The fabrication of commercial cellulose nanofibrils (CNFs) into arrays with long-range ordering is of great significance for their extended applications, which, however, is severely hindered by their high disorder, aggregation, and hornified features. Herein, sub-nanoscale anionic metal oxide clusters (phosphotungstic acid, H3PW12O40, PTA) are applied to complex with commercial CNFs (dried powder DCNF and aqueous suspension WCNF) in aqueous media, and a long-range ordered layer structure can be facilely fabricated via typical unidirectional freezing. The surface complexation of the commercial CNFs and PTA can be confirmed through the small-angle scattering studies of the complex hydrogels. The hydrogels present similar correlation lengths in small-angle X-ray and neutron scattering measurements, suggesting the homogeneous distribution of PTA along the commercial CNFs. This gives rise to the negatively charged surface feature and further leads to strong repulsion among the commercial CNFs. Due to the disparity in sizes, the influence of PTA on the density of hydrogel networks is suppressed, and the network density is mainly dependent on the mass content of CNFs. The studies provide guidance to fabricate hydrogels with catalytic and photosensitive properties and also to design and stabilize long-range ordered structured aerogels during the removal of the nonfreezing bound water absorbed by the commercial CNFs after unidirectional freezing. This facile strategy shows great potential to broaden the application of commercial CNFs in thermal insulators, super-adsorbent materials, and supercapacitors in electrical devices.
将商业规模化生产的纤维素纳米微纤丝（CNF）制备长程有序结构材料对扩展其应用具有重要意义。但由于其高度无序且聚集严重，严重阻碍了其用于制备长程有序结构材料。本文将亚纳米级金属阴离子簇（磷钨酸、H3PW12O40、PTA）与商业化生产的CNF（干粉DCNF和水悬浮WCNF）复合，进而通过单向冷冻实现长程有序层结构气凝胶的简易制备。通过分析复合水凝胶的小角散射数据，证实了PTA在CNF表面的络合。复合水凝胶的SAXS和SANS数据拟合的相关长度结果相近，表明PTA沿CNF分布。这导致CNF表面带有丰富负电荷，进而引起CNFs之间产生强烈电荷排斥作用。但由于PTA与CNF之间的尺寸差异大，PTA对水凝胶网络密度的影响被抑制，复合凝胶的网络密度主要取决于样品中CNF的含量。这些研究为制备具有催化和光敏特性的水凝胶及在冻干过程中去除CNF结合水并保留CNF长程有序结构中提供了重要指导。这一方法对拓展商业规模化生产的CNF制备隔热材料、超级吸收材料以及超级电容器方面显现出巨大潜力。
文章信息：
Wang, H.; Song, R.; Li, M.; Liu, C.; Ke, Y.; Yin, P.* Surface Doping of Anionic Clusters Facilitated Direct Fabrication of Commercial Cellulose Nanofibrils for Long-Range Ordered Layer Structures. Biomacromolecules2022, ASAP, DOI: 10.1021/acs.biomac.2c00438. (https://pubs.acs.org/doi/10.1021/acs.biomac.2c00438)