Vanadium dioxide-polydiacetylene thermochromic composite films and their solar regulation properties

Vanadium dioxide (VO₂) with thermally induced phase transition has demonstrated a good regulation ability in the range of near-infrared light, and widely used in smart windows. However, the VO₂-based smart windows still face critical challenges in practical use, such as the unfavorable brown-yellow color of the VO₂ thin film, and lack of indicative color-changing for the phase transition process, which are key factors limiting its applications in smart glass. Combining VO₂ with other chromogenic materials could effectively improve the appearance color of smart window coatings and endow it indicative color-changing function. In this study, it is successful to obtain VO₂ multifunctional composite film with reversible thermochromic polydiacetylene (PDA-1, from blue to red) through a bilayer structure strategy. The composite film not only shows favorable grayish-blue color, but also exhibits good solar light regulation ability and luminescence transmittance (solar light regulation ability ΔT_sol=7.64%, luminescence transmittance at low temperature T_{l, lum}=56.23%, luminescence transmittance at high temperature T_{h, lum}=62.37%). In addition, the thermochromic temperature of the PDA-1 is close to the phase transition temperature of monoclinic VO₂ (~68℃). With the temperature increases, the appearance color of the composite film can change from grayish-blue to red color, and also regulating the near-infrared transmittance, which is conducive to the visual display and further promotion for the thermochromic smart windows.