Olson Emily, Li Yifan, Lin Fang-Yi, Miller Ana, Liu Fei, Tsyrenova Ayuna, Palm Devin, Curtzwiler Greg W, Vorst Keith L, Cochran Eric, Jiang Shan
Division of Materials Science & Engineering , Ames National Laboratory , Ames , Iowa 50011 , United States.
ACS Appl Mater Interfaces. 2019 Jul 10;11(27):24552-24559. doi: 10.1021/acsami.9b05383. Epub 2019 Jun 27.
A waterborne, UV-blocking, and visually transparent nanocomposite coating was formulated with ZnO nanoparticles and 2-hydroxyethyl cellulose (HEC). The coating is highly effective (<5% UV and ∼65% visible transmittance), and the film thickness (0.2-2.5 μm) is ∼100 times thinner than the conventional coatings of similar UV-blocking performance. The superior properties are due to the fractal structures of ZnO nanoparticles assembled within the HEC matrix, revealed by scanning electron microscopy and small-angle X-ray scattering (SAXS). Changing the binder to 2-hydroxyethyl starch (HES) diminishes the UV-blocking performance, as ZnO nanoparticles form dense globular aggregates, with an aggregation number measured by SAXS 3 orders of magnitude larger than the HEC coating. Since HEC and HES share the same repeating glucose unit in the polymer backbone, it suggests that the conformational characteristics of the binder polymer have a strong influence on the nanoparticle aggregation, which plays a key role in determining the optical performance. Similar structures were achieved with TiO nanoparticles. This study not only offers a cost-effective and readily scalable method to fabricate transparent UV-blocking coating but also demonstrates that the unique fractal aggregation structures in a nanocomposite material can provide high performance and functionality without fully dispersing the nanoparticles.
采用氧化锌纳米颗粒和2-羟乙基纤维素（HEC）制备了一种水性、抗紫外线且视觉透明的纳米复合涂层。该涂层高效（紫外线透过率<5%，可见光透过率约65%），且膜厚（0.2 - 2.5μm）比具有类似抗紫外线性能的传统涂层薄约100倍。通过扫描电子显微镜和小角X射线散射（SAXS）揭示，这些优异性能归因于在HEC基质中组装的氧化锌纳米颗粒的分形结构。将粘合剂换成2-羟乙基淀粉（HES）会降低抗紫外线性能，因为氧化锌纳米颗粒形成致密的球状聚集体，通过SAXS测量其聚集数比HEC涂层大3个数量级。由于HEC和HES在聚合物主链中具有相同的重复葡萄糖单元，这表明粘合剂聚合物的构象特征对纳米颗粒聚集有很大影响，而纳米颗粒聚集在决定光学性能方面起关键作用。用二氧化钛纳米颗粒也能实现类似结构。本研究不仅提供了一种经济高效且易于扩展的制备透明抗紫外线涂层的方法，还表明纳米复合材料中独特的分形聚集结构无需使纳米颗粒完全分散就能提供高性能和功能。
