| 1. |
- Anusuyadevi, Prasaanth Ravi, et al.
(author)
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Synthetic Plant Cuticle Coating as a Biomimetic Moisture Barrier Membrane for Structurally Colored Cellulose Films
- 2023
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In: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 10:7
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Journal article (peer-reviewed)abstract
- Photonic films based on cellulose nanocrystals (CNCs) are sustainable candidates for sensors, structurally colored radiative cooling, and iridescent coatings. Such CNC-based films possess a helicoidal nanoarchitecture, which gives selective reflection with the polarization of the incident light. However, due to the hygroscopic nature of CNCs, the structural colored material changes and may be irreversibly damaged at high relative humidity. Thus, moisture protection is essential in such settings. In this work, hygroscopic CNC-based films are protected with a bioinspired synthetic plant cuticle; a strategy already adopted by real plants. The protective cuticle layers altered the reflected colors to some extent, but more importantly, they significantly reduced the water vapor permeance by more than two orders of magnitude, from 2.1 × 107 (pristine CNC/GLU film) to 12.3 × 104 g µm m−2 day−1 atm−1 (protected CNC/GLU film). This expands significantly the time window of operation for CNC/GLU films at high relative humidity.
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| 2. |
- Banerjee, Debashree, et al.
(author)
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Electrical tuning of radiative cooling at ambient conditions
- 2023
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In: Cell Reports Physical Science. - : ELSEVIER. - 2666-3864. ; 4:2
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Journal article (peer-reviewed)abstract
- Passive radiative cooling forms a sustainable means for cooling of objects through thermal radiation. Along with progress on static cooling systems, there is an emerging need for dynamic control to enable thermoregulation. Here, we demonstrate temperature regu-lation of devices at ambient pressure and temperature by electri-cally tuning their radiative cooling power. Our concept exploits the possibility to electrochemically tune the thermal emissivity and thereby cooling power of a conducting polymer, which enabled reversible control of device temperatures of around 0.25 degrees C at ambient conditions in a sky simulator. Besides tuneable radiative cooling by exposure to the sky, the concept could also contribute to reduced needs for indoor climate control by enabling dynamic control of thermal energy flows between indoor objects, such as be-tween people and walls.
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| 3. |
- Banerjee, Debashree, et al.
(author)
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Elevated thermoelectric figure of merit of n-type amorphous silicon by efficient electrical doping process
- 2018
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In: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 44, s. 89-94
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Journal article (peer-reviewed)abstract
- The currently dominant thermoelectric (TE) materials used in low to medium temperature range contain Tellurium that is rare and mild-toxic. Silicon is earth abundant and environment friendly, but it is characterized by a poor TE efficiency with a low figure of merit, ZT. In this work, we report that ZT of amorphous silicon (a-Si) thin films can be enhanced by 7 orders of magnitude, reaching ∼0.64 ± 0.13 at room temperature, by means of arsenic ion implantation followed by low-temperature dopant activation. The dopant introduction employed represents a highly controllable doping technique used in standard silicon technology. It is found that the significant enhancement of ZT achieved is primarily due to a significant improvement of electrical conductivity by doping without crystallization so as to maintain the thermal conductivity and Seebeck coefficient at the level determined by the amorphous state of the silicon films. Our results open up a new route towards enabling a-Si as a prominent TE material for cost-efficient and environment-friendly TE applications at room temperature.
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| 4. |
- Banerjee, Debashree, et al.
(author)
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The control of thermal conductivity through coherent and incoherent phonon scattering in 2-dimensional phononic crystals by incorporating elements of self-similarity
- 2019
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 115:21
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Journal article (peer-reviewed)abstract
- In this letter, we report the theoretical study on phonon transport in monocrystalline silicon thin-films having unfilled or metal-filled circular holes (i.e., phononic crystals, PnCs) and show that the thermal conductivity, κ" role="presentation">κ, at 1 K can be maximally reduced by using a multiscale structure, which allows us control over the porosity of the structure. The circular scatterers are placed in the square (SQ) and hexagonal (HX) pattern with a fixed 100 nm interhole spacing, and the pit diameter is varied between 10 and 90 nm. Each of the corresponding silicon PnCs shows reduced κ" role="presentation">κ compared to the unpatterned film. The SQ-PnC having tungsten-filled pits shows the greatest reduction in κ" role="presentation">κ when we consider only the effects of coherent scattering. Furthermore, we have computed κ" role="presentation">κ for the PnC where the unit cell, of 100 nm and 500 nm sizes, comprises the Sierpinski gasket (SG) with circular holes of different diameters (depending on the fractal order) in the same cell. It is observed that the κ" role="presentation">κ for the 2nd (100 nm cell) and 3rd order (500 nm cell) SG-PnC is comparable to the SQ- and HX-PnC with a pit diameter of 90 nm. When we add the effect of the diffuse boundary scattering in κ" role="presentation">κ, there is a lowering in κ" role="presentation">κ compared to that when only the coherent effects are considered. The additional κ" role="presentation">κ-reduction due to boundary scattering for the SQ-PnC and HX-PnC (both with 90 nm diam) as well as the 2nd and 3rd order SG-PnCs is 47%, 40%, 80%, and 60%, respectively.
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| 5. |
- 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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| 6. |
- Liao, Mingna, et al.
(author)
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Cellulose-Based Radiative Cooling and Solar Heating Powers Ionic Thermoelectrics
- 2023
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In: Advanced Science. - : WILEY. - 2198-3844. ; 10:8
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Journal article (peer-reviewed)abstract
- Cellulose opens for sustainable materials suitable for radiative cooling thanks to inherent high thermal emissivity combined with low solar absorptance. When desired, solar absorptance can be introduced by additives such as carbon black. However, such materials still shows high thermal emissivity and therefore performs radiative cooling that counteracts the heating process if exposed to the sky. Here, this is addressed by a cellulose-carbon black composite with low mid-infrared (MIR) emissivity and corresponding suppressed radiative cooling thanks to a transparent IR-reflecting indium tin oxide coating. The resulting solar heater provides opposite optical properties in both the solar and thermal ranges compared to the cooler material in the form of solar-reflecting electrospun cellulose. Owing to these differences, exposing the two materials to the sky generated spontaneous temperature differences, as used to power an ionic thermoelectric device in both daytime and nighttime. The study characterizes these effects in detail using solar and sky simulators and through outdoor measurements. Using the concept to power ionic thermoelectric devices shows thermovoltages of >60 mV and 10 degrees C temperature differences already at moderate solar irradiance of approximate to 400 W m(-2).
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| 7. |
- Majee, Subimal, 1984-, et al.
(author)
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Efficient and thermally stable iodine doping of printed graphene nano-platelets
- 2017
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In: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 117, s. 240-245
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Journal article (peer-reviewed)abstract
- We report on an efficient and highly thermally stable doping with iodine on ink-jet printed graphene films. The films consist of pristine few-layer graphene nano-platelates (p-GNPs) that are randomly stacked. With iodine doping simply by soaking in aqueous iodine solution, the printed p-GNPs films are enhanced in electrical conductivity by up to around 2 times. The doping effect exhibits excellent thermal stability up to 500 degrees C under high vacuum condition (10(-6) mBar) evidenced by electrical and spectroscopic means. Furthermore, the doping of iodine leads to a slight increment of work function by 0.07 eV. Using depth profile measurements, it is found that iodine species diffuse deeply into the films and likely intercalate between two adjacent p-GNPs which interpret the aforementioned efficient enhancement and thermal stability of the doping effect. The reported doping scheme offers a viable low-temperature optimization method for conductive electrodes with p-GNPs in the application of printed devices.
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| 8. |
- Rossi, Stefano, et al.
(author)
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Dynamically Tuneable Reflective Structural Coloration with Electroactive Conducting Polymer Nanocavities
- 2021
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 33:49
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Journal article (peer-reviewed)abstract
- Dynamic control of structural colors across the visible spectrum with high brightness has proven to be a difficult challenge. Here, this is addressed with a tuneable reflective nano-optical cavity that uses an electroactive conducting polymer (poly(thieno[3,4-b]thiophene)) as spacer layer. Electrochemical doping and dedoping of the polymer spacer layer provides reversible tuning of the cavity's structural color throughout the entire visible range and beyond. Furthermore, the cavity provides high peak reflectance that varies only slightly between the reduced and oxidized states of the polymer. The results indicate that the polymer undergoes large reversible thickness changes upon redox tuning, aided by changes in optical properties and low visible absorption. The electroactive cavity concept may find particular use in reflective displays, by opening for tuneable monopixels that eliminate limitations in brightness of traditional subpixel-based systems.
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| 9. |
- 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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