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pH‐Dependent Morphology Control of Cellulose Nanofiber/Graphene Oxide Cryogels
Author(s) -
Pan ZhengZe,
Govedarica Aleksandra,
Nishihara Hirotomo,
Tang Rui,
Wang Cong,
Luo Yi,
Lv Wei,
Kang FeiYu,
Trifkovic Milana,
Yang QuanHong
Publication year - 2021
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.202005564
Subject(s) - materials science , nanofiber , graphene , microstructure , lamella (surface anatomy) , dispersion (optics) , cellulose , oxide , chemical engineering , morphology (biology) , rheology , honeycomb , composite material , nanotechnology , physics , engineering , biology , optics , metallurgy , genetics
The precise control of the ice crystal growth during a freezing process is of essential importance for achieving porous cryogels with desired architectures. The present work reports a systematic study on the achievement of multi‐structural cryogels from a binary dispersion containing 50 wt% 2,2,6,6‐tetramethylpiperidin‐1‐oxyl, radical‐mediated oxidized cellulose nanofibers (TOCNs), and 50 wt% graphene oxide (GO) via the unidirectional freeze‐drying (UDF) approach. It is found that the increase in the sol's pH imparts better dispersion of the two components through increased electrostatic repulsion, while also causing progressively weaker gel networks leading to micro‐lamella cryogels from the UDF process. At the pH of 5.2, an optimum between TOCN and GO self‐aggregation and dispersion is achieved, leading to the strongest TOCN‐GO interactions and their templating into the regular micro‐honeycomb structures. A two‐faceted mechanism for explaining the cryogel formation is proposed and it is shown that the interplay of the maximized TOCN‐GO interactions and the high affinity of the dispersoid complexes for the ice crystals are necessary for obtaining a micro‐honeycomb morphology along the freezing direction. Further, by linking the microstructure and rheology of the corresponding precursor sols, a diagram for predicting the microstructure of TOCN‐GO cryogels obtained through the UDF process is proposed.