Carbon Nanotube Wires Sheathed by Aramid Nanofibers

Coaxial fibers are the key elements in many optical, electrical, and biomedical applications. Recent success in materials synthesis has provided versatile choices for the core part, but the search of high‐performance sheath materials remains much less productive. These surface coatings are however as important as the core for their role as protection layers and interaction medium with the externals, thereby critically affecting the real performance of coaxial fibers. Here it is shown that aramid nanofibers (ANFs) with exceptional environmental stability and mechanical properties can be advanced coating materials for both wet‐ and dry‐spun carbon nanotube (CNT) wires. Co‐wet‐spinning ANFs with CNT aqueous dispersion can produce coaxial fibers with a compact sheath comprised of aligned ANFs, showing much enhanced mechanical properties by transferring stress to the sheath without sacrificing the conductivity. On the other hand, an immersion‐precipitation process is used to prepare a porous sheath made from randomly distributed nanofibers on dry‐spun CNT wires, which can be combined with ionic conductive gel electrolyte as a strong packaging layer for flexible solid‐state supercapacitors. The excellent intrinsic characteristics as well as variable ways of structural organizations make ANF‐based coatings an attractive tool for the design of multifunctional high‐performance hybrid materials.     

High Strength Conductive Composites with Plasmonic Nanoparticles Aligned on Aramid Nanofibers

Rapidly evolving fields of biomedical, energy, and (opto)electronic devices bring forward the need for deformable conductors with constantly rising benchmarks for mechanical properties and electronic conductivity. The search for conductors with improved strength and strain have inspired the multiple studies of nanocomposites and amorphous metals. However, finding conductors that defy the boundaries of classical materials and exhibit simultaneously high strength, toughness, and fast charge transport while enabling their scalable production, remains a difficult materials engineering challenge. Here, composites made from aramid nanofibers (ANFs) and gold nanoparticles (Au NPs) that offer a new toolset for engineering high strength flexible conductors are described. ANFs are derived from Kevlar macrofibers and retain their strong mechanical properties and temperature resilience. Au NPs are infiltrated into a porous, free‐standing aramid matrix, becoming aligned on ANFs, which reduces the charge percolation threshold and facilitates charge transport. Further thermal annealing at 300 °C results in the Au‐ANF composites with an electrical conductivity of 1.25 × 10⁴ S cm^?1 combined with a tensile strength of 96 MPa, a Young's modulus of 5.29 GPa, and a toughness of 1.3 MJ m^?3. These parameters exceed those of most of the composite materials, and are comparable to those of amorphous metals but have no volume limitations. The plasmonic optical frequencies characteristic for constituent NPs are present in the composites with ANFs enabling plasmon‐based optoelectronic applications.     

Fabrication,Applications, and Prospects of Aramid Nanofiber

Aramid nanofibers (ANFs) are of great interest in various applications due to its 1D nanoscale, high aspect ratio, high specific surface area, excellent strength, and modulus as well as impressive chemical and thermal stabilities. It is considered as one of the most promising nano‐sized building blocks with excellent properties and has therefore drawn increasing attention since 2011. However, no review has summarized the research progress and the prospective challenges of ANF. Herein, the methods of ANF fabrication and their relative merits are comprehensively discussed together with the challenges and progress in the deprotonation method for preparing ANF. The fabrication methods and development of ANF‐based advanced materials with different macroscopic morphologies, including the 1D ANF aerogel fiber, 2D ANF film/nanopaper/coating, and 3D ANF gel and particle are also described. Furthermore, the applications of ANF in nanocomposite reinforcement, battery separators, electrical insulation nanopaper, flexible electronics, and adsorption and filtration media are presented. Additionally, the possible challenges and outlooks toward the future development of ANF are highlighted. This review indicates that the ANF and ANF‐based materials mentioned herein will boost the development of next‐generation advanced functional materials.     

Aramid Nanofiber Membranes for Energy Harvesting from Proton Gradients

Harvesting osmotic energy from industrial wastewater is an often-overlooked source of electricity that can be used as a part of the comprehensive distributed energy systems. However, this concept requires, a new generation of inexpensive ion-selective membranes that must withstand harsh chemical conditions with both high/low pH, have high temperature resilience, display exceptional mechanical properties, and support high ionic conductance. Here, aramid nanofibers (ANFs) based membranes with high chemical/thermal stability, mechanical strength, toughness, and surface charge density make them capable of high-performance osmotic energy harvesting from pH gradients generated upon wastewater dilution. ANF membranes produce an averaged output power density of 17.3 W m^?2 for more than 240 h at pH 0. Taking advantage of the high temperature resilience of aramid, the output power density is increased further to 77 W m^?2 at 70 °C, typical for industrial wastewater. Such output power performance is 10× better compared to the current state-of-the-art membranes being augmented by Kevlar-like environmental robustness of ANF membranes. The improved efficiency of energy harvesting is ascribed to the high proton selectivity of ANFs. Retaining high output power density for large membrane area and fluoride-free synthesis of ANFs from recyclable material opens the door for scalable wastewater energy harvesting.     

Templated Synthesis of Carbon Nanofibers from Polyacrylonitrile Using Sepiolite

Carbon nanofibers of ca. 1 μm by 20 nm dimensions have been successfully prepared by an improved route, consisting of the graphitization of polyacrylonitrile (PAN) previously formed inside the nanosized pores of sepiolite. This natural microfibrous silicate contains structural tunnels extending along the whole fiber, which are able to include acrylonitrile (AN). This is polymerized to give polyacrylonitrile (PAN), which is further thermally treated to form carbon nanofibers inside the pores. We have clearly shown the mechanisms and the role of the structural tunnels of sepiolite in the adsorption, polymerization, and graphitization of AN by applying spectroscopic techniques as FTIR spectroscopy, ¹³C NMR spectroscopy, in‐situ EIS (electrochemical impedance spectroscopy), and other structural, textural, and analytical tools (powder X‐ray diffraction (PXRD), scanning transmission electron microscopy–energy‐dispersive X‐ray analysis (STEM–EDX), differential thermal analysis (DTA), thermogravimetric analysis (TG), N₂ isotherms, etc.). The resulting solids constitute a new class of conductive carbon–clay nanocomposites, useful for applications in diverse electrochemical devices such as lithium batteries, sensors, or electrocatalysts.     

Achieving Outstanding Mechanical Performance in Reinforced Elastomeric Composite Fibers Using Large Sheets of Graphene Oxide

A simple fiber spinning method used to fabricate elastomeric composite fibers with outstanding mechanical performance is demonstrated. By taking advantage of the large size of as‐prepared graphene oxide sheets (in the order of tens of micrometers) and their liquid crystalline behavior, elastomeric composite fibers with outstanding low strain properties have been fabricated without compromising their high strain properties. For example, the modulus and yield stress of the parent elastomer improved by 80‐ and 40‐fold, respectively, while maintaining the high extensibility of ～400% strain inherent to the parent elastomer. This outstanding mechanical performance was shown to be dependent upon the GO sheet size. Insights into how both the GO sheet size dimension and dispersion parameters influence the mechanical behavior at various applied strains are discussed.     

静电纺丝制备复合纳米纤维研究进展

静电纺丝技术近年来在制备纳米纤维领域得到广泛应用,目前已成功制备出多种不同类型的纳米纤维,尤其在制备复合纳米纤维方面取得了显著成果,被认为是制备纳米纤维最有效的方法之一。总结了静电纺丝技术制备纳米纤维,特别是制备复合型纳米纤维方面的最新研究报道,如天然高分子复合纳米纤维、聚合物复合碳纳米管纤维、聚合物复合金属纳米纤维、共聚物纳米纤维以及无机复合纳米纤维等。静电纺丝纳米纤维将在生物医药、电子光学、制备复合材料等多个领域得到广泛应用。     

Controlled Synthesis of Ag2S,Ag2Se,and Ag Nanofibers by Using a General Sacrificial Template and Their Application in Electronic Device Fabrication

Nanofiber bundles of Ag₂S, Ag₂Se, and Ag have been successfully synthesized by making use of Ag₂C₂O₄ template nanofiber bundles, utilizing both anion‐exchange and redox reactions. The obtained bundles were polycrystalline nanofibers composed of nanoparticles in which the precursor morphology was well‐preserved, indicating that Ag₂C₂O₄ nanofiber bundles acted as a general sacrificial template for the synthesis of silver‐based semiconductor and metal nanofibers. Dispersing media and transforming reactants were found to be key factors influencing the chemical transformation in the system. In particular, separate single‐crystalline Ag nanofibers were obtained via a nontemplate route when ascorbic acid was used as a relatively weak reductant. An electrical transfer and switching device was built with the obtained Ag₂S and Ag nanofiber bundles, utilizing the unique ion‐conductor nature of Ag₂S and revealing their potential applications in electronics.     

Quantitative In Situ Mechanical Characterization of the Effects of Chemical Functionalization on Individual Carbon Nanofibers

Carbon nanofibers (CNFs) have been used for applications in composite material for decades because of their unique mechanical, thermal, and electrical properties. Consequently, an in‐depth understanding of mechanical properties of individual CNFs, particularly after chemical functionalization, would provide important insight into its effective integration into composite materials. Fluorination and amination of CNFs is achieved and systematic chemical characterizations of functionalized CNFs are performed. An in situ tensile testing method, which combines a simple microfabricated device with a quantitative nanoindenter inside a scanning electron microscope (SEM) chamber, is used to measure mechanical properties of individual pristine, fluorinated, and amino‐functionalized CNFs. The nominal CNFs strengths follow the Weibull distribution and the fluorinated CNFs are found to possess higher nominal strength but similar strain when compared with the pristine and amino‐functionalized CNFs. SEM fracture surfaces analysis shows that all nanofibers failed in a similar cup‐and‐cone fashion. Microscopy image sof fluorinated CNFs reveal an unexpected change in the hollow core before and after fiber fracture, which is attributed to the possible effects of fluorination‐induced compression on nanofiber surfaces. The results demonstrate the potential of fluorination for improving both the mechanical properties of CNFs and their successful integration into composites.     

考虑尺度效应的压电半导体纳米纤维力电耦合特性北大核心

文章基于挠曲电和应变梯度效应的共同影响,建立了静拉伸下一维压电半导体力电耦合计算模型,数值分析了挠曲电和应变梯度效应对位移、电势、电位移、载流子分布等物理场的影响。结果表明:两种效应对机械位移场没有影响,但对各电相关物理场的分布影响显著;挠曲电效应对压电结构本身的压电性能有抑制作用,而应变梯度效应却增强了其压电特性。本研究为压电类微纳结构的机电特性分析提供了理论指导。     

Full Recovery of Fracture Toughness Using a Nontoxic Solvent‐Based Self‐Healing System

Two significant advances are reported for solvent‐based self‐healing of epoxy materials. First, an autonomic system yielding complete recovery of fracture toughness after crack propagation was achieved by embedding microcapsules containing a mixture of epoxy monomer and solvent into an epoxy matrix. Healing with epoxy‐solvent microcapsules is superior to capsules that contain solvent alone, and multiple healing events are reported for this system. Second, efficient healing is reported for new solvents, including aromatic esters, which are significantly less toxic than the previously employed solvent, chlorobenzene. Preliminary aging studies using either chlorobenzene or ethyl phenylacetate as the solvent demonstrate the stability of the epoxy‐solvent system under ambient conditions for at least one month.     

Bioinspired Structural Composite Hydrogels with a Combination of High Strength,Stiffness, and Toughness

In the development of artificial hydrogels, emulating the mechanical properties of biological tissues with a desirable combination of stiffness and toughness is crucial. To achieve such properties, a design principle inspired by a natural structural composite to wet hydrogels is applied. The bioinspired structural composite hydrogel consisting of layered microplatelets and polymer matrix with strong polymer–platelet interactions is fabricated by a facile method, that is, drying-induced unidirectional shrinkage and rehydration process coupled with secondary ionic crosslinking. The resulting hydrogels exhibit a combination of high tensile strength and elastic modulus (on the order of several MPa) and high fracture energy (up to ≈ 2 kJ·m⁻²). The results suggest the potential of the bioinspired approach that is limitedly applied in dry composites for developing mechanically robust composite hydrogels.     

One‐Step Wet‐Spinning Process of Poly(3,4‐ethylenedioxythiophene):Poly(styrenesulfonate) Fibers and the Origin of Higher Electrical Conductivity

A simplified wet‐spinning process for the production of continuous poly (3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fibers is reported. Conductivity enhancement of PEDOT:PSS fibers up to 223 S cm^?1 has been demonstrated when these fibers are exposed to ethylene glycol as a post‐synthesis processing step. In a new spinning approach it is shown that by employing a spinning formulation consisting of an aqueous blend of PEDOT:PSS and poly(ethlylene glycol), the need for post‐spinning treatment with ethylene glycol is eliminated. With this approach, 30‐fold conductivity enhancements from 9 to 264 S cm^?1 are achieved with respect to an untreated fiber. This one‐step approach also demonstrates a significant enhancement in the redox properties of the fibers. These improvements are attributed to an improved molecular ordering of the PEDOT chains in the direction of the fiber axis and the consequential enrichment of linear (or expanded‐coil like) conformation to preference bipolaronic electronic structures as evidenced by Raman spectroscopy, solid‐state electron spin resonance (ESR) and in situ electrochemical ESR studies.     

High‐Strength and High‐Toughness Double‐Cross‐Linked Cellulose Hydrogels: A New Strategy Using Sequential Chemical and Physical Cross‐Linking

Polysaccharide‐based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non‐toxicic properties. The feasibility of using polysaccharide‐based hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double‐cross‐linked (DC) cellulose hydrogels is described using sequential chemical and physical cross‐linking, resulting in DC cellulose hydrogels that are mechanically superior to single‐cross‐linked cellulose hydrogels. The formation and spatial distribution of chemically cross‐linked domains and physically cross‐linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading‐unloading cycles are described using compression and tension models. The possible toughening mechanism of double‐cross‐linking is discussed.     

Investigation of Mechanical Behavior of Defective Carbon Nanotubes Using Molecular Dynamics Simulation

Carbon nanotubes(CNTs) having pristine structure(i.e.,structure without any defect) hold very high mechanical properties.However,CNTs suffer from defects which can appear at production stage,purification stage or be deliberately introduced by irradiation with energetic particles or by chemical treatment.In this article,mechanical properties of single-walled nanotubes with defects are studied under both compressive and tensile loads using molecular dynamics(MD) simulations.Two types of defect-Stone-Wales and...