Broadband omnidirectional light reflection and radiative heat dissipation in white beetles Goliathus goliatus.

Abstract

Structural whiteness, stemming from biologically evolutionarily refined structures, provides inspiration for designing promising, reflectance-based materials. White beetles Goliathus goliatus, which can survive in high-temperature-equatorial forests, may suggest undiscovered new physical mechanisms for thermoregulation. Their scales' whiteness is created by the exquisite shell/hollow cylinder structure with two thermoregulatory effects, contributing to a lower equilibrium temperature of elytra under direct sunlight. In the visible regime, they enhance the broadband omnidirectional reflection significantly by synergetic structural effects originating from the thin-film interference, Mie resonance and total reflection. In the mid-infrared (MIR) regime, white scales act as antireflective layers to increase the emissivity in the MIR range, enabling the elytra to reradiate heat to the environment and help the beetles reduce their temperature by as much as ∼7.8 °C in air. These biological strategies for thermoregulation could provide new approaches for bioinspired coatings towards passive radiative cooling.