Preparation And Performance Study Of New Superhydrophobic Building Energy-saving Coatings

Due to the acceleration of global warming,the demand for refrigeration appliance is increasing during the hot summer months,increasing the load on the environment and energy loss.Energy-free radiant cooling is a green and ideal solution to replace air conditioners by reflecting sunlight spontaneously and radiating excess heat into space through atmospheric transparent windows to achieve passive cooling.However,most radiant cooling materials are easily contaminated by dust,rain,etc.,which reduces the cooling capacity in outdoor environments.Therefore,a new superhydrophobic building energy-saving coating based on silica was developed.Firstly,a white superhydrophobic radiant cooling coating with high reflectivity and emissivity that can be applied to multiple substrates was prepared.Secondly,a colored superhydrophobic cooling coating with decorative effect was prepared by introducing colored pigments for the aesthetic appearance of the building.The specific work content are as follows:(1)A superhydrophobic daytime radiative cooling powder based on silica-coated glass bubbles was prepared,and a graded micro-nano structure was achieved by spraying epoxy resin with Poly(vinylidene fluoride-co-hexafluoropropylene)as the binder on the substrate surface to prepare a superhydrophobic cooling coating,which achieved strong sunlight reflectivity(96%)and excellent mid-infrared emissivity(98%).Under direct outdoor sunlight,it effectively produces a temperature drop of 11.1°C compared to the ambient temperature.More importantly the coating has good superhydrophobic properties with water contact angle up to 157° and roll angle up to 1°,which can keep the coating surface free from contamination through selfcleaning properties and effectively maintain good radiative cooling performance.In addition,the prepared coating has superhydrophobicity and good cooling performance when exposed to different p H solutions and long-term UV irradiation.(2)Super white coatings were prepared by mixing kaolin,hollow glass beads and nano-silica in a certain ratio using polyacrylate emulsion and sprayed on the substrate.The super-white superhydrophobic coatings were prepared by manual polishing with PDMS wrapping,which can achieve 96% solar reflectivity and 97% mid-infrared emissivity.On this basis,color superhydrophobic cooling coatings were prepared by introducing different contents of pigments.The average emissivity in the solar spectrum band was 82% for blue coatings and 72% for green;the near-infrared reflectivity was 90% for blue coatings and 91% for green.All of them reached the standard of building energy-saving coatings(65%,80%).The prepared superhydrophobic coatings all have excellent superhydrophobic performance,the maximum water contact angle can reach 158°,and the self-cleaning function is excellent.After the experiments of immersion in different p H solutions,sandpaper abrasion,UV illumination,and electrochemical corrosion,the materials still maintain excellent superhydrophobic and optical properties with a certain degree of temperature drop compared to both the ambient temperature and the original substrate.The prepared coatings have excellent corrosion resistance,chemical stability,mechanical stability and other properties.It also enables large area preparation,which is of great significance for scalable applications of coatings.