Three-Level Hierarchical 3D Network Formation and Structure Elucidation of Wet Hydrogel of Tunable-High-Strength Nanocomposites

The structural characterization of wet gel state hydrogels at multi-length scales ranging from nanometers to micrometers is very challenging and rarely reported. Herein, tunable high-strength nanocomposite hydrogels based on cellulose nanofibers with various cross linkers are synthesized and characterized. Synchrotron tomography and small-angle X-ray scattering methods are combined to quantitatively elucidate 3D hierarchically wet gel state network structures, providing an understanding on the structure–properties relationship of hydrogels. The hierarchical 3D network of wet gel demonstrates three levels of structures: 1) the bundle aggregated by cellulose nanofibers; 2) physically crosslinked bundle networks; and 3) fractal-structure agglomerates composed of aggregated network domains. The finding of fractal agglomerate structures tuned by crosslinker characteristics provides fundamental knowledge to explain a variation of several orders of magnitude of mechanical properties and reveals different formation mechanisms, opening a new and flexible prospect for wet gel state material design and processing control.