Graphene chiral liquid crystals and macroscopic assembled fibres

Millisecond tension-annealing for enhancing carbon nanotube fibers

Mechanically strong carbon nanotube (CNT) fibers have increasingly become the focus of the present research in the fiber industry. However, the weak or even a lack of interconnections between adjacent CNTs induces much inter-tube slippages during fiber failure, and thus results in their low mechanical strength. Moreover, achieving fast cross-linking between neighbouring CNTs on a large scale to prevent the failure by slip is still a big challenge. Herein we report an ultrafast and continuous tension-annealing process to achieve the considerably improved tube alignment and strong covalent cross-linking of neighbouring CNTs in milliseconds, resulting in great improvement of the fiber performance. The CNT fibers were heated to high temperature (∼2450 °C) by Joule heating under the applied tension and subsequently annealed for just 12 ms. Due to the rapid electromechanical response of the fibers, instant nanotube rearrangements coupled by the formation of cross-links robustly bonding the adjacent CNTs occurred at power-on, which could be attributed to the considerable increases of strength and modulus by factors of 2.9 (up to 3.2 GPa) and 4.8 (up to 123 GPa), respectively. The resultant fibers showed high specific strength (2.2 N per tex), comparable with that of PAN-based carbon fibers, and high specific electrical conductivity higher than that of PAN-based carbon fibers. Moreover, the obtained strongly crosslinked and highly dense structures also endowed the fibers with the significantly improved thermal stability under a high-temperature oxidation atmosphere. Moreover, a continuous tension-annealing process was designed to achieve the large scale production of high performance fibers with the average strength of 2.2 GPa. The high-toughness, lightweight and continuous features together with their outstanding mechanical and electrical properties would certainly boost the large-scale applications of CNT fibers.

In Vivo Restoration of Myocardial Conduction With Carbon Nanotube Fibers

BACKGROUND

Impaired myocardial conduction is the underlying mechanism for re-entrant arrhythmias. Carbon nanotube fibers (CNTfs) combine the mechanical properties of suture materials with the conductive properties of metals and may form a restorative solution to impaired myocardial conduction.

METHODS

Acute open chest electrophysiology studies were performed in sheep (n=3). Radiofrequency ablation was used to create epicardial conduction delay after which CNTf and then silk suture controls were applied. CNTfs were surgically sewn across the right atrioventricular junction in rodents, and acute (n=3) and chronic (4-week, n=6) electrophysiology studies were performed. Rodent toxicity studies (n=10) were performed. Electrical analysis of the CNTf-myocardial interface was performed.

RESULTS

In all cases, the large animal studies demonstrated improvement in conduction velocity using CNTf. The acute rodent model demonstrated ventricular preexcitation during sinus rhythm. All chronic cases demonstrated resumption of atrioventricular conduction, but these required atrial pacing. There was no gross or histopathologic evidence of toxicity. Ex vivo studies demonstrated contact impedance significantly lower than platinum iridium.

CONCLUSIONS

Here, we show that in sheep, CNTfs sewn across epicardial scar acutely improve conduction. In addition, CNTf maintain conduction for 1 month after atrioventricular nodal ablation in the absence of inflammatory or toxic responses in rats but only in the paced condition. The CNTf/myocardial interface has such low impedance that CNTf can facilitate local, downstream myocardial activation. CNTf are conductive, biocompatible materials that restore electrical conduction in diseased myocardium, offering potential long-term restorative solutions in pathologies interrupting efficient electrical transduction in electrically excitable tissues.

The Rise of Fiber Electronics

As a new direction in applied chemistry, fiber electronics allow device configuration to evolve from three to two dimensions and then to one dimension. The reduction in dimension brings unique properties, such as ultraflexibility, tissue adaptability, and weavability, enabling their use in a variety of applications, particularly in various emerging fields related to implantable devices and wearable systems. The different types of fiber electrode materials are summarized based on the one-dimensional configuration and their distinctive interfaces, various devices, and promising applications. The remaining challenges and future directions are finally highlighted.

Dual Engineering Interface-Driven Complementary Graphene Oxide-Protein Dimer Supramolecular Architecture Enables Nucleus Imaging and Therapy

Seeking a versatile nanoplatform for multimodal nucleus imaging and therapy is a challenging task. General complementary bottom-up bionanotechnology for controlling a 3D supramolecular coassembly is proposed. The dual engineering interface proof-of-concept of the supramolecular architecture can be demonstrated via a genetically engineered protein dimer and plasmonically engineered graphene oxide (GO). Incorporation of anisotropic plasmonic nanoparticles as an intercalation layer among the GO 3D supramolecular architecture can provide covalent conjugation sites and simultaneously endow tunable optical properties of GO, ranging from the ultraviolet-to-near-infrared region. Interestingly, the precise design of a specific two-site mutation of the plasmid is favorable for giving an organized coassembly instead of random networks of GO, which contributes to giving continuous distinguishable enhanced Raman imaging for tracking cancer cells. Unexpectedly, penetration into the cell nucleus via the submicro 3D supramolecular coassembly exhibits an excellent nucleus therapeutic potential of cancer cells.

Multifunctional reduced graphene oxide-CVD graphene core-shell fibers

The insufficient electrical conductivity and mechanical stretchability of conventional graphene fibers based on reduced graphene oxide liquid crystals (rGO-LCs) has limited their applications to numerous textile devices. Here, we report a simple method to fabricate multifunctional fibers with mechanically strong rGO cores and highly conductive CVD graphene shells (rGO@Gr fibers), which show an outstanding electrical conductivity as high as ∼137 S cm-1 and a failure strain value of 21%, which are believed to be the highest values among polymer-free graphene fibers. We also demonstrate the use of the rGO@Gr fibers for high power density supercapacitors with enhanced mechanical stability and durability, which would enable their practical applications in various smart wearable devices in the future.

Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience

The research field of liquid crystals and their applications is recently changing from being largely focused on display applications and optical shutter elements in various fields, to quite novel and diverse applications in the area of nanotechnology and nanoscience. Functional nanoparticles have recently been used to a significant extent to modify the physical properties of liquid crystals by the addition of ferroelectric and magnetic particles of different shapes, such as arbitrary and spherical, rods, wires and discs. Also, particles influencing optical properties are increasingly popular, such as quantum dots, plasmonic, semiconductors and metamaterials. The self-organization of liquid crystals is exploited to order templates and orient nanoparticles. Similarly, nanoparticles such as rods, nanotubes and graphene oxide are shown to form lyotropic liquid crystal phases in the presence of isotropic host solvents. These effects lead to a wealth of novel applications, many of which will be reviewed in this publication.

Ultra-Thin Conductive Graphitic Carbon Nitride Assembly through van der Waals Epitaxy toward High-Energy-Density Flexible Supercapacitors

Graphitic carbon nitride is an ordered two-dimensional stability. However, its bulk structure with low electrical conductivity (less than 1 S cm^-1) restricts the applications in electrochemical energy storage. This is because conventional synthesis methods lack effective thickness control, and the excessive nitrogen doping (∼50%) leads to poor electrical conductivity. Here, we report an ultrathin conductive graphitic carbon nitride assembly (thickness of ∼1.0 nm) through graphene-templated van der Waals epitaxial strategy with high electrical conductivity (12.2 S cm^-1), narrow pore-size distribution (5.3 nm), large surface area (724.9 m² g^-1), and appropriate nitrogen doping level (18.29%). The ultra-thin structure with nitrogen doping provided numerous channels and active sites for effective ion transportation and storage, while the graphene layers acted as micro current collectors; subsequently, it exhibits high energy storage capability of 936 mF cm^-2 at 1 mA cm^-2 with excellent stability of over 10 000 cycles. Moreover, the all-solid-state supercapacitors showed an ultra-high energy density of 281.3 μWh cm^-2 at 1 mA cm^-2 with high rate capability, Coulombic efficiency, and flexibility. This work represents a general framework for the bottom-up synthesis of ultrathin 2D materials, which may promote the application of graphitic carbon nitride in energy storage.

Microscope Observation of Morphology of Colloidally Dispersed Niobate Nanosheets Combined with Optical Trapping

Although inorganic nanosheets prepared by exfoliation (delamination) of layered crystals have attracted great attention as 2D nanoparticles, in situ real space observations of exfoliated nanosheets in the colloidally dispersed state have not been conducted. In the present study, colloidally dispersed inorganic nanosheets prepared by exfoliation of layered niobate are directly observed with bright-field optical microscopy, which detects large nanosheets with lateral length larger than several micrometers. The observed nanosheets are not strictly flat but rounded, undulated, or folded in many cases. Optical trapping of nanosheets by laser radiation pressure has clarified their uneven cross-sectional shapes. Their morphology is retained under the relation between Brownian motion and optical trapping.

Attapulgite nanofibers and graphene oxide composite membrane for high-performance molecular separation

Graphene oxide (GO) based membranes are widely adopted in molecular separation based on size exclusion effect by stacked GO sheets. Both high flux and efficient rejection of GO-based membranes for long-term operation are highly expected for practical applications. Here, an attapulgite (ATP) nanofibers/ GO composite (ATP/GO) membrane is assembled by filtration of mixed aqueous colloidal suspensions of ATP and GO. Due to the modification of interlayer distance and surface property of GO membrane by ATP, the ATP/GO membrane demonstrates excellent separation performance, with a high water flux of 221.16 Lm^-2 h^-1bar^-1, 7.7 times higher than that of pure GO membrane. Meanwhile, the rejection of ATP/GO is also slightly improved comparing with that of GO membrane. It is also found that increasing the thickness of the membrane is effective to enhance rejection percentage. The ATP/GO membranes reported here show high efficiency for molecular separation, which demonstrates potential applications in water purification and environmental protection.

Porous Graphene-Carbon Nanotube Scaffolds for Fiber Supercapacitors

Fiber nanomaterials can become fundamental devices that can be woven into smart textiles, for example, miniaturized fiber-based supercapacitors (FSCs). They can be utilized for portable, wearable electronics and energy storage devices, which are highly prospective areas of research in the future. Herein, we developed porous carbon nanotube-graphene hybrid fibers (CNT-GFs) for all-solid-state symmetric FSCs, which were assembled through wet-spinning followed by a hydrothermal activation process using environmentally benign chemicals (i.e., H₂O₂ and NH₄OH in deionized water). The barriers that limited effective ion accessibility in GFs were overcome by the intercalation of CNTs in the GFs which enhanced their electrical conductivity and mechanical properties as well. The all-solid-state symmetric FSCs of a precisely controlled activated hybrid fiber (a-CNT-GF) electrode exhibited an enhanced volumetric capacitance of 60.75 F cm^-3 compared with those of a pristine CNT-GF electrode (19.80 F cm^-3). They also showed a volumetric energy density (4.83 mWh cm^-3) roughly 3 times higher than that of untreated CNT-GFs (1.50 mWh cm^-3). The excellent mechanical flexibility and structural stability of a miniaturized a-CNT-GF are highlighted by the demonstration of negligible differences in capacitance upon bending and twisting. The mechanism of developing porous, large-scale, low-cost electrodes using an environmentally benign activation method presented in this work provides a promising route for designing a new generation of wearable, portable miniaturized energy storage devices.

Three-Dimensional Porous Carbon Nanotubes/Reduced Graphene Oxide Fiber from Rapid Phase Separation for a High-Rate All-Solid-State Supercapacitor

Graphene fiber-based supercapacitors (SCs) are rising as having the greatest potential for portable/wearable energy storage devices. However, their rate performance is not well pleasing, which greatly impedes their broad practical applications. Herein, three-dimensional porous carbon nanotube/reduced graphene oxide fibers were prepared by a nonsolvent-induced rapid phase separation method followed by hydrazine vapor reduction. Benefitting from their three-dimensional porous structure, large specific surface area, and high conductivity, the fabricated SC exhibits a high volume capacitance of 54.9 F cm^-3 and high energy and power densities (4.9 mW h cm^-3 and 15.5 W cm^-3, respectively). Remarkably, the SC works well at a high scan rate of 50 V s^-1 and shows a fast frequency response with a short time constant of 78 ms. Furthermore, the fiber-shaped SC also exhibits very stable electrochemical performances when it is subjected to mechanical bending and succeeding straightening process, indicating its great potential application in flexible electronic devices.

Carbon-Nanomaterial-Based Flexible Batteries for Wearable Electronics

Wearable electronics have received considerable attention in recent years. These devices have penetrated every aspect of our daily lives and stimulated interest in futuristic electronics. Thus, flexible batteries that can be bent or folded are desperately needed, and their electrochemical functions should be maintained stably under the deformation states, given the increasing demands for wearable electronics. Carbon nanomaterials, such as carbon nanotubes, graphene, and/or their composites, as flexible materials exhibit excellent properties that make them suitable for use in flexible batteries. Herein, the most recent progress on flexible batteries using carbon nanomaterials is discussed from the viewpoint of materials fabrication, structure design, and property optimization. Based on the current progress, the existing advantages, challenges, and prospects are outlined and highlighted.

A Review of Supercapacitors Based on Graphene and Redox-Active Organic Materials

Supercapacitors are a highly promising class of energy storage devices due to their high power density and long life cycle. Conducting polymers (CPs) and organic molecules are potential candidates for improving supercapacitor electrodes due to their low cost, large specific pseudocapacitance and facile synthesis methods. Graphene, with its unique two-dimensional structure, shows high electrical conductivity, large specific surface area and outstanding mechanical properties, which makes it an excellent material for lithium ion batteries, fuel cells and supercapacitors. The combination of CPs and graphene as electrode material is expected to boost the properties of supercapacitors. In this review, we summarize recent reports on three different CP/graphene composites as electrode materials for supercapacitors, discussing synthesis and electrochemical performance. Novel flexible and wearable devices based on CP/graphene composites are introduced and discussed, with an eye to recent developments and challenges for future research directions.

Hybrid carbon nanostructured fibers: stepping stone for intelligent textile-based electronics

The journey of smart textile-based wearable technologies first started with the attachment of sensors to fabrics, followed by embedding sensors in apparels. Presently, garments themselves can be transformed into sensors, which demonstrates the tremendous growth in the field of smart textiles. Wearable applications demand flexible materials that can withstand deformation for their practical use on par with conventional textiles. To address this, we explore the potential reasons for the enhanced performance of wearable devices realized from the fabrication of carbon nanostructured fibers with the use of graphene, carbon nanotubes and other two-dimensional materials. This review presents a brief introduction on the fabrication strategies to form carbon-based fibers and the relationship between their properties and characteristics of the resulting materials. The likely mechanisms of fiber-based electronic and storage devices, focusing mainly on transistors, nano-generators, solar cells, supercapacitors, batteries, sensors and therapeutic devices are also presented. Finally, the future perspectives of this research field of flexible and wearable electronics are discussed. The present study supplements novel ideas not only for beginners aiming to work in this booming area, but also for researchers actively engaged in the field of fiber-based electronics, dealing with advanced electronics and wide range of functionalities integrated into textile fibers.

Elastomer-Free, Stretchable, and Conformable Silver Nanowire Conductors Enabled by Three-Dimensional Buckled Microstructures

Many three-dimensional (3D) nanomaterial-based assemblies need incorporation with elastomers to attain stretchability-that also compromises their pristine advantages for functional applications. Here, we show the design of elastomer-free, highly deformable silver nanowire (AgNW) conductors through dip-coating AgNWs on a 3D polymeric scaffold and following a simple triaxial compression approach. The resulting 3D AgNW conductors exhibit good stability of resistance under multimodal deformation, such as stretching, compressing, and bending as well as comparable conductivity with those elastomer-based ones. Moreover, the buckled structures endow our 3D conductors with novel negative Poisson's ratio behavior, which can offer good comfortability to curvilinear surfaces. The combination of mechanical properties, conductive performance, and unique deformation characteristics can satisfy multiscale conformal mechanics with a soft, curvilinear human body.

Microfluidics-enabled orientation and microstructure control of macroscopic graphene fibres

Macroscopic graphene structures such as graphene papers and fibres can be manufactured from individual two-dimensional graphene oxide sheets by a fluidics-enabled assembling process. However, achieving high thermal-mechanical and electrical properties is still challenging due to non-optimized microstructures and morphology. Here, we report graphene structures with tunable graphene sheet alignment and orientation, obtained via microfluidic design, enabling strong size and geometry confinements and control over flow patterns. Thin flat channels can be used to fabricate macroscopic graphene structures with perfectly stacked sheets that exhibit superior thermal and electrical conductivities and improved mechanical strength. We attribute the observed shape and size confinements to the flat distribution of shear stress from the anisotropic microchannel walls and the enhanced shear thinning degree of large graphene oxide sheets in solution. Elongational and step expansion flows are created to produce large-scale graphene tubes and rods with horizontally and perpendicularly aligned graphene sheets by tuning the elongational and extensional shear rates, respectively.

Expanded graphene oxide fibers with high strength and increased elongation

We report the role of chemically expanded graphite in the fabrication of high-performance graphene oxide fibers by wet spinning. X-ray diffraction peak showed that the interplanar distance of the expanded graphene oxide (EGO) fiber was more than that of graphene oxide (GO) fiber due to the expanded graphite. X-ray photon spectroscopy analysis revealed that EGO was more oxidized than GO. The hydrogen bonding network and secondary intermolecular interaction made the EGO aqueous solution more stable and crystalline, and it was able to be stretched in the coagulation bath. Morphological analysis showed the excellent alignment and compactness of EGO sheets in the fibers. The increased interplanar distance between the EGO sheets favored the edge-to-edge interaction more than the basal plane interaction within the fiber, thus resulting in high mechanical strength (492 MPa) and increased elongation (6.1%).

Binder-free graphene oxide doughs

Graphene oxide (GO) sheets have been used to construct various bulk forms of GO and graphene-based materials through solution-based processing techniques. Here, we report a highly cohesive dough state of GO with tens of weight percent loading in water without binder-like additives. The dough state can be diluted to obtain gels or dispersions, and dried to yield hard solids. It can be kneaded without leaving stains, readily reshaped, connected, and further processed to make bulk GO and graphene materials of arbitrary form factors and tunable microstructures. The doughs can be transformed to dense glassy solids of GO or graphene without long-range stacking order of the sheets, which exhibit isotropic and much enhanced mechanical properties due to hindered sliding between the sheets. GO dough is also found to be a good support material for electrocatalysts as it helps to form compliant interface to access the active particles.

Graphene oxide (GO) dispersions may be used as starting materials for graphene-based architectures. Here, a malleable and versatile dough state of GO is discovered, completing the GO–water continuum, which can be diluted or converted to glassy GO or graphene solids without long-range stacking order with enhanced mechanical and electrochemical properties

Ultralight, Superelastic, and Fatigue-Resistant Graphene Aerogel Templated by Graphene Oxide Liquid Crystal Stabilized Air Bubbles

Graphene aerogel (GA) has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and multifunctionality. However, it is a great challenge to develop superelastic and fatigue-resistant GA (SFGA) with ultralow density because it is generally contradictory to improve the mechanical properties with reducing density of GA. Herein, we report a simple and efficient approach to prepare ultralight SFGA templated by graphene oxide liquid crystal (GOLC) stabilized air bubbles. The thus-prepared ultralight SFGA (∼2 mg cm^-3) exhibits superelasticity (rapid recovery from >99% compression) and unprecedented fatigue-resistant performance (maintaining shape integrity after 10⁶ compressive cycles at 70% strain and 5 Hz). The ultralow density and excellent dynamic mechanical properties of SFGA are mainly associated with the "volume exclusion effect" of the air bubbles as well as the highly ordered, closely packed, and uniform porous structure of the resultant GA, respectively. This study provides a green and facile strategy for preparing high-performance ultralight SFGA, which has great potential in various applications, including ultrafast dynamic pressure sensors, soft robot, and flexible devices.

Flexible heteroatom-doped graphitic hollow carbon fibers for ultrasensitive and reusable electric current sensing

Flexible, highly conductive, robust nitrogen (N), sulfur (S) co-doped graphitic hollow carbon fibers (CFs) were directly fabricated by vacuum carbonization of “human hairs”.

Application of graphene derivatives and their nanocomposites in tribology and lubrication: a review

Reducing friction and increasing lubrication are the goals that every tribologist pursues. Accordingly, layered graphene materials have attracted great research interest in tribology due to their anti-friction, anti-wear and excellent self-lubricating properties. However, recent studies have found that other forms of graphene derivatives not only perform better in tribological and lubricating applications, but also solve the problem of graphene being prone to agglomeration. Based on a large number of reports, herein, we review the research progress on graphene derivatives and their nanocomposites in tribology and lubrication. In the introduction, the topic of the article is introduced by highlighting the hazards and economic losses caused by frictional wear and the excellent performance of graphene materials in the field of lubrication. Then, by studying the classification of graphene materials, the research status of their applications in tribology and lubrication is introduced. The second chapter introduces the application of graphene derivatives in improving tribological properties. The main types of graphene are graphene oxide (GO), doped graphene (doped elements such as nitrogen, boron, phosphorus, and fluorine), graphene-based films, and graphene-based fibers. The third chapter summarizes the application of graphene-based nanocomposites in improving friction and anti-wear and lubrication properties. According to the different functional modifiers, they can be divided into three categories: graphene–inorganic nanocomposites (sulfides, metal oxides, nitrides, metal nanoparticles, and carbon-containing inorganic nanoparticles), graphene–organic nanocomposites (alkylation, amine functionalization, ionic liquids, and surface modifiers), and graphene–polymer nanocomposites (carbon chain polymers and heterochain polymers). Graphene not only exhibits an excellent performance in traditional processing and lubrication applications, but the fourth chapter proves that it has a good application prospect in the field of ultra-low friction and superlubricity. In the application part of the fifth chapter, the lubrication mechanism proposed by graphene as a nano-lubricant is introduced first; then, the main application research status is summarized, including micro-tribology applications, bio-tribology applications, and liquid lubrication additive applications. The last part is based on the following contents. Firstly, the advantages of graphene-based nanocomposites as lubricants and their current shortcomings are summarized. The challenges and prospects of the commercial applications of graphene-based nanocomposites in tribology and lubrication are further described.

Recent studies have found that other forms of graphene derivatives perform better in tribological and lubricating applications. This paper reviews the research progress of graphene derivatives and their nanocomposites in tribology and lubrication.

A facile route to mechanically robust graphene oxide fibers

Excellent mechanical, electrical, and thermal properties of graphene have been achieved at the macroscale by assembling individual graphene or graphene oxide (GO) particles. Wet-spinning is an efficient and well-established process that can provide GO assemblies in fiber form. The coagulation bath in the wet-spinning process has rarely been considered for the design of mechanically robust GO fibers (GOFs). In this study, locating the amidation reaction in the coagulation bath yielded mechanically improved GOFs. The imides 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were used to form covalent amide bonds between GO flakes and chitosan, thereby reinforcing the GOFs. Evidence and effects of the amidation reaction were systematically examined. The tensile strength and breaking strain of the GOFs improved by 41.6% and 75.2%, respectively, and the toughness almost doubled because of the optimized crosslinking reaction. Our work demonstrated that using a coagulation bath is a facile way to enhance the mechanical properties of GOFs.

Excellent mechanical, electrical, and thermal properties of graphene have been achieved at the macroscale by assembling individual graphene or graphene oxide (GO) particles.

Ultratough Bioinspired Graphene Fiber via Sequential Toughening of Hydrogen and Ionic Bonding

Graphene-based fibers synthesized under ambient temperature have not achieved excellent mechanical properties of high toughness or tensile strength compared with those synthesized by hydrothermal strategy or graphitization and annealing treatment. Inspired by the relationship between organic/inorganic hierarchical structure, interfacial interactions, and moderate growth temperature of natural nacre, we fabricate an ultratough graphene fiber via sequential toughening of hydrogen and ionic bonding through a wet-spinning method under ambient temperature. A slight amount of chitosan is introduced to form hydrogen bonding with graphene oxide nanosheets, and the ionic bonding is formed between graphene oxide nanosheets and divalent calcium ions. The optimized sequential toughening of hydrogen and ionic bonding results in an ultratough graphene fiber with toughness of 26.3 MJ/m³ and ultimate tensile strength of 743.6 MPa. Meanwhile, the electrical conductivity of the resultant graphene fiber is as high as 179.0 S/cm. This kind of multifunctional graphene fiber shows promising applications in photovoltaic wires, flexible supercapacitor electrodes, wearable electronic textiles, fiber motors, etc. Furthermore, the strategy of sequential toughening of hydrogen and ionic bonding interactions also offers an avenue for constructing high-performance graphene-based fibers in the near future.

Electrical Conductivity Modeling of Graphene-based Conductor Materials

Graphene-based conductors such as films and fibers aim to transfer graphene's extraordinary properties to the macroscopic scale. They show great potential for large-scale applications, but there is a lack of theoretical models to describe their electrical characteristics. We present a network simulation method to model the electrical conductivity of graphene-based conductors. The method considers all of the relevant microscopic parameters such as graphene flake conductivity, interlayer conductivity, packing density, and flake size. To provide a mathematical framework, we derive an analytical expression, which reproduces the essential features of the network model. We also find good agreement with experimental data. Our results offer production guidelines and enable the systematic optimization of high-performance graphene-based conductor materials. A generalization of the model to any conductor based on two-dimensional materials is straightforward.

Highly conductive porous graphene/sulfur composite ribbon electrodes for flexible lithium-sulfur batteries

Flexible batteries have become an indispensable component of emerging devices, such as wearable, foldable electronics and sensors. Although various flexible batteries have been explored based on one-dimensional and two-dimensional platforms, developing a high energy density electrode with high structural integrity remains challenging. Herein, a scalable, one-pot wet spinning strategy is used to synthesize a flexible porous cathode for lithium-sulfur batteries (LSBs) for the first time, which consists of reduced graphene oxide (rGO), graphene crumples (GCs) and sulfur powders. The electrode structures are tailored using GCs with different dimensions and functional features that are critical to its robustness under mechanical deformation and electrolyte penetration into the battery components. The optimized rGO/GC/S composite ribbon cathodes deliver a high capacity of 524 mA h g^-1 after 100 cycles at a current rate of 0.2 C. A shape-conformable battery prototype comprising an rGO/GC/S cathode and a lithium anode demonstrates a stable discharge characteristic under repeated bending/flattening cycles. The LSB prototype supported by an elastomer presents stable discharge behavior with high mechanical robustness against an extension of up to 50%. The above-mentioned findings shed new light on developing sulfur cathodes for flexible, high performance LSBs based on the rational design of graphene structures.

Reconstruction of Inherent Graphene Oxide Liquid Crystals for Large-Scale Fabrication of Structure-Intact Graphene Aerogel Bulk toward Practical Applications

The inherently formed liquid crystals (LCs) of graphene oxide (GO) in aqueous dispersions severely restrict the fabrication of large-size and structure-intact graphene aerogel bulk by an industry-applicable method. Herein, by developing a surfactant-foaming sol-gel method to effectively disrupt and reconstruct the inherent GO LCs via microbubbles as templates, we achieve the large-size and structure-intact graphene hydrogel bulk (GHB). After simple freezing and air-drying, the resulting graphene aerogel bulk (GAB) with a structure-intact size of about 1 m² exhibits a superelasticity of up to 99% compressive strain, ultralow density of 2.8 mg cm^-3, and quick solar-thermal conversion ability. The modified GAB (GABTP) shows a high decomposition temperature ( T_max) of 735 °C in air and a low heat storage capacity. These excellent performances make the GABs suitable for many practical applications, as proven in this work, including as high compressive force absorbers, high absorption materials for oils or dangerous solvents, superior solar-thermal management materials for rapid heater or controlled shelter, and high-efficiency fire-resistant and thermal insulation materials. The whole preparation process is easily scalable and cost-effective for mass production of structure-intact multifunctional graphene aerogel bulk toward practical applications.

Bending behavior of CNT fibers and their scaling laws

Carbon nanotube (CNT) fibers are a promising material for wearable electronics and biomedical applications due to their combined flexibility and electrical conductivity. To engineer the bending properties for such applications requires understanding how the bending stiffness of CNT fibers scales with CNT length and fiber diameter. We measure bending stiffness with a cantilever setup interpreted within Euler Elastica theory. We find that the bending stiffness scales with a power law of 1.9 for the fiber diameter and 1.6 for the CNT length. The diameter scaling exponent for fiber diameter agrees with results from earlier experiments and theory for microscopic CNT bundles. We develop a simple model which predicts the experimentally observed scaling exponents within statistical significance.

Microfluidic-spinning construction of black-phosphorus-hybrid microfibres for non-woven fabrics toward a high energy density flexible supercapacitor

Flexible supercapacitors have recently attracted intense interest. However, achieving high energy density via practical materials and synthetic techniques is a major challenge. Here, we develop a hetero-structured material made of black phosphorous that is chemically bridged with carbon nanotubes. Using a microfluidic-spinning technique, the hybrid black phosphorous–carbon nanotubes are further assembled into non-woven fibre fabrics that deliver high performance as supercapacitor electrodes. The flexible supercapacitor exhibits high energy density (96.5 mW h cm⁻³), large volumetric capacitance (308.7 F cm⁻³), long cycle stability and durability upon deformation. The key to performance lies in the open two-dimensional structure of the black phosphorous/carbon nanotubes, plentiful channels (pores <1 nm), enhanced conduction, and mechanical stability as well as fast ion transport and ion flooding. Benefiting from this design, high-energy flexible supercapacitors can power various electronics (e.g., light emitting diodes, smart watches and displays). Such designs may guide the development of next-generation wearable electronics.

Supercapacitors that exhibit flexibility and deformability are attractive for wearable devices; however achieving high energy density remains challenging. Here the authors report a non-woven fabric based on black phosphorus and carbon nanotubes for use in a supercapacitor with notable performance.

Graphene-Based Nanomaterials for Flexible and Wearable Supercapacitors

Along with the quick development of flexible and wearable electronic devices, there is an ever-growing demand for light-weight, flexible, and wearable power sources. Because of the high power density, excellent cycling stability and easy fabrication, flexible supercapacitors are widely studied for this purpose. Graphene-based nanomaterials are attractive electrode materials for flexible and wearable supercapacitors owing to their high surface area, good mechanical and electrical properties, and excellent electrochemical stability. The 2D structure and high aspect ratio of graphene nanosheets make them easy to assemble into films or fibers with good mechanical properties. In recent years, enormous progress has been made in developing flexible and wearable graphene-based supercapacitors. Here, the material and structure design strategies for developing film-shaped and emerging fiber-shaped flexible supercapacitors based on graphene nanomaterials are summarized.

Thermally Responsive Torsional and Tensile Fiber Actuator Based on Graphene Oxide

Graphene-based actuators are of practical interest because of their relatively low cost compared with other nanocarbon materials, such as carbon nanotubes. We demonstrate the simple fabrication of graphene oxide (GO)-based fibers with an infiltrated nylon-6,6 polymer by wet spinning. These fibers could be twisted to form torsional actuators and further coiled to form tensile actuators. By controlling the relative twisting and coiling direction of the GO/nylon fiber, we were able to realize reversible contraction or elongation actuation with strokes as high as -80 and 75%, respectively, when the samples were heated to 200 °C. The tensile actuation showed a remarkably little hysteresis. Moreover, this GO/nylon actuator could lift loads over 100 times heavier than itself and generate a stable actuation at high temperatures over the melting point of the polymer. This novel kind of GO-based actuator, which has a multidirectional actuation, has potential for a wide range of applications such as artificial muscles, robotics, and temperature sensing.

Bioinspired Supertough Graphene Fiber through Sequential Interfacial Interactions

Natural nacre exhibits extraordinary functional and structural diversity, combining high strength and toughness. The mechanical properties of nacre are attributed to (i) a highly arranged hierarchical layered structure of inorganic minerals (95 vol %) containing a small amount only of organic materials (5 vol %), (ii) abundant synergistic interfacial interactions, and (iii) formation under ambient temperature. Herein, inspired by these three design principles originating from natural nacre, the supertough bioinspired graphene-based nanocomposite fibers (BGNFs) are prepared under room temperature via sequential interfacial interactions of ionic bonding and π-π interactions. The resultant synergistic effect leads to a super toughness of 18.7 MJ m^-3 as well as a high tensile strength of 740.1 MPa. In addition, the electrical conductivity of these supertough BGNFs is as high as 384.3 S cm^-1. They can retain almost 80% of this conductivity even after 1000 cycles of loading-unloading testing, which makes these BGNFs promising candidates for application in flexible and stable electrical devices, such as strain sensors and actuators.

Graphene oxide liquid crystals: a frontier 2D soft material for graphene-based functional materials

Graphene, despite being the best known strong and electrical/thermal conductive material, has found limited success in practical applications, mostly due to difficulties in the formation of desired large-scale highly organized structures. Our discovery of a liquid crystalline phase formation in graphene oxide dispersion has enabled a broad spectrum of highly aligned graphene-based structures, including films, fibers, membranes, and mesoscale structures. In this review, the current understanding of the structure-property relationship of graphene oxide liquid crystals (GOLCs) is overviewed. Various synthetic methods and parameters that can be optimized for GOLC phase formation are highlighted. Along with the results from different characterization methods for the identification of the GOLC phases, the typical characteristics of different types of GOLC phases introduced so far, including nematic, lamellar and chiral phases, are carefully discussed. Finally, various interesting applications of GOLCs are outlined together with the future prospects for their further developments.

Photonic-structured fibers assembled from cellulose nanocrystals with tunable polarized selective reflection

Fibers with self-assembled photonic structures are of special interest due to their unique photonic properties and potential applications in the smart textile industry. Inspired by nature, the photonic-structured fibers were fabricated through the self-assembly of chiral nematic cellulose nanocrystals (CNCs) and the fibers showed tunably brilliant and selectively reflected colors under crossed-polarization. A simple wet-spinning method was applied to prepare composite fibers of the mixed CNC matrix and polyvinyl alcohol (PVA) additions. During the processing, a cholesteric CNC phase formed photonic fibers through a self-assembly process. The selective color reflection of the composite fibers in the polarized condition showed a typical red-shift tendency with an increase in the PVA content, which was attributed to the increased helical pitch of the CNC. Furthermore, the polarized angle could also alter the reflected colors. Owing to their excellent selective reflection properties under the polarized condition, CNC-based photonic fibers are promising as the next-generation of smart fibers, applied in the fields of specific display and sensing.

Mussel-Inspired Defect Engineering of Graphene Liquid Crystalline Fibers for Synergistic Enhancement of Mechanical Strength and Electrical Conductivity

Inspired by mussel adhesive polydopamine (PDA), effective reinforcement of graphene-based liquid crystalline fibers to attain high mechanical and electrical properties simultaneously is presented. The two-step defect engineering, relying on bioinspired surface polymerization and subsequent solution infiltration of PDA, addresses the intrinsic limitation of graphene fibers arising from the folding and wrinkling of graphene layers during the fiber-spinning process. For a clear understanding of the mechanism of PDA-induced defect engineering, interfacial adhesion between graphene oxide sheets is straightforwardly analyzed by the atomic force microscopy pull-off test. Subsequently, PDA could be converted into an N-doped graphitic layer within the fiber structure by a mild thermal treatment such that mechanically strong fibers could be obtained without sacrificing electrical conductivity. Bioinspired graphene-based fiber holds great promise for a wide range of applications, including flexible electronics, multifunctional textiles, and wearable sensors.

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 10³ S m^-1. These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

Strong Graphene 3D Assemblies with High Elastic Recovery and Hardness

The rational design and construction of 3D graphene assemblies is a crucial step to extend the graphene properties for practical applications. Here, a novel interfacially reactive self-assembling process is reported to prepare well-organized 3D honeycomb-like graphene assemblies with unique polygonal nanopores interconnected by silicon-oxygen chemical bonds. The newly developed silicate-bridged graphene assembly (SGA) exhibits an exceptionally high hardness of 13.09 GPa, outperforming all existing 3D graphene materials, while maintains high Young's modulus (162.96 GPa), elastic recovery (75.27%), and superb thermal stability (600 °C in air). The observed unusual merits are resulted from unique pore structure combining the mechanical stability of the trihedral-nanopore structure and the deformability of the other polygonal nanopores. As a filling material, a merely 0.05% (w/w) addition of SGA could double the impact resistance of unsaturated resins (e.g., polyester). While SGA is attractive for various applications, including body armors, wearable electronics, space elevators, and multifunctional reinforcement fibers for automobiles, and aerospace vehicles, the novel liquid sodium-water interfacial reactive self-assembling developed in this study could open avenues for further development of various well-defined 3D assemblies from graphene and many other materials.

Coupled Chiral Structure in Graphene-Based Film for Ultrahigh Thermal Conductivity in Both In-Plane and Through-Plane Directions

The development of high-performance thermal management materials to dissipate excessive heat both in plane and through plane is of special interest to maintain efficient operation and prolong the life of electronic devices. Herein, we designed and constructed a graphene-based composite film, which contains chiral liquid crystals (cellulose nanocrystals, CNCs) inside graphene oxide (GO). The composite film was prepared by annealing and compacting of self-assembled GO-CNC, which contains chiral smectic liquid crystal structures. The helical arranged nanorods of carbonized CNC act as in-plane connections, which bridge neighboring graphene sheets. More interestingly, the chiral structures also act as through-plane connections, which bridge the upper and lower graphene layers. As a result, the graphene-based composite film shows extraordinary thermal conductivity, in both in-plane (1820.4 W m^-1 K^-1) and through-plane (4.596 W m^-1 K^-1) directions. As a thermal management material, the heat dissipation and transportation behaviors of the composite film were investigated using a self-heating system and the results showed that the real-time temperature of the heater covered with the film was 44.5 °C lower than a naked heater. The prepared film shows a much higher efficiency of heat transportation than the commonly used thermal conductive Cu foil. Additionally, this graphene-based composite film exhibits excellent mechanical strength of 31.6 MPa and an electrical conductivity of 667.4 S cm^-1. The strategy reported here may open a new avenue to the development of high-performance thermal management films.