Preparation And Properties Of Colored Radiative Cooling Coatings

Radiative cooling technology is to release heat for cooling through the strong infrared radiation of the atmosphere window.In recent years,this energy-free cooling method has attracted a lot of attention around the world.However,most of the radiative cooling materials reported so far are white,which might cause light pollution and are difficult to meet the demands for color in modern buildings and special scenes.In addition,radiative cooling materials have strong cooling ability,but they are not suitable for all seasons and all times of the day.In cold winter,the strong solar reflection will increase the heating load of the building,which is unfavorable for energy saving in regions with severe winter and hot summer.Therefore,the related research on colored radiative cooling coatings and smart radiative cooling coatings based on color regulation is carried out in this paper.The main work and conclusions are as follows:(1)To develop an efficient radiative cooling coating with color regulation,a double-layer structure was designed,which combined a radiative cooling underlayer with spectral selectivity and a colored top layer with low infrared absorption.Meanwhile,the structural scheme of the coating was determined.That is,a white P(Vd F-HFP)porous membrane(PM)or commercial thermal insulation coating(FD or YAG)with a thickness of around 800 μm and 300 μm,respectively,was used for the underlayer,and a colored acrylic resin(AR)layer was used for the top layer.(2)Six kinds of radiative cooling double-layer coatings,which are black,grey and four common camouflage colors,including dark green DG0847,medium green MG1151,sand soil SE2535,and sand soil SE3453,were prepared.Furthermore,the effects of the underlying materials and pigments(dyes)in the top layer on solar reflection performance were investigated.And then,the performance of these radiative cooling double-layer coatings was compared with the single-layer coatings on plastic board and white oxford cloth.It was found that using solvent dyes to achieve color regulation of the radiative cooling coatings maximized the solar reflection advantages of the original radiative cooling materials,especially when the brightness of the top layer was high.The solar reflectance of the double-layer coatings prepared by solvent dyes was higher than that of the double-layer coatings prepared by infrared reflecting pigments and common pigments.The stronger the reflection ability of the underlayer,the higher the overall reflectance.The colored radiative cooling coatings obtained by combining the white porous membrane underlayer and the solvent dye colored top layer have the strongest solar light reflection.The reflectance of the six colored radiative cooling coatings was 47.49%,67.31%,47.55%,52.18%,65.25% and 68.65%,respectively,which was better than the camouflage coatings and the same color coatings reported in the literature.The main reason is the high solar reflection of the porous underlayer and the high infrared transmittance of the solvent dyes on the top layer,both of which are indispensable.(3)The research on double-layer smart radiative cooling coatings based on thermochromic materials was carried out.The effects of pigment concentration in the top layer,the thickness of the porous membrane underlayer,and the color of the coating on the spectral characteristics and solar energy regulation ability of the smart coating were discussed.Moreover,the thermochromic characteristics,light stability,thermal-cold cyclical stability,and outdoor radiative cooling performance of the coatings were investigated.The results show that the concentration of pigments has a significant effect on the UV-visible reflectance of the smart radiative cooling coatings,with a concentration of 10% could balance both the color brightness and the radiative cooling effect.As the temperature rises,the color of the smart radiative cooling coatings faded,and the solar reflectance could be increased from 72.71% to 91.25%,achieving the effect of warmer in winter and cooler in summer.Not only the regulating amplitude of smart radiative cooling coatings is larger than that of commercial thermal insulation coatings,but also has good thermal-cold cyclical stability and light fatigue resistance.Therefore,this work opens up a new way for the promising field of smart building coatings.