pH‐Dependent Morphology Control of Cellulose Nanofiber/Graphene Oxide Cryogels
pH‐Dependent Morphology Control of Cellulose Nanofiber/Graphene Oxide Cryogels
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pH 依赖性纤维素纳米纤维/氧化石墨烯冷冻凝胶的形态控制
DOI：
10.1002/smll.202005564
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发表时间：
2020
期刊：
影响因子：
13.3
通讯作者：
Yang Quan‐Hong
中科院分区：
文献类型：
--
作者：
Pan Zheng‐Ze;Govedarica Aleksandra;Nishihara Hirotomo;Tang Rui;Wang Cong;Luo Yi;Lv Wei;Kang Fei‐Yu;Trifkovic Milana;Yang Quan‐Hong
在冷冻过程中冰晶生长的精确控制对于获得具有所需结构的多孔冷冻凝胶至关重要。本工作报告了通过单向冷冻干燥（UDF）方法从含有50重量%的2，2，6，6-四甲基哌啶-1-氧基、自由基介导的氧化纤维素纳米纤维（TOCN）和50重量%的氧化石墨烯（GO）的二元分散体获得多结构冷冻凝胶的系统研究。发现溶胶pH的增加通过增加的静电排斥赋予两种组分更好的分散，同时也导致逐渐变弱的凝胶网络，从而从UDF过程中产生微片晶冻凝胶。在pH为5.2时，TOCN和GO自聚集和分散之间达到最佳状态，导致最强的TOCN-GO相互作用及其模板化成规则的微蜂窝结构。提出了一种用于解释晶胶形成的两方面机制，并且表明最大化的TOCN-GO相互作用和分散质复合物对冰晶的高亲和力的相互作用对于沿着冷冻方向沿着获得微蜂窝形态是必要的。此外，通过连接相应的前体溶胶的微观结构和流变性，提出了一个图表，用于预测通过UDF过程获得的TOCN-GO冻凝胶的微观结构。
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.