VO2/Si–Al gel nanocomposite thermochromic smart foils: Largely enhanced luminous transmittance and solar modulation

• 20 nm VO2 nanoparticles can be produced with scalable mechanical attrition.
• Tlum (∼60%) combined with ΔTsol (∼12%) surpasses the best reported results.
• Increasing foil thickness reduces Tlum but increases ΔTsol.
• Si–Al gels provide good dispersion of VO2, enhancing thermochromism.

VO2 nanoparticles with a dimension of approximately 20 nm were obtained by simple mechanical bead-milling method, which were well dispersed in transparent silica–alumina (Si–Al) gel matrix to form nanocomposites. The VO2/Si–Al gel thermochromic nanocomposite foils were fabricated with various VO2 solid contents and foil thickness. With 10% VO2 loading and 3 μm foil thickness, high luminous transmittance (Tlum(20°C) = 63.7% and Tlum(90°C) = 54.4%), and large solar modulation ability (ΔTsol = 12%) can be obtained which surpasses the best reported results (nanoporous films:Tlum(20°C) = 43.3%, Tlum(90°C) = 39.9% and ΔTsol = 14.1%). This current approach provided a simple and scalable preparation method with the best combined thermochromic performance.

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