Kharbanda Yashu, Urbańczyk Mateusz, Laitinen Ossi, Kling Kirsten, Pallaspuro Sakari, Komulainen Sanna, Liimatainen Henrikki, Telkki Ville-Veikko
NMR Research Unit, University of Oulu, 90014 Oulu, Finland.
Fibre and Particle Engineering Research Unit, University of Oulu, 90014 Oulu, Finland.
J Phys Chem C Nanomater Interfaces. 2019 Dec 26;123(51):30986-30995. doi: 10.1021/acs.jpcc.9b08339. Epub 2019 Dec 2.
Highly porous cellulose nanofiber (CNF) aerogels are promising, environmentally friendly, reusable, and low-cost materials for several advanced environmental, biomedical, and electronic applications. The aerogels have a complex and hierarchical 3D porous network structure with pore sizes ranging from nanometers to hundreds of micrometers. The morphology of the network has a critical role on the performance of aerogels, but it is difficult to characterize thoroughly with traditional techniques. Here, we introduce a combination of nuclear magnetic resonance (NMR) spectroscopy techniques for comprehensive characterization of pore sizes and connectivity in the CNF aerogels. Cyclohexane absorbed in the aerogels was used as a probe fluid. NMR cryoporometry enabled us to characterize the size distribution of nanometer scale pores in between the cellulose nanofibers in the solid matrix of the aerogels. Restricted diffusion of cyclohexane revealed the size distribution of the dominant micrometer scale pores as well as the tortuosity of the pore network. relaxation filtered microscopic magnetic resonance imaging (MRI) method allowed us to determine the size distribution of the largest, submillimeter scale pores. The NMR techniques are nondestructive, and they provide information about the whole sample volume (not only surfaces). Furthermore, they show how absorbed liquids experience the complex 3D pore structure. Thorough characterization of porous structures is important for understanding the properties of the aerogels and optimizing them for various applications. The introduced comprehensive NMR analysis set is widely usable for a broad range of different kinds of aerogels used in different applications, such as catalysis, batteries, supercapacitors, hydrogen storage,
高度多孔的纤维素纳米纤维（CNF）气凝胶是一种很有前景的环保、可重复使用且低成本的材料，可用于多种先进的环境、生物医学和电子应用。这些气凝胶具有复杂的分级三维多孔网络结构，孔径范围从纳米到数百微米。网络的形态对气凝胶的性能起着关键作用，但用传统技术很难对其进行全面表征。在此，我们引入了核磁共振（NMR）光谱技术的组合，用于全面表征CNF气凝胶的孔径和连通性。气凝胶中吸收的环己烷用作探针流体。NMR低温孔率测定法使我们能够表征气凝胶固体基质中纤维素纳米纤维之间纳米级孔隙的尺寸分布。环己烷的受限扩散揭示了主要微米级孔隙的尺寸分布以及孔网络的曲折度。弛豫滤波微观磁共振成像（MRI）方法使我们能够确定最大的亚毫米级孔隙的尺寸分布。NMR技术是非破坏性的，它们提供有关整个样品体积（不仅是表面）的信息。此外，它们还展示了吸收的液体如何体验复杂的三维孔结构。对多孔结构进行全面表征对于理解气凝胶的性能并针对各种应用对其进行优化很重要。所引入的综合NMR分析集可广泛用于不同应用中使用的各种不同类型的气凝胶，如催化、电池、超级电容器、储氢等。
