Preparation Of VO₂ Nanoparticle Composite Structure And Study On Thermochromic Properties

smart window is an intelligent dimming device composed of transparent base material and dimming material.The smart window which automatically adjusts light transmittance based on ambient temperature is called thermochromic smart window.Thermochromic smart windows have been widely concerned because of the advantages of simple structure and no extra energy consumption.Vanadium dioxide（VO₂）undergoes reversible transition between the metallic phase and the semiconductor phase under thermal excitation,and its structure and optical properties change suddenly before and after the transition.It is an ideal thermochromic smart window dimming material.Phase transition temperature,visible light transmittance and solar modulation ability are important indexes to measure VO₂ thermochromic smart window.Due to the intrinsic absorption of VO₂,the visible light transmittance is usually less than 40%,and the solar modulation ability is difficult to exceed 10%.Moreover,the phase transition temperature of VO₂ is 68℃,which cannot meet the needs of practical applications.Therefore,increasing the visible light transmittance and solar modulation ability and decreasing the phase transition temperature of VO₂have always been the focus of research.In view of the above problems,in this paper,the design and manufacture of W-doped VO₂（W-VO₂）nanoparticles and Polyvinyl Pyrrolidone（PVP）composite structure film was proposed to study the influence of composite structure parameters on the thermochromic properties.The research content mainly includes the following two parts:（1）W-VO₂/PVP composite films were prepared by spin coating method.The influence of W-VO₂ volume concentration on optical properties of composite structures films was studied.The results show that when the film thickness is 6μm,the transmittance of visible light decreases gradually with the increase of W-VO₂volume concentration,and the solar modulation ability increases first and then decreases.When the W-VO₂ volume concentration is 0.75%,the solar modulation ability reaches the maximum of 11.43%.In order to further improve the thermochromic properties of the films,the thickness of W-VO₂/PVP composite films was optimized.When the volume concentration of W-VO₂ is 2.23%,and the film thickness is 3.7μm,the maximum solar modulation ability is 14.22%and the visible light transmittance is 54.51%.Based on the above results,continuous improvement of visible light transmittance without sacrificing the solar modulation ability is the key to improve thermochromic performance.Therefore,W-VO₂/SiO₂/PVP composite films were proposed and prepared to further improve the optical properties of the composite structure films.The results show that when the volume ratio of W-VO₂ nanoparticles to SiO₂ microspheres is 1:1,the visible light transmittance increases from 54.51%to65.04%,an increase of nearly 19.32%.The solar modulation ability of the film remained at 12.62%.It is found that SiO₂ microspheres replace part of W-VO₂/PVP,which reduces the absorption of the film and provides an effective optical path in the film,thus improving the visible light transmittance by FDTD simulation.The smart window model test shows that W-VO₂/SiO₂/PVP coated glass can effectively heat insulation.Compared to blank glass,the indoor temperature dropped by 9.1℃.（2）In order to further improve the thermochromic performance of the composite structure,the vertical column structure was formed by using double-channel anodic alumina（AAO）as template,and the visible transmittance and the solar modulation ability were regulated.The W-VO₂/PVP/AAO composite structure was prepared by filling AAO hole with capillary force of solution.When the volume concentration of W-VO₂ is 0.75%,the solar modulation ability of the film is 11.50%.The optical properties of the film were further optimized by adjusting the viscosity of the precursor solution.The results show that the higher the solution viscosity,the smaller the residual air column in AAO hole,the more continuous W-VO₂/PVP nanorods,and the optimal solar modulation ability reaches 12.07%.The height,diameter and filling factor of W-VO₂/PVP/AAO composite films were optimized by FDTD simulation.The results show that when the height of W-VO₂/PVP/AAO composite films is 3μm,the diameter is 400 nm,and the filling factor is 0.56,the optical properties of the films are further improved.The visible light transmittance is 68.94%,and the solar modulation ability is 17.74%.The W-VO₂/SiO₂/PVP composite structure and W-VO₂/PVP/AAO composite structure proposed in this paper can effectively improve the thermochromic properties of W-VO₂,which is of great significance to promote the development and application of VO₂ thermochromic smart windows.