Research On Mechanism Of Structural Colors And Microstructure Of Typical Butterfly Scales

There are two reasons that gives rise to color of butterfly scale, which is pigment and structure. Just as its name implies, pigment color arises from some pigment, which has ability to absorb certain wavelength light and reflect other wavelength light. Structural colours, also named physics color, is achieved through paper-thin wax layer,spot, gap, which can scatter, intervene, and diffract light, consequently color can be achieved.The research about butterfly structural colours is always discussed hotly by scientists, and research progress have benefited many fields such as military, spaceflight, spin, etc. The theme of this paper is also about butterfly structural colours. After sumed up a great deal literature, 9 familiar species of butterflies were selected as research object in the northeast area of China. Structural color was investigated systemaficly, The scale models based on observing and optimizing microstructure of structural color scales was built. The reflection optics performance of structural color scales was tested, and structural color forming mechanism was analyzed and discovered through the aid of optics knowledge and the scale models. The important conclusions are as follows:1. Papilio maackii Menerries, Papilio xuhtus Linnaeus, Polyommatus eros Ochsenheimer, Apatura laverna Leech(having purple light), Apatura laverna Leech(no having purple light), Gonepteryx machaguru(Gistel), Neptis dejeani Oberthiir, Lopinga achine(Scopoli), and Argynnis paphia (Linnaeus) were chosen as samples. According to the features of structural colours such as iridescence, brightness, color change after dropping alcohol liquid or glycerin, iridescence test, OM test and color change test were designed in order to validate structural colours. By iridescence test, it was observed color of the blue and green scales of Papilio maackii Menerries, purple scales of Apatura laverna Leech(having purple light) changed when angle of view changed, which was called iridescence. By OM test,it was found that brightness of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) was high, and it was metallikecolor. By color change test, it was observed that after alcohol liquid was dropped into scales, the color of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) changed obviously. According to the spectrum, it was found that the reflection peak moved toward shortwave. After alcohol liquid vaporized, primary color could be observed, which was color change phenomenon. Based on the above three tests,the presence of structural colours of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) was ralidated.2. The electron microscope was employed to observe microstructure of structural colours scales. By SEM, it was found that the blue and green scales of Papilio maackii Menerries had continous, drape structure, Polyommatus eros Ochsenheimer had meshwork structure, and Apatura laverna Leech(having purple light) possed strip structure clearly. At the same time, the structure of the scale of Apatura laverna Leech with no purple light was observed. It was found that the upper scales gave rise to purple light. By TEM,the cross section of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) were attained. It was discovered that the blue and green scales of Papilio maackii Menerries comprised multilayer systems incorporating into the scale body. It is the multilayer systems that form concavity profile. The difference between the green scales and the blue scales is that the concavity of the green scales is deeper than that of the blue scales. The layer number of the green scales and the blue scales is 9 and 8, respectively. Laverna Leech comprises multilayer systems incorporating into scale ridging, and its layer number is 8, The microstructure of Polyommatus eros Ochsenheimer is in the form of air-filled alveoli with internal diameter 200nm approximately.3. On the basis of the data of SEM and TEM experiments, the structure models of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) were set up by 3D software UG, which can offer immediate and effective data for analyzing mechanism and construction of biomimetics models.4. By using TU-1901 UV-VIS spectrometer, the reflection optics performance of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) at the spectrum range of 350nm~800nm were measured. It was found that the test results were consistent with the effect observed, which was the main reflection peak in corresponding wave band.5. Based on the interference, scattering.principles and multilayer films theory, considering the models, the mechanism of structural color of the blue and green scales of Papilio maackii Menerries, Polyommatus eros Ochsenheimer and Apatura laverna Leech(having purple light) were analyzed, and other optics phenomena were also explained. The results indicated that the blue and green scales of Papilio maackii Menerries and Apatura laverna Leech(having purple light) generated light in multilayer systems through multilayer interference in the normal way. The color mechanism of green scales is particular. White light incidenting perpendicular to the plane of the scale will undergo interference in the multilayered flat bottoms of the concavities, which have appropriate dimensions to effect yellow reflectivity. Light that strikes the sides of the concavities at 45°to the surfaces, so the multilayers then reflect blue light strongly. The blue light is reflected directly across the concavity to the opposite side strongly, then the second reflection sends the light back along the incident direction. The result is that from incident white light, different regions of the scale strongly reflect blue and yellow, which leads to a blue outer circle and a yellow central core of the concavity. These pointillistic regions are too small to be individually resolved by human eyes, so the luminances and peak wavelengths of the reflected colours make their subsequent additive mixture synthesises the stimulus of green coloration in human vision. The sides of the blue scale concavities have inclinations not more than 30 deg. Consequently, opposite sides of the blue scale concavity are not perpendicular to each other, the blue light can be achieved through calculation, and purple color can be observed by calculation in Apatura laverna Leech(having purple light). The mechanism of structural color of Polyommatus eros Ochsenheimer is explained through Rayleigh scattering, because the dimension of air-filled alveoli meet the requirement of Rayleigh scattering.The results of this paper can provide inference data for the study of stealth effect of butterfly wingscales and the design and manufacturing of vedio stealth biomimetic materials. The research methods of this paper are benefical for the study of other living creatures structural color.