Enhanced conductivity behavior of polydimethylsiloxane (PDMS) hybrid composites containing exfoliated graphite nanoplatelets and carbon nanotubes

Polydimethylsiloxane (PDMS) hybrid composites consisting of exfoliated graphite nanoplatelets (xGnPs) and multiwalled carbon nanotubes functionalized with hydroxyl groups (MWCNTs-OH) were fabricated, and the effects of the xGnP/MWCNT-OH ratio on the thermal, electrical, and mechanical properties of polydimethylsiloxane (PDMS) hybrid composites were investigated. With the total filler content fixed at 4 wt%, a hybrid composite consisting of 75% × GnP/25% MWCNT-OH showed the highest thermal conductivity (0.392 W/m K) and electrical conductivity (1.24 × 10⁻³ S/m), which significantly exceeded the values shown by either of the respective single filler composites. The increased thermal and electrical conductivity found when both fillers are used in combination is attributed to the synergistic effect between the fillers that forms an interconnected hybrid network. In contrast, the various different combinations of the fillers only showed a modest effect on the mechanical behavior, thermal stability, and thermal expansion of the PDMS composite.     

Microstructure and mechanical performance of modified mortar using hemp fibres and carbon nanotubes

Mechanical performance of modified mortar using hemp fibres is studied following various processing conditions. Hemp fibres combined with carbon nanotubes (CNT) are introduced in mortar and their effect is studied as function of curing time. The cement phase is replaced by different percentages of dry or wet hemp fibres ranging from 1.1 wt% up to 3.1 wt% whereas carbon nanotubes are dispersed in the aqueous solution. Our experimental results show that compressive and flexural strengths of wet fibres modified mortar are higher than those for dry hemp-mortar material. The achieved optimal percentage of wet hemp fibres is 2.1 wt% allowing a flexural strength higher than that of reference mortar. The addition of an optimal CNT concentration (0.01 wt%) combined with wet hemp has a reinforcing effect which turns to be related to an improvement of compressive and flexural strengths by 10% and 24%, respectively, in comparison with reference condition.     

Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding

In this study, a new method is introduced for fabricating carbon nanotube (CNT) paper, in which the solvent is sprayed on the CNT sheet while it is wound on a rotating mandrel. As the solvent evaporated, the capillary force pulls CNT closer together, resulting in a CNT paper with a high degree of alignment and a high packing density. Three batches of multi-walled CNTs with different wall thicknesses, tube diameters and lengths are utilized for synthesizing highly oriented CNT papers. It is found that CNTs with smallest diameter of 8 nm form strongest CNT paper with a tensile strength of 563 MPa and a tensile modulus of 15 GPa, while that made with CNTs of 10 nm diameter shows the highest electrical conductivity of 5.5 × 10⁴ S/m.     

Morphology and thermal conductivity of polyacrylate composites containing aluminum/multi-walled carbon nanotubes

Polyacrylate composites with various fillers such as multi-walled carbon nanotube (CNT), aluminum flake (Al-flake), aluminum powders and Al–CNT were prepared by a ball milling. The thermal decomposition temperature increased by as much as 64 °C for polyacrylate/Al-flake 70 wt% composite compared to polyacrylate. The thermal conductivity of polyacrylate/Al–CNT composites increased from 0.50 to 1.67 W/m K as the Al–CNT content increases from 50 to 80 wt%. The thermal conductivity of the composite sheet increases with the sheet thickness. At the given filler concentration (90 wt%), the composite filled with aluminum powder of 13 μm has a higher thermal conductivity than the one filled 3 μm powder, and the composite filled with mixture of two powders showed a synergistic effect on the thermal conductivity. The morphology indicates that the dispersion of CNT in the polyacrylate/Al-flake + CNT composite is not perfect, and agglomeration of CNTs was observed.     

Advanced multifunctional properties of aligned carbon nanotube-epoxy thin film composites

Carbon nanotube (CNT)/epoxy composite films were successfully developed by a combination of layer-by-layer and vacuum-assisted resin transfer molding methods using directly chemical vapor deposition (CVD)-spun CNT plies. CNT fractions in the composite films were found to be dramatically enhanced as the number of CNT plies increased. The as-prepared CNT/epoxy composite films with 24.4 wt.% CNTs exhibited ~ 10 and ~ 5 times enhancements in their strength and Young's modulus, respectively, and high toughness of up to 6.39 × 10³ kJ/m³. Electrical conductivity reached 252.8 S/cm for the 20-ply CNT/epoxy films, which was 20 times higher over those of the CNT/epoxy composites obtained by conventional dispersion methods. This work proposed a route to fabricate high-CNT-fraction CNT/epoxy composites on a large scale. The high toughness of these CNT/epoxy composite films also makes them promising candidates as protective materials.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.     

Heterogeneously structured conductive carbon fiber composites by using multi-scale silver particles

This paper reports a new approach to enhance the through-thickness thermal conductivity of laminated carbon fabric reinforced composites by using nanoscale and microscale silver particles in combination to create heterogeneously structured continuous through-thickness thermal conducting paths. High conductivity of 6.62 W/(m K) with a 5.1 v% silver volume fraction can be achieved by incorporating these nanoscale and microscale silver particles in EWC-300X/Epon862 composite. Silver flakes were distributed within the inter-tow area, while nanoscale silver particles penetrated into the fiber tows. The combination of different sizes of silver fillers is able to effectively form continuous through-thickness conduction paths penetrating fiber tows and bridging the large inter-tow resin rich areas. Positive hybrid effects to thermal conductivity were found in IM7/EWC300X/sliver particle hybrid composites. In addition, microscale fillers in resin rich areas showed less impact on tensile performance than nanoscale particles applied directly on fiber surface.     

Synergistic effect of hybrid graphene nanoplatelet and multi-walled carbon nanotube fillers on the thermal conductivity of polymer composites and theoretical modeling of the synergistic effect

We found that the thermal conductivity of polymer composites was synergistically improved by the simultaneous incorporation of graphene nanoplatelet (GNP) and multi-walled carbon nanotube (MWCNT) fillers into the polycarbonate matrix. The bulk thermal conductivity of composites with 20 wt% GNP filler was found to reach a maximum value of 1.13 W/m K and this thermal conductivity was synergistically enhanced to reach a maximum value of 1.39 W/m K as the relative proportion of MWCNT content was increased but the relative proportion of GNP content was decreased. The synergistic effect was theoretically estimated based on a modified micromechanics model where the different shapes of the nanofillers in the composite system could be taken into account. The waviness of the incorporated GNP and MWCNT fillers was found to be one of the most important physical factors determining the thermal conductivity of the composites and must be taken into consideration in theoretical calculations.     

Electrically conductive carbon nanotube/polypropylene nanocomposite with improved mechanical properties

Conductive polymer nanocomposites based on carbon nanotubes (CNTs) have wide range of applications in the electronics and energy sectors. For many of these applications, such as the electromagnetic interference (EMI) shielding, high nanofiller loading is typically needed to achieve the desired properties. The high nanofiller concentration deteriorates the composite's tensile strength due to the increase in nanofiller aggregation. In this work, highly conductive CNT/polypropylene (PP) nanocomposite with improved tensile strength was prepared by melt mixing. The effects of CNT content on the processing behavior, microstructure, mechanical and electrical properties of the nanocomposite were investigated. Scanning electron microscopy was used to investigate the composite microstructure. Good level of CNT dispersion with remarkable adhesion at the CNT/PP interface was observed. Based on a theoretical model, the interfacial strength was estimated to be in the range of 36–58 MPa. As a result of this microstructure, significant enhancement in ultimate tensile strength was reported with the increase of CNT content. The tensile strength of the 20 wt.% CNT/PP nanocomposite was 80% higher than that of the unfilled PP. Moreover, and due to the good dispersion of CNT particles, an electrical percolation threshold concentration of 0.93 wt.% (0.5 vol.%) was obtained.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

Effect of different carbon nano-fillers on rheological properties and lap shear strength of epoxy adhesive joints

In this work, the rheological properties, thermal stability and the lap shear strength of epoxy adhesive joints reinforced with different carbon nano-fillers such as multi-walled carbon nanotubes (CNT), graphene nanoplatelets (GNP) and single-walled carbon nanohorns (CNH) have been studied. The nano-fillers were dispersed homogeneously using Brabender® Plasti-Corder®. The epoxy pre-polymer with and without the nano-fillers exhibited shear thinning behavior. The nano-filler epoxy mixtures exhibited a viscoplastic behavior which was analyzed using Casson’s model. Thermo-gravimetric analysis indicated an increase in the thermal stability of the epoxy with the addition of carbon nano-fillers. Carbon nano-fillers resulted in increased lap shear strength having high Weibull modulus. The joint strength increased by 53%, 49% and 46% with the addition of 1 wt.% CNT, 0.5 wt.% GNP and 0.5 wt.% CNH, respectively. The strength of the joints having high filler content (>1 wt.%) was limited by mixed mode type of failure.     

Fabrication and characterization of 3-D Cf/ZrC composites by low-temperature liquid metal infiltration

Three-dimensional braided carbon fiber-reinforced ZrC matrix composite, 3-D C_f/ZrC, were prepared by liquid metal infiltration process at 1200 °C using a Zr₂Cu intermetallic compound as infiltrator. The microstructure and properties of the composites were investigated. The results indicated that ZrC with a yield of 35.2 ± 1.8 vol.% was certified as the major phase of the composites. The formation of ZrC was controlled by a solution-precipitation mechanism. The obtained composites exhibited good mechanical properties, with a flexural strength of 293.0 ± 12.1 MPa, a flexural modulus of 82.7 ± 6.4 GPa and a fracture toughness of 9.8 ± 0.9 MPa m^1/2. The mass and linear ablation rates of the composites exposed to oxyacetylene torch were 0.0013 ± 0.0005 g s⁻¹ and −0.0009 ± 0.0003 mm s⁻¹, respectively. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu contributed mainly to the excellent ablation resistance.     

Properties of polypropylene composites containing aluminum/multi-walled carbon nanotubes

Polypropylene/aluminum–multi-walled carbon nanotube (PP/Al–CNT) composites were prepared by a twin-screw extruder. The morphology indicates that the CNTs are well embedded or implanted within Al-flakes rather than attached on the surface. During preparation of composites, the CNTs came apart from Al–CNT so that free CNTs as well as Al–CNT were observed in PP/Al–CNT composite. The crystallization temperatures of PP/CNT and PP/Al–CNT composites were increased from 111 °C for PP to 127 °C for the composites. The decomposition temperature increased by 55 °C for PP/CNT composite and 75 °C for PP/Al–CNT composite. The PP/Al–CNT composite showed higher thermal conductivity than PP/CNT and PP/Al-flake composites with increasing filler content. PP/Al–CNT composites showed the viscosity values between PP/CNT and PP/Al-flake composites. PP/Al–CNT composite showed higher tensile modulus and lower tensile strength with increasing filler content compared to PP/CNT and PP/Al-flake composites.     

Synthesis and electrochemical performance of a simple and low-cost sulfur/porous carbon composite cathode for rechargeable lithium sulfur battery

The sugar and phenolic resin were used as source materials to prepare porous carbons labeled as PC1 and PC2 respectively, which were activated by chemical methods with CaCO₃ as active agent. Sulfur/porous carbon composites were synthesized by thermally treating a mixture of sublimed sulfur and porous carbon. The morphology, structure, and electrochemical performance of the composite were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, and a variety of electrochemical techniques. The electrochemical measurements show that the SPC2 electrode presents a more favorable electrochemical kinetics than the SPC1 electrode. In comparison with SPC1, it is shown that the rate of Li⁺ diffusion with SPC2 is significantly higher and the charge transfer resistance is much lower. The PC2 with high surface area (735.2 m² g⁻¹) and large pore volume (1.56 cm³ g⁻¹) not only increases the electronic conductivity of composites, but also facilitates transfer of the Li ion in the composite electrode.     

Microstructure and mechanical properties of an Al–TiC metal matrix composite obtained by reactive synthesis

A metal matrix composite has been obtained by a novel synthesis route, reacting Al₃Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%.     

Dynamic fracture of carbon nanotube/epoxy composites under high strain-rate loading

We investigate dynamic fracture of three types of multiwalled carbon nanotube (MWCNT)/epoxy composites and neat epoxy under high strain-rate loading (${10}^5''–''{10}^6$ s⁻¹). The composites include randomly dispersed, 1 wt%, functionalized and pristine CNT/epoxy composites, as well as laminated, ∼50 wt% CNT buckypaper/epoxy composites. The pristine and functionalized CNT composites demonstrate spall strength and fracture toughness slightly higher and lower than that of neat epoxy, respectively, and the spall strength of laminated CNT buckypaper/epoxy composites is considerably lower; both types of CNTs reduce the extent of damage. Pullout, sliding and immediate fracture modes are observed; the fracture mechanisms depend on the CNT–epoxy interface strength and fiber strength, and other microstructures such as the interface between CNT laminates. Compared to the functionalized CNT composites, weaker CNT–epoxy interface strength and higher fiber strength lead to a higher probability of sliding fracture and higher tensile strength in the pristine CNT composites at high strain rates. On the contrary, sliding fracture is more pronounced in the functionalized CNT composites under quasistatic loading, a manifestation of a loading-rate effect on fracture modes. Despite their helpful sliding fracture mode and large CNT content, the weak laminate–laminate interfaces play a detrimental role in fracture of the laminated CNT buckypaper/epoxy composites. Regardless of materials, increasing strain rates leads to pronounced rise in tensile strength and fracture toughness.     

Scalable continuous growth of carbon nanotubes on moving fiber substrates

A process is developed to demonstrate the large scale production capability for creating carbon nanotube-based hybrid composite materials. A novel open-ended growth chamber and reel-to-reel scalable processing system is presented for the growth of carbon nanotubes (CNTs) directly on fiber substrates. This work focuses on the growth of the carbon nanotubes, characterization of the achievable CNT morphologies and measurements of the growth dynamics. This work demonstrates a continuous growth process capable of controlled CNT production on moving glass fiber substrates at throughput rates up to 40.7 mm s^?1 via maximum CNT growth rates of over 1.0 μm s^?1.     

Amperometric biosensor based on carbon nanotubes coated with polyaniline/dendrimer-encapsulated Pt nanoparticles for glucose detection

A novel amperometric glucose biosensor based on the nanocomposites of multi-wall carbon nanotubes (CNT) coated with polyaniline (PANI) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) is prepared. CNT coated with protonated PANI is in situ synthesized and Pt-DENs is absorbed on PANI/CNT composite surface by self-assembly method. Then Glucose oxidase (GOx) is crosslink-immobilizated onto Pt-DENs/PANI/CNT composite film. The results show that the fabricated GOx/Pt-DENs/PANI/CNT electrode exhibits excellent response performance to glucose, such as low detection limit (0.5 µM), wide linear range (1 µM–12 mM), short response time (about 5 s), high sensitivity (42.0 µA mM^? 1 cm^? 2) and stability (83% remains after 3 weeks).     

Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.