Design,Performance And Application Of VO₂/Cs_xWO₃ Composite Thermal Insulation Materials

Vanadium dioxide（VO₂）is a thermochromic material which occurs metal-semiconductor transition at 68°C.At low temperature,the band gap of semiconductor phase VO₂（M）allows visible light and near-infrared（NIR）light transmission.At high temperature,the metallic phase VO₂（R）will reflect NIR light and decrease the NIR transmittance,while maintaining the high transmittance for visible light.Based on this phase transition characteristic,VO₂exhibits excellent solar light modulation ability,which can be applied to smart window field.At present,there are still some problems with VO₂,such as high phase transition temperature,poor stability and difficulty in achieving a balance between visible light transmittance(T_lum)and solar light modulation ability(T_sol),which gteatly limit its application.If these problems have been solved,it will significantly promote the application of VO₂ smart windows.The above problems of VO₂ can be solved by combining VO₂ with other materials,such as tungsten bronze.Cesium tungsten bronze（Cs_xWO₃）is a compound formed by doping cesium ions into WO₃.It is widely used in energy-saving windows due to its high visible light transmittance and excellent NIR absorption performance.At the same time,Cs_xWO₃ has good photothermal conversion performance,which is beneficial to promote the phase transition of VO₂ and improve the NIR shielding performance of VO₂ films.Therefore,the composite of VO₂ and Cs_xWO₃ will make full use of their advantages and enhance the practical application value.However,the simple physical mixing of VO₂ and Cs_xWO₃ has the problems such as weak binding force and low heat transfer efficiency,and the problem of poor stability of VO₂can not be effectively solved,so it still can not meet the practical application requirements.Therefore,it is necessary to carry on the modification to VO₂ and Cs_xWO₃ and further improve the applicability of smart windows.In order to solve the above key factors that limit the application of VO₂ based smart windows,several measures have been employed to realize the synergetic optimization of stability,optical property and phase transition characteristic.The main research contents are summarized as below:1.Firstly,VO₂（M）with good crystallinity was prepared using a two-step method（ball milling and calcination）,and ascorbic acid（AA）was used to modify VO₂ to reduce its phase transition temperature,activate the surface hydroxyl group and improve stability.Secondly,surface modifiers（silane coupling agent KH550,cationic surfactant CTAB,non-ionic surfactant PVP,anionic surfactant SDS）were used to further modify VO₂.Under the long chain protection and steric hindrance effect of surface modifiers,the stability and dispersibility of VO₂ have been further improved.Finally,the performance optimization process and mechanism of different surface modifiers on VO₂ have been explored through experimental characterization.2.Firstly,Cs_xWO₃ nanoparticles were prepared by solid-state method,and then the Cs_xWO₃ water-based slurry with good dispersion and excellent near-infrared shielding performance was obtained through grinding process.Secondly,VO₂/Cs_xWO₃ composites were prepared successfully and the synergistic effects on their optical properties and phase transition characteristics were investigated systematically.Compared to pure VO₂ films,VO₂/Cs_xWO₃ composite films have better NIR shielding performance and thermochromic properties.Besides that,compared to simple physical blending,the combination of VO₂ and Cs_xWO₃ through electrostatic interaction can significantly enhance the heat transfer between VO₂ and Cs_xWO₃,shorten the VO₂ phase transition time,and further optimize the thermochromic performance of VO₂.Meanwhile,compared with blank glass,the smart glass coated with VO₂/Cs_xWO₃ composite film has excellent heat insulation performance,which can effectively reduce indoor temperature by 10°C.3.In order to further optimize the stability and optical performances of VO₂/Cs_xWO₃composites,the Stober method was used to uniformly coat the Si O₂ shell on the surface of the KAVW（KH550-AA-VO₂/Cs_xWO₃）composite powder to obtain KAVW@Si O₂ particles.It was found that both of KAVW@Si O₂ particles and films show excellent acid resistance,water resistance,and high visible light transmittance(T_lum>60%)properties.Meanwhile,compared to the KAVW sample without Si O₂ shell protection,the KAVW@Si O₂ sample can withstand the change of environment better and keep the excellent optical properties,which exhibits a wide practical application prospect.