Reflectivity of solid and hollow microsphere composites and the effects of uniform and varying diameters
Reflectivity of solid and hollow microsphere composites and the effects of uniform and varying diameters
复制标题
DOI：
10.1063/5.0015650
复制
发表时间：
2020-08
影响因子：
3.2
通讯作者：
Ziqi Yu;Xiao Nie;A. Yuksel;Jaeho Lee
中科院分区：
文献类型：
--
作者：
Ziqi Yu;Xiao Nie;A. Yuksel;Jaeho Lee
虽然实心和空心微球复合材料作为太阳反射体或选择性发射体受到了极大的关注，但其光学性能的驱动机制仍然相对不清楚。在这里，我们研究了直径从0.125μm到8μm的实心微球和空心微球在0.4-2.4μm波长范围内的太阳反射率。基于Mie理论和有限差分时域模拟，我们的分析表明，壳层较薄的空心微球比固体微球更能有效地散射光线，并导致更高的太阳反射率。由于中空微球具有较高的折射率对比度和较大的界面密度，使得低折射率材料具有较高的太阳反射率。当粒径均匀时，0.75μm SiO_2中空微球的太阳反射率最大，为0.81。当直径变化时，随机分布的0.5-1μm SiO_2中空微球的太阳反射率最大，为0.84。变直径效应的特点是在电场中有很强的后向散射。这些发现将指导光学和热管理系统的微球复合材料和分级材料的优化设计。
While solid and hollow microsphere composites have received significant attention as solar reflectors or selective emitters, the driving mechanisms for their optical properties remain relatively unclear. Here, we study the solar reflectivity in the 0.4–2.4 μm wavelength range of solid and hollow microspheres with the diameter varying from 0.125 μm to 8 μm. SiO2 and TiO2 are considered as low- and high-refractive-index microsphere materials, respectively, and polydimethylsiloxane is considered as a polymer matrix. Based on the Mie theory and finite-difference time-domain simulations, our analysis shows that hollow microspheres with a thinner shell are more effective in scattering the light, compared to solid microspheres, and lead to a higher solar reflectivity. The high scattering efficiency, owing to the refractive-index contrast and large interface density, in hollow microspheres allows low-refractive-index materials to have a high solar reflectivity. When the diameter is uniform, 0.75 μm SiO2 hollow microspheres provide the largest solar reflectivity of 0.81. When the diameter is varying, the randomly distributed 0.5–1 μm SiO2 hollow microspheres provide the largest solar reflectivity of 0.84. The effect of varying diameter is characterized by strong backscattering in the electric field. These findings will guide optimal designs of microsphere composites and hierarchical materials for optical and thermal management systems.