Investigation on color variation of Morpho butterfly wings hierarchical structure based on PCA

Morpho butterfly wings show brilliant blue color, which has a close relationship with the hierarchical micro/nano structures on the surface of scales. When liquids such as methanol, ethanol and isopropanol with different refractive indexes drop onto the scales, the reflectance of wings would decrease. The main peaks of reflectance shift to the right and the scales turn to yellow-green. After the liquids volatilizes completely, the scales revert to the original blue color. The typical micro/nano structures of Morpho butterfly wing scales are modeled, and the reflectance variation in the course of dropping liquids is simulated. Furthermore, the principal component analysis (PCA) method is employed to analyze the experimental and simulation reflectance data, extract principal components and reduce dimensions. As a result, the curves mapping the reflectance variation are clearly shown in the coordinate system consisting of three principal components. The typical color variation of scales during the dropping process could be monitored, and different kinds of liquids could be obviously distinguished according to the distributed regions of mapping points. This study provides guidance to environmental media detecting as well as data processing, and enhances the fabrication and application of the mimic Morpho butterfly wings micro/nano structures.