Thermochromic Fenestration Elements Based on the Dispersion of Functionalized VO₂ Nanocrystals within a Polyvinyl Butyral Laminate

Abstract

The energy required to heat, cool, and illuminate buildings continues to increase with growing urbanization, engendering a substantial global carbon footprint for the built environment. Passive modulation of the solar heat gain of buildings through the design of spectrally selective thermochromic fenestration elements holds promise for substantially alleviating energy consumed for climate control and lighting. The binary vanadium­(IV) oxide VO2 manifests a robust metalinsulator transition that brings about a pronounced modulation of its near-infrared transmittance in response to thermal activation. As such, VO2 nanocrystals are potentially useful as the active elements of transparent thermochromic films and coatings. Practical applications in retrofitting existing buildings requires the design of workflows to embed thermochromic fillers within industrially viable resins. Here, we describe the dispersion of VO2 nanocrystals within a polyvinyl butyral laminate commonly used in the laminated glass industry as a result of its high optical clarity, toughness, ductility, and strong adhesion to glass. To form high-optical-clarity nanocomposite films, VO2 nanocrystals are encased in a silica shell and functionalized with 3-methacryloxypropyltrimethoxysilane, enabling excellent dispersion of the nanocrystals in PVB through the formation of siloxane linkages and miscibility of the methacrylate group with the random copolymer. Encapsulation, functionalization, and dispersion of the coreshell VO2@SiO2 nanocrystals mitigates both Mie scattering and light scattering from refractive index discontinuities. The nanocomposite laminates exhibit a 22.3% modulation of NIR transmittance with the functionalizing moiety engendering a 77% increase of visible light transmittance as compared to unfunctionalized coreshell particles. The functionalization scheme and workflow demonstrated, here, illustrates a viable approach for integrating thermochromic functionality within laminated glass used for retrofitting buildings.

Enhanced Thermochromic Performance of VO2 Nanoparticles by Quenching Process

“…Unfortunately, these matrixes require a strict annealing atmosphere or precisely uniform dispersion of VO 2 in the nanocomposite films. Compared to inorganic matrix, organic agents, such as polyvinyl pyrrolidone (PVP) [13,27], polyurethane (PU) [28], polyvinyl butyral (PVB) [29], and acrylic resin [30], have become more favorable hosts due to their low refractive index and facile fabrication process. Gao et al [31] synthesized a flexible coating by dispersing SiO 2 capsuled monocrystal VO 2 with good crystallinity, fine grain size (VO 2 @SiO 2 ) into PU, which showed good optical properties (T lum = 55.3%, ∆T sol =7.5%).…”