Construction Of Superhydrophobic Surfaces Of Vanadium Dioxide Thermochromic Composite Films And Their Properties

Vanadium dioxide(VO2)is an excellent thermochromic material that can respond to changes in ambient temperature,maintaining good transmission of infrared light at low temperatures and regulating the conversion of infrared light to a reflective state at high temperatures.while maintaining the transmission of visible light and regulating near-infrared radiation.The thermochromic properties of VO2 can be applied to temperature-controlled packaging to regulate the internal temperature of the package.In addition,when the outer package is exposed to air for a long time,it is susceptible to contamination by external dust and dirt.Therefore,the development of new self-cleaning temperature-controlled packaging materials has received much attention from researchers and has great potential for application in the packaging field.The main contents of this paper are as follows:Firstly,vanadium pentoxide(V2O5)was used as the vanadium source and oxalic acid(C2H2O4)as the reducing agent to prepare M-phase VO2 particles with a particle size of about 500 nm,regular morphology and "poplar" like structure by hydrothermal method,and then VO2@SiO2 with SiO2 as the shell was synthesized by a modified Stober method.It was found that the thickness of the SiO2 shell layer increased with the increase of TEOS dosage,and the thickness of the SiO2 shell layer was between 36-53 nm.The enthalpy change values of VO2@SiO2 composite particles with different shell layer thicknesses vary little,and their metal-insulator phase transition temperatures are around 66.8℃,and the phase transition temperature difference does not exceed 0.3℃,which proves the small effect of SiO2 shell layer thickness on VO2 phase transition temperature.In addition,VO2@SiO2 composite particles aqueous polyurethane and cast on the PET surface to obtain VO2@SiO2 composite films,and the transmittance of such composite films reached up to 49.14%in the visible region,and their solar modulation ability increased with the increase of VO2@SiO2 composite particle content up to 2.57%,indicating that the VO2@SiO2 composite particles The optical properties of the prepared composite films were strongly correlated with those of the VO2@SiO2 composite particles.Then,the superhydrophobic composite films were prepared by constructing rough surfaces on VO2@SiO2 composite films using polysiloxane and hydrophobic nano-silica as low surface energy materials,and their water contact angle could reach up to 156°.It was shown that the best performance of the prepared superhydrophobic composite films was achieved when the curing temperature was 60℃.The pH of the environment had less effect on the surface wettability of the composite films,and the water contact angle exceeded 150° under different pH conditions.In addition,different temperatures of water droplets on the material surface will change its contact state,and the contact state of water droplets on the composite film can be regulated by changing the temperature of water droplets.Finally,it is demonstrated that the micro-nanostructure can"trap" more air to improve the superhydrophobicity by constructing a rough surface,and the mechanism of micro-nanostructure affecting the surface wettability is revealed.In this paper,the VO2 surface is coated with SiO2 shell layer to improve the oxidation resistance of VO2,and the VO2@SiO2 core-shell structure composite particles with excellent dispersion are produced,and the superhydrophobic composite films of VO2 with excellent hydrophobicity are obtained by constructing superhydrophobic surfaces with polysiloxane and hydrophobic nano-silica.This provides an experimental basis and theoretical support for the development of low-cost,high-performance temperature-controlled packaging materials.