Facile fabrication of VO2 composite film with enhanced significantly solar modulation performance by adjusting viscosity of VO2/PU dispersion

The facile fabrication of VO2 thermochromic film with outstanding solar modulation ability along with high luminous transmittance is still challenging for the large-scale practical application of VO2 films. The dispersity of VO2 in polymer matrix can determine the optical performance of VO2 thermochromic film to some content. Herein, the VO2 nanoparticles were prepared by one-step hydrothermal method and directly dispersed in polyurethane (PU) sol with different viscosity to cast the VO2 composite film. The solar modulation ability (ΔTsol) almost increased linearly with the logarithm of viscosity for PU sol, and ΔTsol can be enhanced to 14.5% from 6.6% while maintaining a high Tlum beyond 54% only by changing the content of thickener. The ΔTsol increased further to 20.0% for the three layers film. The enhanced optical performances might be attributed to the good dispersity of VO2 nanoparticles and pore structure in PU matrix. This study provides a novel strategy in preparing VO2 film for the applications in smart windows.