Clay Assisted Dispersion of Carbon Nanotubes in Conductive Epoxy Nanocomposites

Clay was introduced into single‐walled carbon nanotube (SWNT)/epoxy composites to improve nanotube dispersion without harming electrical conductivity or mechanical performance. Unlike surfactant or polymer dispersants, clay is mechanically rigid and known to enhance the properties (e.g., modulus, gas barrier, and flame retardation) of polymer composites. Combining nanotubes and clay allows both electrical and mechanical behavior to be simultaneously enhanced. With just 0.05 wt % SWNT, electrical conductivity is increased by more than four orders of magnitude (from 10^–9 to 10^–5 S cm^–1) with the addition of 0.2 wt % clay. Furthermore, the percolation threshold of these nanocomposites is reduced from 0.05 wt % SWNT to 0.01 wt % with the addition of clay. SWNTs appear to have an affinity for clay that causes them to become more exfoliated and better networked in these composites. This clay‐nanotube synergy may make these composites better suited for a variety of packaging, sensing, and shielding applications.     

Carbon nanotubes and silver flakes filled epoxy resin for new hybrid conductive adhesives

Combining conductive micro and nanofillers is a new way to improve electrical conductivity. Micrometric silver flakes and nanometric carbon nanotubes (CNTs) exhibit high electrical conductivity. A new type of hybrid conductive adhesives filled with silver flakes and carbon nanotubes (DWCNTs or MWCNTs) were investigated. High electrical conductivity is measured as well as improved mechanical properties at room temperature. Small agglomerates and free MWCNTs dispersed in the silver/epoxy composites improve the electrical conductivity and a synergistic effect between MWCNTs and micro sized silver flakes is observed in hybrid composites. Glassy and rubbery storage moduli of the hybrid composites increase with increasing silver loading at fixed CNTs volume fraction. High value of the storage modulus, measured in DWCNTs/μAg hybrid composites at rubbery state, is caused by strong agglomeration of DWCNTs bundles. The electrical and mechanical properties are consistent with the morphologies of the hybrid composites characterized by SEM.     

基于激光作用的含CNTs复合涂层的摩擦磨损研究

碳纳米管具有超强的力学性能,极高的纵横比、高的化学和热稳定性及导电性,是制备复合材料的理想组元。本文采用大功率CO2激光器,以45碳钢为基体,制备了激光熔覆的CNTs复合涂层。研究了在激光作用下,工艺参数对涂层性能的影响,并对复合涂层进行了摩擦磨损试验。试验结果表明:经激光熔覆处理制备的CNTs复合涂层,其耐磨性能显著提高,磨损失重是未处理的38%,摩擦系数也显著下降,是未处理试样的37%。     

Stretchable Electrode Based on Laterally Combed Carbon Nanotubes for Wearable Energy Harvesting and Storage Devices

Carbon nanotubes (CNTs) are a promising material for use as a flexible electrode in wearable energy devices due to their electrical conductivity, soft mechanical properties, electrochemical activity, and large surface area. However, their electrical resistance is higher than that of metals, and deformations such as stretching can lead to deterioration of electrical performances. To address these issues, here a novel stretchable electrode based on laterally combed CNT networks is presented. The increased percolation between combed CNTs provides a high electrical conductivity even under mechanical deformations. Additional nickel electroplating and serpentine electrode designs increase conductivity and deformability further. The resulting stretchable electrode exhibits an excellent sheet resistance, which is comparable to conventional metal film electrodes. The resistance change is minimal even when stretched by ≈100%. Such high conductivity and deformability in addition to intrinsic electrochemically active property of CNTs enable high performance stretchable energy harvesting (wireless charging coil and triboelectric generator) and storage (lithium ion battery and supercapacitor) devices. Monolithic integration of these devices forms a wearable energy supply system, successfully demonstrating its potential as a novel soft power supply module for wearable electronics.     

Effect of Carbon Nanotubes on the Shear Strength and Electrical Resistivity of a Lead-Free Solder

In this study, the influence of carbon nanotubes (CNTs) on the shear strength and electrical resistivity of 95.8Sn-3.5Ag-0.7Cu lead-free solder was investigated. Composite solders containing various weight percentages of CNTs were synthesized, and electrical resistivity results of the bulk composite solders revealed that the presence of CNTs did not degrade the electrical performance of such solders. Tests conducted on lap-shear solder joint samples showed an improvement in the shear strength of the composite solders. However, at higher amounts of CNT additions (0.04 wt.% and 0.07 wt.%), the strength improvement was only marginal compared to that of the monolithic solder joint. A comparison of yield stress and ultimate stress test results between the solder joint and bulk solder also showed good agreement. Furthermore, the presence of CNTs in the solder matrix had a minimal influence on the thickness of the interfacial intermetallic compound layer formed during soldering.     

激光辐照诱导PVDF导电性的研究

采用波长为248 nm的准分子激光辐照聚偏氟乙烯(PVDF)薄片，可使其表面电导率从10-13 (Ω·cm)-1上升到10-4 (Ω·cm)-1，实现了由绝缘到导电的转变。通过调整激光能量密度、环境气氛、脉冲频率和辐照脉冲数等参数，确定出激光辐照诱导PVDF导电性的最佳工艺条件。通过对被辐照样品进行X射线衍射谱(XRD)、拉曼散射光谱和显微分析可知：紫外激光打断了PVDF的C-F键，并在样品表面生成了石墨导电层是PVDF由绝缘态向导电态转变的原因。     

Conductivity photoquenching effect in polymer–ferrocene composites

Based on a nonpolar polymer—i.e., high-density polyethylene, polar polyvinylidene fluoride, and di-π-cyclopentadienyl iron (π-(C₅H₅)₂Fe, ferrocene)—matrix composites are obtained that exhibit the conductivity photoquenching effect. Charge states and photoelectret and photoconductive properties of films of these composites are studied. In the visible region, the degree of conductivity photoquenching of matrix composites depends heavily on charge transport features in the heterogeneous polymer-ferrocene system and on reversible changes in electrical and chemical properties of ferrocene structures upon exposure to the electric field and light. A possible mechanism of the conductivity photoquenching effect in polymer-ferrocene composites is proposed that adequately accounts for experimental results. As light is turned off, the dark current is restored, which indicates the reversibility of the observed effect. The negative photoconductivity does not appear when CdS is used instead of ferrocene in composites of polymers under study. The negative photoconductivity effect increases when the third component, i.e., CdS photosensitive semiconductor, is introduced into the polymer-ferrocene composite.     

Intelligently Actuating Liquid Crystal Elastomer‐Carbon Nanotube Composites

Strategies for obtaining materials that respond to external stimuli by changing shape are of intense interest for the replacement of traditional actuators. Here, a strategy that enables programmable, multiresponsive actuators that use either visible light or electric current to drive shape change in composites comprising carbon nanotubes (CNTs) in liquid crystal elastomers (LCEs) is presented. In the nanocomposites, the CNTs function not only in the traditional roles of mechanical reinforcement and enhancers of thermal and electrical conductivity but also serve as an alignment layer for the LCEs. By controlling the orientation, location, and quantity of layers of CNTs in LCE/CNT composites, programmed, patterned actuators are built that respond to visible light or electrical current. Photothermal LCE/CNT film actuators undergo fast shape change, within 1.2 s using 280 mW cm^?2 light input, and complex, programmed localized deformations. Furthermore, twisting LCE/CNT composite films into a fiber increases uniaxial muscle stroke and work capacity for electrothermal actuation, thereby enabling about 12% actuation strain and 100 kJ m^?3 of work capacity in response to an applied DC voltage of 15.1 V cm^?1.     

Ultrahigh Electrical Conductivity of Graphene Embedded in Metals

Highly efficient conductors are strongly desired because they can lead to higher working performance and less energy consumption in their wide range applications. However, the improvements on the electrical conductivities of conventional conductors are limited, such as purification and growing single crystal of metals. Here, by embedding graphene in metals (Cu, Al, and Ag), the trade‐off between carrier mobility and carrier density is surmount in graphene, and realize high electron mobility and high electron density simultaneously through elaborate interface design and morphology control. As a result, a maximum electrical conductivity three orders of magnitude higher than the highest on record (more than 3,000 times higher than that of Cu) is obtained in such embedded graphene. As a result, using the graphene as reinforcement, an electrical conductivity as high as ≈117% of the International Annealed Copper Standard and significantly higher than that of Ag is achieved in bulk graphene/Cu composites with an extremely low graphene volume fraction of only 0.008%. The results are of significance when enhancing efficiency and saving energy in electrical and electronic applications of metals, and also of interest for fundamental researches on electron behaviors in graphene.     

High‐Conductivity Polymer Nanocomposites Obtained by Tailoring the Characteristics of Carbon Nanotube Fillers

We present a detailed study of the influence of carbon nanotube (CNT) characteristics on the electrical conductivity of polystyrene nanocomposites produced using a latex‐based approach. We processed both industrially‐produced multi‐wall CNT (MWCNT) powders and MWCNTs from vertically‐aligned films made in‐house, and demonstrate that while the raw CNTs are individualized and dispersed comparably within the polymer matrix, the electrical conductivity of the final nanocomposites differs significantly due to the intrinsic characteristics of the CNTs. Owing to their longer length after dispersion, the percolation threshold observed using MWCNTs from vertically‐aligned films is five times lower than the value for industrially‐produced MWCNT powders. Further, owing to the high structural quality of the CNTs from vertically‐aligned films, the resulting composite films exhibit electrical conductivity of 10³ S m^?1 at 2 wt% CNTs. On the contrary, composites made using the industrially‐produced CNTs exhibit conductivity of only tens of S m^?1. To our knowledge, the measured electrical conductivity for CNT/PS composites using CNTs from vertically‐aligned films is by far the highest value yet reported for CNT/PS nanocomposites at this loading.     

A Pyrenylpropyl Phosphonic Acid Surface Modifier for Mitigating the Thermal Resistance of Carbon Nanotube Contacts

Efforts to utilize the high intrinsic thermal conductivity of carbon nanotubes (CNTs) for thermal transport applications, namely for thermal interface materials (TIMs), have been encumbered by the presence of high thermal contact resistances between the CNTs and connecting materials. Here, a pyrenylpropyl‐phosphonic acid surface modifier is synthesized and applied in a straight forward and repeatable approach to reduce the thermal contact resistance between CNTs and metal oxide surfaces. When used to bond nominally vertically aligned multi‐walled CNT forests to Cu oxide surfaces, the modifier facilitates a roughly 9‐fold reduction in the thermal contact resistance over dry contact, enabling CNT‐based TIMs with thermal resistances of 4.6 ± 0.5 mm² K W^?1, comparable to conventional metallic solders. Additional experimental characterization of the modifier suggests that it may be used to reduce the electrical resistance of CNT‐metal oxide contacts by similar orders of magnitude.     

The Fusion of Imidazolium‐Based Ionic Polymer and Carbon Nanotubes: One Type of New Heteroatom‐Doped Carbon Precursors for High‐Performance Lithium–Sulfur Batteries

Rational design of sulfur host materials with high electrical conductivity and strong polysulfides (PS) confinement is indispensable for high‐performance lithium–sulfur (Li–S) batteries. This study presents one type of new polymer material based on main‐chain imidazolium‐based ionic polymer (ImIP) and carbon nanotubes (CNTs); the polymer composites can serve as a precursor of CNT/NPC‐300, in which close coverage and seamless junction of CNTs by N‐doped porous carbon (NPC) form a 3D conductive network. CNT/NPC‐300 inherits and strengthens the advantages of both high electrical conductivity from CNTs and strong PS entrapping ability from NPC. Benefiting from the improved attributes, the CNT/NPC‐300‐57S electrode shows much higher reversible capacity, rate capability, and cycling stability than NPC‐57S and CNTs‐56S. The initial discharge capacity of 1065 mA h g^?1 is achieved at 0.5 C with the capacity retention of 817 mA h g^?1 over 300 cycles. Importantly, when counter bromide anion in the composite of CNTs and ImIP is metathesized to bis(trifluoromethane sulfonimide), heteroatom sulfur is cooperatively incorporated into the carbon hosts, and the surface area is increased with the promotion of micropore formation, thus further improving electrochemical performance. This provides a new method for optimizing porous properties and dopant components of the cathode materials in Li–S batteries.     

In Situ Electrical Network Activation and Deactivation in Short Carbon Fiber Composites via 3D Printing

Prior studies on carbon-filler based, conductive polymer composites have mainly investigated how conductive filler morphology and concentration can tailor a material's electrical conductivity and overlooks the effects of filler alignment due to the difficulty to control and quickly quantify the filler alignment. Here, direct ink write 3D printing's unique ability is utilized to control carbon fiber alignment with a single process parameter, velocity ratio, to instantaneously activate or deactivate the electrical network in composites. Maximum electrical conductivity is achieved by randomly aligning carbon fibers that enhances the chance of direct fiber-to-fiber contact and, thus, activating the electrical network. However, aligning the fibers by increasing the velocity ratio disrupts the electrical network by minimizing fiber-to-fiber contact that resulted in a drastic decrease in electrical conductivity by as much as five orders of magnitude in both short and long carbon fiber composites. With this study, this study demonstrates that electrically conductive or insulative composites can be fabricated sequentially with a single ink. This novel ability to instantaneously control the electrical conductivity of carbon fiber reinforced composites allow to directly embed conductive pathways into designs to 3D print multifunctional composites that are capable of localized heating and self-sensing.     

Carbon Nanotube Alignment via Electrohydrodynamic Patterning of Nanocomposites

Electrohydrodynamic (EHD) pattern formation in carbon nanotube‐polymer composite films yields well‐defined patterns on the micrometer scale along with the alignment of carbon nanotubes (CNTs) within these patterns. Conductive pathways in nanotube networks formed during EHD patterning of nanocomposite films results in a substantial increase in the composites’ conductivity at loadings exceeding the percolation threshold. The degree of nanotube alignment can be tuned by adjusting the EHD parameters and the degree of alignment is mirrored by the conductivity across the film. Using etching techniques or by embedding relatively long nanotubes, patterned surfaces decorated by CNT brushes were generated.     

Towards Thermoconductive,Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers

Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20‐fold thermal conductivity improvement in BNNT‐containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT‐loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat‐releasing materials.     

Single‐Walled Carbon Nanotube Networks: The Influence of Individual Tube–Tube Contacts on the Large‐Scale Conductivity of Polymer Composites

Over two decades after carbon nanotubes started to attract interest for their seemingly huge prospects, their electrical properties are far from being used to the maximum potential. Composite materials based on carbon nanotubes still have conductivities several orders of magnitude below those of the tubes themselves. This study aims at understanding the reason for these limitations and the possibilities to overcome them. Based on and validated by real single‐walled carbon nanotube (SWCNT) networks, a simple model is developed, which can bridge the gap between macroscale and nanoscale down to individual tube–tube contacts. The model is used to calculate the electrical properties of the SWCNT networks, both as‐prepared and impregnated with an epoxy‐amine polymer. The experimental results show that the polymer has a small effect on the large‐scale network resistance. From the model results it is concluded that the main contribution to the conductivity of the network results from direct contacts, and that in their presence tunneling contacts contribute insignificantly to the conductivity. Preparing highly conductive polymer composites is only possible if the number of direct, low‐resistance contacts in the network is sufficiently large and therefore these direct contacts play the key role.     

Copper-matrix molybdenum particle composites made from copper coated molybdenum powder

Copper-matrix molybdenum particle composites containing 33 ~73 wt.% Mo were fabricated by hot pressing copper coated molybdenum powder. For comparison, corresponding composites fabricated by hot pressing a mixture of copper and molybdenum powders were also made. The former method gave composites of lower porosity, higher hardness, higher compressive yield strength, lower coefficient of thermal expansion, lower electrical resistivity and higher thermal conductivity than the latter method. These differences are partly due to the separation of the molybdenum particles by the copper coating in the former case. In contrast, molybdenum particle clustering occurred in the latter case when the Mo content exceeded 53 wt.%.     

Fabrication of CNTs/Cu composite thin films for interconnects application

Carbon nanotubes/copper (CNTs/Cu) composite thin films were fabricated by combined electrophoresis and electroplating techniques. Electrical properties and structure of both CNTs/Cu thin films and the reference pure Cu thin films were investigated after annealing at different temperatures. The sheet electrical resistance of CNTs/Cu films decreases faster than that of pure Cu films with increase of annealing temperature. The grain size of CNTs/Cu film becomes much larger than that of pure Cu film at the same annealing temperature. The peak relative intensity of Cu (1 1 1) plane in CNTs/Cu film was stronger than that of pure Cu film. CNTs/Cu composite thin films, with better electrical properties than that of conventional pure Cu thin films, have been fabricated by electrophoresis and electroplating deposition techniques.     

Composites of Polyacrylonitrile and Multiwalled Carbon Nanotubes Prepared by Gelation/Crystallization from Solution

Composite films of polyacrylonitrile (PAN) and multiwalled carbon nanotubes (MWNTs) have been prepared by gelation/crystallization from solution. The contents of MWNTs were 5–10 wt.‐%, measured against PAN. The electrical and mechanical properties have been studied in comparison with those of the homopolymer PAN films prepared from the same method. Furthermore, stabilization and the carbonization have been carried out by using the drawn PAN–MWNTs as a new precursor to prepare carbon films with a cross‐sectional area much larger than that of a commercial carbon fiber (> 3000 times). The MWNTs within the PAN matrix promote the formation of a condensed aromatic ladder structure during the stabilization process and play an important role in preparing PAN‐based carbon material with high carbon quality and high mechanical properties. When the stabilized composites with 10 wt.‐% MWNTs are carbonized at 1000 °C, the Young's modulus reaches 37.5 GPa, and the electrical conductivity reaches 10² S cm^–1. The carbonized PAN homopolymer does not form an adequately robust bulk film for the mechanical properties to be measured.     

Electrical Conductivity of Thick Films Made from Silver Methylcarbamate Paste

We have explored the electrical conductivity of thick films made from silver methylcarbamate paste using metallic silver as the electrically conductive phase. The paste was composed of 30 wt.% to 90 wt.% organic vehicle and 10 wt.% to 70 wt.% functional phase precursor (silver methylcarbamate). After the paste was sintered, films with thickness of 4.50 μm to 12.70 μm were obtained, in which the elemental percentage of silver varied from about 5 wt.% to above 99 wt.%. Experiments showed that both the electrical conductivity and the elemental percentage were mainly affected by the initial silver content in the paste and the parameters of the sintering process. For given sintering conditions, higher initial silver content led to higher elemental percentage of silver, improving the electrical conductivity of the thick film. The conditions of the sintering process had a significant influence on the evaporation and decomposition rates of the paste components, the elemental percentage of silver, and the microstructure of the thick film. Higher temperatures, longer times, lower heating rates, and more oxygen-rich sintering atmospheres were found to accelerate the evaporation and decomposition and increase the elemental percentage of silver, both of which served to enhance the electrical conductivity. For initial silver contents less than about 10 wt.%, the lowest electrical resistivity of the thick film only reached the order of 10^?4 Ω cm, irrespective of the sintering conditions. For contents between 10 wt.% and 25 wt.%, it was possible to attain lowest resistivity values on the order of 10^?5 Ω cm. Above 25 wt.%, the lowest resistivity could reach 10^?6 Ω cm, comparable to that of bulk silver.