High Conductivity Fibers Research Articles

Biobased, recyclable, and multi-functional high-performance composites for electromagnetic interference shielding

High-performance fiber-reinforced thermoset composites (FRTCs) are highly demanded in modern society but are challenged because they depend on nonrenewable fossil-based feedstocks, are hard to recycle after service, and lack advanced functions. Here, we report a methodology to fabricate sustainable, recyclable, high-performance, and multifunctional FRTCs from renewable feedstocks such as vanillin, glycerol triglycidyl ether, 1,10-diaminodecane, and basalt fiber. We designed a mussel-inspired approach to prepare high conductive basalt fiber (CBF), and combined the CBF with a fully biobased covalent adaptable network (CAN) based on dynamic imine bonds to produce the composites i.e., CAN/CBF laminar composites through a solvent-free method. The CAN/CBF composites showed highly reinforced mechanical properties and multiple functionalities including electromagnetic interference shielding, shape memory, and self-adhesion characters through combination in the advantages and functions of both CAN and CBF. Furthermore, we demonstrated that the CAN matrix and the reinforced CBF can be recycled separately and can be further reformed to the CAN/CBF composites due to the dynamic nature of the CAN matrix. Our study thus provides an urgently applicable approach for advanced manufacturing toward the green and circular advanced composites economy.

Core-sheath smart polymer fiber composites with high elasticity and thermal conductivity

Thermal conductive polymer fibers have broad development prospects because of its excellent thermal and mechanical properties. However, currently reported polymer fibers cannot simultaneously possess high thermal conductivity and high resilience, which greatly limits the application of thermal conductive polymer fibers. Therefore, preparing fibers with high thermal conductivity and high resilience is extremely challenging. The thermoplastic polyurethane/boron nitride liquid metal (TPU/BN-LMs) fiber with core sheath structure is prepared by coaxial wet spinning technology, the boron nitride (BN) doped in thermoplastic polyurethane elastomer (TPU) as sheath and the liquid metal (LMs) as core. The maximum tensile strength of the fiber is 3.9 MPa, and the elongation can reach 400 %. After multiple cycles of stretching, it can return to its original state. In addition, the thermal conductivity of the fiber in the horizontal direction and the vertical direction are 10.0 W m−1 K−1 and 4.6 W m−1 K−1, respectively. This work solves the current problem of high thermal conductivity and high resilience of thermally conductive polymer fibers that are difficult to be compatible. And it provides a new research idea for the design and preparation of new high thermal conductivity and high resilience polymer fiber materials.

Graphene Interlocking Carbon Nanotubes for High-Strength and High-Conductivity Fibers

Carbon nanotubes (CNTs) are promising building blocks for the fabrication of novel fibers with structural and functional properties. However, the mechanical and electrical performances of carbon nanotube fibers (CNTFs) are far lower than the intrinsic properties of individual CNTs. Exploring methods for the controllable assembly and continuous preparation of high-performance CNTFs is still challenging. Herein, a graphene/chlorosulfonic acid-assisted wet-stretching method is developed to produce highly densified and well-aligned graphene/carbon nanotube fibers (G/CNTFs) with excellent mechanical and electrical performances. Graphene with small size and high quality can bridge the adjacent CNTs to avoid the interfacial slippage under deformation, which facilitates the formation of a robust architecture with abundant conductive pathways. Their ordered structure and enhanced interfacial interactions endow the fibers with both high strength (4.7 GPa) and high electrical conductivity (more than 2 × 106 S/m). G/CNTF-based lightweight wires show good flexibility and knittability, and the high-performance fiber heaters exhibit ultrafast electrothermal response over 1000 °C/s and a low operation voltage of 3 V. This method paves the way for optimizing the microstructures and producing high-strength and high-conductivity CNTFs, which are promising candidates for the high-value fiber-based applications.

Modeling Ampacity in Advanced Electrical Conductors

Abstract An enabling advantage of carbon-based conductors is their low density and high thermal conductivity. To put this in the perspective of applications, current rating of carbon-based and copper nanocomposite conductors of different lengths are modeled. For comparison, the current and current density required to raise the maximum temperature of studied conductors to 150 °C are calculated with a joule heating model. The model is validated with an experimental setup equipped with a thermal camera. It is shown that while doped carbon nanotube (CNT) conductors may potentially result in improved performance compared with copper on a weight basis, ultra-conductive copper (UCC) can outperform copper on both volume and weight bases. Additionally, a hypothetical copper-matrix composite conductor with different volume fractions of high thermal conductivity and lightweight graphene fibers (Cu–C composite) is included in the analysis. The properties of the Cu–C composite are evaluated based on the Lewis–Nielson and rule of mixture models, as inputs for the joule heating model. The results show that while the improved thermal conductivity of the composite is beneficial for improving the current rating in micro-electronics applications, the tradeoff for the decreased electrical conductivity results in lower current carrying capacity in applications that use longer conductors.

Three-dimensional micro-pipelines high thermal conductive C/SiC composites

Carbon/silicon carbide (C/SiC) composites are usually regarded as thermal protective system materials and widely applied in hypersonic vehicles or ramjet. However, poor thermal conductivity of C/SiC composites, leading to severe heat concentration and thermal stress during the high-speed operation of hypersonic vehicle, limits their broad-range of practical applications. Modification with high thermal conductive fillers is an optional method; however, controllable dispersion and orientation of the fillers to construct continuous and ordered heat conductive channel has been proven to be a challenging task. Herein, based on high thermal conductivity fibers, a three-dimensional micro-pipeline preform was developed for the preparation of structure–function integrated C/SiC composites. The technical feasibility of the method, the characteristics of microstructures, and the thermal conductivity and bending strength of the as-obtained composites were systematically studied. Results revealed that the thermal conductivities of as-obtained composites reached 150.2 and 46.7 W m −1 K −1 for in-plane and out-of-plane direction, respectively. The bending strength obtained herein is 264.4 MPa, which is lower than that of polyacrylonitrile C/SiC composites. However, the fine control over the component and microstructure or densification could provide a higher value in the future research. In sum, the proposed method provides a convenient and feasible approach to prepare high thermal conductive C/SiC composites.

Fabrication of a type of silk/PEDOT conductive fibers for wearable sensor

Flexible high-conductivity fibers have attracted much attention due to their great potential in the field of wearable electronic devices. However, how to ensure high conductivity and flexibility is still a challenge. In this paper, the flexible silk fibers were used as the substrate, and manganese oxides were generated on the surface by potassium permanganate treatment. On this basis, the flexible high conductivity silk fibers with a resistivity of 1.47 Ω·cm were prepared by in-situ chemical polymerization of 3,4-ethylenedioxythiophene(EDOT) on the surface of silk fibers. The surface morphology and chemical composition of silk fibers were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma emission spectrometry (ICP). The results confirmed that a large amount of MnO 2 was synthesized and deposited on the surface of the silk fibers. The flexible conductive silk prepared by this method had good temperature sensitivity (- 0.47%/K), good stability and repeatability under cyclic tension, and the relative resistance change rate was 9.1%. Meanwhile, due to the binding force between the surface-active groups of the silk fibers and poly(3,4-ethylenedioxythiophene) (PEDOT), the conductive silk fibers exhibited good stability against water washing, demonstrating a broad application prospects in the field of wearable sensors.

Polyaniline-based multifunctional glass fiber reinforced conductive composite for strain monitoring

In this study, polyaniline (PANI) was introduced for improving the self-sensing capability of glass fiber reinforced polymer composites. A PANI-based conductive polymer matrix was employed to develop high conductive glass fiber reinforced conductive composite (GFRCP). Piezoresistive characterization studies were conducted on the GFRCP specimens by subjecting to monotonic and cyclic loading. Further thermal study was performed to ratify the thermal stability of the composite. During all tests, the DC resistance was measured to correlate the strain. The gauge factor of the sensor was estimated as 1.5. Moreover, stability, reversibility and repeatability of the self-sensing GFRCP composites are estimated. The responses of the GFRCP composite established the material has outstanding self-sensing abilities to monitor the strain. This new GFRCP composite not only acts as a self-sensing structural strain sensor but also its high electrical conductivity can open up new opportunities to explore its’ other functionality, like damage detection, lightning strike protection (LSP), mechanical vibration sensing, and self-protection from an electromagnetic wave (EMI shielding).

Wearable supercapacitors based on conductive cotton yarns

High-performance fiber- and yarn-shaped supercapacitors based on commonly available fiber materials and production technologies are needed to meet the fast developing electronic textile market. In this investigation, natural cotton and stainless steel fibers (SSFs) are blended to form a conductive yarn for constructing novel high-performance two-ply yarn supercapacitors. The supercapacitors show very high areal capacitance, energy density, flexibility and electrochemical stability. The excellent performance is attributed to the high porosity, high conductivity and distributive metal fiber network formed in the blended yarn, coupled with the high electrochemical efficiency of the nanostructured polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) pseudocapacitance materials. The SSF-cotton blended yarn is economic to produce and retains the flexibility of a normal cotton yarn that is commonly used in apparel textiles. This greatly facilitates the integration of the two-ply yarn supercapacitor into electronic textiles.

Methods for increasing the thermal conductivity of polymers and polymer composite materials

This article summarizes data of research and development in the field of increasing the thermal conductivity of polymers and polymer composite materials by using high thermal conductivity particles and fibers.

Charged iodide in chains behind the highly efficient iodine doping in carbon nanotubes

The origin of highly efficient iodine doping of carbon nanotubes is not well understood. Relying on first-principles calculations, we found that iodine molecules $({\mathrm{I}}_{2})$ in contact with a carbon nanotube interact to form monoiodide or/and polyiodide from two and three ${\mathrm{I}}_{2}$ as a result of removing electrons from the carbon nanotube $(p$-type doping). Charge per iodine atom for monoiodide ion or iodine atom at end of iodine chain is significantly higher than that for ${\mathrm{I}}_{2}$. This atomic analysis extends previous studies showing that polyiodide ions are the dominant dopants. Moreover, we observed isolated I atoms in atomically resolved transmission electron microscopy, which proves the production of monoiodide. Finally, using Raman spectroscopy, we quantitatively determined the doping level and estimated the number of conducting channels in high electrical conductivity fibers composed of iodine-doped double-wall carbon nanotubes.

Melt-processed P3HT and PE Polymer Nanofiber Thermal Conductivity

ABSTRACT Thermal management is a growing challenge for electronics packaging because of increased heat fluxes and device miniaturization. Thermal interface materials (TIMs) are used in electronic devices to transfer heat between two adjacent surfaces. TIMs need to exhibit high thermal conductivity and must be soft to minimize thermal contact resistance. Polymers, despite their relative softness, suffer from low thermal conductivity (∼0.2 W/m-K). To overcome this challenge, we infiltrate nanoporous anodic aluminum oxide (AAO) templates with molten polymer to fabricate large area arrays of vertically aligned polymer nanofibers. Nanoscale confinement effects and flow induced chain elongation improve polymer chain alignment (measured using polarized Raman spectroscopy) and thermal conductivity (measured using the photoacoustic method) along the fiber’s long axis. Conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) and non- conjugated polyethylene (PE) of various molecular weights are explored to establish a relationship between polymer structure, nanofiber diameter, and the resulting thermal conductivity. In general, thermal conductivity improves with decreasing fiber diameter and increasing polymer molecular weight. Thermal conductivity of approximately 7 W/m-K was achieved for both the ∼200 nm diameter HDPE fibers and the 100 nm diameter P3HT fibers. These results pave the way for optimization of the processing conditions to produce high thermal conductivity fiber arrays using different polymers, which could potentially be used in thermal interface applications.

Optimal design and loss mechanism analysis of microwave absorbing unidirectional SiC fiber composites with broad absorption band and good polarization stability

A microwave-absorbing unidirectional SiC fiber composite with wide absorption and good polarization stability was designed by genetic algorithm. The anisotropic nature of unidirectional fiber composites was considered in the design by characterizing tensor permittivity. This special composite is composed of two kinds of SiC fibers that separately exhibit relatively high conductivity and low conductivity. The electromagnetic loss mechanism of this composite was examined for polarizations that differ in the electric field of the incident wave, applied either in the direction of the fiber or in the transverse direction, perpendicular to the fibers. For both polarizations, the absorption band of our composite can reach 6 GHz and the lowest microwave reflectivity was about −20 dB over a range of 8–18 GHz. When the electric field is polarized parallel to fibers, strong coupling among the high-conductivity fibers can induce a strong current and thus efficiently dissipate the electromagnetic energy. When the electric field is polarized perpendicular to fibers, the electromagnetic loss mechanism in the composite resembles the electric energy loss in capacitors and currents in the transverse direction are obstructed by the fibers resulting in attenuation of the electromagnetic energy in the matrix.

Evaluation of heat transfer by sublimation for the application to the divertor heat sink for high fusion energy conversion

Thermal and structural responses of divertor target were evaluated by using finite element method. High heat flux simulating ELMs at the level of 100MW/m2 was assumed onto the tungsten armor, and surface temperature profile was obtained. When dynamic heat load over 100MW/m2 was applied, the maximum surface temperature exceeded 1300°C, and it caused recrystallization of tungsten regardless of the heat transfer below it. The result was used to conduct dynamic heat load experiment on tungsten, and material behavior of tungsten was evaluated under dynamic heat load. This study also proposed new concept of divertor heat sink which can distribute high heat flux and transfers the heat to high temperature medium. It consists of tungsten armor, composite enhanced with high thermal conductivity fiber, and heat transport system applying phase transition. High heat flux simulating ELMs was also applied to target surface of the divertor, temperature gradient, thermal stress of tungsten and composite were evaluated. Based on the results of analysis, thermal structural requirement was considered.

Fabrication of High Conductive S/C Cathode by Sulfur Infiltration into Hierarchical Porous Carbon/Carbon Fiber Weave-Structured Materials via Vapor-Melting Method

A high-rate sulfur/carbon cathode is prepared by using high conductive hierarchical porous carbon-carbon fiber weave-structured (HPC-CF) materials as carbon host to disperse sulfur. Sulfur is infiltrated into porous carbon with meso/micropores by using an improved vapor-melting adsorption method, which aims to enhance sulfur dispersion and interaction with carbon host. Meanwhile, carbon fiber with weaved structure can connect the dispersed micron S/HPC particles on the current collector. As a result, a highly conductive network around the sulfur particles finally forms in the sulfur/carbon cathode. Results show that improved vapour-melting method can efficiently enhance the sulfur dispersion and interaction with carbon host. Electrochemical measurements show that both of the rate capacity and cycle stability of the sulfur/carbon cathode are significantly improved. It delivers a very high initial discharge capacity of 1692.9 mAh g−1 at 0.1C, and maintains 1030 mAh g−1 after 130 cycles at 0.5C. Furthermore, the weave-structured HPC-CF carbon materials increases the conductivity effectively, which enhances the rate performance of the prepared S/HPC-CF cathode. It shows 670.8 mAh g−1 at the first cycle and remains 520 mAh g−1 after 200 cycles at 6.0C with an average coulombic efficiency of 97.8%. The excellent cycle and rate performance of the prepared Sv-m/HPC-CF can be attributed to the high cathode conductivity, high sulfur utilization and strong interaction between sulfur and the HPC-CF materials.

Two-Dimensional Deterministic Model of a Thin Body with Randomly Distributed High-Conductivity Fibers

By using ergodic theory of subadditive processes and variational convergence, we study the macroscopic behavior of a thin 3D composite made up of high-conductivity fibers that are randomly distributed according to a stochastic point process in a bounded open set of ℝ3. The thickness of the body, the conductivity and the size of the cross sections of the fibers depend on a small parameter e. The variational limit functional energy obtained when e tends to 0 is deterministic and depends on two variables: one is the solution of a variational problem posed in a 2D bounded open set and describes the behavior of the medium; the other captures the limit behavior of suitably rescaled solutions in the fibers when the thickness and the size section become increasingly thin and the conductivity of the fibers becomes increasingly large.

Effect of acidification conditions on the properties of carbon nanotube fibers

Carbon nanotube (CNT) fibers prepared by dry-spun method were functionalized by mixture of nitric and sulfuric acids. The effects of acidification conditions on the electrical conductivity and tensile properties of CNT fibers were investigated. A strong, high conductive CNT fiber was obtained under the optimal mixture ratio and processing time, with a electrical conductivity and tensile strength up to 3.2×104S/m and 1103MPa, respectively. It showed that the acids densified the surface of the CNT fiber and introduced functional groups onto the tubes, both of which contributed to the conductivity improvement of the CNT fiber. The infrared spectroscopy, Raman and fracture analysis indicated that acidification process resulted in two competitive effects on the tensile properties of CNT fibers, one was the positive contribution by the enhancement of interactions between CNTs through the densification and functional groups, and the other was the negative effect due to the structural destruction of the tubes.

Can carbon nanotube fibers achieve the ultimate conductivity?—Coupled-mode analysis for electron transport through the carbon nanotube contact

Recent measurements of carbon nanotube (CNT) fibers electrical conductivity still show the values lower than that of individual CNTs, by about one magnitude order. The imperfections of manufacturing process and constituent components are described as culprits. What if every segment is made perfect? In this work, we study the quantum conductance through the parallel junction of flawless armchair CNTs using tight-binding method in conjunction with non-equilibrium Green's function approach. Short-range oscillations within the long-range oscillations as well as decaying envelopes are all observed in the computed Fermi-level (low bias) conductance as a function of contact length, L. The propagation of CNTs' Bloch waves is cast in the coupled-mode formalism and helps to reveal the quantum interference nature of various behaviors of conductance. Our analysis shows that the Bloch waves at the Fermi-level propagate through a parallel junction without reflection only at an optimal value of contact length. For quite a long junction, however, the conductance at the Fermi level diminishes due to the perturbation of periodic potential field of close-packed CNTs. Thus, a macroscopic fiber, containing an infinite number of junctions, forms a filter that permits passage of electrons with specific wave vectors, and these wave vectors are determined by the collection of all the junction lengths. We also argue that the energy gap introduced by long junctions can be overcome by small voltage (∼0.04 V) across the whole fiber. Overall, developing long individual all-armchair metallic CNTs serves as a promising way to the manufacture of high-conductivity fibers.

Transient heat flow in unidirectional fiber–polymer composites during laser flash analysis: Experimental measurements and finite element modeling

Laser flash analysis (LFA), an unsteady-state technique originally developed for measuring the thermal diffusivity of homogenous materials, was used to estimate the thermal conductivity of carbon fibers consolidated in an epoxy matrix to form axially aligned unidirectional composites. Experimental studies were conducted for P-25 and K-1100 mesophase pitch-based carbon fibers whose conductivity values bracket almost two orders of magnitude (∼10 and 1000 W/m·K). Experimentally determined fiber thermal conductivity values were generally consistent with those cited in the literature after appropriate corrections were applied to account for the extremely high conductivity (low thermal resistance) of highly graphitic fibers, relative to the graphite coating. Finite element analysis was used to simulate heat flow patterns that may occur in a uniaxial fiber–polymer composite due to the large differences in the thermal conductivities of carbon fibers and polymer matrices. Simulations reveal that fiber thermal conductivity is accurately determined from composite response for high volume fraction of fibers (≥0.6) regardless of fiber conductivity, or for lower conductivity fibers (10–100 W/m·K) regardless of volume fractions. However, for composites containing high thermal conductivity fibers (100–1000 W/m·K) at low volume fractions (≤0.2), fiber thermal conductivity may not be accurately determined due to transverse heat flow within the graphite layers that channel heat through the highly conductive fiber. Thus, under certain conditions, heat flow paths deviate from the one-dimensional heat flow assumption inherent to laser flash analysis and rule-of-mixtures.

Analytical Monte Carlo Ray Tracing simulation of radiative heat transfer through bimodal fibrous insulations with translucent fibers

In this study, a Monte Carlo Ray Tracing (MCRT) simulation technique is developed to study steady-state radiative heat transfer through fibrous insulation materials. The simulations are conducted in 3-D disordered virtual fibrous media with unimodal and/or bimodal fiber diameter distributions consisting of fibers whose surfaces are specularly reflective, and are translucent to Infrared (IR) radiation. Scattering within the realm of geometric optics is incorporated into our MCRT simulations using Snell’s Law for ray refraction. Fibers’ optical properties are obtained from Fresnel’s law and Beer’s law based on the refractive index of the material. Two different treatments of “high” and “low” conductivities are considered for the fibers and their effects are discussed. Our results indicate that heat flux through a fibrous medium with translucent fibers decreases with increasing packing fraction of the fibers. It was observed that IR transmittance through the media increases with increasing through-plane orientation of the fibers, but is independent of their in-plane orientations. It was also found that fiber orientation has generally a negligible effect on the temperature profile across the media’s thickness. However, for the case of high-conductivity fibers, increasing fibers’ through-plane orientation tends to flatten the temperature profile. The results obtained from simulating bimodal fibrous structures indicate that increasing the fiber-diameter dissimilarity, or the mass fraction of the coarse fibers, slightly increases the radiation transmittance through the media, and accordingly reduces the temperature gradient across the thickness. Our simulation results are compared with those from the two-flux model and good agreement is observed.

Thermal Conductivity of High-Strength Polyethylene Fiber and Applications for Cryogenic Use

The local temperature rise of the tape is one of instabilities of the conduction-cooled high temperature superconducting (HTS) coils. To prevent the HTS tape from locally raising a temperature, high thermal conductive fiber reinforced plastic was applied to coil bobbin or spacer for heat drain from HTS tape. The thermal conductivity of ramie fibers increases by increasing orientation of molecular chains with drawing in water, and decreases by chain scission withγ-rays irradiation or by bridge points in molecular chains with vapor-phase-formaldehyde treatments. Thermal conductivity of high strength ultra-high-molecular-weight (UHMW) polyethylene (PE) fiber increases lineally in proportion to tensile modulus and decreases by molecular chain scissions withγ-rays irradiation. This result suggested the contribution of the long extended molecular chains due to high molecular weight on the high thermal conductivity of high strength UHMW PE fiber. Thermal conductivity of high strength UHMW PE fiber reinforced plastics in parallel to fiber direction is proportional to the cross sectional ratio of reinforcement oriented in the conduction direction. Heat drain effect of high strength UHMW PE fiber reinforced plastic from HTS tape is higher than that of glass fiber reinforced plastic (GFRP) and lower than that of aluminum nitride (AlN). In the case of HTS coil, the thermal stability wound on coil bobbin made of high strength UHMW PE fiber reinforced plastic is good as that of AlN, and better than that of GFRP.