Passive daytime radiative cooling (PDRC) is an efficient strategy to achieve cooling through spectrally selective emission and high solar spectrum reflection. Current preparation strategies for PDRC materials mainly involve doping inorganic micro-nanoparticles into polymers, but their solar reflectance is usually insufficient. Here, we designed a super-white inorganic coating on different substrates based on natural halloysite nanotubes (HNTs) through the doctor blade method. Polyvinyl alcohol (PVA) and water-based acrylic resin (AR) were introduced to increase the adhesion for obtaining robust inorganic coating. HNTs/PVA/AR composite coating shows excellent water resistance, wear resistance, and environmental tolerance, which is mainly due to the strong interfacial interactions between HNTs, PVA, and AR. Compared with the uncoated transparent plastic, the coated plastic exhibits a super-white appearance (whiteness of ∼95%) and maximum solar reflectance of ∼97%. The maximum temperature difference of the HNTs/PVA/AR coated and pristine copper sheet is 15 °C under simulated sunlight. The PDRC property is related to the high surface roughness of the coating composed of disordered high-aspect ratio nanotubes and the high whiteness of the raw halloysite materials. The composite coating can tolerate pH from 1–13, temperature change (−60∼250 °C), and different salt environments. The composite coating increases thermal stability, flame retardancy, and giving protective effect of dye against UV degradation. In addition, the HNTs/PVA/AR coated plastic as packaging materials can maintain good freshness of different fruits under strong solar irradiation. The robust HNTs/PVA/AR composite coating with high PDRC properties shows promising application in food packaging, building energy conservation, metal anticorrosive coating, and sunscreen products.

中文翻译：

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基于埃洛石纳米管/聚合物复合材料的坚固耐磨涂层，用于被动日间辐射冷却

被动日间辐射冷却（PDRC）是一种通过光谱选择性发射和高太阳光谱反射实现冷却的有效策略。目前PDRC材料的制备策略主要是将无机微纳米颗粒掺杂到聚合物中，但其太阳反射率通常不足。在这里，我们通过刮刀法在不同的基材上设计了基于天然埃洛石纳米管（HNT）的超白无机涂层。引入聚乙烯醇（PVA）和水性丙烯酸树脂（AR）来增加附着力，以获得坚固的无机涂层。 HNTs/PVA/AR复合涂层表现出优异的耐水性、耐磨性和耐环境性，这主要归功于HNTs、PVA和AR之间强烈的界面相互作用。与未涂覆的透明塑料相比，涂覆的塑料呈现出超白的外观（白度~95%）和最大太阳光反射率~97%。在模拟阳光下，HNTs/PVA/AR涂层与原始铜板的最大温差为15°C。 PDRC性能与无序高长径比纳米管组成的涂层的高表面粗糙度和埃洛石原料的高白度有关。该复合涂层可以耐受1-13的pH值、温度变化（-60∼250°C）和不同的盐环境。复合涂层提高了热稳定性、阻燃性，并赋予染料防止紫外线降解的保护作用。此外，HNTs/PVA/AR涂层塑料作为包装材料可以在强烈的太阳照射下保持不同水果良好的新鲜度。这种坚固的HNTs/PVA/AR复合涂层具有高PDRC性能，在食品包装、建筑节能、金属防腐涂料和防晒产品等领域具有广阔的应用前景。