輻射冷卻是一種被動冷卻方式，在不需要輸入能量的情況下，藉由大氣窗口區域(波長8至13微米)向外太空散發熱輻射。二氧化矽(SiO2)在大氣窗口具備良好的熱發射性質，因此，本實驗結合SiO2與聚甲基丙烯酸甲酯(PMMA)顆粒製備被動輻射冷卻塗層(SiO2-PMMA coating)，並由穩定塗層製程、調配固含量及優化塗層性質三個階段，建構出理想的塗層。以掃描式電子顯微鏡、白光干涉儀、迴轉式動態流變儀、傅立葉轉換紅外線光譜儀、紫外光/可見光/近紅外光譜儀及日曬溫度量測來鑑定其表面形貌、表面粗糙度、分散性、紅外光發射光譜、漫反射光譜以及塗層的冷卻效果。
首先，比較刷塗、刮刀塗佈、噴槍塗佈以及噴塗後刮平等製程方式製備塗層，刮刀塗佈法能夠獲得相對穩定的塗層性質，另外，為了維持粉體在懸浮液中的分散性，先調整分散劑的添加量，接著製備不同SiO2顆粒體積比(25~45%)的塗層，優化固含量的組成，並探討厚度變化以及添加5 vol% 的金紅石相二氧化鈦(rutile TiO2)顆粒對塗層冷卻性質的影響。
實驗結果顯示在35 vol% SiO2的塗層為最佳的固含量組成，相較未塗佈的基板，厚度75微米的SiO2-PMMA和TiO2-SiO2-PMMA塗層在相同測量條件下最高降溫達到9.4和9.8 °C。

Radiative cooling is a passive cooling technology that releases heat radiation towards outer space through the atmospheric window (8~13 μm wavelength). In the atmospheric window, SiO2 exhibits a strong emissivity. As a result, the radiative cooling coatings used in this work were composed of SiO2 and polymethyl methacrylate (PMMA) particles. The experiment was divided into three steps to improve the coating and accomplish the cooling properties: coating preparation, solid content adjustment, and coating optimization. Surface morphology, surface roughness, particle distribution, emissive spectrum, solar reflectance spectrum, and cooling performance of the coatings were studied using a scanning electron microscope (SEM), white light interferometry (WLI) modular compact rheometer (MCR), Fourier transform infrared spectrometer (FT-IR), UV-Vis-NIR spectrometer, and temperature data logger.
First, comparing the various fabrication processes, including brush coating, blade coating, spray coating, and scrape after spray coating, revealed that the blade coating approach produced coating with relatively stable coat characteristics. In addition, the dispersant concentration in the suspension preparation was adjusted to maintain the powder's dispersibility. Then, to optimize the composition of the solid content, coats with various volume ratios of SiO2 particles have been prepared. Finally, the effect of coating thickness and the addition of 5 vol% of rutile TiO2 particles were discussed.
Based on the temperature test, the SiO2-PMMA coating with 35 vol% SiO2 particles had the best cooling properties. The 75 μm SiO2-PMMA and TiO2-SiO2-PMMA coatings successfully decreased the temperature by 9.4 and 9.8 °C, respectively, compared to the uncoated substrate.

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