Precise analysis of coating defect formation on nanoparticles/polymer composite thin films

我们工作的最终目的是获得对纳米颗粒/聚合物复合薄膜的脱湿行为的正确理解，以确定膜无缺陷和光滑涂层的最佳条件。本文首先从以下几个方面进行了研究。采用移相干涉显微镜、激光共聚焦显微镜和原子力显微镜观察了含CeO_2纳米粒子的聚苯乙烯（PS）薄膜在十八烷基三乙氧基硅烷包覆的硅玻璃板上的脱湿行为，将PS薄膜自旋涂覆在硅烷包覆的衬底上，然后在353 K下退火。采用有机配体辅助超临界水热法对纳米CeO_2表面进行癸酸修饰，得到的纳米CeO_2为立方形状，平均边长为4 ~ 6 nm，可在有机溶剂中完全分散。膜厚度约为20 ~ 30nm。结果，在含有纳米粒子的PS膜上出现了由脱湿过程引起的几个孔，即带有边缘的干斑，这些孔扩大并相互靠近。然后，靠近的孔成为桥接丝，最后破裂并在基板上留下孤立的小液滴。此外，虽然我们无法定量地讨论添加纳米粒子和不添加纳米粒子对PS膜的脱湿行为的比较，但由于无法观察到初始阶段没有纳米粒子的脱湿行为，所以我们无法对添加纳米粒子和不添加纳米粒子的PS膜的脱湿过程进行比较。实验发现，当纳米颗粒加入后，在衬底上留下的小液滴尺寸变小了。此外，考虑到纳米颗粒的加入对脱湿的增强是由于膜的表观Hamaker常数的变化，基于润滑近似对脱湿过程进行了数值模拟。少

The ultimate aim of our work is to acquire correct understandings for the dewetting behavior of nanoparticles/polymer composite thin films in order to determine the optimum conditions for a defect-free and smooth coating of the films. In the present work, the following points were investigated as the first step.The dewetting behavior of polystyrene (PS) thin films containing CeO_2 nanoparticles on a silica glass plate coated with octadecyltrietoxysilane was observed using a phase-shifting interference microscopy, a laser scanning confocal microscopy and an atomic force microscopy, where the PS film was spin coated on the silane-coated substrate, and then was annealed at 353 K. The surface of the CeO_2 nanoparticles used here were modified with decanoic acid through the organic-ligand-assisted supercritical hydrothermal process, and consequently, the nanoparticles obtained were cubic-shaped ones with average edge length of 4-6 nm and could be dispersed completely in organic solvents. Th … More e film thickness was approximately 20-30 nm. As a result, several holes, i.e., dry patches with a rim, caused by the dewetting process appeared on the PS film containing nanoparticles, expanded and approached one another. Then, the approaching holes became a bridging filament, and finally, broke and left behind isolated small droplets on the substrate. Also, it seemed that the dewetting process of the PS film containing nanoparticles was faster than that without nanoparticles, although we could not discuss quantitatively the comparison between the dewetting behaviors with and without nanoparticles because the dewetting behavior without nanoparticles at the initial stage could not be observed. It was found that the size of the small droplets left on the substrate became smaller when the nanoparticles were added.In addition, numerical simulations of dewetting process based on the lubrication approximation were carried out, considering that the enhancement of dewetting by addition of nanoparticles was due to the variation of apparent Hamaker constant of the film. Less