Diffusion in Hierarchical Mesoporous Materials: Applicability and Generalization of the Fast-Exchange Diffusion Model
Diffusion in Hierarchical Mesoporous Materials: Applicability and Generalization of the Fast-Exchange Diffusion Model
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DOI：
10.1021/la2047432
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发表时间：
2012-02-21
期刊：
影响因子：
3.9
通讯作者：
Valiullin, R.
中科院分区：
文献类型：
--
作者：
Zeigermann, P.;Naumov, S.;Valiullin, R.
利用脉冲场梯度核磁共振研究了环己烷在具有有序双峰孔结构的二氧化硅材料中的输运性质。一个特定的组织的定义明确的孔结构，由一个集合的空间有序的，球形介孔通过狭窄的蠕虫状孔互连，允许在介质中的扩散过程的定量分析与空间有序分布的流体密度为广泛的气液平衡。测量的扩散数据进行解释的有效扩散系数，这是确定在一个微观模型内考虑远程分子轨迹通过组装交替件的位移在两个构成孔隙空间。已经进一步发现，对于所研究的系统，特别是对于具有多个孔隙率的介孔材料，一般来说，这种广义模型简化为文献中使用的常规快速交换模型。因此，不仅是合理的快速交换模型的适用性提供了多样性的介孔材料，但进入快速交换模型的扩散参数也被准确地定义。发现以这种方式产生的方程很好地再现了实验确定的扩散率，建立了一种方法，用于有针对性地微调具有多个孔隙度的分层材料中流体的传输特性。
Transport properties of cyclohexane confined to a silica material with an ordered, bimodal pore structure have been studied by means of pulsed field gradient nuclear magnetic resonance. A particular organization of the well-defined pore structure, composed of a collection of spatially ordered, spherical mesopores interconnected via narrow worm-like pores, allowed for a quantitative analysis of the diffusion process in a medium with spatially ordered distribution of the fluid density for a broad range of the gas-liquid equilibria. The measured diffusion data were interpreted in terms of effective diffusivities, which were determined within a microscopic model considering long-range molecular trajectories constructed by assembling the alternating pieces of displacement in the two constituting pore spaces. It has further been found that for the system under study, in particular, and for mesoporous materials with multiple porosities, in general, this generalized model simplifies to the conventional fast-exchange model used in the literature. Thus, not only was justification of the applicability of the fast-exchange model to a diversity of mesoporous materials provided, but the diffusion parameters entering the fast-exchange model were also exactly defined. The equation resulting in this way was found to nicely reproduce the experimentally determined diffusivities, establishing a methodology for targeted fine-tuning of transport properties of fluids in hierarchical materials with multiple porosities.