Flexible reduced graphene oxide (rGO) sheets are being considered for applications in portable electrical devices and flexible energy storage systems. However, the poor mechanical properties and ...electrical conductivities of rGO sheets are limiting factors for the development of such devices. Here we use MXene (M) nanosheets to functionalize graphene oxide platelets through Ti-O-C covalent bonding to obtain MrGO sheets. A MrGO sheet was crosslinked by a conjugated molecule (1-aminopyrene-disuccinimidyl suberate, AD). The incorporation of MXene nanosheets and AD molecules reduces the voids within the graphene sheet and improves the alignment of graphene platelets, resulting in much higher compactness and high toughness. In situ Raman spectroscopy and molecular dynamics simulations reveal the synergistic interfacial interaction mechanisms of Ti-O-C covalent bonding, sliding of MXene nanosheets, and π-π bridging. Furthermore, a supercapacitor based on our super-tough MXene-functionalized graphene sheets provides a combination of energy and power densities that are high for flexible supercapacitors.
Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in ...diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.
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The demand for high-modulus, high-strength, lightweight materials has continuously driven the bottom-up assembly of carbon nanostructures into high-performance bulk carbon materials, such as graphene ...sheets and carbon nanotube yarns. Carbyne, often called linear carbon, has a higher predicted gravimetric modulus and gravimetric strength than any other form of carbon, but possibly reacts under near-ambient conditions because of the extended sp 1 hybridization. The successful fabrication of carbon nanotube wrapped single carbyne chain (Shi et al. Nat. Mater. 2016, 15, 634) suggests the possibility of carbyne’s bulk production. Herein, we designed a type of carbon assembly that includes a possibly large array of carbyne chains confined within a single-walled nanotube sheath (nanotube wrapped carbynes, NTWCs), in which carbyne chains act as reinforcing building blocks, and the carbon nanotube sheath protects the multiple carbyne chains against chemical or topochemical reaction. We showed that NTWCs exhibit confinement-enhanced stabilities, even when they contain multiple neighboring carbyne chains. We developed a mechanics model for exploring the mechanical properties of NTWCs. On the basis of this model, the gravimetric modulus (and strength) of NTWCs was predicted to increase from 356.4 (50.25) to 977.2 GPa·g–1·cm3 (71.20 GPa·g–1·cm3) as the mass ratio of carbyne carbons to sheath carbons increases, which is supported by atomistic simulations. The highest calculated gravimetric modulus and strength of NTWCs are 174.2% and 41.7%, respectively, higher than those of either graphene or carbon nanotubes. The corresponding highest values of engineering modulus and strength of NTWCs with a density of 1.54 g·cm–3 are 1505 and 109.6 GPa, respectively. Hence, NTWCs are promising for uses in high-modulus, high-strength, lightweight composites.
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The goal of this work is to develop an inexpensive low‐temperature process that provides polymer‐free, high‐strength, high‐toughness, electrically conducting sheets of reduced graphene oxide (rGO). ...To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+), a π–π bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the π–π bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and π–π bonding agents maximizes tensile strength, toughness, long‐term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and π–π bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m−3), and electrical conductivity (416 S cm−1) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.
An inexpensive, low‐temperature process is demonstrated that provides polymer‐free, high strength, tough, electrically conducting, and foldable graphene sheets via sequential ionic and π bridging between reduced graphene oxide platelets. The sequentially bridged graphene sheets have a similar in‐plane strength as the carbon fiber composites used for airplanes, and much higher ability to absorb mechanical energy in all sheet plane directions.
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The Power of Fiber Twist Zhou, Xiang; Fang, Shaoli; Leng, Xueqi ...
Accounts of chemical research,
06/2021, Volume:
54, Issue:
11
Journal Article
Peer reviewed
Conspectus Nature’s evolution over billions of years has led to the development of different kinds of twisted structures in a variety of biological species. Twisted fibers from nanoscale- to ...micrometer-scale diameter have been prepared by mimicking natural twisted structures. Mechanically inserting twist in a yarn is an efficient and important method, which generates internal stress, changes the macromolecular orientation, and increases compactness. Recently, twist insertion has been found to produce interesting fiber properties, including chemical, mechanical, electrical, and thermal properties. This Account summarizes recent progress in how twist insertion affects the chemical and physical properties of fibers and describes their applications in artificial spider silk, artificial muscles, refrigeration, and electricity generation. Twist and associated chirality widely arise in nature from molecules to nano- and microscale materials to macroscopic objects such as DNA, RNA, peptides, and chromosomes. Such twisted architectures play an important role in improving the mechanical properties and enabling biological functions. Inspired by the beauty and interesting properties of twisted structures, a wide range of artificial chiral materials with twisted or coiled structures have been prepared, from organic and inorganic nanorods, nanotubes, and nanobelts to macroscopic architectures and buildings. An efficient way to prepare twisted materials is by inserting twist in fibers or yarns, which is an ancient technique used to make yarns or ropes (Wang, R., et al. Science 2019, 366, 216–221. Mu, J., et al. Science 2019, 365, 150–155). During the twisting process, torque is generated in fibers or yarns, the structure of the polymer chains becomes helically oriented, and the fibers in a yarn become more compact. Therefore, the twisting of fibers and yarns can produce novel chemical, mechanical, electrical, and thermal properties (Dou, Y., et al. Nat. Commun. 2019, 10, 1–10. Kim, S. H., et al. Science 2017, 357, 773–778). This Account focuses on the novel properties generated by twist insertion. The mechanical stress and strain can be optimized in a yarn by twist insertion, and different types of fibers exhibit rather different mechanisms. In the first section, we will focus on recent progress in improving the mechanical properties of twisted fibers, including carbon nanotube yarns, single-filament fibers, and hydrogel fibers. Torque was generated by twist insertion in a fiber or a yarn, and the balance of internal torsional stress can be changed by causing a change in yarn volume. This will result in twist release and torsional and tensile actuations of the yarn, which will be described in the second section. Twisting a yarn generally makes it more compact, which will result in a mechanically induced change in capacitance, supercapacitance, and other useful electrochemical properties when a conducting yarn is in an electrolyte. Such processes were used to develop novel devices for twist-based electricity generation, called twistrons, which will be discussed in the third section. Twist insertion or release also changes the polymer chain orientation or crystal structure, resulting in changes in entropy. This is called the twistocaloric effect, which was used to develop a new cooling method, and will be discussed in the last section.
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Yarn‐shaped supercapacitors (YSCs) once integrated into fabrics provide promising energy storage solutions to the increasing demand of wearable and portable electronics. In such device format, ...however, it is a challenge to achieve outstanding electrochemical performance without compromising flexibility. Here, MXene‐based YSCs that exhibit both flexibility and superior energy storage performance by employing a biscrolling approach to create flexible yarns from highly delaminated and pseudocapacitive MXene sheets that are trapped within helical yarn corridors are reported. With specific capacitance and energy and power densities values exceeding those reported for any YSCs, this work illustrates that biscrolled MXene yarns can potentially provide the conformal energy solution for powering electronics beyond just the form factor of flexible YSCs.
MXene‐based yarn‐shaped supercapacitors (YSCs) that exhibit flexibility and superior energy storage performance are fabricated by the biscrolling approach with ultrahigh loading of MXene sheets trapped within helical carbon nanotube corridors. This work illustrates that biscrolled MXene yarns with ultrahigh specific capacitance and energy density can potentially provide the energy solution for powering wearable electronics.
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New twist on artificial muscles Haines, Carter S.; Li, Na; Spinks, Geoffrey M. ...
Proceedings of the National Academy of Sciences - PNAS,
10/2016, Volume:
113, Issue:
42
Journal Article
Peer reviewed
Open access
Lightweight artificial muscle fibers that can match the large tensile stroke of natural muscles have been elusive. In particular, low stroke, limited cycle life, and inefficient energy conversion ...have combined with high cost and hysteretic performance to restrict practical use. In recent years, a new class of artificial muscles, based on highly twisted fibers, has emerged that can deliver more than 2,000 J/kg of specific work during muscle contraction, compared with just 40 J/kg for natural muscle. Thermally actuated muscles made from ordinary polymer fibers can deliver long-life, hysteresis-free tensile strokes of more than 30% and torsional actuation capable of spinning a paddle at speeds of more than 100,000 rpm. In this perspective, we explore the mechanisms and potential applications of present twisted fiber muscles and the future opportunities and challenges for developing twisted muscles having improved cycle rates, efficiencies, and functionality. We also demonstrate artificial muscle sewing threads and textiles and coiled structures that exhibit nearly unlimited actuation strokes. In addition to robotics and prosthetics, future applications include smart textiles that change breathability in response to temperature and moisture and window shutters that automatically open and close to conserve energy.
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By introducing twist during spinning of multiwalled carbon nanotubes from nanotube forests to make multi-ply, torque-stabilized yarns, we achieve yarn strengths greater than 460 megapascals. These ...yarns deform hysteretically over large strain ranges, reversibly providing up to 48% energy damping, and are nearly as tough as fibers used for bulletproof vests. Unlike ordinary fibers and yarns, these nanotube yarns are not degraded in strength by overhand knotting. They also retain their strength and flexibility after heating in air at 450°C for an hour or when immersed in liquid nitrogen. High creep resistance and high electrical conductivity are observed and are retained after polymer infiltration, which substantially increases yarn strength.
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Twistable and stretchable fiber-based electrochemical devices having high performance are needed for future applications, including emerging wearable electronics. Weavable fiber redox supercapacitors ...and strain sensors are here introduced, which comprise a dielectric layer sandwiched between functionalized buckled carbon nanotube electrodes. On the macroscopic scale, the sandwiched core rubber of the fiber acts as a dielectric layer for capacitive strain sensing and as an elastomeric substrate that prevents electrical shorting and irreversible structural changes during severe mechanical deformations. On the microscopic scale, the buckled CNT electrodes effectively absorb tensile or shear stresses, providing an essentially constant electrical conductance. Consequently, the sandwich fibers provide the dual functions of (1) strain sensing, by generating approximately 115.7% and 26% capacitance changes during stretching (200%) and giant twist (1700 rad·m–1 or 270 turns·m–1), respectively, and (2) electrochemical energy storage, providing high linear and areal capacitances (2.38 mF·cm–1 and 11.88 mF·cm–2) and retention of more than 95% of initial energy storage capability under large mechanical deformations.
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Conversion of low-grade waste heat into electricity is an important energy harvesting strategy. However, abundant heat from these low-grade thermal streams cannot be harvested readily because of the ...absence of efficient, inexpensive devices that can convert the waste heat into electricity. Here we fabricate carbon nanotube aerogel-based thermo-electrochemical cells, which are potentially low-cost and relatively high-efficiency materials for this application. When normalized to the cell cross-sectional area, a maximum power output of 6.6 W m(-2) is obtained for a 51 °C inter-electrode temperature difference, with a Carnot-relative efficiency of 3.95%. The importance of electrode purity, engineered porosity and catalytic surfaces in enhancing the thermocell performance is demonstrated.
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