Controllable Preparation And Evaluation Of Integrated Properties On VO₂-Based Composite Film With High Performance

Vanadium dioxide(VO₂)is the best known thermochromic material since it exhibits semiconductor-to-metal phase transition(SMT)accompanied by the notable variation in physical properties such as optics and electricity,which make it suitable for civilian and military applications.For the huge change in near-infrared region from transmitting to reflecting,VO₂can be used in many fields such as infrared camouflage,smart windows,and laser protection.Thin film is the best form for VO₂material application.There are two most common VO₂film preparation methods:one is to prepare suitable VO₂nanoparticles in advance by chemical methods,and then combine them with polymer materials to prepare flexible films by coating or stretching;The other is to use physical methods such as magnetron sputtering to achieve coating on flexible(such as PI film)or rigid(such as glass)substrates.These two preparation methods have their own characteristics,and have been applied in some fields,such as energy-saving window films,according to demand.But so far,the large-scale industrialization of VO₂films still faces huge challenges,mainly as follows:(1)the inherent yellow color of the film caused by short-wavelength absorption,(2)the luminous transmission caused by the low adjustment rate of the visible light band,(3)the low solar modulation efficiency,as well as the lack of sufficient visual display effect accompanying the phase change,(4)the poor stability of the crystal structure due to the variable valence state of metal V and the deterioration of the film performance in the application environment.Solving the above bottleneck issues has become the only way to promote the industrialization of VO₂films.This research focuses on the above-mentioned topics.For the chemically obtained VO₂nanoparticles and VO₂magnetron sputtering physical coating,the optical performance optimization and environmental stability improvement are carried out respectively.The specific performance is based on the color control of VO₂nanoparticles,its weather resistance research,the design of optical multilayer film based on VO₂magnetron sputtering physical coating and the improvement of solar modulation efficiency,to maximize the optical performance of VO₂and apply it to the research of laser protection.The research contents and main results are summarized as follows:(1)The VO₂nanoparticles were combined with the orgainic thermochromic material to enhance the regulation in visible wavelength which can achieve an efficient regulation in a wide spectral range(from visible to near-infrared region)and change color as the response to temperature change.We studied the thermochromic performance of VO₂-based composite films which can present reversible broad-spectrum absorption from nearly transparent to black during heating and cooling process,provided promising additional capacity of visible light modulation for thermochromic VO₂-based coatings and thus enlarge the modulation range of VO₂.The composite film showed a ultra-high solar modulation efficiency(?T_sol=27.25%),relatively high luminous transmittance(T_lum,l=61.33%and T_lum,h=36.16%)and visible color modulation ability.The novel broadband modulation composite film exhibited superior application potential in smart window application.(2)Further,we carried out research on the stability of VO₂nanoparticles.Using Al O_xand Zn O as shell materials,VO₂-based core-shell structure was successfully prepared.And we studied the durability and opticle propties of VO₂-based core-shell film with different coating materials and optimization methods(introduction of ascorbic acid,high temperature post-annealing,etc.).We compared the durability of differentcore-shellstructures(VO₂@Al(OH)₃,VO₂@Al₂O₃-Anneal,VO₂@AA-Al(OH)₃,VO₂@AA-Zn O,VO₂@Zn O)to meet different application requirements.AA could effectively improve the acid resistance of compound powder,and VO₂@Al₂O₃-Anneal had the best stability which could exist more than126 days in the 60?and 90%relative humidity.(3)Based on the design of multilayer structure,we introduced“movable”antireflective(AR)coating to VO₂film due to the single passive regulation mode and unsatisfactory optical performance in actual use.The“movable”AR layer such as H₂O,not only endowed VO₂with active-passive regulation mode,but also dramatically enhanced the thermochromic performance.It was found that a great enhancement of the solar modulation ability(?T_sol=17.2%)and obvious improvement of luminous transmittance(T_lum,l=42.5%)compared to VO₂single layers were observed after employing H₂O layer.Through further structural optimization,the introduction of interlayer materials such as Si O₂and Hf O₂not only greatly improved the optical performance,but also prolonged the service life.And the VO₂/Hf O₂/H₂O multilayer structure with excellent optical performance(T_lum,lt=42.5%,?T_sol=20.8%).(4)In order to broaden the application range of VO₂,we studied the VO₂-based multilayer film applied in laser protection.Through magnetron sputtering method,we fabricated VO₂-based multilayer structure on different substrates(sapphire and silicon)to increase the modulation ability and optical propties at 3-5?m.The transmittance in the specific band before the phase change could reach more than 80%,the transmittance after the phase change is less than 1%,the switching ratio reaches 100times,was expected to applied in laser protection.Meanwihle,we analyzed the damage mechanism of VO₂-based laser protective layer.