The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.

中文翻译：

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外差动态光散射探测反蛋白石中金纳米粒子的扩散

在理解、建模和优化许多技术过程的背景下，多孔材料内纳米粒子的扩散行为引起了很多兴趣。动态光散射 (DLS) 是表征自由介质中粒子扩散行为的一种非常强大的技术。然而，由于存在多种散射源，该方法在多孔介质中的适用性被认为是相当困难的。与以前的大多数方法相比，在本研究中，DLS 方法的应用没有确保溶剂和多孔基质的折射率匹配。为了测试该方法的能力，分析了球形金纳米粒子在反蛋白石的相互连接的周期性纳米孔内的扩散。尽管这个系统很复杂，它涉及许多界面和不同的折射率，获得了与多孔介质内粒子运动相关的清晰信号。正如预期的那样，与自由介质中的粒子扩散相比，多孔样品内部的扩散过程减慢了。发现获得的有效扩散系数与波矢量相关。它们随着探测粒子浓度波动的空间扩展的增加而线性增加。平均而言，这项工作中测量的减速因子与文献数据的组合不确定性一致。发现获得的有效扩散系数与波矢量相关。它们随着探测粒子浓度波动的空间扩展的增加而线性增加。平均而言，这项工作中测量的减速因子与文献数据的组合不确定性一致。发现获得的有效扩散系数与波矢量相关。它们随着探测粒子浓度波动的空间扩展的增加而线性增加。平均而言，这项工作中测量的减速因子与文献数据的组合不确定性一致。