Thermochromic Behavior of VO2/Polymer Nanocomposites for Energy Saving Coatings

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.

Solution-Processed VO2 Nanoparticle/Polymer Composite Films for Thermochromic Applications

“…As a result, we chose two polymersPVA and PVP-K30to prepare VO 2 /PVA and VO 2 /PVP composite films as they improved NP dispersion by maintaining/enhancing the optical performance of VO 2 and fulfill the temperature requirement. The ratio between VO 2 /polymers plays a significant role in the thermochromic properties of the composite thin films . As shown in Figure , it is only with an optimum VO 2 /polymer ratio high-quality thermochromic thin films can be achieved.…”

“…However, due to the multivalent nature of the vanadium ions, VO 2 is highly oxygen or air sensitive and is oxidized into other polymorphs of VO x with severely deteriorated thermochromic performances upon air exposure. , The stability and uniformity while retaining or enhancing the desired functionality of VO 2 thin films prepared from solution-based processes are crucial factors for practical applications. Forming composites with polymers represent one important strategy in improving the uniformity and stability of oxide NP-based films. , Recent studies have demonstrated VO 2 /polymer composite films prepared using crystalline VO 2 NPs. − However, most of these processes involve limited scalability and complex processing, which are not favorable for large-scale applications. − In addition, the films have offered inadequate IR modulation , and experienced a dramatic drop of luminous transmittance when heated . Further, the widely used spray-coating method typically requires delicate formulations of inks (such as solvent, concentration, and composition) and frequently results in non-uniform films, whereas spin coating is limited to prepare small-area thin films. , It is thus of great significance to explore facile and scalable solution-based strategies to achieve uniform and stable VO 2 -based thermochromic thin films to facilitate their practical applications.…”

Thermochromic and opacity behaviors in vanadium dioxide nanofilms: a theoretical study

“…The expression above is obtained by identifying the critical transition temperature through heating (T t max ), 68 °C, and cooling temperature (T t min ), 62 °C. As such, we can calculate W, the width of the transition, and include information about the temperature width of the IMT transitions for VO 2 nanofilm, which is calculated by [16,21] and given as.…”

Recent Progress in Polymer-Based Building Materials

“…Besides the fire-retardant coatings and waterproof coatings, there are many other functional coatings, such as heat insulation coatings [111][112][113][114], self-healing coatings [115,116], sterilization coatings [117], icephobic coatings [118], and anticorrosive coatings [119], which are also indispensable in construction engineering.…”