Corkery Robert W, Tyrode Eric C
Department of Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden.
Department of Applied Mathematics, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia.
Interface Focus. 2017 Aug 6;7(4):20160154. doi: 10.1098/rsfs.2016.0154. Epub 2017 Jun 16.
butterflies from the genera , and have evolved remarkable biophotonic gyroid nanostructures within their wing scales that have only recently been replicated by nanoscale additive manufacturing. These nanostructures selectively reflect parts of the visible spectrum to give their characteristic non-iridescent, matte-green appearance, despite a distinct blue-green-yellow iridescence predicted for individual crystals from theory. It has been hypothesized that the organism must achieve its uniform appearance by growing crystals with some restrictions on the possible distribution of orientations, yet preferential orientation observed in confirms that this distribution need not be uniform. By analysing scanning electron microscope and optical images of 912 crystals in three wing scales, we find no preference for their rotational alignment in the plane of the scales. However, crystal orientation normal to the scale was highly correlated to their colour at low (conical) angles of view and illumination. This correlation enabled the use of optical images, each containing up to 10-10 crystals, for concluding the preferential alignment seen along the [Formula: see text] at the level of single scales, appears ubiquitous. By contrast, [Formula: see text] orientations were found to occur at no greater rate than that expected by chance. Above a critical cone angle, all crystals reflected bright green light indicating the dominant light scattering is due to the predicted band gap along the [Formula: see text] direction, independent of the domain orientation. Together with the natural variation in scale and wing shapes, we can readily understand the detailed mechanism of uniform colour production and iridescence suppression in these butterflies. It appears that the combination of preferential alignment normal to the wing scale, and uniform distribution within the plane is a near optimal solution for homogenizing the angular distribution of the [Formula: see text] band gap relative to the wings. Finally, the distributions of orientations, shapes, sizes and degree of order of crystals within single scales provide useful insights for understanding the mechanisms at play in the formation of these biophotonic nanostructures.
凤蝶属、粉蝶属和斑蝶属的蝴蝶在其翅鳞片内进化出了非凡的生物光子螺旋状纳米结构，这些结构直到最近才被纳米级增材制造技术复制出来。尽管从理论上预测单个晶体具有明显的蓝绿黄虹彩，但这些纳米结构选择性地反射可见光谱的部分区域，呈现出其特有的非虹彩哑光绿色外观。据推测，生物体必须通过生长晶体来实现其均匀外观，且对晶体取向的可能分布有一定限制，但在粉蝶属中观察到的优先取向证实这种分布不必是均匀的。通过分析三个翅鳞片中912个晶体的扫描电子显微镜图像和光学图像，我们发现它们在鳞片平面内的旋转排列没有偏好。然而，在低（圆锥）视角和光照角度下，垂直于鳞片的晶体取向与其颜色高度相关。这种相关性使得能够利用每个包含多达10 - 10个晶体的光学图像，得出在单个鳞片水平上沿[公式：见正文]方向观察到的优先排列似乎无处不在的结论。相比之下，发现[公式：见正文]取向出现的频率并不高于随机预期的频率。在一个临界圆锥角以上，所有晶体都反射亮绿色光，表明主要的光散射是由于沿[公式：见正文]方向预测的带隙，与畴取向无关。结合鳞片和翅膀形状的自然变化，我们可以很容易地理解这些蝴蝶中均匀颜色产生和虹彩抑制的详细机制。似乎垂直于翅鳞片的优先排列和平面内的均匀分布相结合，是使[公式：见正文]带隙相对于翅膀的角度分布均匀化的近乎最优的解决方案。最后，单个鳞片内晶体的取向、形状、大小和有序度分布为理解这些生物光子纳米结构形成过程中起作用的机制提供了有用的见解。
