Fabrication And Properties Of The Films With Superhydrophobic And Radiative Cooling Functions

Growing human economic activity is increasing energy consumption year on year and exacerbating the greenhouse effect.At the same time,energy consumption for temperature control has increased rapidly due to people’s desire for comfort.Radiative cooling has become a hot research topic in recent years.It can regulate the temperature of objects within a certain range without external energy consumption.Highly efficient radiative cooling materials have important application prospects in many fields such as solar cells,aerospace,architecture,buildings,transportation,and human and environmental cooling.Traditional cooling devices mainly use phase transformable materials in the vaporisation and evaporation process to achieve ambient temperature control.The operation of these devices requires energy consumption,otherwise they cannot work properly.Obviously,it is obvious that in special environments where energy cannot be adequately provided,such as spacecraft,space stations and spacecraft operating in the outer space of the universe,passive radiative cooling is the only solution to reduce their internal temperature.Considering from energy saving,radiative cooling is also a green and important energy-saving method worth promoting.Radiative cooling uses infrared thermal radiation from the surface of an object to release heat into a cold background（e.g.,outer space,low-temperature dark room）environment while reducing the absorption of sunlight energy,thereby cooling the surface of the object.The use of materials with high surface emissivity can effectively release infrared radiation to the outside,thus achieving cooling.How to obtain large-area,low-cost,high-efficiency and long-life radiative cooling materials is still the main problem to be solved.The surface of superhydrophobic materials has a special micro/nano double rough structure and low surface energy.This feature makes the surface of superhydrophobic materials form a solid-gas-liquid three-phase line interface with liquid droplets,reducing the contact area between water droplets and the substrate.It is easier to make the water droplets on the superhydrophobic surface roll and carry away the dust attached to the surface.Therefore,superhydrophobic materials can be widely used for self-cleaning and anti-fouling of equipment and facilities.In practical applications,the dust and raindrops accumulated on the surface of radiative cooling materials can reduce the reflectivity and thermal infrared emissivity of their surfaces,leading to the degradation of cooling performance.Therefore,it is necessary to achieve both radiative cooling properties and superhydrophobicity on the same material surface in order to protect the cooling efficiency and extend the life of radiative cooling materials.In this paper,we first obtain various specific sub-band spectral properties to be satisfied for radiative cooling requirements by systematically analysing the radiative cooling mechanism.Then,we select the materials with excellent inhibition of cooling to construct films with porous structure around specific target spectral properties,and use the formed micro/nano double rough structure and low surface energy to make the film surface superhydrophobic.Finally,a high-efficiency,low-cost and eco-friendly composite film with both superhydrophobic radiative cooling function is obtained and verified by an experimental platform built independently.The paper will be developed from two application scenarios of cooling and hydrophobic,and the specific work is as follows:（1）The superhydrophobic porous films of KH-570@Si O₂ were prepared by spin-coating method using nano-Si O₂（particle size of 100 nm）,γ-methacryloxypropyltrimethoxysilane（KH-570）and ethyl acetate as the preparation materials.The film has excellent superhydrophobic properties due to its micro-nano double rough structure and low surface energy,which makes the prepared porous film.（2）Based on the study of KH-570@Si O2 superhydrophobic porous film,the paper proposed to combine the intrinsic absorption mechanism of silicon oxide（Si O₂）particles and polydimethylsiloxane（PDMS）organic materials on this system to construct the atmospheric window selective infrared radiation.Eventually,the KH-570@Si O₂/PDMS@Si O₂ composite film（referred to as K/P composite film）with superhydrophobic radiative cooling function was prepared by scratch coating method.The K/P composite film exhibits excellent optical properties with reflectivity higher than 85%in the visible wavelength range and emissivity higher than 0.95 in the mid-infrared wavelength range of 8-13μm.