Surface Doping of Anionic Clusters Facilitated Direct Fabrication of Commercial Cellulose Nanofibrils for Long-Range Ordered Layer Structures

Abstract

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, H 3 PW 12 O 40 , 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.

Metal oxide cluster-assisted assembly of anisotropic cellulose nanocrystal aerogels for balanced mechanical and thermal insulation properties

“…The self-consistent of correlation length in PTA-incorporated hybrid gels from different scattering tests unambiguously demonstrates that the PTA clusters are deposited onto the surfaces of CNCs. 33…”

“…This indicated a homogenous distribution of the nanoscaled PTA clusters inside the gel skeletons due to strong attractions among the CNC rods and PTA units. 33 As a way to extract a more structure information about the gels, typical Lorentzian models (Fig. S3, ESI †) were exploited to fit the experimental SAXS data.…”

“…The self-consistent of correlation length in PTA-incorporated hybrid gels from different scattering tests unambiguously demonstrates that the PTA clusters are deposited onto the surfaces of CNCs. 33 Unidirectional freezing, also named freeze-casting, was applied to produce anisotropic CNC and its composite aerogels. During the unidirectional freezing process, the ice crystals gradually grow due to the imposed temperature gradient, which provides confined environments at nanometer scales to drive the alignment of CNCs along a specific direction.…”