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

Nicholas I Cool; Carlos A Larriuz; Randall James; Jaime R Ayala; Anita; Mohammed Al-Hashimi; Sarbajit Banerjee

doi:10.1021/acsengineeringau.2c00027

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

ACS Eng Au. 2022 Dec 21;2(6):477-485. doi: 10.1021/acsengineeringau.2c00027. Epub 2022 Jul 21.

Authors

Nicholas I Cool^{1

2}, Carlos A Larriuz^{1

3}, Randall James¹, Jaime R Ayala^{1

2}, Anita^{1

2}, Mohammed Al-Hashimi⁴, Sarbajit Banerjee^{1

2}

Affiliations

¹ Department of Chemistry, Texas A&M University, College Station, Texas 77843-3012, United States.
² Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843-3012, United States.
³ Department of Chemistry, University of Puerto Rico, Cayey, Puerto Rico 00736, United States.
⁴ Department of Chemistry, Texas A&M University at Qatar, Doha 23874, Qatar.

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.