appl. Phys. Lett. 2002, 81, 2493-2495.


Page 66 of 80

Page 67 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(81) Yamauchi, Y.; Imasu, J.; Kuroda, Y.; Kuroda, K.; Sakka, Y. Facile Patterning of Assembled Silica Nanoparticles with a Closely Packed Arrangement through Guided Growth. J. Mater. Chem. 2009, 19, 1964-1967. (82) Lee, S. K.; Yi, G. R.; Yang, S.-M. High-Speed Fabrication of Patterned Colloidal Photonic Structures in Centrifugal Microfluidic Chips. Lab Chip 2006, 6, 1171-1177. (83) Shiu, J. Y.; Kuo, C. W.; Chen, P. Actively Controlled Self-Assembly of Colloidal Crystals in Microfluidic Networks by Electrocapillary Forces. J. Am. Chem. Soc. 2004, 126, 8096-8097. (84) Shiu, J. Y.; Chen, P. Active Patterning Using an Addressable Microfluidic Network. Adv. Mater. 2005, 17, 1866-1869. (85) Yang, S. M.; Ozin, G. A. Opal Chips: Vectorial Growth of Colloidal Crystal Patterns Inside Silicon Wafers. Chem. Commun. 2000, 2507-2508. (86) Yang, S. M.; Miguez, H.; Ozin, G. A. Opal Circuits of Light - Planarized Microphotonic Crystal Chips. Adv. Funct. Mater. 2002, 12, 425-431. (87) Ferrand, P.; Egen, M.; Griesebock, B.; Ahopelto, J.; Müller, M.; Zentel, R.; Romanov, S. G.; Sotomayor Torres, C. M. Self-Assembly of Three-Dimensional Photonic Crystals on Structured Silicon Wafers. Appl. Phys. Lett. 2002, 81, 2689-2691. (88) Míguez, H.; Yang, S. M.; Ozin, G. A. Optical Properties of Colloidal Photonic Crystals Confined in Rectangular Microchannels. Langmuir 2003, 19, 3479-3485. (89) Ye, J.; Zentel, R.; Arpiainen, S.; Ahopelto, J.; Jonsson, F.; Romanov, S. G.; Sotomayor Torres, C. M. Integration of Self-Assembled Three-Dimensional Photonic Crystals onto Structured Silicon Wafers. Langmuir 2006, 22, 7378-7383. (90) Gu, Z. Z.; Fujishima, A.; Sato, O. Patterning of a Colloidal Crystal Film on a Modified Hydrophilic and Hydrophobic Surface. Angew. Chem. Int. Ed. 2002, 41, 2068-2070.



(91) Fustin, C. A.; Glasser, G.; Spiess, H. W.; Jonas, U. Site-Selective Growth of Colloidal Crystals with Photonic Properties on Chemically Patterned Surfaces. Adv. Mater. 2003, 15, 1025-1028. (92) Fustin, C.-A.; Glasser, G.; Spiess, H. W.; Jonas, U. Parameters Influencing the Templated Growth of Colloidal Crystals on Chemically Patterned Surfaces. Langmuir 2004, 20, 9114-9123. (93) Fan, F.; Stebe, K. J. Assembly of Colloidal Particles by Evaporation on Surfaces with Patterned Hydrophobicity. Langmuir 2004, 20, 3062-3067. (94) Brozell, A. M.; Muha, M. A.; Parikh, A. N. Formation of Spatially Patterned Colloidal Photonic Crystals through the Control of Capillary Forces and Template Recognition. Langmuir 2005, 21, 11588-11591. (95) Ko, H.-Y.; Park, J.; Shin, H.; Moon, J. Rapid Self-Assembly of Monodisperse Colloidal Spheres in an Ink-Jet Printed Droplet. Chem. Mater. 2004, 16, 4212-4215. (96) Wang, D.; Park, M.; Park, J.; Moon, J. Optical properties of single droplet of photonic crystal assembled by ink-jet printing. Appl. Phys. Lett. 2005, 86, 241114. (97) Park, J.; Moon, J.; Shin, H.; Wang, D.; Park, M. Direct-write fabrication of colloidal photonic crystal microarrays by ink-jet printing. J. Colloid Interface Sci. 2006, 298, 713-719. (98) Park, J.; Moon, J. Control of Colloidal Particle Deposit Patterns within Picoliter Droplets Ejected by Ink-Jet Printing. Langmuir 2006, 22, 3506-3513. (99) Keller, K.; Yakovlev, A. V.; Grachova, E. V.; Vinogradov, A. V. Inkjet Printing of Multicolor Daylight Visible Opal Holography. Adv. Funct. Mater. 2018, 28, 1706903. (100) Ding, H.; Zhu, C.; Tian, L.; Liu, C.; Fu, G.; Shang, L.; Gu, Z. Structural Color Patterns by Electrohydrodynamic Jet Printed Photonic Crystals. ACS Appl. Mater. Interfaces 2017, 9, 11933-11941.


Page 68 of 80

Page 69 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(101) Wang, L.; Wang, J.; Huang, Y.; Liu, M.; Kuang, M.; Li, Y.; Jiang, L.; Song, Y. Inkjet Printed Colloidal Photonic Crystal Microdot with Fast Response Induced by Hydrophobic Transition of Poly(N-isopropyl acrylamide). J. Mater. Chem. 2012, 22, 21405-21411. (102) Hou, J.; Zhang, H.; Su, B.; Li, M.; Yang, Q.; Jiang, L.; Song, Y. Four-Dimensional Screening Anti-Counterfeiting Pattern by Inkjet Printed Photonic Crystals. Chem. Asian J. 2016, 11, 2680-2685. (103) Cui, L.; Li, Y.; Wang, J.; Tian, E.; Zhang, X.; Zhang, Y.; Song, Y.; Jiang, L. Fabrication of Large-Area Patterned Photonic Crystals by Ink-Jet Printing. J. Mater. Chem. 2009, 19, 5499-5502. (104) Wu, S.; Liu, B.; Su, X.; Zhang, S. Structural Color Patterns on Paper Fabricated by Inkjet Printer and Their Application in Anticounterfeiting. J. Phys. Chem. Lett. 2017, 8, 2835-2841. (105) Allard, D.; Lange, B.; Fleischhaker, F.; Zentel, R.; Wulf, M. Opaline Effect Pigments by Spray Induced Self-Assembly on Porous Substrates. Soft Materials 2005, 3, 121-131. (106) Cui, L. Y.; Zhang, Y. Z.; Wang, J. X.; Ren, Y. B.; Song, Y. L.; Jiang, L. Ultra-Fast Fabrication of Colloidal Photonic Crystals by Spray Coating. Macromol. Rapid Commun. 2009, 30, 598-603. (107) Sprafke, A. N.; Schneevoigt, D.; Seidel, S.; Schweizer, S. L.; Wehrspohn, R. B. Automated Spray Coating Process for the Fabrication of Large-Area Artificial Opals on Textured Substrates. Opt. Express 2013, 21, A528-A538. (108) Gao, Z. W.; Huang, C.; Yang, D.; Zhang, H. B.; Guo, J. B.; Wei, J. Dual-Mode Multicolored Photonic Crystal Patterns Enabled by Ultraviolet-Responsive Core-Shell Colloidal Spheres. Dyes Pigm. 2018, 148, 108-117.



(109) Ding, T.; Luo, L.; Wang, H.; Chen, L.; Liang, K.; Clays, K.; Song, K.; Yang, G.; Tung, C.-H. Patterning and Pixelation of Colloidal Photonic Crystals for Addressable Integrated Photonics. J. Mater. Chem. 2011, 21, 11330-11334. (110) Ding, T.; Smoukov, S. K.; Baumberg, J. J. Stamping Colloidal Photonic Crystals: A Facile Way Towards Complex Pixel Colour Patterns for Sensing and Displays. Nanoscale 2015, 7, 1857-1863. (111) Subramanian, G.; Manoharan, V. N.; Thorne, J. D.; Pine, D. J. Ordered Macroporous Materials by Colloidal Assembly: A Possible Route to Photonic Bandgap Materials. Adv. Mat. 1999, 11, 1261-1265. (112) 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 2010, 107, 10354-10359. (113) Phillips, K. R.; Vogel, N.; Hu, Y.; Kolle, M.; Perry, C. C.; Aizenberg, J. Tunable Anisotropy in Inverse Opals and Emerging Optical Properties. Chem. Mater. 2014, 26, 16221628. (114) Meng, Y.; Liu, F.; Umair, M. M.; Ju, B.; Zhang, S.; Tang, B. Patterned and Iridescent Plastics with 3D Inverse Opal Structure for Anticounterfeiting of the Banknotes. Adv. Opt. Mater. 2018, 6, 1701351. (115) Fang, Y.; Ni, Y.; Leo, S. Y.; Taylor, C.; Basile, V.; Jiang, P. Reconfigurable Photonic Crystals Enabled by Pressure-Responsive Shape-Memory Polymers. Nat. Commun. 2015, 6, 7416. (116) Matsubara, K.; Watanabe, M.; Takeoka, Y. A Thermally Adjustable Multicolor Photochromic Hydrogel. Angew. Chem. Int. Ed. 2007, 46, 1688-1692.


Page 70 of 80

Page 71 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(117) Wang, Y.; Aurelio, D.; Li, W.; Tseng, P.; Zheng, Z.; Li, M.; Kaplan, D. L.; Liscidini, M.; Omenetto, F. G. Modulation of Multiscale 3D Lattices through Conformational Control: Painting Silk Inverse Opals with Water and Light. Adv. Mater. 2017, 29, 1702769. (118) Lee, S. Y.; Kim, S.-H.; Heo, C. J.; Hwang, H.; Yang, S.-M. Lithographically-Featured Photonic Microparticles of Colloidal Assemblies. Phys. Chem. Chem. Phys. 2010, 12, 1186111868. (119) Lee, S. Y.; Kim, S.-H.; Hwang, H.; Sim, J. Y.; Yang, S.-M. Controlled Pixelation of Inverse Opaline Structures towards Reflection-Mode Displays. Adv. Mater. 2014, 26, 23912397. (120) 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 2015, 11, 4334-4340. (121) Lee, S. K.; Yi, G. R.; Moon, J. H.; Yang, S.-M.; Pine, D. J. Pixellated Photonic Crystal Films by Selective Photopolymerization. Adv. Mater. 2006, 18, 2111-2116. (122) Lee, J.-S.; Je, K.; Kim, S.-H. Designing Multicolored Photonic Micropatterns through the Regioselective Thermal Compression of Inverse Opals. Adv. Funct. Mater. 2016, 26, 4587-4594. (123) Holt, A. L.; Vahidinia, S.; Gagnon, Y. L.; Morse, D. E.; Sweeney, A. M. Photosymbiotic Ggiant Cclams are Ttransformers of Solar Flux. J. R. Soc. Interface 2014, 11, 20140678. (124) Lopez-Garcia, M.; Masters, N.; O'Brien, H. E.; Lennon, J.; Atkinson, G.; Cryan, M. J.; Oulton, R.; Whitney, H. M. Light-Induced Dynamic Structural Color by Intracellular 3D Photonic Crystals in Brown Algae. Sci. Adv. 2018, 4, eaan8917.



(125) Lee, H.; Jeon, T. Y.; Lee, S. Y.; Lee, S. Y.; Kim, S.-H. Designing Multicolor Micropatterns of Inverse Opals with Photonic Bandgap and Surface Plasmon Resonance. Adv. Funct. Mater. 2018, 28, 1706664. (126) Holtz, J. H.; Asher, S. A. Polymerized Colloidal Crystal Hydrogel Films as Intelligent Chemical Sensing Materials. Nature 1997, 389, 829-832. (127) Muscatello, M. M.; Stunja, L. E.; Asher, S. A. Polymerized Crystalline Colloidal Array Sensing of High Glucose Concentrations. Anal. Chem. 2009, 81, 4978-4986. (128) Kim, S.-H.; Park, H. S.; Choi, J. H.; Shim, J. W.; Yang, S.-M. Integration of Colloidal Photonic Crystals toward Miniaturized Spectrometers. Adv. Mater. 2010, 22, 946-950. (129) Kim, S.-H.; Lim, J.-M.; Jeong, W. C.; Choi, D.-G.; Yang, S.-M. Patterned Colloidal Photonic Domes and Balls Derived from Viscous Photocurable Suspensions. Adv. Mater. 2008, 20, 3211-3217. (130) Kim, S.-H.; Kim, S.-H.; Yang, S.-M. Patterned Polymeric Domes with 3D and 2D Embedded Colloidal Crystals using Photocurable Emulsion Droplets. Adv. Mater. 2009, 21, 3771-3775. (131) Jiang, P.; Smith, D. W.; Ballato, J. M.; Foulger, S. H. Multicolor Pattern Generation in Photonic Bandgap Composites. Adv. Mater. 2005, 17, 179-184. (132) Chen, K.; Fu, Q.; Ye, S.; Ge, J. Multicolor Printing Using Electric-Field-Responsive and Photocurable Photonic Crystals. Adv. Funct. Mater. 2017, 27, 1702825. (133) Vogel, N.; Retsch, M.; Fustin, C. A.; del Campo, A.; Jonas, U. Advances in Colloidal Assembly: The Design of Structure and Hierarchy in Two and Three Dimensions. Chem. Rev. 2015, 115, 6265-6311. (134) Dimitrov, A. S.; Nagayama, K. Continuous Convective Assembling of Fine Particles into Two-Dimensional Arrays on Solid Surfaces. Langmuir 1996, 12, 1303-1311.


Page 72 of 80

Page 73 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(135) Prevo, B. G.; Velev, O. D. Controlled, Rapid Deposition of Structured Coatings from Micro-and Nanoparticle Suspensions. Langmuir 2004, 20, 2099-2107. (136) Malaquin, L.; Kraus, T.; Schmid, H.; Delamarche, E.; Wolf, H. Controlled Particle Placement through Convective and Capillary Assembly. Langmuir 2007, 23, 11513-11521. (137) Park, J.; Moon, J. Control of Colloidal Particle Deposit Patterns within Picoliter Droplets Ejected by Ink-Jet Printing. Langmuir 2006, 22, 3506-3513. (138) Park, C.; Lee, T.; Xia, Y. N.; Shin, T. J.; Myoung, J.; Jeong, U. Quick, Large-Area Assembly of a Single-Crystal Monolayer of Spherical Particles by Unidirectional Rubbing. Adv. Mater. 2014, 26, 4633-4638. (139) Lenzmann, F.; Li, K.; Kitai, A.; Stover, H. Thin-Film Micropatterning Using Polymer Microspheres. Chem. Mater. 1994, 6, 156-159. (140) Aveyard, R.; Clint, J. H.; Nees, D.; Paunov, V. N. Compression and Structure of Monolayers of Charged Latex Particles at Air/Water and Octane/Water Interfaces. Langmuir 2000, 16, 1969-1979. (141) Goldenberg, L. M.; Wagner, J.; Stumpe, J.; Paulke, B.-R.; Görnitz, E. Ordered Arrays of Large Latex Particles Organized by Vertical Deposition. Langmuir 2002, 18, 3319-3323. (142) Armstrong, E.; Khunsin, W.; Osiak, M.; Blömker, M.; Torres, C. M. S.; O'Dwyer, C. Ordered 2D Colloidal Photonic Crystals on Gold Substrates by Surfactant-Assisted Fast-Rate Dip Coating. Small 2014, 10, 1895-1901. (143) Watanabe, S.; Inukai, K.; Mizuta, S.; Miyahara, M. T. Mechanism for Stripe Pattern Formation on Hydrophilic Surfaces by Using Convective Self-Assembly. Langmuir 2009, 25, 7287-7295. (144) Kumnorkaew, P.; Ee, Y.-K.; Tansu, N.; Gilchrist, J. F. Investigation of the Deposition of Microsphere Monolayers for Fabrication of Microlens Arrays. Langmuir 2008, 24, 1215012157. 73 ACS Paragon Plus Environment


(145) Jeong, S.; Hu, L.; Lee, H. R.; Garnett, E.; Choi, J. W.; Cui, Y. Fast and Scalable Printing of Large Area Monolayer Nanoparticles for Nanotexturing Applications. Nano Lett. 2010, 10, 2989-2994. (146) Sakamoto, R.; Hataguchi, Y.; Kimura, R.; Tsuchiya, K.; Mori, Y. Stripe and Network Formation of Particle Arrays Fabricated by Convective Self-Assembly. Chem. Lett. 2012, 41, 1207-1209. (147) Horozov, T. S.; Aveyard, R.; Clint, J. H.; Binks, B. P. Order-Disorder Transition in Monolayers of Modified Monodisperse Silica Particles at the Octane-Water Interface. Langmuir 2003, 19, 2822-2829. (148) Law, A. D.; Auriol, M.; Smith, D.; Horozov, T. S.; Buzza, D. M. A. Self-Assembly of Two-Dimensional Colloidal Clusters by Tuning the Hydrophobicity, Composition, and Packing Geometry. Phys. Rev. Lett. 2013, 110, 138301. (149) Weekes, S. M.; Ogrin, F. Y.; Murray, W. A.; Keatley, P. S. Macroscopic Arrays of Magnetic Nanostructures from Self-Assembled Nanosphere Templates. Langmuir 2007, 23, 1057-1060. (150) Vogel, N.; Goerres, S.; Landfester, K.; Weiss, C. K. A Convenient Method to Produce Close- and Non-close-Packed Monolayers using Direct Assembly at the Air–Water Interface and Subsequent Plasma-Induced Size Reduction. Macromol. Chem. Phys. 2011, 212, 17191734. (151) Retsch, M.; Zhou, Z.; Rivera, S.; Kappl, M.; Zhao, X. S.; Jonas, U.; Li, Q. Fabrication of Large-Area, Transferable Colloidal Monolayers Utilizing Self-Assembly at the Air/Water Interface. Macromol. Chem. Phys. 2009, 210, 230-241. (152) Meng, X.; Qiu, D. Gas-FlowIinduced Reorientation to Centimeter-Sized TwoDimensional Colloidal Single Crystal of Polystyrene Particle. Langmuir 2014, 30, 3019-3023.


Page 74 of 80

Page 75 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(153) Isa, L.; Kumar, K.; Muller, M.; Grolig, J.; Textor, M.; Reimhult, E. Particle Lithography from Colloidal Self-Assembly at Liquid-Liquid Interfaces. ACS Nano 2010, 4, 5665-5670. (154) Zhang, X.; Zhang, J.; Zhu, D.; Li, X.; Zhang, X.; Wang, T.; Yang, B. A Universal Approach To Fabricate Ordered Colloidal Crystals Arrays Based on Electrostatic SelfAssembly. Langmuir 2010, 26, 17936-17942. (155) Lumsdon, S. O.; Kaler, E. W.; Williams, J. P.; Velev, O. D. Dielectrophoretic Assembly of Oriented and Switchable Two-Dimensional Photonic Crystals. Appl. Phys. Lett. 2003, 82, 949-951. (156) Dziomkina, N. V.; Hempenius, M. A.; Vancso, G. J. Symmetry Control of Polymer Colloidal Monolayers and Crystals by Electrophoretic Deposition onto Patterned Surfaces. Adv. Mater. 2005, 17, 237-240. (157) Zhang, J.-T.; Wang, L.; Chao, X.; Velankar, S. S.; Asher, S. A. Vertical Spreading of Two-Dimensional Crystalline Colloidal Arrays. J. Mater. Chem. C 2013, 1, 6099-6102. (158) Retsch, M.; Dostert, K.-H.; Nett, S. K.; Vogel, N.; Gutmann, J. S.; Jonas, U. TemplateFree Structuring of Colloidal Hetero-Monolayers by Inkjet Printing and Particle Floating. Soft Matter 2010, 6, 2403-2412. (159) Khanh, N. N.; Yoon, K. B. Facile Organization of Colloidal Particles into Large, Perfect One- and Two-Dimensional Arrays by Dry Manual Assembly on Patterned Substrates. JACS 2009, 131, 14228-14230. (160) Park, C.; Koh, K.; Jeong, U. Structural Color Painting by Rubbing Particle Powder. Sci. Rep. 2015, 5, 8340. (161) Yan, X.; Yao, J.; Lu, G.; Chen, X.; Zhang, K.; Yang, B. Microcontact Printing of Colloidal Crystals. JACS 2004, 126, 10510-10511.



(162) Jiang, P.; Prasad, T.; McFarland, M. J.; Colvin, V. L. Two-Dimensional NonclosePacked Colloidal Crystals formed by Spincoating. Appl. Phys. Lett. 2006, 89, 011908. (163) Yang, H.; Gozubenli, N.; Fang, Y.; Jiang, P. Generalized Fabrication of Monolayer Nonclose-Packed Colloidal Crystals with Tunable Lattice Spacing. Langmuir 2013, 29, 76747681. (164) Hu, H.; Chen, C.; Chen, Q. Magnetically Controllable Colloidal Photonic Crystals: Unique Features and Intriguing Applications. J. Mater. Chem. C 2013, 1, 6013-6030. (165) Kim, H.; Ge, J.; Kim, J.; Choi, S.-e.; Lee, H.; Lee, H.; Park, W.; Yin, Y.; Kwon, S. Structural Colour Printing using a Magnetically Tunable and Lithographically Fixable Photonic Crystal. Nat. Photon. 2009, 3, 534-540. (166) Xuan, R.; Ge, J. Photonic Printing through the Orientational Tuning of Photonic Structures and Its Application to Anticounterfeiting Labels. Langmuir 2011, 27, 5694-5699. (167) Gotoh, Y.; Suzuki, H.; Kumano, N.; Seki, T.; Katagiri, K.; Takeoka, Y. An Amorphous Array of Poly(N-isopropylacrylamide) Brush-Coated Silica Particles for Thermally Tunable AngleIindependent Photonic Band Gap Materials. New J. Chem. 2012, 36, 2171-2175. (168) Reufer, M.; Rojas-Ochoa, L. F.; Eiden, S.; Saenz, J. J.; Scheffold, F. Transport of Light in Amorphous Photonic Materials. Appl. Phys. Lett. 2007, 91, 171904. (169) Katagiri, K.; Tanaka, Y.; Uemura, K.; Inumaru, K.; Seki, T.; Takeoka, Y. Structural Color Coating Films Composed of an Amorphous Array of Colloidal Particles via Electrophoretic Deposition. NPG Asia Mater. 2017, 9, e355. (170) Ge, D. T.; Yang, L. L.; Wu, G. X.; Yang, S. Angle-Independent Colours from Spray Coated Quasi-Amorphous Arrays of Nanoparticles: Combination of Constructive Interference and Rayleigh Scattering. J. Mater. Chem. C 2014, 2, 4395-4400.


Page 76 of 80

Page 77 of 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(171) Harun-Ur-Rashid, M.; Bin Imran, A.; Seki, T.; Ishi, M.; Nakamura, H.; Takeoka, Y. Angle-Independent Structural Color in Colloidal Amorphous Arrays. ChemPhysChem 2010, 11, 579-583. (172) Ueno, K.; Inaba, A.; Sano, Y.; Kondoh, M.; Watanabe, M. A Soft Glassy Colloidal Array in Ionic Liquid, which Exhibits Homogeneous, Non-Brilliant and Angle-Independent Structural Colours. Chem. Commun. 2009, 3603-3605. (173) Ueno, K.; Sano, Y.; Inaba, A.; Kondoh, M.; Watanabe, M. Soft Glassy Colloidal Arrays in an Ionic Liquid: Colloidal Glass Transition, Ionic Transport, and Structural Color in Relation to Microstructure. J. Phys. Chem. B 2010, 114, 13095-13103. (174) Ueno, K.; Inaba, A.; Ueki, T.; Kondoh, M.; Watanabe, M. Thermosensitive, Soft Glassy and Structural Colored Colloidal Array in Ionic Liquid: Colloidal Glass to Gel Transition. Langmuir 2010, 26, 18031-18038. (175) Ueno, K.; Watanabe, M. From Colloidal Stability in Ionic Liquids to Advanced Soft Materials Using Unique Media. Langmuir 2011, 27, 9105-9115. (176) Xuan, R.; Ge, J. Invisible Photonic Prints Shown by Water. J. Mater. Chem. 2012, 22, 367-372. (177) Burgess, I. B.; Mishchenko, L.; Hatton, B. D.; Kolle, M.; Loncar, M.; Aizenberg, J. Encoding Complex Wettability Patterns in Chemically Functionalized 3D Photonic Crystals. JACS 2011, 133, 12430-12432. (178) Heo, Y.; Kang, H.; Lee, J. S.; Oh, Y. K.; Kim, S.-H. Lithographically Encrypted Inverse Opals for Anti-Counterfeiting Applications. Small 2016, 12, 3819-3826. (179) Bai, L.; Xie, Z.; Wang, W.; Yuan, C.; Zhao, Y.; Mu, Z.; Zhong, Q.; Gu, Z. Bio-Inspired Vapor-Responsive Colloidal Photonic Crystal Patterns by Inkjet Printing. ACS Nano 2014, 8, 11094-11100.



(180) Ye, S.; Fu, Q.; Ge, J. Invisible Photonic Prints Shown by Deformation. Adv. Funct. Mater. 2014, 24, 6430-6438. (181) Ge, D. T.; Lee, E.; Yang, L. L.; Cho, Y. G.; Li, M.; Gianola, D. S.; Yang, S. A Robust Smart Window: Reversibly Switching from High Transparency to Angle-Independent Structural Color Display. Adv. Mater. 2015, 27, 2489-2495. (182) Trau, M.; Saville, D.; Aksay, I. Field-Induced Layering of Colloidal Crystals. Science 1996, 272, 706-709. (183) Zhang, K.-Q.; Liu, X.-Y. In Situ Observation of Colloidal Monolayer Nucleation Driven by an Alternating Electric Field. Nature 2004, 429, 739-743. (184) Xie, R.; Liu, X.-Y. Epitaxial Assembly and Ordering of Two-Dimensional Colloidal Crystals. Appl. Phys. Lett. 2008, 92, 083106. (185) Xie, R.; Liu, X.-Y. Electrically Directed On-Chip Reversible Patterning of TwoDimensional Tunable Colloidal Structures. Adv. Funct. Mater. 2008, 18, 802-809. (186) Celio, H.; Barton, E.; Stevenson, K. J. Patterned Assembly of Colloidal Particles by Confined Dewetting Lithography. Langmuir 2006, 22, 11426-11435. (187) Xie, R.; Liu, X.-Y. Controllable Epitaxial Crystallization and Reversible Oriented Patterning of Two-Dimensional Colloidal Crystals. JACS 2009, 131, 4976-4982. (188) Ge, J.; Yin, Y. Magnetically Tunable Colloidal Photonic Structures in Alkanol Solutions. Adv. Mater. 2008, 20, 3485-3491. (189) Hu, H.; Chen, Q.-W.; Tang, J.; Hu, X.-Y.; Zhou, X.-H. Photonic Anti-Counterfeiting Using Structural Colors Derived From Magnetic-Responsive Photonic Crystals with Double Photonic Bandgap Heterostructures. J. Mater. Chem. 2012, 22, 11048-11053. (190) Hu, H.; Tang, J.; Zhong, H.; Xi, Z.; Chen, C.; Chen, Q. Invisible Photonic Printing: Computer Designing Graphics, UV Printing and Shown by a Magnetic Field. Sci. Rep. 2013, 3, 1484. 78 ACS Paragon Plus Environment

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Page 80 of 80

Designing Structural-Color Patterns Composed of Colloidal Arrays

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