Preparation And Performance Of Thermochromic Phase Change Films Based On Nano Vanadium Dioxide

With the rapid development of the economy,energy shortage and environmental protection have become two major issues worldwide.In order to reduce energy consumption and greenhouse gas emissions,people are increasingly paying attention to finding effective energy-saving materials.According to reports,building energy consumption accounts for approximately 30-40%of total energy consumption in the world.However,the energy loss through windows accounts for over 50%of the total energy consumption of buildings.Therefore,the application of energy-saving glass is very important for building energy conservation.VO₂ thermochromic thin films can automatically regulate the solar energy entering the room according to ambient temperature,thereby reducing building energy consumption.Therefore,VO₂thermochromic smart windows have enormous application potential in the field of building energy conservation.The following issues hinder the practical application of VO₂ smart windows:high phase transition temperature（T_c）,limited solar-energy modulation efficiency(ΔT_sol),low luminous transmittance(T_lum),and poor weatherability.These issues need to be addressed in conjunction with key processes such as the synthesis of VO₂ nanoparticles and the final film-forming process.In addition,considering the application prospects of VO₂-based smart windows,the convenience and cost of preparing thin films should also be considered.It is urgent to explore a simple,low-cost,and more universal method for preparing VO₂ thin films,which can promote the commercial application of VO₂ smart windows.Therefore,the main research content and corresponding research conclusions of this paper are as follows:（1）VO₂ nanoparticles with small particle sizes and good crystallinity were synthesized through a one-step hydrothermal method.Then VO₂ nanoparticles were dispersed in a polymer solution.Immediately,the dispersion was cast onto glass to prepare VO₂ thin films.By adjusting the viscosity of the dispersion,the thermochromic performance of the film can be improved.As shown in the research results,VO₂nanoparticles were synthesized by the one-step hydrothermal method at 280℃for 24 h,with an average size of 34.3 nm and phase transition latent heat of 32.3 J/g.VO₂/PU dispersion was cast onto glass to prepare VO₂/PU thin films.This method was low-cost,simple to operate,and easy to synthesize on a large scale.As the viscosity of the dispersion increases,theΔT_sol of VO₂ monolayer film increased from 6.6%to 14.5%,while T_lum remained above 50%.By casting multiple times,VO₂ three-layer thin film was obtained,and theΔT_sol increased to 20.0%.The good dispersion of VO₂ nanoparticles and and pore structure in the PU matrix were the main reasons for enhancing the optical properties of composite films.This thin film preparation method can also prepare VO₂thin films on flexible polymer substrates,expanding the application range of VO₂ thin films.（2）The phase transition temperature of VO₂ powder was reduced by doping tungsten,and the effect of W-doping concentration on VO₂ phase transition was studied.VO₂ thin films with phase transition temperatures close to room temperature were prepared based on the previous film preparation method.VO₂ nanoparticles with different W-doping concentrations were prepared using ammonium metatungstate as a dopant.In this experiment,the doping of tungsten reduced phase transition temperature at a rate of 18.42℃per at%W.With a W-doping of 1.0 at%,VO₂ powder had a phase transition temperature of 29.9℃,which was beneficial for practical applications.Unfortunately,T_lum andΔT_solof VO₂ thin films decreased due to tungsten doping.When the content of W was 1.0 at%,theΔT_sol of VO₂ single-layer thin film was 7.1%,and that of three-layer thin film was11.7%.（3）Using the improved St?ber method,the surface of VO₂ nanoparticles was coated with a layer of Si O₂ to prepare VO₂@Si O₂nanoparticles.Based on the previous film preparation method,VO₂@Si O₂ thin films were prepared to enhance antioxidant performance.As shown in the research results,compared with uncoated VO₂ films,the T_lum of the VO₂@Si O₂ thin film（prepared by 0.4 m L TEOS）increased by 13.6%to 58.6%,while theΔT_sol remained unchanged and the antioxidant capacity was enhanced.The V_0.99W_0.01O₂@Si O₂ thin film（prepared by 0.8 m L TEOS）showed optical performance of T_lum=56.0%（20℃）andΔT_sol=10.1%.Compared with the uncoated film,the T_lumincreased by 20.7%while theΔT_sol increased by 24.5%.The coating of Si O₂ significantly improved the optical performance and antioxidant property of doping samples.Considering the phase change temperature,the V_0.99W_0.01O₂@Si O₂ thin film was beneficial for practical application.（4）ATO powders were introduced into VO₂ thin films to further reduce infrared transmittance and improve infrared shielding performance.The 3%ATO/VO₂ film exhibited a T_lum of 18.2%and aΔT_sol of 6.3%.The 5%ATO/VO₂ film exhibited a T_lum of38.5%and aΔT_sol of 5.1%.Insulation tests were conducted on the prepared film.Compared with blank glass,the indoor temperature of the VO₂ film model house rose more slowly,which was 8.3℃lower after stabilization.For 3%ATO/VO₂ film,the stable temperature of the model house was 3.1℃lower than that of VO₂ film.For 5%ATO/VO₂film,the stable temperature of the model house was 4.2℃lower than that of VO₂film.Introducing ATO into VO₂ films improved the infrared shielding effect of the films.