Surface resistivity of carbonaceous fiber/PTFE antistatic coatings

Abstract： PAN （Polyacrylonitrile）-based carbonaceous fibers were prepared at the heat treatment temperature （HTT） range of 650 to 900 ℃. The relationships among HTT, carbon content and volume resistivity of the carbonaceous fibers were investigated. The carbonaceous fibers/PTFE （Polytetrafluoroethylene） antistatic coatings were prepared by the spraying technology and the effects of carbonaceous fibers and pigments on surface resistivity of the coatings were systematically discussed. Micrographs provide insight into the antistatic mechanism of the coating. The results show that carbon content of the carbonaceous fibers increases from 68.8% to 74.8% （mass fraction） and the volume resistivity decreases drastically from 1.94× 10^-3 to 8.27× 10 ^-2.cm. The surface resistivity of the antistatic coating is adjustable between 10^5 and 10^8Ω2 to fit the different antistatic materials. Static is dissipated by a conductive network of short fibers and the tunneling effect between the neighboring fibers and conductive pigments. Conductive pigments make the conductive network more perfect and improve the antistatic ability, but insulating pigments acting as barriers for the formation of conductive channel increases the surface resistivity of the coatings. The influence of pigments on the surface resistivity drops gradually with the decrease of the carbonaceous fibers volume resistivity.

Graphite Wrapped FeNi_(3)/Co with Carbon Nanotubes Anchored on MgO@Carbon Fiber Reinforcements via Continuous Fabrication for High-Efficiency Microwave Attenuation

Carbon fiber(CF)has emerged as a promising candidate for microwave absorbers to resolve the escalating electromagnetic wave(EMW)pollution issue,not just serving as a structural reinforcement.However,the drawbacks,such as high conductivity,limit its ability to strongly absorb EMWs over a wide bandwidth.To address these challenges,graphite wrapped FeNi_(3)/Co with carbon nanotubes(CNTs)anchored on MgO@CF heterostructures were synthesized by introducing MgO nanofilms on a CF surface and subsequent chemical vapor deposition catalyzed by two-phase catalysts.The synthesis of MgO sup-presses the etching of CF during the experimental processes,effectively maintaining the inherent structure of CF,which is conducive to constructing rich conductive networks and developing excellent mechanical properties.By modulating the catalyst concentration,deposited CNTs with appropriate defects increase the conduction loss and stimulate defect polariza-tion loss.The abundant interfaces formed by multiple components lead to fulfilling interface polarization,while the doping of O heteroatoms causes dipole polarization.In addition,the introduction of FeNi_(3)/Co generates effective magnetic loss and optimizes electromagnetic parameters to form more matching impedance conditions.At a low filler loading of 23 wt%,the stable sample obtains a remarkable minimum reflection loss of up to-72.08 dB at merely 1.38 mm with an effective absorption bandwidth reaching 4.88 GHz at only 1.44 mm,which is superior to that of numerous distinguished carbon-based composites in regard to being“thin,light,wide and strong”.CST simulation reveals that the maximum radar cross section reduction acquires 26.88 dBm2,ascertaining the radar stealth capability of the distinctive heterostructure.Moreover,great mechanical and electromagnetic interference shielding performance is demonstrated by epoxy composites.Henceforth,this study proposes profound insights into the intricate relationship between the structure and EMW absorbing mechanism,and elucidates an attractive strategy for mass-producing modified CF-based hybrids for versatile applications.

Anodic Oxidation on Structural Evolution and Tensile Properties of Polyacrylonitrile Based Carbon Fibers with Different Surface Morphology

Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.

Metal–Organic Framework‑Derived Hierarchical Cu_(9)S_(5)/C Nanocomposite Fibers for Enhanced Electromagnetic Wave Absorption

Refining the electromagnetic wave absorption characteristics of traditional metal–organic framework(MOF)-derived carbon composites remains a challenge because of their discontinuous conductive path.To overcome this limitation,in this work,MOF-derived hierarchical Cu_(9)S_(5)/C nanocomposite fibers are fabricated by electrospinning and subsequent carbonization-sulfurization process.Morphological analyses show that MOF-derived octahedral Cu_(9)S_(5)/C particles are evenly monodis-persed inside carbonaceous fibers.This configuration creates a unique hierarchical structure,ranging from Cu_(9)S_(5)particle embedding,MOF-derived skeleton,to a three-dimensional network.The optimized composite fibers(Cu_(9)S_(5)/C-40)exhibit extraordinary electromagnetic wave absorption performance at a low mass fraction(20 wt%):the minimum reflection loss value reaches-69.6 dB,and the maximum effective absorption bandwidth achieves 5.81 GHz with an extremely thin thick-ness of only 1.83 mm.Systematic investigations demonstrate that constructing the three-dimensional conductive network to connect MOF derivatives is crucial for activating performance enhancement.The unique nano-micro hierarchical structure synergized with elaborate-configured components endows the materials with optimal impedance matching and amplifies the loss capacity of each part.This work provides a reliable example and theoretical guidance for fabricating new-generation high-efficiency MOF-derived fibrous electromagnetic wave absorbers.

Smart Cotton Fabric with CO_(2)-Responsive Wettability for Controlled Oil/Water Separation

Stimuli-responsive materials with switchable wettability have promising practical applications in oil/water separation.A novel CO_(2)-responsive cotton fabric for controlled oil/water separation was fabricated based on mussel-inspired reaction and polymerized with 2-(dimethylamino)ethyl methacrylate(DMAEMA).As expected,the modified fabric exhibited switchable hydrophilicity and hydrophobicity after CO_(2)/N_(2) alternation,and it could be used for gravity-driven CO_(2)-controlled oil/water separation.Water was selectively penetrated through the fabric and separated from oil after treating by CO_(2).A reversed wettability could be generated through simply treated with N2.It is expected that the as-prepared fabrics could be applied in smart oil/water separation due to the attractive properties of CO_(2)-switchable system.