| 1. |
- Chen, Shangzhi, et al.
(author)
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Tunable Structural Color Images by UV-Patterned Conducting Polymer Nanofilms on Metal Surfaces.
- 2021
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 33:33
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Journal article (peer-reviewed)abstract
- Precise manipulation of light-matter interactions has enabled a wide variety of approaches to create bright and vivid structural colors. Techniques utilizing photonic crystals, Fabry-Pérot cavities, plasmonics, or high-refractive-index dielectric metasurfaces have been studied for applications ranging from optical coatings to reflective displays. However, complicated fabrication procedures for sub-wavelength nanostructures, limited active areas, and inherent absence of tunability of these approaches impede their further development toward flexible, large-scale, and switchable devices compatible with facile and cost-effective production. Here, a novel method is presented to generate structural color images based on monochromic conducting polymer films prepared on metallic surfaces via vapor phase polymerization and ultraviolet (UV) light patterning. Varying the UV dose enables synergistic control of both nanoscale film thickness and polymer permittivity, which generates controllable structural colors from violet to red. Together with grayscale photomasks this enables facile fabrication of high-resolution structural color images. Dynamic tuning of colored surfaces and images via electrochemical modulation of the polymer redox state is further demonstrated. The simple structure, facile fabrication, wide color gamut, and dynamic color tuning make this concept competitive for applications like multifunctional displays.
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| 2. |
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| 3. |
- Gamage, Sampath, et al.
(author)
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Reflective and transparent cellulose-based passive radiative coolers
- 2021
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In: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 28, s. 9383-9393
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Journal article (peer-reviewed)abstract
- Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we control the solar light interaction from highly reflective (> 90%, porous structure) to highly transparent (approximate to 90%, homogenous structure). Both cellulose materials show high thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 15 degrees C and 5 degrees C, respectively.
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| 4. |
- Gamage, Sampath, et al.
(author)
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Transparent nanocellulose metamaterial enables controlled optical diffusion and radiative cooling
- 2020
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 8:34, s. 11687-11694
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Journal article (peer-reviewed)abstract
- Materials that provide independent control of infrared thermal radiation and haze in the visible could benefit many areas and applications, including clothing, packaging and photovoltaics. Here, we study this possibility for a metamaterial composite paper based on cellulose nanofibrils (CNF) and silicon dioxide (SiO2) microparticles with infrared (IR) Fröhlich phonon resonances. This CNF-SiO2composite shows outstanding transparency in the visible wavelength range, with the option of controlling light diffusion and haze from almost zero to 90% by varying the SiO2microparticle concentration. We further show that the transparent metamaterial paper could maintain high thermal emissivity in the atmospheric IR window, as attributed to strong IR absorption of both the nanocellulose and the resonant SiO2microparticles. The high IR emissivity and low visible absorption make the paper suitable for passive radiative cooling and we demonstrate cooling of the paper to around 3 °C below ambient air temperature by exposing it to the sky.
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| 5. |
- Shanker, Ravi, et al.
(author)
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Noniridescent Biomimetic Photonic Microdomes by Inkjet Printing
- 2020
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In: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 20:10, s. 7243-7250
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Journal article (peer-reviewed)abstract
- Certain bird species have evolved spectacular colors that arise from organized nanostructures of melanin. Its high refractive index (similar to 1.8) and broadband absorptive properties enable vivid structural colors that are nonsusceptible to photo-bleaching. Mimicking natural melanin structural coloration could enable several important applications, in particular, for non-iridescent systems with colors that are independent of incidence angle. Here, we address this by forming melanin photonic crystal microdomes by inkjet printing. Owing to their curved nature, the microdomes exhibit noniridescent vivid structural coloration, tunable throughout the visible range via the size of the nanoparticles. Large-area arrays (>1 cm(2)) of high-quality photonic microdomes could be printed on both rigid and flexible substrates. Combined with scalable fabrication and the nontoxicity of melanin, the presented photonic microdomes with noniridescent structural coloration may find use in a variety of applications, including sensing, displays, and anticounterfeit holograms.
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| 6. |
- Shanker, Ravi, et al.
(author)
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Structurally Colored Cellulose Nanocrystal Films as Transreflective Radiative Coolers
- 2022
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:7, s. 10156-10162
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Journal article (peer-reviewed)abstract
- Radiative cooling forms an emerging direction in which objects are passively cooled via thermal radiation to cold space. Cooling materials should provide high thermal emissivity (infrared absorptance) and low solar absorptance, making cellulose an ideal and sustainable candidate. Broadband solar-reflective or transparent coolers are not the only systems of interest, but also more pleasingly looking colored systems. However, solutions based on wavelength-selective absorption generate not only color but also heat and thereby counteract the cooling function. Intended as coatings for solar cells, we demonstrate a transreflective cellulose material with minimal solar absorption that generates color by wavelength-selective reflection, while it transmits other parts of the solar spectrum. Our solution takes advantage of the ability of cellulose nanocrystals to self-assemble into helical periodic structures, providing nonabsorptive films with structurally colored reflection. Application of violet-blue, green, and red cellulose films on silicon substrates reduced the temperature by up to 9 °C under solar illumination, as result of a combination of radiative cooling and reduced solar absorption due to the wavelength-selective reflection by the colored coating. The present work establishes self-assembled cellulose nanocrystal photonic films as a scalable photonic platform for colored radiative cooling.
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