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Comprehensive NMR Analysis of Pore Structures in Superabsorbing Cellulose Nanofiber Aerogels
journal contribution
posted on 2019-12-13, 20:40 authored by Yashu Kharbanda, Mateusz Urbańczyk, Ossi Laitinen, Kirsten Kling, Sakari Pallaspuro, Sanna Komulainen, Henrikki Liimatainen, Ville-Veikko TelkkiHighly 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. T2 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, etc.