Chi Fangting, Zeng Yiyang, Liu Cheng, Liang Dan, Li Yuanli, Xie Ruishi, Pan Ning, Ding Congcong
Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory, Southwest University of Science and Technology, Mianyang 621010, China.
College of Physics and Space Science, China West Normal University, Nanchong 637009, China.
ACS Appl Mater Interfaces. 2020 Apr 8;12(14):16887-16895. doi: 10.1021/acsami.0c00579. Epub 2020 Mar 25.
Optical coatings with controllable ultralow refractive indices are of profound significance in optical areas. However, it remains a challenge to fabricate such coatings using a simple method. Here we develop an effective and simple approach to create ultra-low-index coatings. This approach was based on a modified sol-gel process, with a key process that involved the aggregation of silica nanoparticles via the addition of a polymer surfactant (e.g., polyvinylpyrrolydone) in sols before coating. The approach involves three steps: the synthesis of silica sols under ammonia catalysis in ethanol (Stöber method), the addition of polyvinylpyrrolydone in the silica sols to induce the aggregation of the silica nanoparticles, and the formation of ultra-low-index coatings by depositing the aggregated silica sols on substrates. Through varying the aggregation extent, this approach produced coatings with controllable refractive indices ranging from 1.17 to 1.07. To the best of our knowledge, the minimum index value of 1.07 from our coating is among the lowest refractive indices ever reported. The ultra-low-index coatings demonstrated excellent optical properties, with which perfect quarter-wavelength antireflection coatings (maximum transmittance ∼100%) and broadband antireflection coatings (transmittance >98% from 400 to 1100 nm) can be prepared. One advantage of the antireflection coatings is that their transmission is less dependent on the refractive index and the thickness of the stacking layer, which make it promising in large-scale production. Moreover, the coatings can be made hydrophobic (water contact angle 136°) by exposing the coatings to a hexamethyldisilazane atmosphere, exhibiting high environmental stability in a humid environment. The aggregation of silica nanoparticles in sol-gel processes provides a scalable alternative to the current approaches for creating ultra-low-index coatings.
具有可控超低折射率的光学涂层在光学领域具有深远意义。然而，用简单方法制造此类涂层仍然是一项挑战。在此，我们开发了一种有效且简单的方法来制备超低折射率涂层。该方法基于改进的溶胶 - 凝胶工艺，关键步骤是在涂覆前通过在溶胶中添加聚合物表面活性剂（如聚乙烯基吡咯烷酮）使二氧化硅纳米颗粒聚集。该方法包括三个步骤：在乙醇中氨催化下合成二氧化硅溶胶（斯托伯法），在二氧化硅溶胶中添加聚乙烯基吡咯烷酮以诱导二氧化硅纳米颗粒聚集，以及通过将聚集的二氧化硅溶胶沉积在基板上形成超低折射率涂层。通过改变聚集程度，该方法制备出折射率可控范围为1.17至1.07的涂层。据我们所知，我们涂层的最低折射率值1.07是有史以来报道的最低折射率之一。超低折射率涂层表现出优异的光学性能，利用这些性能可以制备出完美的四分之一波长抗反射涂层（最大透过率约100%）和宽带抗反射涂层（400至1100nm透过率>98%）。抗反射涂层的一个优点是其透射率对堆叠层的折射率和厚度的依赖性较小，这使其在大规模生产中具有前景。此外，通过将涂层暴露在六甲基二硅氮烷气氛中可使涂层具有疏水性（水接触角136°），在潮湿环境中表现出高环境稳定性。溶胶 - 凝胶过程中二氧化硅纳米颗粒的聚集为当前制备超低折射率涂层的方法提供了一种可扩展的替代方案。
