The challenges stemming from climate change demand the proactive adoption of energy-efficient tactics to reduce carbon dioxide (CO₂) emissions and harness sustainable energy resources. "Smart" window films composed of thermochromic vanadium dioxide (VO₂) can adaptively harness solar energy to regulate building temperatures, thereby reducing power consumption and CO₂ emissions. However, the existing challenge lies in economically and mass-producing VO₂ nanomaterials and films with high solar energy modulation. In this study, we have developed a scalable flow synthesis process and explore a spectrum of parameters, aiming to synthesize monoclinic M-phase VO₂ nanoparticles with controlled sizes and morphologies. Additionally, we have explored doped nanostructures and surface modifications to enable control over the metal-to-insulator transition temperature. Our approaches encompass (i) altering the morphology of nanoparticles to a nanorod structure, (ii) surface modification using low refractive index ligand coatings, and (iii) incorporating secondary thermochromic materials to improve solar energy modulation and attaining an aesthetically appealing "green" appearance as an alternative to the conventional brownish-yellow tint. By manipulating the thermochromic and optical properties of VO₂ nanoparticles, we have achieved 10.0% for as-synthesized VO₂/polymer nanocomposite films and 19.9% solar energy modulation for PFDA-VO₂/NLET hybrid smart films. Moreover, the nanorod composed film achieved doubled solar energy modulation in the infrared region, Δ at 2000 nm, and enhanced the solar energy modulation, Δ_sol, by 68% as compared to that of its nanoparticle counterpart in the inclusion of low refractive index ligands. This work provides insights into the design and development of advanced VO₂/polymer smart window films.

Justin Griffith

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