Publisher DOI: 10.1021/acsami.0c17012
Title: Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel
Language: English
Authors: Forgács, Attila 
Papp, Vanda 
Paul, Geo 
Marchese, Leonardo 
Len, Adél 
Dudás, Zoltán 
Fábián, István 
Gurikov, Pavel 
Kalmár, József 
Keywords: aerogel; hydration; NMR; SANS; structural characterization
Issue Date: 20-Jan-2021
Source: ACS Applied Materials and Interfaces 2 (13): 2997-3010 (2021-01-20)
Abstract (english): 
The most relevant properties of polysaccharide aerogels in practical applications are determined by their microstructures. Hydration has a dominant role in altering the microstructures of these hydrophilic porous materials. To understand the hydration induced structural changes of monolithic Ca-alginate aerogel, produced by drying fully cross-linked gels with supercritical CO2, the aerogel was gradually hydrated and characterized at different states of hydration by small-angle neutron scattering (SANS), liquid-state nuclear magnetic resonance (NMR) spectroscopy, and magic angle spinning (MAS) NMR spectroscopy. First, the incorporation of structural water and the formation of an extensive hydration sphere mobilize the Ca-alginate macromolecules and induce the rearrangement of the dry-state tertiary and quaternary structures. The primary fibrils of the original aerogel backbone form hydrated fibers and fascicles, resulting in the significant increase of pore size, the smoothing of the nanostructured surface, and the increase of the fractal dimension of the matrix. Because of the formation of these new superstructures in the hydrated backbone, the stiffness and the compressive strength of the aerogel significantly increase compared to its dry-state properties. Further elevation of the water content of the aerogel results in a critical hydration state. The Ca-alginate fibers of the backbone disintegrate into well-hydrated chains, which eventually form a quasi-homogeneous hydrogel-like network. Consequently, the porous structure collapses and the well-defined solid backbone ceases to exist. Even in this hydrogel-like state, the macroscopic integrity of the Ca-alginate monolith is intact. The postulated mechanism accounts for the modification of the macroscopic properties of Ca-alginate aerogel in relation to both humid and aqueous environments.
ISSN: 1944-8244
Journal: ACS applied materials & interfaces 
Institute: Entwicklung und Modellierung neuartiger nanoporöser Materialien V-EXK2 
Document Type: Article
Project: Stofftransportprozesse bei der Herstellung von biopolymerbasierten Aerogelen: in situ Charakterisierung und Modellierung 
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