| Smart windows can change the transmittance of the light in the solar radiation band(380-2500 nm)according to the changes of the external environment(light,electricity,heat,etc.),which is conducive to reducing the energy consumption of cooling in summer and heating in winter.VO2(M)is a thermochromic material that can undergo a phase change at 68℃.Under the condition of ensuring the transmittance of visible light,it can spontaneously perform solar energy modulation through external temperature changes.VO2(M)is an ideal intelligent window material,but its many phase states make it difficult to synthesize pure phase,and the synthesis time is long,the two control states can not fully meet the user’s expectations.In this paper,microwave-assisted hydrothermal-calcination method was used to synthesize VO2(M).The effect of different reaction conditions on the metastable state of hydrothermal products was studied.The role of microwave in hydrothermal reaction was investigated through simulation.Optimize the synthesis reaction conditions of VO2(M).The optical simulation of VO2/PDLC composite film is used to realize the electric-thermal dual-band optical control.Through microwave-assisted hydrothermal synthesis of VO2 metastable state,the study found that with the increase of reaction time,the amount of reactants added and the reaction temperature,the proportion of product D phase will increase,and the rapid heating method is helpful to obtain M phase.The GROMACS software was used to simulate the hydrothermal reaction system in the presence/absence of microwave.The study found that microwaves can have an effect on the elemental structure and thus the product phase state.They can also affect the number of hydrogen bonds and electrostatic forces in the system to promote diffusion and increase the reaction rate.The impact on the thermodynamics of the reaction mainly comes from the effect on the entropy change of the reaction.The optimal synthesis conditions were selected as follows:1g of vanadium source,reaction temperature 240℃,reaction time 30 min;heat treatment temperature 600℃;selection of different tungsten content for doping,found that with the increase of tungsten doping concentration,the crystallinity of WxVl-xO2 will increase first and then decrease,and the phase transition temperature after doping can be reduced to 38.2℃.The optical calculation using COMSOL shows that the visible light transparent state Tlum reaches 50.97%,which is higher than that of the pure state VO2 coating;the phase change of vanadium dioxide leads to a decrease in transmittance in the near infrared band,and △Tsol(2-1)reaches 28.78%;The scattering of PDLC leads to a decrease in the transmittance of the visible light band,△Tsol(3-1)reaches 43.13%;in mode 4,the transmittance of the visible light and near-infrared band simultaneously decreases,and the solar modulation efficiency △sol(4-1)reaches 50.79%.In addition,adding 1 μm and 8 μm SiO2 microspheres to the composite system can increase the emissivity of the composite system in the atmospheric window to improve the thermal control performance. |
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