Bioinspired maskless structural colour patterning via tunable nanoparticle segregation

Domain: physics
Published: 2026-03-17
Editorial outcome: minor_revision

Abstract
Structural colouration arises from the interaction of light with nanoscale structures and offers sustainable alternatives to pigment-based colours. However, current structural colour patterning methods rely on multi-step lithographic processes or multiple ink formulations, limiting scalability and spatial resolution. Inspired by melanosome self-assembly in bird feathers, we develop a one-step, mask-free strategy to generate high-resolution structural colour patterns via tunable nanoparticle segregation. During photocuring, silica nanoparticles dispersed in acrylic resin migrate toward oxygen-permeable substrates, forming an nanoparticle-enriched disordered layer. Such segregation is driven by interfacial oxygen inhibition and kinetically governed by the photocuring rate. Using grayscale digital light processing printing, we programmably control the local segregation thickness to create high-resolution structural colour patterns for visual display and information encryption. The segregation structure also affects mid-infrared reflectivity, allowing for infrared camouflage. This scalable approach establishes a mechanistically guided route to multifunctional photonic materials.

Introduction
Structural colours are generated by reflection of specific wavelengths of light from periodic or aperiodic micro/nano-structures, offering environmentally friendly alternatives to pigment-based colouration1,2. Structural colour patterning can be widely used in decoration3, anti-counterfeiting4–6, information encryption7,8, camouflage9,10, sensor11,12, and display13,14. However, conventional structural colour patterning typically relies on lithography-like strategies, where unmasked regions with initial nanostructures are first photocured, followed by immobilization of masked regions with different nanostructures. To adjust nanostructures for different colours, external stimuli such as magnetic fields15,16, electric fields17, temperature6, or solvents4 are applied upon curing to locally manipulate the arrangements of assembly units (nanoparticle, liquid crystal, block copolymer, etc.). These approaches require physical masks and multiple photocuring steps, limiting scalability and spatial resolution. A one-step, mask-free strategy for precisely controlling local nanostructures remains a key challenging in advancing structural colour patterning.

Printing technology has been used to fabricate structurally coloured materials with high flexibility and customization18–20. However, printing various colours often requires multiple resin formulations across methods such as inkjet printing, direct ink writing, or vat photopolymerization3,18,21–24. To the best of our knowledge, only a few studies have preliminarily explored the concept of printing different colours using a single ink. Two-photon printing can locally customize the periodic nanostructures for structural colour patterns25,26, but suffers from low throughput and high cost. Li et al. inkjet printed a full spectrum of structural colours by controlling the sizes of printed microdomes to tuning their total internal reflections (TIR)27. These TIR-based colours can only be observed from the backside of the printed samples. Liao et al. achieved spatial colour contrast in printed colloidal photonic crystal hydrogels by locally tuning the amount of cured monomers and the cross-linking density28. Jeon et al. used direct ink writing of bottlebrush block copolymer solutions and printed different colours via kinetically trapping distinct nanostructures during the evaporation-driven self-assembly29. These methods are limited to hydrogel or bottlebrush polymeric systems and offer relatively low resolution, with printed pattern features typically on the millimetre scale. It remains challenging to fabricate high-resolution structural colour patterns from a single ink via printing technology.

Nanoparticle segregation or stratification offers a route to spatially control compositions at the microscale. Driven by entropic and enthalpic interactions, nanoparticle segregation can prevent film dewetting30–32, promote defect healing33,34, and fabricate a strain sensor or antenna array35. Recently, structural colours have been manipulated by the interfacial segregations of melanin nanoparticles during emulsion self-assembly36,37. In bird feathers, melanosomes migrate toward the periphery of barbule cells, forming close-packed structures that reflect iridescent colours (Fig. 1a). This process is driven by depletion attraction during the late stage of keratin polymerization in feather development38,39. These provide inspiration to take advantage of interfacial nanoparticle segregation to locally tune nanostructures for structural colour patterning.

In this work, we integrate photopolymerization-induced nanoparticle segregation and digital light processing (DLP) grayscale printing to achieve one-step and mask-free structural colour patterning. During photocuring, monodisperse nanoparticles in acrylic resin migrate toward the resin-substrate interface, forming an nanoparticle-segregated layer. This segregation easily occurs on oxygen-permeable substrates, and the layer thickness can be tuned from 0.37 ± 0.02 μm to 3.21 ± 0.09 μm by adjusting photocuring kinetics and nanoparticle volume fractions. Due to the segregation layer, printed samples have Janus optical features with the segregated side exhibiting low-angle-dependent structural colours and the opposite side showing bright iridescent colours. By spatially modulating the irradiance via grayscale DLP printing, we precisely control the local segregation thickness and achieve high-resolution structural colour patterns for display or encryption. Furthermore, the microscale segregation leads to the manipulation of mid-infrared reflectivity, expanding the functionality to infrared camouflage. This work offers a versatile, scalable route to structural colour patterning for applications in anti-counterfeiting, camouflage, sensing, and display.

Results
Nanoparticle segregation driven by photopolymerization
We explore the effect of nanoparticle segregation using photocurable ink that contains monodisperse silica nanoparticles in an acrylic resin precursor. The precursor comprises ethylene glycol phenyl ether acrylate (EGPEA), 4-hydroxybutyl acrylate (HBA), poly(ethylene glycol) diacrylate (PEGDA), and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO). EGPEA is the main acrylic monomer to ensure sufficient refractive index contrast between the silica nanoparticles and the resin. HBA improves the dispersion of silica nanoparticles (Supplementary Fig. 1), PEGDA acts as a cross linking agent, and TPO serves as a photoinitiator. To enhance colour saturation, we add a small amount of carbon black (0.015% w/w) to suppress the multiple scattering. As shown in Fig. 1b, photonic ink colour shifts from blue to pink due to increased interparticle spacing as the volume fraction decreases.

We first investigate the effect of substrate on nanoparticle segregation during photopolymerization. As shown in Fig. 1c, the photonic ink is sandwiched between a coverslip and a transparent substrate. Under UV irradiation, silica nanoparticles segregate toward the ink-substrate interface across various substrates (Fig. 1d), similarly to the segregation of melanosomes at the periphery of barbule cell membranes in bird feathers38. When the substrate is polydimethylsiloxane (PDMS) and fluorinated ethylene propylene copolymer (FEP), the segregation layer thickness is 3.73 ± 0.15 μm and 1.88 ± 0.06 μm. For poly(methyl methacrylate) (PMMA) and polyethylene terephthalate (PET), the segregation thickness decreases to 0.62 ± 0.06 μm and 0.32 ± 0.04 μm. No segregation is observed on the glass substrate. When both the cover and substrate are FEP (Fig. 1d-vi), silica nanoparticles segregate toward both interfaces, ruling out the gravity effect and suggesting the interfacial effect caused by the substrate is the primary driver of the segregation during photopolymerization.

To explore why the degree of segregation depends on the substrate, we measure the substrate surface energy using the Owens-Wendt-Rabel-Kaelble (OWRK) method based on static contact angles of water and diiodomethane (Supplementary Table 1)40. The measured surface energy of PDMS, FEP, PMMA, PET, and glass is 18.7 ± 0.6, 21.4 ± 2.1, 37.8 ± 2.3, 39.8 ± 1.2, and 64.2 ± 2.7 mJ m−2, respectively. As the substrate surface energy increases from 18.7 mJ m−2 to 64.2 mJ m−2, the segregation layer thickness decreases from 3.73 ± 0.15 μm to 0 μm (Supplementary Fig. 2).

We compare the enthalpy change upon segregation to examine whether the substrate surface energy is the key factor that affects the segregation. As shown in Supplementary Fig. 3, this enthalpy change is calculated by determining the interfacial energy difference between segregated and unsegregated states, ΔH = γ s-p - (γ m-s + γ m-p), where γ s-p, γ m-s, and γ m-p are interfacial energies of substrate-particle, matrix-substrate, and matrix-particle. As shown in Supplementary Table 2 and Supplementary Fig. 4, ΔH is the highest for the PDMS substrate and the lowest for the glass substrate, which suggests segregation would occur onto the glass substrate instead of PDMS. This is conflicting with our experimental observations, and thus, the enthalpy effect alone does not explain the segregation phenomenon. Therefore, the segregation is not a thermodynamically controlled process.

We further conduct both fast and slow polymerization to reveal whether the nanoparticle segregation occurs before or after the polymerization. At 5% w/v photoinitiator and 500 mW cm−² irradiance, rapid curing freezes the structure, resulting in a uniform distribution of silica nanoparticles in the matrix with negligible segregation even at the ink-FEP interface (Fig. 1d-vii). In contrast, thermal polymerization leads to a thicker segregation layer (4.76 ± 0.10 μm) (Fig. 1d-viii). That is likely due to the slower curing process (~20 min), which allows sufficient time for nanoparticles to migrate toward the interface before the matrix viscosity becomes too high. These results indicate that the segregation layer forms during the polymerization, and the segregation is strongly influenced by the polymerization rate.

Inspired by previous studies that show oxygen diffusion through polymeric substrates inhibits polymerization41,42, we compare the oxygen permeabilities of different substrates with the segregation thicknesses in the samples. Surprisingly, the segregation layer thickness is positively correlated with the oxygen permeability (Supplementary Fig. 5 and Table 3). To further investigate the role of oxygen, we photocure the photonic ink on an FEP film in a glove box (oxygen concentration <1 ppm), the segregation thickness significantly decreases to 0.34 ± 0.04 μm from 2.39 ± 0.07 μm, even under an irradiance of 0.4 mW cm−2 (Fig. 2a,b). When placing the substrate in a glove box for 24 h to remove its absorbed oxygen and then starting photocuring, the segregation layer entirely disappears for both FEP and PDMS films (Fig. 2c,d).

To verify the presence of an uncured layer adjacent to the oxygen-permeable substrate due to oxygen inhibition, we irradiate the photonic ink (2 mW cm−2) with varied exposure time from the FEP side in air (Fig. 2e). We observe that photopolymerization starts in the middle of the film and then gradually progresses toward the coverslip first and then the FEP side. After 11 s of irradiation, the cured layer reaches and adheres to the glass coverslip, allowing us to measure the cured thickness after washing away the uncured portion adjacent to the FEP substrate. For an 86 μm-thick photonic ink, it takes 16 s to fully cure the layer. As the exposure time extends from 11 s to 16 s, the cured thickness increases from 64.2 ± 0.7 μm to 85.7 ± 1.0 μm (Fig. 2f). This indicates that the layer near the FEP substrate remains unpolymerized due to oxygen inhibition.

Based on the above findings, we propose that the nanoparticle segregation is caused by interfacial oxygen inhibition. As shown in Fig. 2g, oxygen diffuses through polymeric substrates into the photonic ink and its concentration decays with the distance from the substrate, as also suggested by the previous work42. The ink polymerizes first in regions farther away from the oxygen-permeable substrate, while the oxygen inhibits the polymerization near the substrate, generating a monomer concentration gradient between the cured and uncured regions. Such a gradient drives monomer diffusion to the cured area and nanoparticles migration towards the substrate. The degree of migration determines the segregation thickness, which depends on how rapidly the oxygen-containing region is cured.

Manipulation of segregation via 3D printing
Digital light processing (DLP) 3D printing offers customized control over photopolymerization-driven nanoparticle segregation due to its tunable light intensity, layer-by-layer resolution, and customizable printing geometries. A commercial FEP film is selected as the substrate, as it promotes nanoparticle segregation while minimizing adhesion between the printed structure and the substrate. For ease of characterization, we print a 1 mm thick slab using a layer thickness of 50 μm. As shown in Fig. 3a, silica nanoparticles migrate to the ink-substrate interface during the layer-by-layer printing. The printed slab exhibits a multilayer structure, where each individual layer contains three distinct zones (Fig. 3b and Supplementary Fig. 6). In details, the nanoparticle-enriched segregation zone lies adjacent to a ~10 μm nanoparticle-depleted zone, while the rest zone of the layer contains uniformly distributed nanoparticles (Fig. 3c and Supplementary Fig. 7).

We systematically examine how photocuring conditions affect nanoparticle segregation. As the irradiance increases from 2.0 to 28.0 mW cm−², the segregation layer thickness decreases from 2.02 ± 0.06 μm to 0.73 ± 0.03 μm, accompanied by a gradual reduction of the adjacent nanoparticle-depleted region (Fig. 3d and Supplementary Figs. 8 and 9). A similar reduction occurs when the photoinitiator concentration increases from 0.5% to 5% w/v, leading to a decrease in segregation thickness from 2.02 ± 0.06 μm to 0.85 ± 0.04 μm (Supplementary Fig. 10). By regulating the irradiance and the photoinitiator concentration, we can control the photocuring rate to manipulate the segregation thickness from 0.37 ± 0.02 μm to 2.02 ± 0.06 μm for samples containing 15% v/v silica nanoparticles (Fig. 3e and Supplementary Fig. 11). In addition, raising the silica volume fraction from 5% to 30% produces an almost linear increase in the segregation thickness from 0.46 ± 0.02 μm to 2.60 ± 0.04 μm (Supplementary Figs. 12 and 13), while the particle size (128–286 nm) has little effect on segregation (Supplementary Figs. 14 and 15). Since the segregation is also observed in low volume fraction samples without long-range order, nanoparticle segregation is largely insensitive to whether the nanoparticles form long-range ordered assemblies. Collectively, these data reveal that segregation is suppressed by faster curing kinetics but promoted by higher nanoparticle loading. A multivariable power-law fit quantitatively captures these relationships as ts = 11.42 cPI−0.30 I−0.28 ϕ0.96 (R2 = 0.962), where ts, cPI, I, and ϕ represent the segregation thickness, the photoinitiator concentration, the irradiance, and the nanoparticle volume fraction (Fig. 3f). This empirical relation provides quantitative guidance for tuning segregation thickness through formulation and processing parameters.

We can further manipulate segregation using different acrylate monomers (Fig. 3g and Supplementary Fig. 16). For example, 2-hydroxyethyl methacrylate (7.15 ± 0.28 μm) and poly(ethylene glycol) dimethacrylate (2.09 ± 0.04 μm) lead to thicker segregation layers than 2-hydroxyethyl acrylate (2.56 ± 0.07 μm) and poly(ethylene glycol) diacrylate (0.50 ± 0.02 μm). This is because methacrylates have lower reactivity than acrylates and need a longer time to overcome the oxygen inhibition. As monomer functionality increases from mono- to tri-functional, the segregation thickness decreases from 2–4 μm to negligible levels. This reduction rises from faster polymerization rate and earlier vitrification of multifunctional acrylates that rapidly immobilize the system and suppress nanoparticle migration.

The interaction between resin and silica nanoparticles offers another route to modulate segregation. Monomers bearing hydroxyl groups, such as 2-hydroxyethyl acrylate, yield weaker segregation (2.56 ± 0.07 μm) than non-hydroxylated monomers EGPEA (3.75 ± 0.12 μm) (Fig. 3g). This likely rises from stronger hydrogen bonds between monomer hydroxyl groups and surface silanols on silica compared to those formed between silanols and carbonyl or ester groups43, which hinders nanoparticle mobility during photocuring. Silica nanoparticles with grafting hydrophobic alkyl chains have weaker interaction with resin and lead to slightly thicker segregation layers (1.76 ± 0.12 μm, Fig. 3h and Supplementary Fig. 17). Conversely, silica nanoparticles grafted with methacrylate groups can chemically cross-link with the matrix, which prevents nanoparticle migration and results in slightly reduced segregation (1.18 ± 0.07 μm, Supplementary Fig. 17). When using nanoparticles such as polystyrene, zinc sulfide (ZnS), and ZnS@SiO2, the segregation thickness ranges from 1.53 μm to 1.89 μm (Fig. 3h and Supplementary Fig. 18). Therefore, the effect of the nanoparticle type on segregation thickness is much smaller than that of acrylate monomers and we primarily use silica to tune optical properties.

Multiple optical responses
Silica nanoparticles dispersed in acrylic resins can self-assemble into uniform long-range ordered structures once their concentration reaches a threshold, which is often regarded as being driven by the steric repulsion of solvation layers44,45 and electrostatic repulsion5,46 (Supplementary Table 4). As the silica volume increases from 5% to 30%, the arrangement of silica nanoparticles becomes more ordered as evidenced by both SEM images (Supplementary Fig. 12) and ultra-small-angle X-ray scattering (USAXS) measurements (Supplementary Fig. 19). The disorder-order-transition occurs at approximately 15% v/v and thus we use the volume fraction above this threshold for all subsequent structurally coloured samples.

3D printed samples with nanoparticle segregation have optically distinct features on two sides. As shown in Fig. 4a, the backside, which contacts the printer platform, displays a bright metallic colour. Its reflectance spectrum shows a sharp peak, shifting from 605 nm to 536 nm as the measurement angle changes from 20° to 50° (Supplementary Fig. 20). This optical feature arises from the long-range ordered arrangement of nanoparticles, as further evidenced by the FFT image showing clear diffraction spots. In contrast, the exposed side, which faces the light source, exhibits a less saturated blue grey colour with nanoparticles packing in a disordered manner. Correspondingly, its FFT image presents concentric rings, indicating the loss of long-range order. Its reflectance spectrum contains a peak at 440 nm, remaining almost unchanged as the measurement angle changes (Supplementary Fig. 20), consistent with the disordered arrangement.

Different levels of Janus optical features are observed across various particle sizes and volume fractions as shown in Fig. 4b. The back side shows a shift from high-wavelength (red tone) to low-wavelength (blue tone) colours with increasing volume fraction or decreasing particle size, aligning well with Bragg’s law (Supplementary Fig. 21). For samples containing silica nanoparticles (128 nm) with the volume fractions increasing from 15% to 30%, the reflection peak on back side changes from 543 nm (green) to 434 nm (bluish violet) (Fig. 4b and Supplementary Fig. 22). In contrast, the colour of the exposed side is highly sensitive to the particle size but less dependent on the volume fraction. We further calculate the CIE 1976 colour difference (ΔE) between the two sides. At a volume fraction of 20%, particles between 128 nm and 174 nm yield similar colours on both sides with ΔE smaller than 5 (Supplementary Fig. 23). This is because the secondary reflectance peak of the exposed side falls in the ultraviolet range and the colour of the exposed side mainly comes from the primary reflectance peak of the ordered bulk (Fig. 4c and Supplementary Fig. 24). For larger particles (194–286 nm), the primary reflectance peak from the ordered bulk shifts toward the near infrared and it no longer contributes to the colour, while the secondary reflection from the disordered segregation layer falls within the visible spectrum. These together cause the back side to show achromatic colour (grey) while the exposed side exhibits chromatic colour, increasing ΔE up to 29.

The exposed side colour is more affected by the segregation layer compared to the back side (Supplementary Fig. 25). To tune this colour, we manipulate the segregation thickness using photonic ink containing 30% v/v silica nanoparticles (194 nm). As the irradiance increases from 2.0 mW cm−2 to 28.0 mW cm−2, the segregation thickness decreases from 3.21 ± 0.09 μm to 1.70 ± 0.12 μm (Supplementary Fig. 26) and the secondary reflectance peak from the disordered segregation layer weakens (Supplementary Fig. 27). The exposed side’s spectrum becomes resembled that of the back side and the colour of the exposed side changes from blue to red with a colour difference of 4.8 (Supplementary Figs. 27). We may further modulate irradiance beyond the tested range to induce larger variations in segregation thickness, producing colour difference comparable to or even larger than those between the exposed and back sides in Fig. 4b.

To stand out the colour contribution of the segregation layer, we employ a low silica volume fraction of 15% while varying the particle size from 128 nm to 286 nm. This suppresses the ordered packing in the uniform zone for weak Bragg reflection while shifting the reflection peak to near infrared and making the segregation layer dominate the colour of the exposed side. Consequently, the effect of photocuring irradiance on the exposed side’s colour becomes more pronounced as the particle size increases from 128 nm to 286 nm (Fig. 4d). For the samples containing 223 nm silica nanoparticles, only the secondary reflectance peak appears in the visible range. As the irradiance increases, this peak weakens and broadens, causing the colour to shift from pink to grey (Fig. 4d,e). For the grey sample, we can estimate the segregation thickness to be 0.82 μm based on the empirical relation in Fig. 3f, indicating that this thickness is too thin to produce a brilliant colour. These findings demonstrate that the colours of the exposed side can be adjusted by controlling the vertical distribution of nanoparticles through photocuring intensity.

We also examine the influence of printing thickness on the colour. As the printing thickness increases from 10 μm to 100 μm, the segregation thickness remains within the range of 2.85–3.06 μm (Supplementary Fig. 28). With a thin layer (10 μm), the exposed side’s spectrum is governed by the secondary reflectance peak from the disordered segregation layer since the segregation layer dominates the structure (Supplementary Fig. 29). At 20 μm, the primary reflectance peak emerges from the ordered bulk. Beyond 50 μm, the reflectance spectrum stabilizes, suggesting that the uppermost ~50 μm determines the observed colour. Therefore, the printing thickness can be used to balance the optical contributions from the segregation layer and the underlying ordered bulk, enabling colour tuning of the exposed side.

The colour quality of the printed objects is determined by both the ordered uniform and the disordered segregation zones. The packing in the segregation zone is difficult to control because of the rapid migration process during the polymerization reaction. In the uniform zone, nanoparticle arrangement remains unchanged under different photopolymerization conditions, as evidenced by the stable position of primary reflection peak across irradiance levels (Supplementary Fig. 27). This motivates us to increase the precuring time for silica nanoparticles to form a more ordered packing. Specifically, we vary the precuring time from 0 to 120 s, corresponding to the interval between lifting the printing platform and starting the photocuring of the ink. As shown in Supplementary Fig. 30, the reflectance peak becomes sharper and more intense with longer precuring time, leading to improved colour quality for both exposed and back sides. In the future work, we might try additional approaches to increase the degree of order in nanoparticle arrangements for improving colour quality, such as increasing nanoparticle surface charge47 and decreasing the ionic strength of the medium48. For faster processing, we still use precuring time of 0 s for the following studies.

While the structural colour originates from scattering of silica nanoparticles in visible wavelengths, the segregation layer introduces a micrometre-scale thickness comparable to mid-infrared wavelengths, prompting us to investigate its mid-infrared property. As shown in Fig. 4f, a broad, low reflectance peak shows up in the mid-wave infrared wavelengths (MWIR, 3-8 μm) while a high, sharp peak locates at 9.02 μm in the long-wave infrared wavelengths (LWIR, 8-14 μm). As the irradiance increases and the segregation layer decreases, the MWIR peak blue shifts while the intensity of the LWIR peak increases with a slight red shift.

To elucidate the underlying mechanism on the peak shift for MWIR and LWIR with segregation, we calculate the reflectance spectra of the hierarchical structures using the transfer matrix method (TMM, see Supplementary Information), which explicitly accounts for Fresnel reflections at each interface and interference within layered media49. Each printed layer is modelled as three sublayers: a segregation zone, a nanoparticle-depleted zone, and a uniformly distributed zone (Supplementary Fig. 31). By inputting the complex refractive index for each sublayer (Supplementary Figs. 32 and 33), the calculated reflectance spectrum remains unchanged with increasing layer numbers (Supplementary Fig. 34). This suggests the reflection primarily comes from the top layer, which is consistent with the fact that the penetration depth of sample is comparable to or much less than the printing thickness (50 μm) (Supplementary Fig. 35). Using the one-layer hierarchical model, we find that the MWIR peak has a blue shift with reducing segregation thickness, while the LWIR peak slightly increases—consistent with experimental observations (Supplementary Fig. 36). These results demonstrate that controlling the segregation layer thickness provides an effective strategy to manipulate infrared reflectivity beyond visible colouration. In future work, we might optimize nanoparticle and matrix formulations for an even broader tunable range in the infrared.

Tunable structural colour patterning
Grayscale DLP printing offers pixel-level control of light intensity, providing a controllable method for spatially manipulating nanoparticle segregation to generate structural colour patterns. As displayed in Fig. 5a, a grayscale panda image is projected to locally manipulate nanoparticle segregation, resulting in a structurally coloured panda pattern. Regions exposed to higher curing intensity have weaker nanoparticle segregation and show angle-dependent structural colour, while the low-intensity regions in the black portions of the panda pattern have strong segregation and the colours are less sensitive to viewing angles. As the illumination angle changes from 45° to 135°, the background colour turns from purple to green, whereas the colour in the black region of the panda barely changes (Fig. 5b).

This grayscale printing strategy also enables high-resolution and complex patterning. As demonstrated in Fig. 5c–g, we can print high-resolution Chinese characters (Fig. 5c), the Golden Sun Bird motif (Fig. 5d–f), and a Chinese landscape painting with colour gradients (Fig. 5g). Notably, Chinese characters on a flat film exhibit visual three-dimensionality due to optical contrast (Fig. 5c). Using the same resin formulation and printing conditions, we can print pixels with nearly identical reflectance spectra across spatial locations and independent samples, demonstrating the reproducibility of this printing strategy (Supplementary Fig. 37). Our system can achieve a minimum structural colour pixel size of 50 μm and an image resolution of 508 ppi (Fig. 5f), which exceeds the majority of reported macroscopic structural colour patterns4,6,28,29.

The resolution might be further improved higher than 508 ppi when using a DLP printer equipped with a finer DMD mirror pitch and a larger demagnification factor50. To explore the resolution limits, we cure the ink using photomasks with pixels sizes of 12, 8, and 5 μm. Gradual changes in segregation thickness near pixel boundaries are observed, making the pixels unresolvable smaller than 8 μm (Supplementary Fig. 38). These suggest that lateral oxygen diffusion from low-irradiance to high-irradiance regions51, along with light scattering in the colloidal system52, can both result in slanted segregation thickness near boundaries and ultimately constrain the achievable patterning resolution.

Beyond the visible regime, nanoparticle segregation also affects infrared reflectance. With an infrared source, such as radiation from a human palm (Fig. 5h), an infrared camera can detect spatial variations in LWIR reflectivity based on local differences in segregation thickness (Fig. 5i). In the absence of active infrared illumination, the pattern becomes indistinguishable from the background (Supplementary Fig. 39). Based on this principle, we can encode information that is invisible to the naked eye but becomes detectable under infrared imaging. As shown in Fig. 5j, we use photonic ink without carbon black to print a panda pattern. This sample shows uniformly white under ambient light due to intense multiple scattering, while the pattern becomes visible under active infrared detection even in darkness.

To achieve a higher level of information encryption, we fabricate a double-layer film through layer-by-layer grayscale printing (Fig. 5k). In the reflection mode, surface features appear as visible codes, while the transmission mode reveals hidden patterns based on the transparency differences caused by nanoparticle segregation. Each pixel in the pattern is encoded as either a quaternary number or a mathematical operator. These quaternary sequences are mapped to ASCII characters. For example, (1103)4 corresponds to “S”, (1023)4 to “K”, (1021)4 to “I”, (1010)4 to “D”. Surface information alone yields an incorrect output (“SKID”), while integrating the hidden layer allows recovery of the correct message (“CODE”). This dual-layer encoding scheme demonstrates a robust strategy for secure, multi-level information storage.

We further fabricate 3D coloured objects with anti-counterfeiting patterns. As shown in Fig. 5l, we print a Sanxingdui bronze statue containing a hidden anti-counterfeiting pattern on its top surface, which is almost indistinguishable to the naked eye but clearly revealed by infrared imaging. In addition, we print a 3D bird-shaped sample where the wings and body show two different colours, brown and cyan (Fig. 5m). This strategy of combining 3D printing with 2D structural colour patterning significantly enhances the security of anti-counterfeiting labels.

Methods
Synthesis of silica nanoparticles
Silica nanoparticles were synthesized using a modified seed regrowth method53. Firstly, L-arginine (0.1 g) was dissolved in deionized water (100 mL) in a 250 mL flask at room temperature. Tetraethyl orthosilicate (TEOS, 6.4 mL) was then added to the solution, and the mixture was heated to 70 °C with stirring for 24 h to form a silica seed dispersion. Next, ethanol (200 mL), deionized water (14 mL), ammonia solution (8 mL), and seed dispersion (1 mL) were sequentially added to a 500 mL flask under stirring at room temperature. TEOS (40 mL) was then added dropwise into the mixture under continuous stirring, and the reaction proceeded for an additional 4 h. After the reaction, we purified silica nanoparticles (128 nm) by centrifugation and ultrasonic dispersion (in ethanol) for at least four cycles. The final product was then dried at 70 °C for 24 h and redispersed in ethanol at a concentration of 10% w/v for use. By adjusting the feed ratio of the seed dispersion to TEOS, the size of silica nanoparticles was tunable from 100 to 300 nm.

Photonic ink preparation
The monomers (EGPEA and HBA), crosslinker (PEGDA), silica ethanol suspension, photoinitiator (TPO), and carbon black were thoroughly mixed, and then placed in an oven at 70 °C for 8 h to evaporate ethanol. This yielded a structurally coloured photonic ink. Unless otherwise specified, the volume ratio of EGPEA, HBA, and PEGDA was 8:1:1, and the contents of TPO and carbon black in the acrylic resin were 1% w/v and 0.015% w/w. Following a previous report44, the volume fraction of silica was limited to ≤30% to prevent a liquid-to-solid transition.

Structural colour printing
Samples were printed using a commercial DLP 3D printer (M-One Pro 50, MakeX) equipped with a 405 nm light source. The exposure intensity could be adjusted from 0 to 32 mW cm−2. The STL files were designed in AutoCAD and then converted into a series of cross-sectional images with specific slicing thicknesses (50 μm unless otherwise specified) using a slicing software (XMicro). With specific exposure intensity and layer thickness, we adjusted the curing time to achieve optimal printing accuracy. For grayscale printing, we used XMicro to convert a series of customized grayscale images into an MKP file, allowing real-time control of irradiance in each pixel. After printing, the objects were rinsed with isopropanol to remove residual ink from their surfaces. A post-curing step was performed under a 405 nm light (~50 mW cm−2) for 3 min.

Characterization
Scanning electron microscopy (SEM) images were taken on a Phenom Pharos G2 instrument using a secondary electron detector and an acceleration voltage of 5 kV. The samples underwent gold sputtering before observation. For each printed sample, we randomly measured the segregation thickness for at least three different layers. Static contact angle measurements were implemented on an optical contact angle measuring instrument (KRUSS DSA25) using deionized water and diiodomethane as standard probing liquids. The substrate surface energy was calculated directly by the software provided with the instrument using the OWRK method. The optical images of the samples were captured using a digital camera (Sony α7 III). Optical micrographs were directly imaged using an optical microscope (Nikon LV100ND) under a dark-field mode. Reflectance spectra were recorded with an ultraviolet-visible-near-infrared microspectrophotometer (CRAIC 20/30 PV Pro) with 30 W deuterium and 100 W halogen lamps for the light source. A white Teflon tape (Thorlabs, PMR10P1) was used as a white standard. We measured spectra at five different locations (82 μm × 82 μm) for each sample. Angle-resolved scattering measurements were conducted using a home-built goniometer with a deuterium-halide light source (Ideaoptics iDH2000-BSC) and an ultraviolet-visible-near-infrared spectrometer (Ideaoptics PG2000-PRO-EX). The strong peak around 655 nm in the reflectance spectra, arising from the deuterium light source, has been removed for clarity, and the original spectral data are available in the Source Data. Mid-infrared reflectance spectra were measured on an infrared microsystem (Hyperion 1000, Bruker) with a KBr beam splitter and an HgCdTe (MCT) detector. A gold mirror was used as a reflectance standard. Infrared images were taken on a FLIR T620 thermal imager with a FOL25 camera lens.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "General Comment: This manuscript presents a novel approach for structural color patterning via tunable nanoparticle segregation. The authors disperse the silica nanoparticles in acrylic resin. Driven by interfacial oxygen inhibition, the silica nanoparticles can migrate toward oxygen-permeable substrates, forming the nanoparticle-enriched disordered layer. By controlling the local segregation thickness, high-resolution structural colour patterns can be created. The authors apply the grayscale digital light processing printing to customize the structural-color images and graphics, which are promising for visual display and information encryption. Furthermore, they demonstrate the infrared camouflage based on the selective mid-infrared reflectivity. The integration of digital printing and tunable nanoparticle segregation shows technical maturity and creativity, yet several critical points require further clarification.\n1. Title: The term “programmable” literally means “capable of being programmed” and typically implies the reciprocating cyclicity of actions. However, in this paper, the aggregation of nanoparticles is unidirectional and lacks recyclable cyclicity. Therefore, using the term “programmable” would lead to ambiguity. It is recommended to replace it with other appropriate terms, such as “tunable” or “customized”, which merely need to indicate the tunability of aggregation thickness.\n2. Introduction: Background literature is insufficiently comprehensive. Current research on structural colors is extensive. Firstly, structural colors can be fabricated not only via lithographic methods but also through additive approaches like self-assembly. Additionally, the color-generating structures are not limited to nanoscale. Microscale TIR structures can also generate intense structural colors. Furthermore, for structural-color patterning, 3D printing is only a minor representative. Compared with other techniques like inkjet printing, 3D printing offers lower degrees of freedom, precision, and customization capability. Therefore, regarding the research background, the authors are suggested to provide further supplements that are not be limited to 3D printing.\n3. Main text: Is it possible to provide a precise quantitative definition of disordered photonic structures, i.e., the range distinguishing ordered and disordered self-assembled structures? Furthermore, the unique optical properties brought by disordered photonic structures should be emphasized. While the authors have noted that ordered and disordered structures exhibit differences in iridescent properties in the word descriptions, this distinction is not reflected in the figures of the main text. It is suggested to supplement this content accordingly.\n4. Fig. 1c: From this schematic diagram, it is hard to understand the differences in polymerization degree between the upper and lower regions. If the authors aim to demonstrate the influence of the substrate on polymerization degree, this aspect should be prominently emphasized.\n5. Fig. 4b: Generally speaking, the color of ordered photonic structures is brighter than that of disordered ones. However, based on the results, the color intensity of ordered photonic structures is instead weaker. Furthermore, as the nanoparticle size increases, the color of the ordered surfaces does not show any change. What is the reason for this phenomenon?\n6. Fig. 4: The term “hierarchical” typically refers to multi-scale hierarchical changes ranging from the nanoscale to the microscale. Obviously, it is inappropriate in this system, as the optical effect-generating system relies primarily on nanostructures and does not involve hierarchical characteristics. It is recommended to replace it with other appropriate terms.", "reviewer_2": "This work presents a new method to achieve structural color patterns via tunable nanoparticle segregation. During photocuring, silica nanoparticles dispersed in acrylic resin migrate toward oxygen-permeable substrates, forming a nanoparticle-enriched disordered layer. Such segregation is driven by interfacial oxygen inhibition and kinetically governed by the photocuring rate. As a result, by employing the grayscale digital light processing printing, programmably controlling the local segregation thickness to create pixelized structural color patterns is demonstrated. In the meantime, some potential applications such as visual display, information encryption, and infrared camouflage are illustrated.\nHowever, structural colors are not new, with many examples in recent years to realize vivid color patterns. Though the method proposed in this research can be potentially used for structural colors, the really awesome results are still not demonstrated, just taking the bioinspired bird feathers of grassquit for an example. Maybe, some other fantastic applications or further optimizations for structural colors need to be exploited.\nOn the other hand, some technical issues are also remaining to be addressed:\n1. Though the segregation of silica nanoparticles depends on the conditions like the substrate material, oxygen addition, and light intensity, the self-assembly process is still the most important. How to get the vivid color patterns simply, effectively and repetitively is the basic question that needs to be answered. It seems more like an engineering aspect.\n2. In line 252, “As shown in Fig. 3a” should be “As shown in Fig. 4a”. How to define the “highly saturated colour”? And also, in line 268, how to define the “vivid colouration”? In Fig. 4b, the change of colors according to the increasing volume fraction is not so obvious, especially for the particle size below 194nm.\n3. After the line 287, photonic ink containing different percentage of silica nanoparticles and the size of nanoparticles changes very often, making a common understanding of how to select the specific configuration of operations difficult to follow.\n4. For the infrared camouflage, infrared imaging seems in the LWIR waveband. So, what is the purpose and usage of the related part for the MWIR? It should be given in a more explicit way to show the relationship.", "reviewer_3": "This manuscript suggests a one-step, mask-free strategy for high-resolution structural color patterning by exploiting programmable nanoparticle segregation during photocuring. Silica nanoparticles dispersed in acrylic resin migrate toward oxygen-permeable substrates, forming a disordered, nanoparticle(NP)-enriched layer driven by interfacial oxygen inhibition. It was revealed that during each layer's curing using grayscale digital light processing (DLP), three distinct zones are formed, and the thickness of the NP-enriched layer is primarily determined by the photocuring rate. The thin-film interference occurring at the distinct zones enables infrared reflectivity. The meticulous elucidation of NP segregation at an oxygen-permeable interface is not trivial and holds value as a scientific discovery, but several necessary scientific descriptions are missing. I propose the following content for revision:\n1. When patterned photocuring occurs at an oxygen-permeable interface, lateral oxygen diffusion (also known as reaction diffusion) parallel to the substrate is known to occur, leading to the formation of a gradient microstructure. Considering this, how are the different zones formed in the lateral direction at the boundary of different doses?\n2. The principle by which the particles undergo crystallization (ordering) within the acrylate resin is not described. There should be an introductory mention of crystallization driven by interparticle repulsion from the overlap of solvation layers.\n3. Without this explanation, the subsequent mention of other particles like polystyrene (PS) and ZnS is problematic, as PS typically does not crystallize in acrylate resins and has only been reported to achieve ordering within a very small processing window via entirely different mechanisms, yet this distinction is not addressed. Additionally, PS particles must be swollen by acrylic resins and there must be no interparticle repulsions in the PS system. Therefore, their migration and dispersion in the upper layer are not likely to occur in the same way.\n4. Can 3D architectures with different structural colors be printed with the same silica nanoparticles by controlling the photocuring rate? Fig. 4d doesn’t imply it’s possible, but Fig. 5c may suggest that it is feasible.\n5. The illustration of the illumination setting in Fig. 5b shows specular reflection. However, considering that all the panda images are in the same size, the observation might have occurred in the normal direction, which is a setting of diffusive scattering, not specular reflection. If the observation was done in the specular reflection, the colors from the photonic glasses should also change anyway.\n6. In Figure 4d, 15 vol% was seemingly used. Calculating with the 154 nm particles, the structural coloration from the ordered non-close-packed array should result in a red color, likely in the low to mid 600 nm range, although this depends on the acrylic resin's refractive index. However, red is barely visible across the entire irradiance spectrum. Why is this the case?\n7. The possibility of infra-red camouflage is interpreted as arising from thin-film interference, but the description is insufficient. It appears on line 323 of page 14 without a transition or explanation relating it to different coloration mechanisms.\n8. Is there a possibility that the acrylic resin used in this research could penetrate and cause swelling of the oxygen-permeable substrate? Can the monomer flux into the polymer film also induce an additional extent of particle segregation at the interface on top of the currently discussed mechanism?\n9. Can you specify whether MWIR reflection comes from the segregation zone or the depleted zone, and whether LWIR reflection comes from the depleted zone or the uniform zone?"}, "author_response": "RESPONSES TO REVIEWERS’ COMMENTS FOR NCOMMS-25-91219\nReviewer #1\nComment 1.1\nGeneral Comment: This manuscript presents a novel approach for structural color patterning via\ntunable nanoparticle segregation. The authors disperse the silica nanoparticles in acrylic resin.\nDriven by interfacial oxygen inhibition, the silica nanoparticles can migrate toward oxygen-\npermeable substrates, forming the nanoparticle-enriched disordered layer. By controlling the local\nsegregation thickness, high-resolution structural colour patterns can be created. The authors apply\nthe grayscale digital light processing printing to customize the structural-color images and graphics,\nwhich are promising for visual display and information encryption. Furthermore, they demonstrate\nthe infrared camouflage based on the selective mid-infrared reflectivity. The integration of digital\nprinting and tunable nanoparticle segregation shows technical maturity and creativity, yet several\ncritical points require further clarification.\nResponse 1.1\nWe thank the reviewer for the summary of this work and positive comments.\nComment 1.2\nTitle: The term “programmable” literally means “capable of being programmed” and typically\nimplies the reciprocating cyclicity of actions. However, in this paper, the aggregation of\nnanoparticles is unidirectional and lacks recyclable cyclicity. Therefore, using the term\n“programmable” would lead to ambiguity. It is recommended to replace it with other appropriate\nterms, such as “tunable” or “customized”, which merely need to indicate the tunability of\naggregation thickness.\nResponse 1.2\nTaking the reviewer’s suggestion, we have replaced the term “programmable” in tittle with\n“tunable”. Correspondingly, we have revised the relevant term in the main text by replacing\n“programmable” with terms such as “tunable” “customized” and “controllable” to enhance accuracy.\nComment 1.3\nIntroduction: Background literature is insufficiently comprehensive. Current research on structural\ncolors is extensive. Firstly, structural colors can be fabricated not only via lithographic methods but\nalso through additive approaches like self-assembly. Additionally, the color-generating structures are not limited to nanoscale. Microscale TIR structures can also generate intense structural colors. Furthermore, for structural-color patterning, 3D printing is only a minor representative. Compared\nwith other techniques like inkjet printing, 3D printing offers lower degrees of freedom, precision,\nand customization capability. Therefore, regarding the research background, the authors are\nsuggested to provide further supplements that are not be limited to 3D printing.\nResponse 1.3\nWe thank the reviewer for the comment regarding the breadth of the literature. We have\nsupplemented other strategies for making structural colour patterns in the main text, including\nassembly technique, two-photon printing and inkjet printing. Accordingly, we have made relevant\nedits to the revised manuscript:\n[Page 1, Line 29-34] “However, conventional structural colour patterning typically relies on\nlithography-like strategies, where unmasked regions with initial nanostructures are first photocured,\nfollowed by immobilization of masked regions with different nanostructures. To adjust\nnanostructures for different colours, external stimuli such as magnetic fields15,16, electric fields17,\ntemperature6, or solvents4 are applied upon curing to locally manipulate the arrangements of\nassembly units (nanoparticle, liquid crystal, block copolymer, etc.).”\n[Page 2, Line 39-46] “Printing technology has been used to fabricate structurally coloured\nmaterials with high flexibility and customization18–20. However, printing various colours often\nrequires multiple resin formulations across methods such as inkjet printing, direct ink writing, or\nvat photopolymerization3,18,21–24. To the best of our knowledge, only a few studies have preliminarily\nexplored the concept of printing different colours using a single ink. Two-photon printing can locally\ncustomize the periodic nanostructures for structural colour patterns25,26, but suffer from low\nthroughput and high cost. Li et al. inkjet printed a full spectrum of structural colours by controlling\nthe sizes of printed microdomes to tuning their total internal reflections (TIR)27. These TIR based\ncolours can only be observed from the backside of the printed samples.”\nAdded references include:\nRef 15: Xu, J. et al. Magnetoresponsive cellulose nanofiber hydrogels: dynamic structuring,\nselective light transmission, and information encoding. ACS Nano 19, 14063–14072 (2025).\nRef 20: Yang, W., Li, J., Wang, J. & Jiang, L. Bioinspired digital structural color patterning based\non photonic paper/ink systems. Adv. Funct. Mater. e27923 (2025) doi:10.1002/adfm.202527923.\nRef 25: Liu, K. et al. 3D printing colloidal crystal microstructures via sacrificial-scaffold-mediated\ntwo-photon lithography. Nat. Commun. 13, 4563 (2022).\nRef 26: Wang, J. et al. Nanograting-based dynamic structural colors using heterogeneous materials.\nNano-Micro Lett. 17, 59 (2025).\nRef 27: Li, K. et al. Facile full-color printing with a single transparent ink. Sci. Adv. 7, eabh1992\n(2021).\nComment 1.4\nMain text: Is it possible to provide a precise quantitative definition of disordered photonic structures,\ni.e., the range distinguishing ordered and disordered self-assembled structures? Furthermore, the\nunique optical properties brought by disordered photonic structures should be emphasized. While\nthe authors have noted that ordered and disordered structures exhibit differences in iridescent\nproperties in the word descriptions, this distinction is not reflected in the figures of the main text. It\nis suggested to supplement this content accordingly.\nResponse 1.4\nWe thank the reviewer for raising questions about the degree of order and optical properties. In our\nsystems, disordered photonic structures are isotropic, short-range correlated without long-range\norder. Various approaches can be used to examine the existence of long-rang order, such as fast\nFourier transform (FFT) analysis of SEM images (Macromolecules 2022, 55, 8345−8354; Nat.\nCommun. 2024, 15, 1874) and small X-ray scattering measurements (ACS Nano 2024, 18,\n33864−33874). We have supplemented the FFT images of SEM images for the back and exposed\nsides in Fig. 4a. The FFT image of the back side with clear diffraction spots indicates a long-range\nordered structure, while the back side shows concentric rings indicating the loss of long-range order.\nTo emphasize the different optical effects from the ordered and disordered structures, we have added\nthe angle-resolved spectra and photos of the back and exposed sides of the sample in Supplementary\nFig. 20. Accordingly, we have made relevant edits to the revised manuscript:\n[Page 11, Line 258-266] “As shown in Fig. 4a, the back side, which contacts the printer platform,\ndisplays bright metallic colour. Its reflectance spectrum shows a sharp peak, shifting from 605 nm\nto 536 nm as the measurement angle changes from 20° to 50° (Supplementary Fig. 20). This optical\nfeature arises from the long-range ordered arrangement of nanoparticles, as further evidenced by\nthe FFT image showing clear diffraction spots. In contrast, the exposed side, which faces the light\nsource, exhibits a less saturated blue grey colour with nanoparticles packing in a disordered manner.\nCorrespondingly, its FFT image presents concentric rings, indicating the loss of long-range order.\nIts reflectance spectrum contains a peak at 440 nm remaining almost unchanged as the measurement\nangle changes (Supplementary Fig. 20), consistent with the disordered arrangement.”\nFig. 4(a). Janus optical features driven by ordered structures in the back side and disordered\nstructures in the exposed side. The photographs (0.8×0.8 cm), schematic diagram, and SEM images\ncontaining their fast Fourier transform (FFT) images are presented, respectively. Scale bar, 1 μm.\nSupplementary Fig. 20. Angle-resolved specular reflectance spectra. (a) The back side and (b) the\nexposed side. The insets show the corresponding photos with different viewing angles. The sample\nis made from photonic ink containing 30 % v/v silica nanoparticles (194 nm) and 1% w/v TPO\nphotocured under the irradiance of 2.0 mW/cm2.\nComment 1.5\nFig. 1c: From this schematic diagram, it is hard to understand the differences in polymerization\ndegree between the upper and lower regions. If the authors aim to demonstrate the influence of the\nsubstrate on polymerization degree, this aspect should be prominently emphasized.\nResponse 1.5\nWe thank the review for the comment. Fig. 1c was intended to show how we prepare samples in Fig.\n1d. To avoid confusion, we have added nanoparticles to show the segregation towards the substrate\nin new Fig.1c.\nFig. 1(c). Schematic showing the preparation of the photonic film for verifying the segregation\nphenomenon on different substrates.\nComment 1.6\nFig. 4b: Generally speaking, the color of ordered photonic structures is brighter than that of\ndisordered ones. However, based on the results, the color intensity of ordered photonic structures is\ninstead weaker. Furthermore, as the nanoparticle size increases, the color of the ordered surfaces\ndoes not show any change. What is the reason for this phenomenon?\nResponse 1.6\nWe agree the colour of ordered photonic structures is generally brighter than that of disordered ones.\nAs shown in Fig. 4c, the reflectance of the primary peaks in the ordered surfaces (back sides) is\nhigher than that of the secondary peaks in the disordered surfaces (exposed sides). As the\nnanoparticle size increases, especially larger than 194 nm, the primary peak moves to near infrared\nregion and no longer contributes to the colour, so the colour of the back size (ordered surface)\nbecomes weak. Accordingly, we have made relevant edits to the revised manuscript:\n[Page 11, Line 279-283] “For larger particles (194-286 nm), the primary reflectance peak from the\nordered bulk shifts toward the near infrared and it no longer contributes to the colour, while the\nsecondary reflection from the disordered segregation layer falls within the visible spectrum. These\ntogether cause the back side to show achromatic colour (grey) while the exposed side exhibits\nchromatic colour, increasing ΔE up to 29.”\nComment 1.7\nFig. 4: The term “hierarchical” typically refers to multi-scale hierarchical changes ranging from\nthe nanoscale to the microscale. Obviously, it is inappropriate in this system, as the optical effect-\ngenerating system relies primarily on nanostructures and does not involve hierarchical\ncharacteristics. It is recommended to replace it with other appropriate terms.\nResponse 1.7\nFollowing the reviewer’s suggestion, we change “Hierarchical optical responses” to “Multiple\noptical responses” in Fig. 4 caption and subsection title.\nReviewer #2\nComment 2.1\nThis work presents a new method to achieve structural color patterns via tunable nanoparticle\nsegregation. During photocuring, silica nanoparticles dispersed in acrylic resin migrate toward\noxygen-permeable substrates, forming a nanoparticle-enriched disordered layer. Such segregation\nis driven by interfacial oxygen inhibition and kinetically governed by the photocuring rate. As a\nresult, by employing the grayscale digital light processing printing, programmably controlling the\nlocal segregation thickness to create pixelized structural color patterns is demonstrated. In the\nmeantime, some potential applications such as visual display, information encryption, and infrared\ncamouflage are illustrated.\nHowever, structural colors are not new, with many examples in recent years to realize vivid color patterns.\nThough the method proposed in this research can be potentially used for structural colors,\nthe really awesome results are still not demonstrated, just taking the bioinspired bird feathers of\ngrassquit for an example. Maybe, some other fantastic applications or further optimizations for\nstructural colors need to be exploited.\nResponse 2.1\nWe thank the reviewer’s comments. We agree that structural colours themselves are not new and\nachieving vivid colour patterns remains an important research direction (for example, Adv. Funct.\nMater. 2025, e27923). However, the aim of this work is not to outperform existing structural colour\nsystems in terms of colour saturation or brilliance. Instead, our key contribution lies in introducing\nand exploiting a polymerization-induced nanoparticle segregation mechanism to make high-\nresolution structural colour patterns in a simple, one-step and mask-free manner.\nThis segregation mechanism provides several advantages, including the use of a single ink\nformulation to generate different colours, elimination of complex multi-step assembly or external\nfields, and spatial manipulation of nanostructures through printing parameters rather than predefined\nmasks or templates. More importantly, the underlying principle is universal and we can extend it to\nother functional materials beyond structural colours. As shown in Response 2.2, there are some\npotential approaches to make colour more vivid, but these are engineering extensions of this\nmechanism, which can be done in our future studies.\nComment 2.2\nOn the other hand, some technical issues are also remaining to be addressed:\nThough the segregation of silica nanoparticles depends on the conditions like the substrate material,\noxygen addition, and light intensity, the self-assembly process is still the most important. How to\nget the vivid color patterns simply, effectively and repetitively is the basic question that needs to be\nanswered. It seems more like an engineering aspect.\nResponse 2.2\nWe agree that self-assembly of nanoparticles is the fundamental origin of structural colour. To\nachieve vivid structural colours, we need to improving the degree of order in assembled\nnanostructures. In the original manuscript, we have showed that extending the assembly time can\nimprove the quality of structural colour (Supplementary Fig. 30). We might try additional\napproaches, such as increasing nanoparticle surface charge or decreasing the ionic strength of the\nmedium, to help increase the degree of order in nanoparticle arrangements. Considering that our\nwork focuses on controlling the local spatial distribution of nanoparticles to make colour patterns,\nthe optimization of colour quality will be interesting to explore in our future work. Accordingly, we\nhave made relevant edits to the revised manuscript:\n[Page 14, Line 341-343] “In the future work, we might try additional approaches to increase the\ndegree of order in nanoparticle arrangements for improving colour quality, such as increasing\nnanoparticle surface charge45 and decreasing the ionic strength of the medium46.”\nAdded references include:\nRef 45: Xing, Y., Fei, X. & Ma, J. Ultra‐fast fabrication of mechanical‐water‐responsive\ncolor‐changing photonic crystals elastomers and 3d complex devices. Small 20, 2405426 (2024).\nRef 46: Fan, Q. et al. Unveiling enhanced electrostatic repulsion in silica nanosphere assembly:\nformation dynamics of body-centered-cubic colloidal crystals. J. Am. Chem. Soc. 145, 28191–28203\n(2023).\nComment 2.3\nIn line 252, “As shown in Fig. 3a” should be “As shown in Fig. 4a”. How to define the “highly\nsaturated colour”? And also, in line 268, how to define the “vivid colouration”? In Fig. 4b, the\nchange of colors according to the increasing volume fraction is not so obvious, especially for the\nparticle size below 194 nm.\nResponse 2.3\nWe have corrected “As shown in Fig. 3a” as “As shown in Fig. 4a” in the revised manuscript.\nThe use of “highly saturated” and “vivid” was to qualitatively describe the visual difference between\nthe two sides of the printed samples rather than to quantify colour saturation or chromaticity. To\navoid ambiguity, we have revised the manuscript by replacing these subjective descriptors with\ndirect and concrete colour descriptions:\n[Page 11, Line 258-264] “As shown in Fig. 4a, the back side, which contacts the printer platform,\ndisplays bright metallic colour... In contrast, the exposed side, which faces the light source, exhibits\na less saturated blue grey colour with nanoparticles packing in a disordered manner…”\n[Page 11, Line 281-283] “These together cause the back side to show achromatic colour (grey) while the exposed side exhibits\nchromatic colour, increasing ΔE up to 29.”\nThe colour change with increasing volume fraction does not span the full colour spectrum but\nremains clearly observable. Taking the samples with 128 nm silica nanoparticles as example, with\nthe volume fractions increasing from 15% to 30%, the reflection peak on back side only changes\nfrom 543 nm (green) to 434 nm (bluish violet). Accordingly, we have made relevant edits to further\naccount for the adjustable colour range in the revised manuscript:\n[Page 11, Line 271-273] “For samples containing silica nanoparticles (128 nm) with the volume\nfractions increasing from 15% to 30%, the reflection peak on back side changes from 543 nm (green)\nto 434 nm (bluish violet) (Fig. 4b and Supplementary Fig. 22).”\nSupplementary Fig. 22. Reflectance spectra of the back side for samples with varying silica (128\nnm) volume fractions. All samples are made from inks containing 1% w/v TPO under the irradiance\nof 4.0 mW/cm2.\nComment 2.4\nAfter the line 287, photonic ink containing different percentage of silica nanoparticles and the size\nof nanoparticles changes very often, making a common understanding of how to select the specific\nconfiguration of operations difficult to follow.\nResponse 2.4\nWe thank the reviewer for this comment. We vary the silica volume fraction and particle size to\ndisentangle the optical contributions from the segregation layer and the order bulk. To improve\nclarity, we have added an explicit explanation before presenting the parameter-dependent results in\nthe revised manuscript:\n[Page 13, Line 311-316] “To stand out the colour contribution of the segregation layer, we employ\na low silica volume fraction of 15% while varying the particle size from 128 nm to 286 nm. This\nsuppresses the ordered packing in the uniform zone for weak Bragg reflection while shifting the\nreflection peak to near infrared and making the segregation layer dominate the colour of the exposed\nside. Consequently, the effect of photocuring irradiance on the exposed side’s colour becomes more\npronounced as the particle size increases from 128 nm to 286 nm (Fig. 4d).”\nComment 2.5\nFor the infrared camouflage, infrared imaging seems in the LWIR waveband. So, what is the purpose\nand usage of the related part for the MWIR? It should be given in a more explicit way to show the\nrelationship.\nResponse 2.5\nWe thank the reviewer for this insightful comment. Infrared camouflage is typically evaluated in the\n3-5 μm and 8-14 μm (Mater. Today 2025, 85, 253-281). In this work, we observe a large tunable\nrange of reflectance in the LWIR region (8-14 μm), leading us to use this band for infrared thermal\nimaging. The reflectance of our samples in the MWIR region (3-8 μm) is relatively low, however,\nits tunability suggests that this system may also be applicable to infrared camouflage in the MWIR\nregion through further optimization of material composition and structural design. Presenting the\ninfrared reflectance over the entire 3–14 μm range provides a comprehensive picture of the infrared\noptical response of this system. To further emphasize the tunability of the infrared optical response,\nwe have made the following additions in the main text:\n[Page 15, Line 365-368] “These results demonstrate that controlling the segregation layer thickness\nprovides an effective strategy to manipulate infrared reflectivity beyond visible colouration. In the\nfuture work, we might optimize nanoparticle and matrix formulations for an even broader tunable\nrange in the infrared.”\nReviewer #3\nComment 3.1\nThis manuscript suggests a one-step, mask-free strategy for high-resolution structural color\npatterning by exploiting programmable nanoparticle segregation during photocuring. Silica\nnanoparticles dispersed in acrylic resin migrate toward oxygen-permeable substrates, forming a\ndisordered, nanoparticle(NP)-enriched layer driven by interfacial oxygen inhibition. It was revealed\nthat during each layer's curing using grayscale digital light processing (DLP), three distinct zones\nare formed, and the thickness of the NP-enriched layer is primarily determined by the photocuring\nrate. The thin-film interference occurring at the distinct zones enables infrared reflectivity. The\nmeticulous elucidation of NP segregation at an oxygen-permeable interface is not trivial and holds\nvalue as a scientific discovery, but several necessary scientific descriptions are missing. I propose\nthe following content for revision:\nResponse 3.1\nWe thank the reviewer for accurate summary of this work and their encouraging positive comments.\nComment 3.2\nWhen patterned photocuring occurs at an oxygen-permeable interface, lateral oxygen diffusion (also\nknown as reaction diffusion) parallel to the substrate is known to occur, leading to the formation of\na gradient microstructure. Considering this, how are the different zones formed in the lateral\ndirection at the boundary of different doses?\nResponse 3.2\nWe thank the reviewer’s comment. While lateral oxygen diffusion can in principle occur at the\nboundary of different irradiance during patterned photocuring, we observe that nanoparticle\nsegregation is dominate by vertical migration of nanoparticles toward the oxygen-permeable\nsubstrate rather than by lateral reaction-diffusion effects in experiments.\nAs shown in Supplementary Fig. 37, we first expose the photonic ink to high irradiance through a\nphotomask, followed by uniform low irradiance photocuring without the mask. Cross-sectional\nSEM images of these films show horizontal segregation layers at the low irradiance region, but there\nis no any vertical segregation layers due to lateral reaction-diffusion effects (Fig. R1). Instead, the\nsegregation thickness at the low-irradiance regions tapers near the boundary, reaching a minimum\nvalue. This likely arises from light scattering from adjacent high-irradiance regions, which partially\nconsumes oxygen near the boundary and suppress the vertical segregation there. In addition, rapid\ngelation in high-irradiance region kinetically traps nanoparticles, preventing their lateral migration\ntowards low-irradiance region. As a result, lateral reaction–diffusion effects are negligible under our\nexperimental conditions.\nFig. R1. Schematic of mass transport during the polymerization process. For clarity, monomers and\npolymers are omitted.\nComment 3.3\nThe principle by which the particles undergo crystallization (ordering) within the acrylate resin is\nnot described. There should be an introductory mention of crystallization driven by interparticle\nrepulsion from the overlap of solvation layers.\nResponse 3.3\nWe thank the reviewer’s suggestion. The particle crystallization within the acrylate resin in our\nsystem is mainly driven by electrostatic repulsion between particles rather than solvation effects, as\ndemonstrated in recent studies (Ref 5, Nat. Commun. 2024,15, 5643; Ref 44, Adv. Funct. Mater.\n2024, 34, 2411670). These works show that even trace amounts of ionic species can suppress the\ncrystallization of silica nanoparticles in acrylate systems. Therefore, the electrostatic repulsion is\nthe primary driving force for silica crystallization, considering that electrostatic repulsion is\nsensitive to ion strength, whereas solvation repulsion is not. The above studies. Accordingly, we\nhave made relevant edits to the revised manuscript:\n[Page 10, Line 250-251] “Silica nanoparticles dispersed in acrylic resins can self-assemble into\nuniform long-range ordered structures once their concentration reaches a threshold, primarily\ndriven by electrostatic repulsion5,44.”\nComment 3.4\nWithout this explanation, the subsequent mention of other particles like polystyrene (PS) and ZnS\nis problematic, as PS typically does not crystallize in acrylate resins and has only been reported to\nachieve ordering within a very small processing window via entirely different mechanisms, yet this\ndistinction is not addressed. Additionally, PS particles must be swollen by acrylic resins and there\nmust be no interparticle repulsions in the PS system. Therefore, their migration and dispersion in\nthe upper layer are not likely to occur in the same way.\nResponse 3.4\nWe thank the reviewer’s comment. We agree PS and ZnS nanoparticles especially without chemical\nmodification are difficult to crystallize in acrylate resins as shown in Supplementary Fig. 18. For\nsilica nanoparticles, segregation is observed even when the volume fraction is below crystallization\nthreshold (~15%), and the segregation layer thickness linearly increases with nanoparticle volume\nfraction (Supplementary Fig. 1a-b). These results indicate that nanoparticle segregation happens not\nmatter whether the nanoparticles form crystalline assemblies. Although PS and ZnS nanoparticles\nare difficult to crystallize in acrylate resins, we can still use these nanoparticles to demonstrate the\ngenerality of the segregation mechanism. Additionally, the non-polar polystyrene generally has poor\ncompatibility with polar acrylates, so PS particles in this acrylate resin doesn’t show obviously swell\n(Soft Matter 2021, 17, 5772–5779). Accordingly, we have made relevant edits to the revised\nmanuscript:\n[Page 8, Line 203-205] “Since the segregation is also observed in low volume fraction samples\nwithout long-range order, nanoparticle segregation is largely insensitive to whether the\nnanoparticles form long-range ordered assemblies.”\nComment 3.5\nCan 3D architectures with different structural colors be printed with the same silica nanoparticles\nby controlling the photocuring rate? Fig. 4d doesn’t imply it’s possible, but Fig. 5c may suggest\nthat it is feasible.\nResponse 3.5\nIt remains challenging to printing truly three-dimensional architectures with different structural\ncolours using a single ink in our systems. In this work, nanoparticle segregation is confined to the\ntwo-dimensional xy plane, which limits the ability to print three-dimensional objects with multiple\ncolours using a single ink. The sample shown in Fig. 5c is a flat film rather than a three-dimensional\narchitecture. Although the Chinese characters exhibit apparent three-dimensionality due to optical\ncontrast, the structure itself is planar. Accordingly, we have made relevant edits to the revised\nmanuscript:\n[Page 15, Line 383-384] “Notably, Chinese characters on a flat film exhibit visual three-\ndimensionality due to optical contrast (Fig. 5c).”\nComment 3.6\nThe illustration of the illumination setting in Fig. 5b shows specular reflection. However,\nconsidering that all the panda images are in the same size, the observation might have occurred in\nthe normal direction, which is a setting of diffusive scattering, not specular reflection. If the\nobservation was done in the specular reflection, the colors from the photonic glasses should also\nchange anyway.\nResponse 3.6\nAs shown in Fig. 5b, we fix the angle between the observer and the sample plane to 45° while\nchanging the illumination direction. To avoid misunderstanding, we have modified Fig. 5b and its\ncaption to make it easier to identify. Additionally, we also provide reflectance spectra and photos\nunder the condition of specular reflection in Supplementary Fig. 20. Accordingly, we have made\nrelevant edits to the revised manuscript:\n[Page 11, Line 258-266] “As shown in Fig. 4a, the back side, which contacts the printer platform,\ndisplays bright metallic colour. Its reflectance spectrum shows a sharp peak, shifting from 605 nm\nto 536 nm as the measurement angle changes from 20° to 50° (Supplementary Fig. 20). This optical\nfeature arises from the long-range ordered arrangement of nanoparticles, as further evidenced by\nthe FFT image showing clear diffraction spots. In contrast, the exposed side, which faces the light\nsource, exhibits a less saturated blue grey colour with nanoparticles packing in a disordered manner.\nCorrespondingly, its FFT image presents concentric rings, indicating the loss of long-range order.\nIts reflectance spectrum contains a peak at 440 nm remaining almost unchanged as the measurement\nangle changes (Supplementary Fig. 20), consistent with the disordered arrangement.”\nFig. 5(b). Photographs of the printed panda pattern using photonic ink containing 30% v/v silica\nnanoparticles (194 nm) under different illumination angles. We fix the angle between the\nobservation direction and the sample plane at 45° while varying the illumination angle with the\nsample plane (θ) from 45° to 135°.\nSupplementary Fig. 20. Angle-resolved specular reflectance spectra. (a) The back side and (b) the\nexposed side. The insets show the corresponding photos with different viewing angles. The sample\nis made from photonic ink containing 30 % v/v silica nanoparticles (194 nm) and 1% w/v TPO\nphotocured under the irradiance of 2.0 mW/cm2.\nComment 3.7\nIn Figure 4d, 15 vol% was seemingly used. Calculating with the 154 nm particles, the structural\ncoloration from the ordered non-close-packed array should result in a red color, likely in the low to\nmid 600 nm range, although this depends on the acrylic resin's refractive index. However, red is\nbarely visible across the entire irradiance spectrum. Why is this the case?\nResponse 3.7\nWe thank the reviewer’s question. When the volume faction of silica nanoparticles reaches to 15%,\nthe non-close-packed array is located at a transitional stage from disorder to order according to the\nUSAXS measurements (Supplementary Fig.19). The disorder in the system leads to incoherent\nscattering and weakens Bragg reflection peak, thus red colour is barely observed when the sample\ncontains 15% v/v silica (154 nm).\nComment 3.8\nThe possibility of infra-red camouflage is interpreted as arising from thin-film interference, but the\ndescription is insufficient. It appears on line 323 of page 14 without a transition or explanation\nrelating it to different coloration mechanisms.\nResponse 3.8\nBased on the reviewer’s suggestion, we have added a transitional sentence before introducing the\ninfrared reflection results and briefly explained the underlying physical mechanism of infrared\nreflection. The relevant text has been revised as follows:\n[Page 14, Line 346-348] “While the structural colour originates from scattering of silica\nnanoparticles in visible wavelengths, the segregation layer introduces a micrometer-scale thickness\ncomparable to mid-infrared wavelengths, prompting us to investigate its mid-infrared property.”\n[Page 14, Line 354-357] “To elucidate the underlying mechanism on the peak shift for MWIR and\nLWIR with segregation, we calculate the reflectance spectra of the hierarchical structures using the\ntransfer matrix method (TMM, see Supplementary information), which explicitly accounts for\nFresnel reflections at each interface and interference within layered media47.”\nComment 3.9\nIs there a possibility that the acrylic resin used in this research could penetrate and cause swelling\nof the oxygen-permeable substrate? Can the monomer flux into the polymer film also induce an\nadditional extent of particle segregation at the interface on top of the currently discussed mechanism?\nResponse 3.9\nAs far as we know, the swelling doesn’t happen here. The oxygen-permeable substrate used in this\nwork is fluorinated ethylene propylene copolymer (FEP), which is a commercial substrate for vat\npolymerization 3D printing. Such fluorinated polymers are difficult to be swollen by solvents (Aust.\nJ. Chem. 2015, 68, 13–22). In this work, the vast majority of samples were prepared on the same\nFEP film. The reproducible segregation behavior observed across various samples confirms the\nexcellent resistance of FEP to swelling by the acrylate resin.\nComment 3.10\nCan you specify whether MWIR reflection comes from the segregation zone or the depleted zone,\nand whether LWIR reflection comes from the depleted zone or the uniform zone?\nResponse 3.10\nWe thank the reviewer’s comment. The final MWIR and LWIR reflectance arises from the combined\ncontributions of the segregation layer, the nanoparticle-depleted zone, and the uniform zone. Each\npart possesses a distinct effective refractive index and optical thickness, and their superposition\ncollectively determines the overall MWIR and LWIR reflection. Therefore, it is not appropriate to\nattribute the infrared reflection exclusively to a specific layer. It arises from the integrated vertical\ndistribution of nanoparticles formed during photopolymerization."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have thoroughly and effectively addressed all the reviewer’s comments, and the revised manuscript is now significantly clearer and more accessible to readers. Their supplementary experimental demonstrations substantially enhance the scientific impact of this work. I therefore recommend the publication of this paper.", "reviewer_2": "Some of my concerns have been covered. However, all the engineering-related issues are still missing.", "reviewer_3": "I appreciate the reviewers for answering all the comments carefully. I only have comments for first to comments, Comment 3.2 and Comment 3.3. All other comments are well addressed with well-supported rationales. I sincerely appreciate the careful response from the authors.\nFor Comment 3.2, what I intended to ask was exactly about the gradient height of the particle segregation which was made by lateral diffusion of oxygen. Namely, I didn't mean to ask \"vertical segregation layers\" but the slanted height of the segregation layer. Previous papers about reaction diffuison formed cone-shaped particles by using this vertical diffusion of oxygen, which seems to happen in this case, too. I do agree that vertical segregation layer will not happen, but the slanted formation of the layer will occur. Therefore, I suppose this will also affect the resolution that is argued in this paper. I think it is worth mentioning the gradient height change of horizontal segration layers in terms of resolution. Otherwise, readers would think there will be a sharp contrast at the boundary of strong and weak doses.\nFor Comment 3.3, I do understand that many papers are still arguing that the crystallization of silica particles dispersed in acrylate polymer is mainly due to electrostatic repulsion. But, many paper do not. Please refer to the paper from one of the pioneers in this silica-acrylate system, who is Dr. Peng Jiang. J. Am. Chem. Soc. 126, 13778-13786 (2004). Its title is \"Large-scale fabrication of wafer-size colloidal crystals, macroporous polymers and nanocomposites by spin-coating.\" Here, in the right paragraph on page 13785, although Dr. Jiang once stated that electrostatic repulsion drove the colloidal crystallization in this system, this JACS paper clearly states:\n1) \"The interparticle electrostatic repulsion plays only a minor role due to the low dielectric constant of the ETPTA medium (​3 at optical frequency)\"\n2) \"We also tested salt effect on the colloidal crystallization process during spin coating by adding 10-3 M tetrabutylammonium chloride to the silica-ETPTA dispersion (10% v/v 200-proof ethanol was added as cosolvent) to screen interparticle electrostatic repulsion and make silica colloids more “hard-sphere” like. The resultant spin-coated nanocomposite exhibits the same in-plane particle separation (~1.41D) and optical transmission spectrum as those samples made without the addition of salt, indicating minor contribution of the electrostatic force to the colloidal crystallization.\"\nIt is different from salt, but even the addition of a trace amount of ethanol and water into this silica-acrylate system will destroy the crystallized state and induce particle network, which means the main driving force of repulsion is diminished by the solvents. If it would have been electrostatic repulsion, there is no reason the addition of water decrease the repulsive force but increase the attractive force. (Adv. Mater. 36, 2307917 (2023). Its title is \"Advanced Additive Manufacturing of Structurally-Colored Architectures\")\nAcrylate groups form hydrogen bonds with silanol groups of silica partciles and they form solvation layers. When different solvation layers overlap, disjoining pressure makes the particles repel one another, which can be also stated as steric hindrance. I think acrylate polymer is not like water, and cannot induce electrostatic repulsion strong enough to drive the whole crystallization. While water, with a high dielectric constant of 80, can facilitate ionic dissociation and induce strong electrostatic repulsion, organic media such as acrylates hinder ionization due to their low dielectric constants. Consequently, the Debye screening length becomes extremely short, making it difficult for electrostatic forces to operate over a long range.\nTherefore, I think the sentence that states the driving force for crystallization is MAINLY theelectrostatic force is not correct, but at least it has to include steric hindrance or disjoining pressure from the overlap of solvation layers.\nIf the authors address these points by incorporating a brief discussion or a minor revision to the current statement regarding the crystallization mechanism, I believe the manuscript will be fully suitable for publication."}, "author_response": "RESPONSES TO REVIEWERS’ COMMENTS FOR NCOMMS-25-91219A\nReviewer #1\nComment 1.1\nThe authors have thoroughly and effectively addressed all the reviewer’s comments, and the revised\nmanuscript is now significantly clearer and more accessible to readers. Their supplementary\nexperimental demonstrations substantially enhance the scientific impact of this work. I therefore\nrecommend the publication of this paper.\nResponse 1.1\nWe sincerely thank the reviewer for the encouraging feedback and recognition of our work.\nReviewer #2\nComment 2.1\nSome of my concerns have been covered. However, all the engineering-related issues are still\nmissing.\nResponse 2.1\nWe agree that applying our technology into real product will require engineering multiple\nparameters to optimize the colour saturation and contrast. However, colour optimization is not the\nprimary focus of our work as we emphasized in our previous responses.\nAnother engineering-related issue is about the reproducibility. To evaluate repeatability of the\npatterning technology, we have fabricated three samples with identical binary patterns using the\nsame resin formulation and printing conditions. Within a single sample, spectra collected at four\ndifferent locations under the same exposure conditions nearly overlap (new Supplementary Fig.\n37A). Moreover, nearly identical spectra are observed for the same locations across three\nindependently printed samples. These results demonstrate that the proposed patterning strategy is\nreproducible across both spatial locations and independent samples. Accordingly, we have made\nrelevant edits to the revised manuscript:\n[Page 15, Line 385-387] “Using the same resin formulation and printing conditions, we can print\npixels with nearly identical reflectance spectra across spatial locations and independent samples,\ndemonstrating the reproducibility of this printing strategy (Supplementary Fig. 37).”\nSupplementary Fig. 37. Reproducibility of structural colour patterning. (a) Reflectance spectra at\ndifferent locations under the same exposure in a single sample. (b) Reflectance spectra of the same\nlocations across three samples. The insets show the photos of the binary patterns with circles\nrepresenting the measured spots (7.6 μm × 7.6 μm). The printing ink contains 30% v/v silica\nnanoparticles (247 nm). The irradiances of red-brown and yellow-green regions are 28.0 mW/cm2\nand 8.4 mW/cm2, respectively. These patterns are exposed for 30 seconds. Scale bars, 0.5 cm.\nReviewer #3\nComment 3.1\nI appreciate the reviewers for answering all the comments carefully. I only have comments for first\nto comments, Comment 3.2 and Comment 3.3. All other comments are well addressed with well-\nsupported rationales. I sincerely appreciate the careful response from the authors.\nResponse 3.1\nWe thank the reviewer for the reassessment of responses and approving most of the revisions.\nComment 3.2\nFor Comment 3.2, what I intended to ask was exactly about the gradient height of the particle\nsegregation which was made by lateral diffusion of oxygen. Namely, I didn't mean to ask \"vertical\nsegregation layers\" but the slanted height of the segregation layer. Previous papers about reaction\ndiffusion formed cone-shaped particles by using this vertical diffusion of oxygen, which seems to\nhappen in this case, too. I do agree that vertical segregation layer will not happen, but the slanted\nformation of the layer will occur. Therefore, I suppose this will also affect the resolution that is\nargued in this paper. I think it is worth mentioning the gradient height change of horizontal\nsegregation layers in terms of resolution. Otherwise, readers would think there will be a sharp\ncontrast at the boundary of strong and weak doses.\nResponse 3.2\nWe thank the reviewer for the clarification and agree that lateral oxygen diffusion at boundaries\nbetween pixels can lead to a gradual change in segregation layer thickness, rather than an abrupt\nstep. As the reviewer mentioned, this effect is well know in reaction-diffusion systems and has been\nreported in pure acrylate resin system, for example in the formation of microneedles due to oxygen\ndiffusion in the work RSC Adv. 2022, 12, 9550–9555.\nIn our system, which contains a high loading of colloidal particles (5-30% v/v), lateral oxygen\ndiffusion is accompanied by light scattering across pixel boundaries. These combined effects lead\nto the gradient height change of segregation layers near the boundary between high- and low-\nirradiance regions, as we observed in Supplementary Fig. 38h-i. Importantly, this gradient is\nconfined to a narrow interfacial region, while the segregation layer remains laterally uniform away\nfrom the boundary. Accordingly, we have discussed these effects on colour patterning resolution in\nthe revised manuscript:\n[Page 16, Line 391-395] “The resolution can be further improved higher than 508 ppi when using\na DLP printer equipped with a finer DMD mirror pitch and a larger demagnification factor50. To\nexplore the resolution limits, we cure the ink using photomasks with pixels sizes of 12, 8, and 5 μm.\nGradual changes in segregation thickness near pixel boundaries are observed, making the pixels\nunresolvable smaller than 8 μm (Supplementary Fig. 38). These suggest that lateral oxygen diffusion\nfrom low-irradiance to high-irradiance regions51, along with light scattering in the colloidal\nsystem52, can can both result in gradual changes in segregation thickness near pixel boundaries and\nultimately constrains the achievable patterning resolution.”\nAdded references include:\nRef 51: Kim, S., Lee, H., Choi, H., Yoo, K.-Y. & Yoon, H. Investigation on photopolymerization\nof PEGDA to fabricate high-aspect-ratio microneedles. RSC Adv. 12, 9550–9555 (2022).\nRef 52: Korčušková, M., Lepcio, P. & Jančář, J. Metal oxide-functionalized photopolymers: a\nperspective in 3D printing. ACS Polym. Au 5, 458–480 (2025).\nComment 3.3\nFor Comment 3.3, I do understand that many papers are still arguing that the crystallization of silica\nparticles dispersed in acrylate polymer is mainly due to electrostatic repulsion. But, many paper do\nnot. Please refer to the paper from one of the pioneers in this silica-acrylate system, who is Dr. Peng\nJiang. J. Am. Chem. Soc. 126, 13778-13786 (2004). Its title is \"Large-scale fabrication of wafer-\nsize colloidal crystals, macroporous polymers and nanocomposites by spin-coating.\" Here, in the\nright paragraph on page 13785, although Dr. Jiang once stated that electrostatic repulsion drove the\ncolloidal crystallization in this system, this JACS paper clearly states:\n1) \"The interparticle electrostatic repulsion plays only a minor role due to the low dielectric constant\nof the ETPTA medium (3 at optical frequency)\"\n2) \"We also tested salt effect on the colloidal crystallization process during spin coating by adding\n10-3 M tetrabutylammonium chloride to the silica-ETPTA dispersion (10% v/v 200-proof ethanol\nwas added as cosolvent) to screen interparticle electrostatic repulsion and make silica colloids more\n“hard-sphere” like. The resultant spin-coated nanocomposite exhibits the same in-plane particle\nseparation (~1.41D) and optical transmission spectrum as those samples made without the addition\nof salt, indicating minor contribution of the electrostatic force to the colloidal crystallization.\"\nIt is different from salt, but even the addition of a trace amount of ethanol and water into this silica-\nacrylate system will destroy the crystallized state and induce particle network, which means the\nmain driving force of repulsion is diminished by the solvents. If it would have been electrostatic\nrepulsion, there is no reason the addition of water decrease the repulsive force but increase the\nattractive force. (Adv. Mater. 36, 2307917 (2023). Its title is \"Advanced Additive Manufacturing of\nStructurally-Colored Architectures\")\nAcrylate groups form hydrogen bonds with silanol groups of silica partciles and they form solvation\nlayers. When different solvation layers overlap, disjoining pressure makes the particles repel one\nanother, which can be also stated as steric hindrance. I think acrylate polymer is not like water, and\ncannot induce electrostatic repulsion strong enough to drive the whole crystallization. While water,\nwith a high dielectric constant of 80, can facilitate ionic dissociation and induce strong electrostatic\nrepulsion, organic media such as acrylates hinder ionization due to their low dielectric constants.\nConsequently, the Debye screening length becomes extremely short, making it difficult for\nelectrostatic forces to operate over a long range.\nTherefore, I think the sentence that states the driving force for crystallization is MAINLY the\nelectrostatic force is not correct, but at least it has to include steric hindrance or disjoining pressure\nfrom the overlap of solvation layers.\nIf the authors address these points by incorporating a brief discussion or a minor revision to the\ncurrent statement regarding the crystallization mechanism, I believe the manuscript will be fully\nsuitable for publication.\nResponse 3.3\nWe thank the reviewer for the insightful discussion and agree that nanoparticle crystallization in\nacrylate systems can arise from multiple repulsive interactions. While some studies, including the\npioneering work by Jiang et al. (J. Am. Chem. Soc. 2004, 126, 13778-13786), indicate that\nelectrostatic repulsion plays a minor role due to the low dielectric constant of acrylate media, other\nreports have shown that the introduction of organic salts or changes in solvent composition can\nsignificantly disrupt ordered structures (such as Nat. Commun. 2024, 15, 5643; Adv. Funct. Mater.\n2024, 34, 2310861), suggesting a non-negligible contribution from electrostatic interactions under\ncertain conditions.\nAs summarized in new Supplementary Table 4, these seemingly contrasting observations likely arise\nfrom differences in particle surface chemistry, resin formulation, ionic impurities, and solvent\nevaporation process. In our system, multiple acrylic resins are used in the formulation, and these\nresins (or chemically similar monomers) have been involved in previous studies discussing both\nsolvation-induced steric repulsion and electrostatic interactions.\nImportantly, our work does not rely on a particular crystallization mechanism. We observe that\nnanoparticle segregation occurs even in regimes where long-range crystalline ordering is absent,\nindicating that the segregation mechanism investigated here is robust and largely independent of\nwhether the nanoparticles form a crystalline or disordered assembly.\nWe have incorporated two possible mechanisms into our revised manuscript:\n[Page 10, Line 250-252] “Silica nanoparticles dispersed in acrylic resins can self-assemble into\nuniform long-range ordered structures once their concentration reaches a threshold, which is often\nregarded as being driven by the steric repulsion of solvation layers44,45 and electrostatic repulsion5,46\n(Supplementary Table 4).”\nSupplementary Table 4. Comparisons of the assembly mechanism of silica\nnanoparticle in acrylic resin.\nProposed Volume\nSolvents Monomers References\nmechanism fraction\n20%-\nEthanol Poly(ethylene glycol) phenyl ether acrylate 8\n40%\nEthoxylated trimethylolpropane triacrylate,\nSolvation layer ＞15% Ethanol poly(ethylene glycol) phenyl ether acrylate, 9\npolyurethane acrylate (mw ≈ 1400 g mol−1))\nEthanol,\n41% Polyurethane acrylate (mw ≈ 7000 g mol−1) 10\nwater\n33% Ethanol Ethoxylated trimethylolpropane triacrylate 11\nDi(ethylene glycol) ethyl ether acrylate,\nElectrostatic 30% Ethanol polyethylene glycol mono-phenyl ester 12\nrepulsion acrylate\n30%-\nEthanol Poly(ethylene glycol) diacrylate 13\n45%\nSolvation layer,\n2-Carboxyethyl acrylate, poly(ethylene\nelectrostatic\n20%- glycol) methacrylate, poly(ethylene glycol)\nrepulsion, and Ethanol 14\n50% diacrylate, trimethylolpropane ethoxylate\npolymerization-\ntriacrylate\nInduced\nSolvation layer\nand electrostatic 25% Ethanol Trimethylolpropane ethoxylate triacrylate 15\nrepulsion\nSolvation layer Ethylene glycol phenyl ether acrylate, 4-\n15%-\nand electrostatic Ethanol hydroxybutyl acrylate, poly(ethylene glycol) This work\n30%\nrepulsion diacrylate\nAdded references in the main tex include:\nRef 44: Kim, J. B., Lee, H., Chae, C., Lee, S. Y. & Kim, S. Advanced additive manufacturing of\nstructurally‐colored architectures. Adv. Mater. 36, 2307917 (2023).\nRef 45: Lee, G. H. et al. Chameleon-inspired mechanochromic photonic films composed of non-\nclose-packed colloidal arrays. ACS Nano 11, 11350–11357 (2017).\nAdded references in Supplementary information include:\nRef 8: Lee, G. H. et al. Chameleon-inspired mechanochromic photonic films composed of non-\nclose-packed colloidal arrays. ACS Nano 11, 11350–11357 (2017).\nRef 9: Kim, J. B., Chae, C., Han, S. H., Lee, S. Y. & Kim, S.-H. Direct writing of customized\nstructural-color graphics with colloidal photonic inks. Sci. Adv. 7, eabj8780 (2021).\nRef 10: Kim, J. B., Lee, H., Chae, C., Lee, S. Y. & Kim, S. Advanced additive manufacturing of\nstructurally‐colored architectures. Adv. Mater. 36, 2307917 (2023).\nRef 11: Kim, S., Jeon, S., Jeong, W. C., Park, H. S. & Yang, S. Optofluidic synthesis of\nelectroresponsive photonic janus balls with isotropic structural colors. Adv. Mater. 20, 4129–\n4134 (2008).\nRef 12: Hu, Y., Qi, C., Ma, D., Yang, D. & Huang, S. Multicolor recordable and erasable\nphotonic crystals based on on-off thermoswitchable mechanochromism toward inkless\nrewritable paper. Nat. Commun. 15, 5643 (2024).\nRef 13: Hu, Y., Yang, D., Ma, D., Qi, C. & Huang, S. Structural color‐based smart liquid\nwindows address the tradeoff between high optical transparency and brilliant color. Adv. Funct.\nMater. 34, 2310861 (2024).\nRef 14: Yang, D., Qin, Y., Ye, S. & Ge, J. Polymerization‐induced colloidal assembly and\nphotonic crystal multilayer for coding and decoding. Adv. Funct. Mater. 24, 817–825 (2014).\nRef 15: Nah, S. H., Kim, J. B., Chui, H. N. T., Suh, Y. & Yang, S. Enhanced colorimetric detection\nof volatile organic compounds using a dye‐incorporated photonic crystal‐based sensor array.\nAdv. Mater. 36, 2409297 (2024)."}]

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