Research On Liquid Crystal Smart Glass Suitablr For Various Environment Conditions

In recent years,the problem of energy scarcity in society has become increasingly prominent,and smart glass as a high-performance optoelectronic device can greatly save building energy and reduce electricity consumption.An ideal smart glass should have the dual functions of scattering visible light to avoid the use of curtains and regulating the transmission of near-infrared（NIR）light to maintain a comfortable room temperature.However,most of the current smart glasses can only adjust the room brightness or temperature singularly,which is not ideal.In this paper,we propose a novel method for the preparation of electrically-thermally dual-excitation tunable flexible liquid crystal smart glass based on vanadium dioxide（VO₂）film with tunable NIR transmittance and polymer stabilized cholesteric liquid crystal（PSCT）with tunable visible light transmittance.The main research of this paper is as follows.（1）A series of VO₂ doped polyvinylpyrrolidone（PVP）mixed solutions were prepared by doping and spin-coated into films,and the effects of the doping concentration of VO₂ nanoparticles and the spin-coating times of the mixed solutions on the optical properties of the composite films were systematically investigated.It was shown that when the relative mass ratio of VO₂ to PVP was set at 130%,the VO₂ doped PVP composite film with a thickness of 250 nm could be prepared after five times repeated spin coating.The visible light transmission rate of this composite film atλ=585nm was 49.42%.When it was heated to the phase transition temperature of VO₂ nanoparticles（68°C）,the NIR transmittance of the composite film atλ=2500 nm was reduced by 16.30%.In order to further reduce the phase transition temperature of the composite film,a newW_{0.0 03}V_{0.9 97}O₂doped PVP composite film was prepared by replacing the VO₂ nanoparticles with tungsten doped vanadium dioxide(W_{0.0 03}V_{0.9 97}O₂)nanoparticles,which could undergo the phase transition at 40°C with a decrease in phase transition temperature of about 28°C compared with the VO₂ doped PVP composite film.When the relative mass ratio ofW_{0.0 03}V_{0.9 97}O₂ to PVP was set at 130%,the W_{0.0 03}V_{0.9 97}O₂ doped PVP composite film with 248 nm thickness was prepared by two times repeated spin coating,and its visible transmittance atλ=585 nm was as high as 65.01%,and its NIR transmittance atλ=2500 nm was reduced by 15.15%after the phase transition.（2）Based on the polymer monomer RM257,the chiral agent S811 and the highly thermally stable nematic liquid crystal YP-011,a new PSCT with a pitch of about 1μm and high thermal stability,high contrast and near-infrared reflection was prepared by UV photopolymerization-induced phase separation technique.The structure of the network can be controlled by adjusting the doping concentration of monomer in the PSCT hybrid system,thus improving the electro-optical properties of PSCT.When the monomer concentration is lower than 3%,the sparse polymer network has a significant hindering effect in the reversible construction of cholesteric phase liquid crystals,so that the PSCT leaves a foggy state after power-off.Continuing to increase the monomer concentration can construct a dense polymer network structure and enhance its anchoring effect on the liquid crystal molecules,which effectively improves the contrast of PSCT and shortens the response time of PSCT.When 3%of RM257 was doped in PSCT,the threshold voltage,turn-on response time and turn-off response time of PSCT were 22.908 V,85.442 ms and 18.617 ms,respectively.（3）A new liquid crystal smart glass（WVO-PSCT）was prepared by spin coating a W_{0.0 03}V_{0.9 97}O₂ doped PVP composite film onto the surface of a PSCT liquid crystal cartridge.At room temperature,WVO-PSCT can inherently reflect NIR light in the wavelength range of 1050nm-1550 nm due to the cholesteric phase liquid crystal helical structure.The solar modulation efficiency of WVO-PSCT under electro-thermal excitation is further investigated,and the results show that the WVO-PSCT can change to a fuzzy state within 104 ms with a solar modulation efficiency of 3.28%by applying a voltage of 32.172 V at room temperature.When the ambient temperature increases to 55°C,the solar modulation efficiency of the normally transparent WVO-PSCT increases to 16.48%by the influence of the infrared cut-off characteristics of the composite film,and the solar modulation efficiency reaches 24.65%by the synergistic effect of the electric field after the application of 32.172V.By replacing three pieces of ordinary glass on the wooden house model with WVO-PSCT,the temperature inside the house can be effectively reduced by 4.8℃.Finally,the flexible smart glass prepared based on PET substrate can be bent under a bending radius of 15 mm and maintain its original high transparency without any obvious damage,and has good mechanical stability.Therefore,the electric-thermal dual excitation tunable liquid crystal smart glass prepared in this paper independently and effectively modulates the visible and near-infrared light transmission rates in four different modes,which not only has excellent infrared cut-off characteristics,good electro-optical properties and high thermal stability,but also provides a new research direction for flexible smart glass.