Scalable Synthesis of Uniform VO2(M) Nanoparticles for High-Performance Flexible Thermochromic Films

The synthesis of uniformly sized VO2(M) nanoparticles for flexible films with efficiently thermochromic properties remains a challenge. This work reports a facile, scalable sol-gel method combined with post-annealing to synthesize spherical VO2(M) nanoparticles by controlling the concentration of H2O2 solution, the oxygen intake, annealing time and annealing temperature. The obtained nanoparticles possess a narrow size distribution, high crystallinity, and good dispersibility. The thermochromic properties of the VO2(M) nanoparticles were investigated by measuring their transmittance in the visible and near-infrared regions as a function of temperature. The results showed that the nanoparticles exhibit excellent thermochromic properties, with a reversible change in transmittance of up to 60% between 25 °C and 85 °C. Furthermore, flexible films were prepared by incorporating the VO2(M) nanoparticles into a polyvinyl alcohol (PVA) matrix. The films exhibit excellent flexibility and adhesion, as well as efficient thermochromic properties. The reversible transmittance change of the films can reach up to 45% between 25 °C and 85 °C, which is comparable to that of the bulk VO2(M) materials. Overall, this approach provides a simple and scalable method for preparing high-quality VO2(M) nanoparticles with excellent thermochromic properties. The flexible films based on these nanoparticles have great potential for practical applications in smart windows, energy-saving coatings, and other related fields.