Design, Fabrication And Properties Of The Composite Coatings Inspired By Lotus Leaf With Antireflection And Self-cleaning

The phenomenon of light reflection and pollutant accumulation on the surface of different substrate materials including metal and silicon will cause adverse effects such as poor stealth performance of military equipment and low solar energy utilization.It will seriously restrict the promotion and application of materials,and limit the improvement of comprehensive properties of materials.Therefore,it is of great significance and practical value for the research of functional materials.Through the reasonable design and control of the surface chemistry and the surface microstructures of the materials,it can effectively suppress the light reflection and improve the self-cleaning performance.However,the existing functional materials have some problems,such as single function,poor mechanical stability,and difficult industrial application.Based on this,it has become the hot and difficult point to find functional optimization and high reliability antireflective and self-cleaning materials.Biology in nature provides a source of innovation for the exploration of new structures,new materials and new methods because of its perfect balance of their own functional characteristics.The bionic approach has become an effective strategy to solve engineering problems,and has important practical value.From the perspective of bionics,this study takes lotus leaves as biological prototypes,and focuses on the optical properties of the ventral and back surfaces of fresh and dried lotus leaves.Firstly,the reflection spectrum and wettability of the surface of the lotus leaf were measured by using optical fiber spectrometer and contact angle measuring instrument,respectively.It is found that the surface of the lotus leaf has excellent antireflection in the wavelength range of 450-950 nm and superhydrophobic characteristics.In particular,the ventral surface of lotus leaf also has good self-cleaning property.Then,the surface structures of lotus leaf were characterized by the scanning electron microscope and 3D super-depth of field microscope.The chemical composition of its surface was also analyzed.Combined with the characteristic size parameters of biomimetic structures,the three-dimensional visual antireflective structure model was established.The antireflective mechanism of the lotus leaf surface was revealed by using the FDTD optical simulation method.Micron-sized mastoid structures can make light reflect,refract,diffract and scatter between adjacent structures,thereby increasing the length of light propagation paths,and decrease the light reflection through the multiple effects of light.Meanwhile,nanostructures on the microstructure surfaces can also effectively suppress the Fresnel reflection of light.Under the combined effect of the two,the lotus leaf surface has excellent antireflective performance.Inspired by the structural and functional characteristics of the lotus leaf,the bionic design and preparation of functional materials with antireflective and self-cleaning properties were carried out.Taking inorganic silica particles as structural materials,combining light absorbing materials and adhesive materials,the microroughness structures and surface free energy of materials can be controlled by adjusting and optimizing the synergistic ratio of the material components,so as to synthesize inorganic-organic hybrid materials with the best functional characteristics.Subsequently,three kinds of biomimetic composite coatings with antireflective and self-cleaning properties were successfully prepared on the surface of aluminum alloy by using spray deposition technology.They possessed the micro-/nano roughness structures similar to the lotus leaf surface.Through the effective combination of different light-absorbing materials,bioinspired structures and adhesive materials,not only the three lotus-leaf-like functional structures of the coating surfaces are reproduced,but also their antireflection and self-cleaning performances are gradually improved.With the above strategy,the fluorine-free bioinspired multifunctional composite coating was also successfully prepared on paper surface to expand the application of the micro-/nano hierarchical structures on lotus leaf surface.The surface structures,surface roughness,surface chemical composition and element distribution,optical and wetting characteristics of the four bio-inspired composite coatings were systematically investigated through a series of characterization testing techniques.The results indicate that the coating surfaces have micro-/nano hierarchical structures and low surface free energy,and exhibit excellent antireflection and superhydrophobic self-cleaning properties,which is very similar to the characteristic structures of the lotus leaf surface.In addition,a series of performance tests for the four bio-inspired composite coatings were performed including self-cleaning test,droplet bounce test,adhesive tape adhesion test,knife scratch test,friction and wear test,impact test and outdoor lighting test,etc.The test results show that the four coatings have good self-cleaning properties,mechanical stability,chemical stability,high temperature resistance and long-term weather resistance,and so on.These properties provide favorable guarantee for the practical application of bio-inspired functional coatings.Based on the idea of bionics,the composite coatings mimicking the function and structures of the lotus leaf were prepared in this study,which were suitable for the spectrum,wettability and mechanical stability.In order to aim at seeking the functional optimization balance,the integrated demand of dual structures for antireflection,wetting and wear resistance performances are achieved by adjusting and optimizing the coordination ratio of the microsphere structures,light-absorbing materials and adhesive materials.Furthermore,it provides a certain theoretical basis and data reference for the design and preparation of practical coating materials with antireflective and self-cleaning performances.