Abstract
Vanadium dioxide (VO2) is a well-known thermochromic material that can potentially be used as a smart coating on glazing systems in order to regulate the internal temperature of buildings. Most growth techniques for VO2 demand high temperatures (>250 °C), making it impossible to comply with flexible (polymeric) substrates. To overcome this problem, hydrothermally synthesized VO2 particles may be dispersed in an appropriate matrix, leading to a thermochromic coating that can be applied on a substrate at a low temperature (<100 °C). In this work, we reported on the thermochromic properties of a VO2/Poly-Vinyl-Pyrrolidone (PVP) nanocomposite. More specifically, a fixed amount of VO2 particles was dispersed in different PVP quantities forming hybrids of various VO2/PVP molar ratios which were deposited as films on fused silica glass substrates by utilizing the drop-casting method. The crystallite size was calculated and found to be 35 nm, almost independent of the PVP concentration. As far as the thermochromic characteristics are concerned, the molar ratio of the VO2/PVP nanocomposite producing VO2 films with the optimum thermochromic properties was 0.8. These films exhibited integral solar transmittance modulation (overall wavelengths) ΔTrsol = 0.35%–1.7%, infrared (IR) switching at 2000 nm ΔTrIR = 10%, visible transmittance at 550 nm TrVis = 38%, critical transition temperature TC = 66.8 °C, and width of transmittance hysteresis loop ΔTC = 6.8 °C. Moreover, the critical transition temperature was observed to slightly shift depending on the VO2/PVP molar ratio.
Highlights
Versatile solutions to the expanding and rapid increase in worldwide energy demands as well as the restrictions concerning environmental pollution by utilizing renewable energy sources and energy-efficient materials have already attracted both scientific interest and commercial attention.The energy consumption in buildings alone is estimated to be approximately 40% of the world’s total energy consumption, and it is anticipated it will increase steadily [1,2,3]
The thermochromic behavior of the VO2 particles was confirmed by the differential scanning calorimetry (DSC) diagram of Figure 1b, from which the critical transition temperature and the hysteresis width were calculated and found to be TC = 66.6 ◦ C and ∆TC = 12.1 ◦ C
VO2 /PVP nanocomposite films were fabricated by polymer-assisted deposition on fused silica commercial glass at low treatment temperatures (
Summary
Versatile solutions to the expanding and rapid increase in worldwide energy demands as well as the restrictions concerning environmental pollution by utilizing renewable energy sources and energy-efficient materials have already attracted both scientific interest and commercial attention.The energy consumption in buildings alone is estimated to be approximately 40% of the world’s total energy consumption, and it is anticipated it will increase steadily [1,2,3]. Versatile solutions to the expanding and rapid increase in worldwide energy demands as well as the restrictions concerning environmental pollution by utilizing renewable energy sources and energy-efficient materials have already attracted both scientific interest and commercial attention. Ventilation, and air conditioning are the main energy consumers, being responsible for about 30% of annual carbon dioxide emissions [3]. Heat transmittance and insulation inefficiency of windows are responsible for 15%–22% of a building’s energy loss [4,5,6,7]. In recent years, ‘smart’ windows have received widespread attention as one of the potential solutions to reducing energy consumption by air conditioning in modern architecture. ‘Smart’ windows are able to intelligently self-regulate the amount of transmitted heat, while keeping the visible transmission mainly unchanged. Vanadium dioxide (VO2 ) is one of the most promising solid-sate materials for smart windows due to its unique optical properties related to its inherent and ultrafast reversible structural (phase-change) transition from a monoclinic VO2 (M) to tetragonal rutile VO2 (R)
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