Hybrid Nanocomposite Films Comprising Dispersed VO₂ Nanocrystals: A Scalable Aqueous-Phase Route to Thermochromic Fenestration

Abstract

Buildings consume an inordinate amount of energy, accounting for 30-40% of worldwide energy consumption. A major portion of solar radiation is transmitted directly to building interiors through windows, skylights, and glazed doors where the resulting solar heat gain necessitates increased use of air conditioning. Current technologies aimed at addressing this problem suffer from major drawbacks, including a reduction in the transmission of visible light, thereby resulting in increased use of artificial lighting. Since currently used coatings are temperature-invariant in terms of their solar heat gain modulation, they are unable to offset cold-weather heating costs that would otherwise have resulted from solar heat gain. There is considerable interest in the development of plastic fenestration elements that can dynamically modulate solar heat gain based on the external climate and are retrofittable onto existing structures. The metal-insulator transition of VO is accompanied by a pronounced modulation of near-infrared transmittance as a function of temperature and can potentially be harnessed for this purpose. Here, we demonstrate that a nanocomposite thin film embedded with well dispersed sub-100-nm diameter VO nanocrystals exhibits a combination of high visible light transmittance, effective near-infrared suppression, and onset of NIR modulation at wavelengths <800 nm. In our approach, hydrothermally grown VO nanocrystals with <100 nm diameters are dispersed within a methacrylic acid/ethyl acrylate copolymer after either (i) grafting of silanes to constitute an amorphous SiO shell or (ii) surface functionalization with perfluorinated silanes and the use of a perfluorooctanesulfonate surfactant. Homogeneous and high optical quality thin films are cast from aqueous dispersions of the pH-sensitive nanocomposites onto glass. An entirely aqueous-phase process for preparation of nanocrystals and their effective dispersion within polymeric nanocomposites allows for realization of scalable and viable plastic fenestration elements.

Responsive Smart Windows from Nanoparticle–Polymer Composites

“…[51] Thus, it has been mixed with various metal oxides through in situ polymerization or sol-gel reactions. [52] PU [34] and copolymers of methacrylic acid and ethyl acrylate [35] can be used to uniformly disperse thermochromic VO 2 NPs that tend to aggregate, thus allowing for casting homogeneous composite films for applications including thermo-responsive solar cells and smart windows. [34,35] Another way to minimize NP aggregation is to control NP dispersions during the polymerization process.…”

“…[52] PU [34] and copolymers of methacrylic acid and ethyl acrylate [35] can be used to uniformly disperse thermochromic VO 2 NPs that tend to aggregate, thus allowing for casting homogeneous composite films for applications including thermo-responsive solar cells and smart windows. [34,35] Another way to minimize NP aggregation is to control NP dispersions during the polymerization process. [53] For example, composite films of PMMA/ TiO 2 NPs are prepared by in situ polymerization of methyl methacrylate (MMA) dispersed with PMMA chains surface grafted TiO 2 NPs.…”

Elucidating the Crystallite Size Dependence of the Thermochromic Properties of Nanocomposite VO2 Thin Films

“…Polymer dispersion was carried out as reported in a previous work and is schematically outlined in Figure 3. 59 VO 2 @SiO 2 core–shell nanocrystals was dispersed in 10 mL of an alkaline aqueous solution (pH of ca. 11.3 prepared by addition of 2-amino-2-methyl-1-propanol containing 5% added water (Amresco) to deionized water) in a glass vial by ultrasonication.…”

In situ Resource Utilization and Reconfiguration of Soils Into Construction Materials for the Additive Manufacturing of Buildings

“…As such, kinetics of gelation and cross-linking are of vital importance and necessitate the incorporation of catalysts and retardants that enable precise modulation of temporal strengthening profiles. As with the design of functional nanocomposites, embedding additional components that imbue properties such as chemical resistance or protection against UV radiation, deter colonization by microbes, increase thermal insulation, and provide selfcleaning or liquid repellant properties requires introduction of gradients of material inclusions, use of microcapsules and coatings, and anchoring of the inclusions within the continuous matrix (White et al, 2001;Shchukin et al, 2006;Zheludkevich et al, 2007;Dennis et al, 2015;Fleer et al, 2017). The idea of self-healing is one that is particularly important for the design of resilient structures and has been explored by embedding monomeric species within nanoscale containers; the monomers are released in response to mechanical or chemical stimuli and are cross-linked to heal damage (White et al, 2001;Cho et al, 2009;Cotting and Aoki, 2016).…”