PDF(Pubmed)
Abstract：
Energy efficiency in habitation spaces is a pivotal topic for maintaining energy sufficiency, cutting climate impact, and facilitating economic savings; thus, there is a critical need for solutions aimed at tackling this problem. One viable approach involves complementing active cooling methods with powerless or passive cooling ones. Moreover, considerable scope remains for the development of passive radiative cooling solutions based on sustainable materials. Cellulose, characterized by its abundance, renewability, and biodegradability, emerges as a promising material for this purpose due to its notable radiative cooling potential exploiting the mid-infrared (MIR) atmospheric transmission window (8-13 μm). In this work, we propose the utilization of thermochromic (TC) materials in conjunction with cellulose nanofibrils (CNF) to confer temperature-dependent adaptivity to hybrid CNF films. We employ a concept where high reflection, coupled with MIR emission in the heated state, facilitates cooling, while high visible light absorption in the cold state allows heating, thus enabling adaptive thermal regulation. CNF films were doped with black-to-leuco TC particles, and a thin silver layer was optionally applied to the films. The films exhibited a rapid transition (within 1 s) in their optical properties at ∼22 °C, becoming transparent above the transition temperature. Visible range transmittance of all samples ranged from 60 to 90%, with pronounced absorption in the 8-13 μm range. The cooling potential of the films was measured at 1-4 °C without any Ag layer and ∼10 °C with a Ag layer. In outdoor field testing, a peak cooling value of 12 °C was achieved during bright sunshine, which is comparable to a commercial solar film. A simulation model was also built based on the experimental results. The concept presented in this study extends beyond applications as standalone films but has applicability also in glass coatings. Overall, this work opens the door for a novel application opportunity for green cellulose-based materials.
摘要：
居住空间的能源效率是保持能源充足的关键主题，减少气候影响，促进经济储蓄；因此，迫切需要解决这一问题的解决方案。一种可行的方法包括用无功率或被动冷却方法补充主动冷却方法。此外，基于可持续材料的无源辐射冷却解决方案的开发仍有相当大的范围。纤维素,以其丰富为特征，可再生性，和生物降解性，由于其利用中红外（MIR）大气传输窗口（8-13μm）的显着辐射冷却潜力，因此成为有前途的材料。在这项工作中,我们建议将热致变色（TC）材料与纤维素纳米原纤维（CNF）结合使用，以赋予混合CNF膜的温度依赖性适应性。我们采用高反射的概念，加上加热状态下的MIR发射，有利于冷却，而在冷态下的高可见光吸收允许加热，从而实现自适应热调节。CNF薄膜掺杂有黑色到隐色TC颗粒，并且将薄的银层任选地施加到膜上。这些薄膜在~22°C时的光学性能表现出快速转变(在1s内)，在转变温度以上变得透明。所有样品的可见透射率范围为60-90%,在8-13μm范围内具有明显的吸收。在没有任何Ag层的1-4°C和有Ag层的~10°C下测量膜的冷却电势。在户外现场测试中，在明亮的阳光下达到12°C的峰值冷却值，相当于商业太阳能膜。根据实验结果建立了仿真模型。本研究中提出的概念超出了作为独立薄膜的应用范围，但也适用于玻璃涂层。总的来说,这项工作为绿色纤维素基材料的新应用机会打开了大门。
