Light-Thermal Research On Phase Change Azobenzene/Boron Nitride Aerogel

Phase change energy storage technology with light regulation function is one of the key technologies to realize energy efficient and controllable utilization in extreme environment.However,for the limitation of molecular structure,organic phase change molecules have the problems of narrow temperature range,low phase transition enthalpy and difficulty in realizing low temperature heat release,which limit its application in controllable phase change energy storage technology.In order to solve this problem,the reversible phase transition of azobenzene molecule was used to realize the energy recycling under light induction.Azobenzene phase transition molecules(AZO-L5,AZO-L6 and AZO-L7)with different alkyl substituents were synthesized on the basis of molecular design.The results show that the phase transition temperature of these azobenzene with long alkyl chain is near room temperature,and the reversible structure transition of phase change azobenzene will occur under the action of light excitation.The change of space configuration and molecular level interaction would affect the crystallinity and molecular interaction force of phase change molecules,and then adjust the phase transition temperature and phase transition enthalpy.flexible porous materials(aerogels or flexible fabrics)are used as encapsulating materials for phase change azobenzene.The synergistic effect of azobenzene and boron nitride aerogels is expected to obtain phase modulated composites with optical properties.Differential scanning calorimetry(DSC)analysis showed that the solid-liquid transition temperatures and glass transition temperatures of CIS and trans structures of AZO-L5 and AZO-L7 were 37.94,46.01 ? and-78.36,-81.71 ?,respectively.The results show that the phase transition enthalpy and photothermal storage density of azobenzene are 90.77 and 114.3 J/g,respectively.At low temperature,AZO-L5 molecules can be induced to release 172.04 J/g heat in 4 minutes by blue light(420nm),which realizes the recycling of photothermal and phase transition enthalpy.On this basis,the boron nitride aerogels with good transmittance and self-supporting properties were prepared by improved directional freezing-drying method,and AZO-L5 was filled into boron nitride aerogels.Scanning electron microscopy showed that the boron nitride aerogels filled with a large number of micropores before filling,and the micropores disappeared after filling,indicating that azobenzene was filled evenly.UV-vis absorption spectra showed that AZO-L6 in BN could still undergo isomerization and recovery;infrared thermal imager showed that the system temperature could be increased by 0.8 ? by controllable heat release at low temperature(-10 ?).The related research provides a basis for the subsequent development of phase change energy storage materials with light regulation function.