Research On Coupling Microstructure And Its Optical Characteristics And Bionics In Typical Butterfly Scales

In nature, living creatures grow up strong camouflage and stealth characteristics to fit the living environment and avoid being caught by its natural enemies, which is the result of its evolution and optimization over millions of centuries. Structural color is one of the typical characteristics, which is a ubiquitous natural phenomenon for living creatures fitting the living environment and avoiding being caught by its natural enemies.Structural color and its forming mechanism and application is a multidiscipline project related with physics, chemistry, biology, material science, and engineering, etc, and research foreland and hotspot in the world, which was highly regarded by academic, industrial and military organization and had very important scientific significance, practical application merit and wide application foreground. This project was studied and explored by academic, industrial and military organization for devoting a lot of manpower, materials resources and money.As research work supported by the National Defence Basic Research Project, the National Natural Science Foundation of China (Grant No. 30570235), the Key Project of Chinese Ministry of Education (Grant No. 101020) and Fok Ying Tong Education Foundation (Grant No. 101020), the core and emphases of the paper is from engineering bionics viewpoint to study configuration, structure, optics performance and its interrelation, color changing mechanism, and bionic coupling design principle of configuration, structure for butterfly scales, which provide reference data and design basis for video frequency bionic steallth materials design and manufacturing, and a new research thought. The configuration and structure of butterfly scales are very important for structural color, and main factors for the forming mechanism of butterfly scales. In this paper, the configuration and structure of several typical butterfly scales in the northeast part of China were investigated more systemicly, and the structural color in butterfly Apatura laverna and butterfly Apatura ilia was found for the first time. The configuration and structure of the above butterfly were investigated, and the forming mechanism of structural color was maken clear.The optic microscope, scanning electron microscope (SEM), transmission electron microscopy (TEM) were used to observe, test and analyze the surface configuration and cross section structure of five kinds of butterfly scales. It was found that there are periodic order structures like ridge and ditch in these butterfly scales, and each periodic structure layer was composed of chitin layer and air layer alternate. Small difference of the structural form, density, size, space, thickness, layer number, distribution style will effect the light wave reflection and refraction interference. At the same time, it was found that the surface configuration mainly has concave form, ridge-line form and grid form. The cross-section structure has the shape of pagoda tree and samdwich. Three-dimensional structures has are the multilayer structure of concaves and the multilayer structure of ridge-line.The optics performance test is an important approach for the investigation of structural color effect of configuration and structure and action mechanism. The reflectivity in visible light range of butterfly scales was tested by UV-Visible Spectrophotometer, and the relation between configuration, structure and optics performance was revealed. It was found in the experiments that the reflectivity of butterfly scales was related with not only the configuration and structure in micron and nano size, but also the distribution of scales, the watching distance and the angle of incidence.The scales of samples are more uniformity in distribution and color up, the reflectivity waves are more similar to the average reflectivity. From the scanning curve, it was also concluded that the blue scales of butterflies almost have higher reflect character, and the reflectivity value is more than 70%. The green scales show higher absorbency of light-wave, and reflectivity is mostly less than 20%.The color changing experiments were designed to study the color changing phenomenon of butterfly scales. The color changing phenomenon was investigated by changing the filling medium or changing the angle of incidence, which was an effective method for finding and distinguishing structural color of butterfly scales. It was found that butterfly scales have abundant colors, but the structural colors are mainly blue, green, and purple. The color and brightness of structural color can vary with the change of the angle of incidence of ray, for example, the wing scales of Apatura ilia shows bright purple flash going with the angle variety. When the refractive index of medium was changed, the structural color of scales would also produce distinct change color phenomenon. If alcohol aqua was filled into the air layers of scale microstructure, it was found that an instantaneous color change-return process took place in the scales. For the blue scales surface of butterflies, the process of color changing was showed from blue to green then to blue, but the process of green scales changed from green to red then return to green.The color of butterfly scales come from structural color. The structural color was the result that there was interactional coupling of configuration and structure such as ditches, ridges, film layers and holes in micron and nanometer size on the wing scales, and the tiny difference from density, shape, size, distancee, distribution, and angle of these structures made the light-wave produce the reflection, refraction and interference effect. The mechanisms on coloration were divided into two aspects for the first time, color rendering and color variation, which were revealed, and the phyical model of optics performance was built. Color rendering mechanism is that the multilayer-films structure was spaced out by air, and the distance was unchangable. These reflected lights produced interference and presented the surface color. The scales color comes from the multilayer-films configuration and structure coupling, which makes the interference of light. Color changing mechanism is that when the medium with different refractive index, such as alcohol aqua or air, was filled into the multilayer of scales, the incidence light was effected by the difference of refractive index of alcohol aqua and air, and altered in the interface between the film layer and the medium layer. Because the refractive index of alcohol aqua is higher than that of air, when alcohol aqua is filled into the medium layer, the reflecting wavelength becomes longer than the medium air. As a result, the phenomenon of color changing is produced. According to Interference equation, the relation between structural color of butterfly scales and film thichness, refractive index, the angle and the wavelength of the incident light was studied. The phyical model of refractive light performance in scales structure was built, and theoretical analysis and calculation was carried on to reveal the color changing mechanism of butterfly scale structural color quantificationally.The aims of the research of configuration, structure and optics performance of butterfly scales is bionic design of multilayer film coupling structure, and provide data and model for design and preparation of video frequency bionic stealth materials. Based on the test and experimental results of micro configuration, structure and optic performance of butterfly scales, the homochromatic parallel multilayer structure film with higher reflectivity and the multilayer structure film of multiple color with higher absorbency were optimized and designed for the first time, and a video frequency bionic stealth multilayer structure of A-B-A type was built. When structure one is same with structure two, the film is the type of higher reflectivity, and is the type of higher absorbency on the contrary. Based on the tricolor principle, the color changing bionic structure of M type changeable angle and model were designed.Photonic crystal is the periodic electric medium structure with photon band gap, and the light cannot spread in the photon band gap. Photonic crystal is one of the research hotspots in the optics field. The typical structure of photonic crystal materials is three-dimension object with periodic refractive index, whose period is light wavelengh. When the refractive index changes more, the electron energy band and gap appear similarly in the electron condition. The aclinic parallel multilayer structure of butterfly scale can be considered as the one-dimension photonic crystal structure.According to the structure parameters of the butterfly scales, the calculational software of optic band gap-Translight was employed to calculate the optics performance of the bionic parallel multilayer structure in visible light range, and the calculational results are in agreement with the experimental results, which will provide manufacturing parameters and theoretical model for double photon polymerization manufacturing vedio frequency bionic stealth materials like butterfly scales structures.