輻射冷卻是指物體表面具備放射大氣窗波段(8 μm – 13 μm)輻射之能力，使輻射熱能有效穿越大氣層至外太空，同時抑制在短波長之放射率以降低太陽熱吸收。常見之輻射冷卻裝置組成包含中紅外光放射層與太陽光反射層，前者放射大氣窗波段輻射，後者反射太陽熱輻射。本研究利用電泳沉積法在不鏽鋼與白金基板上沉積甲殼素薄膜，並量測樣本短波長(0.4 μm – 1.8 μm)與長波長(2 μm – 13 μm)之半球反射率，再利用克希荷夫定律推得樣本之半球放射率。上述結構中，金屬基板可以反射大部分太陽熱輻射甲殼素薄膜在8 μm - 13 μm具備高放射率，而在短波長波段(0.4 μm – 1.8 μm)則為非吸收膜，二者結合足以達到被動輻射冷卻。現有研究之輻射冷卻裝置多為一維光子晶體結構或超穎材料組成，本研究所提出之輻射冷卻裝置相較於現有輻射冷卻研究裝置(如：光子晶體、超穎材料等)成果具備兩項優勢，一為製程簡易，本研究之薄膜僅須透過電泳沉積甲殼素溶液，大幅降低製程難度，進而降低製作成本。二為取材自然，甲殼素具有良好的生物相容性、無毒性與可分解性，更可自蝦、蟹殼等廢棄物中大量提取，因此本研究極具產業應用潛力。

Radiative cooling is to achieve net thermal radiation emission from surfaces to space which will achieve effect without energy consumption. It is important to have high absorptance between 8 – 13 μm which is called atmospheric window. Where atmosphere is transparent to this band. It is also necessary to consider minimizing heat gains from the sun. Radiative cooling device is generally composed of IR radiator, solar reflector and substrate. IR radiator is selective material which emits radiation within wavelengths of 8 – 13 μm. Solar reflector reflects irradiance from the sun. This study is going to employ electrophoretic deposition of chitosan on stainless steel and platinum substrate. Then measuring hemispherical radiative properties within wavelength of 0.4 – 1.8 μm and 2 – 13 μm. The emissivity is obtained by using energy conservation law and Kirchhoff's law. The chitosan film is used as IR radiator to emit radiation within wavelengths of 8 – 13 μm and metallic substrate is used as solar reflector to reflect solar radiation. Combining those two properties can achieve passive radiative cooling. Most of recent studies about radiative cooling are based on photonic device and metamaterial microstructure. Which is difficult to fabricate on complex shape and the cost of manufacturing process is high. Chitosan is famous for being non-toxic, bio-degradable, and abundant in living creatures. It can be extracted at a very low cost. Electrophoretic deposition of chitosan on metallic substrate largely reduces the fabrication cost and challenges in operation. Theoretical and experimental results show that the chitosan coating can emit radiant power within atmospheric window to decrease net radiant power absorbed metallic substrates. Which has great industrial application potential.

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