Excellent Color Sensitivity of Butterfly Wing Scales to Liquid Mediums

The ultrastructure characteristic and vivid colors of butterfly wing scales have attracted considerable attention recently. Surprisingly, these hyperfine structures also endow butterfly Trogonoptera brookiana wing scales the excellent color sensitive property to liquid mediums. In this work, the characteristic features of this excellent functional surface and the mechanism of its highly sensitive response characteristics were investigated. Firstly, the extraordinary and ordered nanostructures of this butterfly wing scales were characterized by a Field Emission Scanning Electron Microscope (FESEM). Then, the ultra-depth three-dimensional (3D) microscope was used to observe the sensitive discoloration effect of the scales to liquid mediums. Afterwards, the highly spectral sensitive feature was identified by a mini spectrometer. In addition, the mechanism of this color sensitive effect of butterfly wing scales was revealed through modelling, calculation and simulation. It was found that this sensitivity is caused by the combined action of the microscale scales and the ultra-fine nanoscale structures in scale surface. On one hand, the arched and bended cover scales were stretched and superimposed by the filled ether solution. So, the color of the scales became reddish brown in an instant. On the other hand, the change of the fill mediums with different reflective index induced the modification of the surface interference, resulting in the peak shift of the reflectance spectrum. More importantly, the results of simulation and theoretical calculation were both in agreement with the experimental results. It illustrated that the butterfly Trogonoptera brookiana wings have repeatable sensitivity to liquid mediums, and obvious discoloration sensitive effect. This spectral sensitivity of butterfly wing scales has great prospect and meaning for the basic research and application of cheap, environmentally free and biodegradable sensitive element for water quality monitoring and analysis system.