Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Langmuir. 2011 Jun 21;27(12):7860-7. doi: 10.1021/la200790g. Epub 2011 May 17.
Automated spray-layer-by-layer (LbL) assembly was used to create highly reflective structurally colored thin films with high reflectance at near-UV light wavelengths. Reflectance peaks were tuned by fabricating alternating stacks of high (TiO(2) nanoparticles) and low (SiO(2) nanoparticles) refractive index materials using a non-quarter-wave design. Spray-assembled multilayer heterostructures fabricated with up to 840 individual polymer or nanoparticle deposition steps presented similar roughness and refractive index values compared to Bragg stacks obtained via immersion LbL assembly. Such complex multilayer heterostructures, however, could be fabricated in significantly shorter times; the time required to deposit a complete bilayer was only about 90 s, compared to 36 min for the immersion assembly of the same system. Optimization of the experimental parameters was performed to achieve uniform coatings and relatively smooth interfaces and surfaces. We observed that the spraying times of the nanoparticle and polymer solutions are the main parameters that determine the thickness, optical properties, and uniformity of the assembled films. Ellipsometry, atomic force microscopy (AFM), UV-vis spectroscopy, and transmission electron microscopy (TEM) were used to characterize the samples. The nanoparticle thin films were iridescent and presented relatively narrow peaks of high reflectance (∼90%) at visible and near-UV wavelengths of light.
采用自动化逐层喷涂（LbL）技术，通过构建高折射率（TiO2 纳米粒子）和低折射率（SiO2 纳米粒子）材料的交替堆叠结构，成功制备了在近紫外光波长下具有高光反射率的结构色薄膜。通过非四分之一波长设计对反射峰进行调谐。采用喷涂法制备的多层异质结构，其粗糙度和折射率与浸没法 LbL 组装得到的布拉格堆叠相似，但其最多可包含 840 个单独的聚合物或纳米粒子沉积步骤。与浸没法组装相比，这种复杂的多层异质结构可以显著缩短制备时间；完全沉积一个双层所需的时间仅约为 90s，而相同体系的浸没法组装则需要 36min。通过优化实验参数，可以实现均匀的涂层和相对平滑的界面和表面。我们观察到，纳米粒子和聚合物溶液的喷涂时间是决定组装薄膜厚度、光学性能和均匀性的主要参数。采用椭圆光度法、原子力显微镜（AFM）、紫外可见分光光度法和透射电子显微镜（TEM）对样品进行了表征。所得的纳米粒子薄膜具有虹彩效应，在可见光和近紫外光波长范围内具有较高的反射率（约 90%）窄峰。
