Infrared optical and thermal properties of microstructures in butterfly wings
Infrared optical and thermal properties of microstructures in butterfly wings
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DOI：
10.1073/pnas.1906356117
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发表时间：
2020-01-21
影响因子：
11.1
通讯作者：
Lee, Jaeho
中科院分区：
文献类型：
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作者：
Krishna, Anirudh;Nie, Xiao;Lee, Jaeho
虽然蝴蝶翅膀的表面微观结构在可见光谱范围内的结构着色或光学特性已经得到了广泛的研究，但它们在红外波段的特性与温度调节的潜在联系相对未知。7.5 ~ 14 μ m的中红外波长由于与大气透射窗口重叠，对环境中的辐射传热尤为重要。例如，高中红外发射率可以促进表面冷却，而低中红外发射率可以最大限度地减少对周围环境的热损失。本文利用傅里叶变换红外光谱（FTIR）和红外热成像技术发现，来自墨西哥瓦哈卡州的Archaeoprepona demophoon和厄瓜多尔皮欣查市的Heliconius sara等温暖气候地区的蝴蝶翅膀的中红外发射率比来自科罗拉多州Celastrina echo和佛罗里达州Limenitis arthemis等寒冷气候地区的蝴蝶翅膀的中红外发射率高出2倍。我们的光学计算使用单位细胞方法再现光谱数据，并解释周期性微结构如何在中红外中发挥关键作用。发射光谱控制着蝴蝶翅膀的温度，我们证明了在同样的阳光下，在加州欧文晴朗的天空中，回声蝴蝶的翅膀比demophoon蝴蝶的翅膀多加热8℃。此外，我们的热计算表明，在各自栖息地的蝴蝶翅膀可以通过平衡太阳吸收和红外发射来保持适度的温度范围。这些发现表明，蝴蝶翅膀的表面微观结构可能有助于体温调节，并为了解蝴蝶的生存提供了线索。
While surface microstructures of butterfly wings have been extensively studied for their structural coloration or optical properties within the visible spectrum, their properties in infrared wavelengths with potential ties to thermoregulation are relatively unknown. The midinfrared wavelengths of 7.5 to 14 mu m are particularly important for radiative heat transfer in the ambient environment, because of the overlap with the atmospheric transmission window. For instance, a high midinfrared emissivity can facilitate surface cooling, whereas a low midinfrared emissivity can minimize heat loss to surroundings. Here we find that the midinfrared emissivity of butterfly wings from warmer climates such as Archaeoprepona demophoon (Oaxaca, Mexico) and Heliconius sara (Pichincha, Ecuador) is up to 2 times higher than that of butterfly wings from cooler climates such as Celastrina echo (Colorado) and Limenitis arthemis (Florida), using Fourier-transform infrared (FTIR) spectroscopy and infrared thermography. Our optical computations using a unit cell approach reproduce the spectroscopy data and explain how periodic microstructures play a critical role in the midinfrared. The emissivity spectrum governs the temperature of butterfly wings, and we demonstrate that C. echowings heat up to 8 degrees C more than A. demophoon wings under the same sunlight in the clear sky of Irvine, CA. Furthermore, our thermal computations show that butterfly wings in their respective habitats can maintain a moderate temperature range through a balance of solar absorption and infrared emission. These findings suggest that the surface microstructures of butterfly wings potentially contribute to thermoregulation and provide an insight into butterflies' survival.