Quantitative studies on self-assembled hematite/silica nanoparticle (NP) bilayers on mica were performed by applying scanning electron microscopy (SEM), atomic force microscopy (AFM), and streaming potential measurements. The coverage of the supporting hematite layers was adjusted by changing the bulk concentration of the suspension and the deposition time. The coverage was determined by direct enumeration of deposited particles from AFM images and SEM micrographs. Afterward, silica nanoparticle monolayers were assembled under diffusion-controlled transport. A unique functional relationship was derived connecting the silica coverage with the hematite precursor layer coverage. The formation of the hematite monolayer and the hematite/silica bilayer was also monitored in situ by streaming potential measurements. It was confirmed that the zeta potential of the bilayers was independent of the supporting layer coverage, exceeding 0.15. These measurements were theoretically interpreted in terms of the general electrokinetic model that allowed for deriving a formula for calculating nanoparticle coverage in the bilayers. Additionally, from desorption experiments, the interactions among hematite/silica particles in the bilayers were determined using DLVO theory. These results facilitate the development of a robust method of preparing nanoparticle bilayers with controlled properties, with potential applications in catalytic processes.

中文翻译：

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云母上的赤铁矿/二氧化硅纳米粒子双层膜：原子力显微镜和电动特性

通过应用扫描电子显微镜（SEM），原子力显微镜（AFM）和流动电势测量，对云母上自组装的赤铁矿/二氧化硅纳米颗粒（NP）双层进行了定量研究。通过改变悬浮液的体积浓度和沉积时间来调整支撑赤铁矿层的覆盖率。通过从AFM图像和SEM显微照片直接枚举沉积颗粒来确定覆盖率。之后，在扩散控制的运输下组装二氧化硅纳米颗粒单层。得出了独特的功能关系，将二氧化硅覆盖率与赤铁矿前体层覆盖率联系起来。还现场监测赤铁矿单层和赤铁矿/二氧化硅双层的形成通过流电势测量。证实了双层的ζ电势与支撑层覆盖率无关，超过0.15。这些测量在理论上是根据一般的电动模型来解释的，该电动模型允许推导用于计算双层中纳米颗粒覆盖率的公式。此外，根据解吸实验，使用DLVO理论确定了双层中赤铁矿/二氧化硅颗粒之间的相互作用。这些结果促进了制备具有受控性能的纳米颗粒双层的稳健方法的发展，在催化过程中具有潜在的应用。