Enhancement of infrared emissivity by the hierarchical microstructures from the wing scales of butterfly Rapala dioetas

Modi Jiang,Benwei Fu,Tao Deng,Runheng Yang,Hanrui Zhu,Shun An,Chenhua Lou,Chengyi Song,Qingchen Shen,Wen Shang,Peng Tao

doi:10.1063/5.0039079

Abstract

Radiative cooling, which normally requires relatively high infrared (IR) emissivity, is one of the insects’ effective thermoregulatory strategies to maintain their appropriate body temperature. Recently, the physical correlation between the delicate biological microstructures and IR emissivity for thermal radiation draws increased attention. Here, a scent patch region on the hindwing of Rapala dioetas butterfly is found to exhibit enhanced IR emissivity compared with the non-scent patch regions. A series of optical simulations are conducted to differentiate the effect of biological structures and material composition on the high IR emissivity. Besides the intrinsic IR absorption (emission) of chitin (the main composition of butterfly wings), the hierarchical microstructures of the scent patch scale further improve the IR absorption (emission) through the increased inner surface area and multi-scattering effect. This enhancement of IR emissivity enables the butterfly to efficiently radiate heat from the scent patch region to the environment with a limited volume of chitin. This study of the correlation between IR emissivity and microstructural designs may offer additional pathways to engineer bioinspired materials and systems for radiative cooling applications.

Highlights

Besides the behavioral thermoregulation strategies the insects have evolved, the radiative cooling effect, which cools an object by emitting thermal radiation to the cold universe with high infrared (IR) emissivity,18,19 plays an important role in the prevention of overheating for many insect species
We demonstrated that the hierarchical microstructures of the scent patch scale improved the IR absorption through the increased inner surface area and multi-scattering effect, which helped the butterfly efficiently dissipate heat from the scent patch region to the environment with a limited volume of chitin
We found that the scent patch region on the hindwing of Rapala dioetas butterfly showed a higher IR emissivity than the non-scent patch region, which was primarily due to the structural difference between the scales in these two regions

Summary

Introduction

Evolution-driven thermoregulatory designs in nature, such as those found in plants, insects, reptiles, birds, and mammals, can effectively help maintain appropriate body temperatures for optimal performances. Temperature regulation is especially critical in insects, whose living tissues require optimal temperature ranges for their survival under different environmental conditions. Besides the behavioral thermoregulation strategies the insects have evolved, the radiative cooling effect, which cools an object by emitting thermal radiation to the cold universe with high infrared (IR) emissivity, plays an important role in the prevention of overheating for many insect species. For example, the silver ants, Cataglyphis bombycina, live under extremely hot conditions through enhancing solar reflectance and thermal emissivity of body surface with a dense array of triangularly shaped hairs to effectively regulate their body temperatures. Cocoon fibers of Argema mittrei represent another example, which are composed of filamentary air voids randomly distributed across the fibers. The silver ants, Cataglyphis bombycina, live under extremely hot conditions through enhancing solar reflectance and thermal emissivity of body surface with a dense array of triangularly shaped hairs to effectively regulate their body temperatures.. Cocoon fibers of Argema mittrei represent another example, which are composed of filamentary air voids randomly distributed across the fibers. This unique biological structure protects the moth pupa from overheating by reflecting solar light and emitting IR radiation effectively.. This unique biological structure protects the moth pupa from overheating by reflecting solar light and emitting IR radiation effectively.24 These biological thermoregulatory systems require efficient interaction between body structure and electromagnetic waves (from visible to mid-IR ranges).. This unique biological structure protects the moth pupa from overheating by reflecting solar light and emitting IR radiation effectively. These biological thermoregulatory systems require efficient interaction between body structure and electromagnetic waves (from visible to mid-IR ranges). Understanding the physical mechanism behind such interaction may offer paths to engineering solutions for radiative cooling systems with increased efficiency

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Conclusion