Study On The Composites Of Vanadium Dioxide With Stilbenes And Tetraphenylethene Luminescent Molecules

In recent years,as the global energy consumption continues to increase,the demand for renewable energy and energy saving becomes increasingly urgent.It is well-known that building energy consumption accounts for a large part of the total energy consumption.As the main heat exchange channel between the buildings and the external environment,windows are one of the least energy efficient components,so the smart windows arise,which can selectively absorb or reflect sunlight under certain stimuli(light,electricity,vapor,heat,etc.),so as to realize the purpose of energy saving.Thermochromic smart window has received much attention because of its simple preparation,low production and cost.As a typical thermochromic material,vanadium dioxide(VO₂)has been widely concerned by researchers.VO₂-based smart window can adjust and control the intake of sunlight according to the change of external temperature,playing the regulating role of the indoor temperature especially in summer.However,the VO₂-based smart window still has some problems,such as the high phase transition temperature,difficult-to-furfill balance between the luminous transmittance(T_lum)and solar regulation efficiency(?T_sol),the intrinsic unpleasant color and poor stability of the films.Therefore,improving the color and stability of VO₂ smart windows is an important measure to promote its applications.Fluorescent brighteners can be excited by ultraviolet light in the sunlight and emit blue light of about 450 nm.The complementary light principle can be used to compensate the absorption of short wavelength in visible range of vanadium dioxide,thus changing the color of VO₂ film.Among them,stilbene fluorescent brighteners have the characteristics of high fluorescence quantum yield,high chemical stability and good whitening effect,so they are selected as a kind of fluorescent brighteners in this paper.In addition,an Aggregation-Induced Emission(AIE)organic small molecule in dilute solution is not emitting but in the state of aggregate or solid is able to strongly emit.It is the most suitable system to solve the aggregation caused quenching problem.AIE molecules also tend to be multi-stimulus responsive and when combined with VO₂,they may add new functions to the VO₂ smart window.This thesis mainly focuses on the development of vanadium dioxide based smart films.Through the combination of vanadium dioxide and fluorescent organic small molecules,the composite films were prepared to improve the color and stability of VO₂-based smart window.Outline of the work is as follows:1.We studied the preparation and properties of vanadium dioxide/stilbenes two-layer composite films.W-doped VO₂ nanoparticles were prepared by hydrothermal method.The vanadium dioxide/stilbenes fluorescent double-layer composite films were prepared by roller coating method.The morphology,photoluminescence,thermochromic performance have been characterized.Compared with the pure VO₂ film,the composite films not only maintain high luminous transmittance and solar regulation efficiency,but also undergo reversible color change from brown-yellow to blue under sunlight,the UV-blocking property is significantly improved as well.2.The preparation and properties of modified vanadium dioxide/stilbenes fluorescent small molecule/organic polymer three-layer composite films are studied.The VO₂@Si O₂-KH550 powder was obtained by coating with silica and surface modification with silane coupling agent.The modification effect was characterized by XRD,TGA and FT-IR,and the stability of the modified powder in acid,water and oxygen was tested.It was found that the stability of the modified powders was greatly improved.We prepared the modified vanadium dioxide/stilbenes fluorescent small molecule/organic polymer three-layer composite films and tested their thermochromic performance.It was found that the visible light transmittance and solar modulation ability of the three-layer composite films were significantly improved compared with that of the two-layer composite films,which was mainly due to the modification of VO₂ powder.The three-layer composite films still appear blue under sunlight,which solves the problem of the brown-yellow color of VO₂ film.At the same time,damp heating,UV aging and acid resistance test were carried out on the three-layer composite films.The results show that the three-layer composite films have better stability.3.The composites of VO₂ and AIE organic small molecule(Br-tetraphenylethene and tetraphenylpyrazine)were preliminary studied.VO₂@Si O₂ and TPE were connected by covalent bond,the fluorescence disappeared.Control experiments show that vanadium dioxide may quench the relatively weak blue fluorescence of TPE,indicating that the system needs to be further optimized.TPP molecule has many advantages compared with other AIE molecules,so we also tried to use TPP molecule and vanadium dioxide to prepare multilayer film,and the thermochromic and photoluminescence properties of the composite films were basically not affected.