| 1. |
- Alam, Mehebub, et al.
(författare)
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The past, present, and future of piezoelectric fluoropolymers: Towards efficient and robust wearable nanogenerators
- 2023
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Ingår i: Nano Research Energy. - : Tsinghua University Press. - 2791-0091. ; 2:4
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Forskningsöversikt (refereegranskat)abstract
- Polyvinylidene difluoride (PVDF) derivatives in metal/PVDF/metal (MPM) sandwich structures have been studied extensively since 1969. Cousin copolymers of the same family have been discovered with fascinating piezoelectric, pyroelectric, electrocaloric, and ferroelectric properties. Solution processing, flexibility, lightweight, and thermal stability make this class of materials complementary to inorganics. Thus, PVDF based polymers potentially compete with inorganic materials for a broad range of technologies such as energy generators, loudspeakers, coolers, and memories. However, the stable non-electroactive α-phase and hydrophobic nature of PVDF are the main barriers for developoing high performing and robust MPM devices in electronic applications. In this review, we present an up-to-date overview on different methods to induce the electroactive β-phase and improve the adhesion strength with metals to ensure robust and durable MPM devices. We go through advantages and disadvantages of several methods and pinpoint future opportunities in this research area. A special attention is paid to wearable piezoelectric nanogenerators for energy harvesting from human body motion, where flexible PVDF derivatives are compared with rigid piezoelectric ceramics. While the piezoelectric coefficient of PVDF (d33 ~ 24–34 pm/V) is one order lower than ceramic materials, novel co-polymers of PVDF display d33 > 1000 pm/V upon bias. This shows promise to bring piezoelectrics to flexible and large-area applications such as smart textiles. We also discussed challenges to improve wearability, such as light weight, breathability, and flexibility.
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| 2. |
- Dastidar, Subham, et al.
(författare)
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Janus cellulose for self-adaptive solar heating and evaporative drying
- 2022
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Ingår i: Cell Reports Physical Science. - : ELSEVIER. - 2666-3864. ; 3:12
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Tidskriftsartikel (refereegranskat)abstract
- Porous cellulose can be tuned dynamically between reflecting and transparent states through reversible wetting with liquids like water while remaining non-absorptive in both states. By combining porous cellulose with an underlying cellulose-carbon nanotube layer, we here report a Janus cellulose that instead switches between reflect-ing and absorptive states. While the material is reflective and low absorbing in its dry state, exposure to water increases the optical transparency of the top layer and enables the bottom layer to absorb solar light and generate heat. In turn, this initiates a self -adaptive process that drives water evaporation and dries the struc-ture, making it reflective again. In situ measurements of scattering intensity, temperature, and water evaporation reveal an intriguing dynamic relationship between the optical and thermal properties of the Janus cellulose. This study highlights the use of cellulose sys-tems for solar and thermal management, demonstrating solar -induced self-adaptive heating, evaporative drying, and thermal regulation.
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| 3. |
- Gamage, Sampath, et al.
(författare)
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Reflective and transparent cellulose-based passive radiative coolers
- 2021
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Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 28, s. 9383-9393
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Tidskriftsartikel (refereegranskat)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. |
- Liao, Mingna, et al.
(författare)
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Cellulose-Based Radiative Cooling and Solar Heating Powers Ionic Thermoelectrics
- 2023
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Ingår i: Advanced Science. - : WILEY. - 2198-3844. ; 10:8
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Sultana, Ayesha, et al.
(författare)
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Enhanced ionic transport in ferroelectric polymer fiber mats
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:39, s. 22418-22427
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Tidskriftsartikel (refereegranskat)abstract
- The limited ionic conductivity is the main issue for the application of solid-state ionic conductors. In this work, we have shown that increasing the ferroelectric phase content in a polymer matrix could enhance the molar ionic conductivity of the incorporated ionic liquid by two orders of magnitude compared to the original films with the same composition. The ferroelectric polymer fiber mats were prepared through electrospinning to induce the ferroelectric phase that ensure the polarization of the dipoles. After analyzing the ferroelectric phase content and polarization of the fiber mats and films containing different ion concentration with FTIR spectroscopy and piezoelectric characterization, a detailed mechanism explaining the improved conductivity in the ferroelectric fiber mats was proposed. Benefiting from the good flexibility, improved ionic conductivity and high temperature coefficient of the fiber mats, we fabricated an organic ionic thermistor. The temperature tracking and mapping function of the ionic thermistor was demonstrated by using two devices with 4 and 16 pixels.
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| 6. |
- Sultana, Ayesha, et al.
(författare)
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The enhanced ionic thermal potential by a polarized electrospun membrane
- 2024
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X.
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Tidskriftsartikel (refereegranskat)abstract
- Inspired by thermally sensitive ion channels in human skin, a polarized membrane composed of a ferroelectric polymer fiber matrix is used to double the heat-induced potential in ionic thermoelectric devices. The comparison of the thermal potentials between different directions of polarization and temperature gradient indicates the importance of cation-dipole interactions for the enhancement. Adding a polarized membrane to ionic thermoelectric devices induces dipole-ion interaction and enhances the thermal voltage by more than double.
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| 7. |
- Sultana, Ayesha, et al.
(författare)
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Toward High-Performance Green Piezoelectric Generators Based on Electrochemically Poled Nanocellulose
- 2023
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 35:4, s. 1568-1578
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Tidskriftsartikel (refereegranskat)abstract
- Internet-of-Everything (IoE) is defined as networked connections of things, people, data, and processes. IoE nodes, preferably shaped as printed flexible systems, serve as the frontier outpost of the Internet and comprise devices to record and regulate states and functions. To power distributed IoE nodes in an ecofriendly manner, a technology to scavenge energy from ambience and self-powered devices is developed. For this, piezoelectricity is regarded as a key property; however, the current technology typically based on polyvinylidene difluoride (PVDF) copolymers is expensive and produced via toxic protocols. We report piezoelectric characteristics of electrochemically poled cellulose nanofiber (CNF) thin films processed from water dispersions. Poling these films under humid conditions causes breaking and reorientation of CNF segments, which results in enhanced crystal alignment rendering the resulting material piezoelectric. Generators based on poled CNF show similar piezoelectric voltage and coefficient, here measured as d(33) = 46 pm V-1, to devices including PVDF copolymer layers of similar thickness. Our findings promise low-cost and printable ecofriendly piezoelectric-powered IoE nodes.
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