Injectable Highly Loaded Cellulose Nanocrystal Fibers and Composites

Assembling nanocelluloses into fibrous materials and their emerging applications

Nanocelluloses, derived from various plants or specific bacteria, represent the renewable and sophisticated nano building blocks for emerging functional materials. Especially, the assembly of nanocelluloses as fibrous materials can mimic the structural organization of their natural counterparts to integrate various functions, thus holding great promise for potential applications in various fields, such as electrical device, fire retardance, sensing, medical antibiosis, and drug release. Due to the advantages of nanocelluloses, a variety of fibrous materials have been fabricated with the assistance of advanced techniques, and their applications have attracted great interest in the past decade. This review begins with an overview of nanocellulose properties followed by the historical development of assembling processes. There will be a focus on assembling techniques, including traditional methods (wet spinning, dry spinning, and electrostatic spinning) and advanced methods (self-assembly, microfluidic, and 3D printing). In particular, the design rules and various influencing factors of assembling processes related to the structure and function of fibrous materials are introduced and discussed in detail. Then, the emerging applications of these nanocellulose-based fibrous materials are highlighted. Finally, some perspectives, key opportunities, and critical challenges on future research trends within this field are proposed.

Alignment of Colloidal Rods in Crowded Environments

Understanding the hydrodynamic alignment of colloidal rods in polymer solutions is pivotal for manufacturing structurally ordered materials. How polymer crowding influences the flow-induced alignment of suspended colloidal rods remains unclear when rods and polymers share similar length scales. We tackle this problem by analyzing the alignment of colloidal rods suspended in crowded polymer solutions and comparing that to the case where crowding is provided by additional colloidal rods in a pure solvent. We find that the polymer dynamics govern the onset of shear-induced alignment of colloidal rods suspended in polymer solutions, and the control parameter for the alignment of rods is the Weissenberg number, quantifying the elastic response of the polymer to an imposed flow. Moreover, we show that the increasing colloidal alignment with the shear rate follows a universal trend that is independent of the surrounding crowding environment. Our results indicate that colloidal rod alignment in polymer solutions can be predicted on the basis of the critical shear rate at which polymer coils are deformed by the flow, aiding the synthesis and design of anisotropic materials.

Towards Truly Wearable Systems: Optimizing and Scaling Up Wearable Triboelectric Nanogenerators

Triboelectric nanogenerator (TENG) is an upcoming technology to harvest energy from ambient movements. A major focus herein is harvesting energy from human movements through wearable TENGs, which are constructed by integrating nanogenerators into clothing or accessories. Textile-based TENGs, which include fiber, yarn, and fabric-based TENG structures, account for the majority of wearable TENGs, with many designs and applications demonstrated recently. This calls for a comprehensive analysis of textile-based TENG technology, and how the state-of-the-art device optimization concepts can be deployed to construct them efficiently. Concurrently, how advanced engineering concepts and industrial manufacturing techniques, which are bound with fiber, yarn, and fabric-related developments, can be applied into the TENG context for their output enhancement is still under investigation. Herein, we fill this vital gap by analyzing the state-of-the-art developments, upcoming trends, output optimization strategies, scalability, and prospects of the textile-based TENG technology, presenting a textile engineering perspective.

Polymer Nanocomposite Data: Curation, Frameworks, Access, and Potential for Discovery and Design

With the advent of the materials genome initiative (MGI) in the United States and a similar focus on materials data around the world, a number of materials data resources and associated vocabularies, tools, and repositories have been developed. While the majority of systems focus on slices of computational data with an emphasis on metallic alloys, NanoMine is an open source platform with the goal of curating and storing widely varying experimental data on polymer nanocomposites (polymers doped with nanoparticles) and providing access to characterization and analysis tools with the long-term objective of promoting facile nanocomposite design. Data on over 2500 samples from the literature and individual laboratories has been curated to date into NanoMine, including 230 samples from the papers bound in this virtual issue. This virtual issue represents an experiment of the flexibility of the data repository to capture the unique experimental metadata requirements of many data sets at one time and to challenge the authors to participate in the curation of their research data associated with a given publication. In principle, NanoMine offers a FAIR platform in which data published in papers becomes directly Findable and Accessible via simple search tools, with open metadata standards that are Interoperable with larger materials data registries, and allows easy Reuse of data, e.g. benchmarking against new results. Our hope is that with time, platforms such as this one could capture much of the newly published data on materials and form nodes in an interconnected materials data ecosystem which would allow researchers to robustly archive their data, add to the growing body of readily accessible data, and enable new forms of discovery by application of data analysis and design tools.

A review of nanocrystalline cellulose suspensions: Rheology, liquid crystal ordering and colloidal phase behaviour

Nanocrystalline cellulose (NCC) is a colloidal rigid rod, referred to by various terms in the literature including cellulose whisker (CW) and cellulose nanocrystal (CNC). These charged colloidal rods exhibit complex colloidal phase and rheological behaviours in aqueous suspensions, that are dependent on volume fraction and interparticle forces. A major shortcoming in the literature of NCC is that the dimensions and morphology of NCC particles vary significantly with the type of raw material and manufacturing conditions, which causes inconsistencies in suspension rheology and colloidal behaviours reported between different works. In this review, we consider the theory and experimentally-determined rheological and colloidal phase behaviours of charged rod suspensions in general, with a focus in particular on NCC. Dilute and semi-dilute NCC suspensions are isotropic liquids, in which NCC particles follow diffusional dynamics. The rheology of these isotropic NCC suspensions can be described by theoretical models that account for the effects of rod dimensions and surface charge, including those based on Doi and Edwards' theory. With increasing NCC concentration, the isotropic phase can undergo a transition to a liquid crystalline state (isotropic-nematic transition) or a transition to a dynamically arrested solid (liquid-solid transition). The liquid crystal ordering and gelation/glass transition are of particular interest because they respectively form an ordered structure and allow a solid-like mechanical response at relatively low solids fraction. For conditions at which the isotropic-nematic and liquid-solid transitions coincide, the formation of an anisotropic structure within a soft solid suspension is possible. Investigation of these two competing transitions led to the discovery of liquid crystal re-entrancy and existence of an anisotropic soft solid (liquid crystal hydroglass, LCH). LCH has a biphasic structure with an attractive glass matrix and a co-existing liquid crystal phase, providing similar viscoelastic properties to hydrogels but permitting reversible orientation of the colloidal rods in the liquid crystalline phase by shear forces; i.e. their structural ordering is programmable. The liquid crystal transition and gelation/glass transitions are quantitatively dependent on rod dimensions i.e. respectively proportional to L²D and L/D. Phase transitions in NCC suspensions including liquid crystal re-entrancy and formation of LCH can be fully described as a function of rod dimension, volume fraction and interparticle forces. This behaviour is independent of NCC source, allowing development of a generalised phased diagram in which separately-reported phase transitions converge to consistent phase boundaries. This validates a key hypothesis for the study of NCC suspensions, that variation in NCC concentration and interparticle forces can explain the complex phase behaviours observed within suspensions formulated using NCC obtained from different sources.

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals

The fabrication of nanocomposite films and fibers based on cellulose nanocrystals (P-tCNCs) and a thermoplastic polyurethane (PU) elastomer is reported. High-aspect-ratio P-tCNCs were isolated from tunicates using phosphoric acid hydrolysis, which is a process that affords nanocrystals displaying high thermal stability. Nanocomposites were produced by solvent casting (films) or melt-mixing in a twin-screw extruder and subsequent melt-spinning (fibers). The processing protocols were found to affect the orientation of both PU hard segments and the P-tCNCs within the PU matrix and therefore the mechanical properties. While the films were isotropic, both the polymer matrix and the P-tCNCs proved to be aligned along the fiber direction in the fibers, as shown using SAXS/WAXS, angle-dependent Raman spectroscopy, and birefringence analysis. Tensile tests reveal that fibers and films, at similar P-tCNC contents, display Young's moduli and strain-at-break that are within the same order of magnitude, but the stress-at-break was found to be ten-times higher for fibers, conferring them a superior toughness over films.