Carbon Nanotube Network Structure Research Articles

High compaction and physical graphitization of CNT bundles and network via extreme-load compression using laser-induced shockwave

The physical properties of carbon nanotube (CNT) networks, which are one-dimensional assemblies of CNTs, are still far short of the theoretical limits of individual CNTs. These lowered physical properties of CNT networks are mainly due to their high porosity and relatively weak inter-tube load/electron/phonon transfer efficiency at van der Waals junctions between CNTs and their bundles. We present a simple post-treatment technique utilizing high-intensity laser-induced shockwaves of up to ∼3 GPa that effectively densify CNT bundles and networks and physically transform CNT bundles into flattened multilayered graphene nanoribbons. CNT assemblies were selectively modified without chemical agents, and the network properties could be tuned by adjusting the laser compression intensity. After laser shockwave compaction, the CNT network structure showed two and three times higher specific strength and modulus than the as-prepared CNT networks. Furthermore, the thermal and electrical conductivities of the CNT networks were also amplified by 400–500% after laser shock compression. These enhancements can be explained by the substantial densification of CNT networks and physically activated graphitization leading to increased load/electron/phonon transfer between flattened CNTs and their bundles.

Excellent and effective interfacial transition layer with an organic/inorganic hybrid carbon nanotube network structure for basalt fiber reinforced high-performance thermoplastic composites

Basalt fiber reinforced high-performance thermoplastic (BFRHTP) composites are promising materials for application in military, aerospace, chemical, automobile, and other high-tech industries. However, their mechanical properties are still largely limited by poor interfacial properties because of the smooth, inert, and low-energy surface of BF. In this study, an organic/inorganic hybrid sizing agent was used for BF surface modification to construct an appropriate modulus transition layer for the interface with a combination of soft and rigid phases. Organic poly(ether nitrile) (PEN) and inorganic carboxylic multi-walled carbon nanotubes (MWCNT-COOH) in hybrid sizing agents (PEN/CNT) were respectively used as soft and rigid phases to design the interfacial structure. The tensile strength, flexural strength, interlaminar and interfacial shear strength of the basalt fiber reinforced poly(phthalazinone ether nitrile ketone) composites were increased by 60, 33, 62, and 144%, respectively. This approach provides a simple, green, and promising strategy for enhancing the interfacial properties of BFRHTP composites.

Enhanced thermal conductivity of polyamide nanocomposites involving expanded graphite–carbon nanotube network structure using supercritical CO2

In this study, supercritical carbon dioxide (scCO2) was used to form a network structure of expanded graphite (EG) and multi-walled carbon nanotube (MWCNT) to achieve high thermal conductivity. Continuous processes, such as supercritical drying and rapid expansion of supercritical solutions were applied to pristine graphite and MWCNT. Polyamide 6 (PA6) nanocomposites with scCO2-treated EG and MWCNT were prepared by twin-screw extruder-based melt compounding. In the PA6 nanocomposites, the EG sheets were homogenously dispersed, while the MWCNTs were located between the EG sheets, thereby acting as a bridge for the EG. Subsequently, the 35 wt.% imbedding in PA6 nanocomposite had an effective heat transfer pathway and high thermal conductivity (2.12 W m−1 K−1). It was observed that supercritical fluid processing is a facile and effective strategy to improve the thermal conductivity of polymer nanocomposites.

Improved thermal conductivities of vertically aligned carbon nanotube arrays using three-dimensional carbon nanotube networks

Vertically aligned carbon nanotube (VACNT) arrays are considered promising thermal interface materials (TIM) due to their superior vertical thermal conductivity. However, the weak interaction between adjacent carbon nanotubes (CNT) leads to the change in orientation of the CNT during polymer infiltration. Therefore, the thermal conductivity of a CNT array/polymer composite does not reach the expected value. Simultaneously, the air gap between adjacent CNT hinders the in-plane heat transfer, and both of the above aspects significantly reduce the thermal conductivities of VACNT-based TIM. In this study, we proposed a novel three-dimensional CNT (3DCNT) network structure comprising VACNT crosslinked by randomly-oriented secondary CNT to provide several in-plane phonon paths and maintain the structural stability of the CNT arrays during polymer infiltration. The network structures formed by the secondary CNT were compared for two different growth times: 10 and 20 min. The 3DCNT network that grew for 20 min exhibited a denser network structure compared to the network that grew for 10 min. The vertical thermal conductivity and horizontal thermal conductivity of the 3DCNT20/Polydimethylsiloxane (3DCNT20/P) composite was 544.77% and 56.06% higher than those of the IVACNT/P composites, respectively.

Detecting Carbon Nanotube Orientation with Topological Analysis of Scanning Electron Micrographs.

As the aerospace industry is increasingly demanding stronger, lightweight materials, ultra-strong carbon nanotube (CNT) composites with highly aligned CNT network structures could be the answer. In this work, a novel methodology applying topological data analysis (TDA) to scanning electron microscope (SEM) images was developed to detect CNT orientation. The CNT bundle extensions in certain directions were summarized algebraically and expressed as visible barcodes. The barcodes were then calculated and converted into the total spread function, V(X, θ), from which the alignment fraction and the preferred direction could be determined. For validation purposes, the random CNT sheets were mechanically stretched at various strain ratios ranging from 0 to 40%, and quantitative TDA was conducted based on the SEM images taken at random positions. The results showed high consistency (R2 = 0.972) compared to Herman’s orientation factors derived from polarized Raman spectroscopy and wide-angle X-ray scattering analysis. Additionally, the TDA method presented great robustness with varying SEM acceleration voltages and magnifications, which might alter the scope of alignment detection. With potential applications in nanofiber systems, this study offers a rapid and simple way to quantify CNT alignment, which plays a crucial role in transferring the CNT properties into engineering products.

Reinforcing urea‐formaldehyde based composite foam by formation of tailored chemical/mechanical interlocking structure

AbstractUrea‐formaldehyde (UF) foam is considered to be a potential alternative for commercial polymeric foams due to its intrinsic flame retardancy and inexpensiveness, but it showed high brittleness and low strength, which restricts its wide applications. In this work, glass fiber powder (GF) was selected as the reinforcing filler, and by formation of tailored chemical/mechanical interlocking structure for the composite system, UF foam was highly reinforced. The surface of GF was coated with granular polydopamine (PDA) layer through self‐polymerization of dopamine, and then, carbon nanotubes (CNTs) were further grafted onto GF surface with high grafting ratio via the bridge effect of PDA to construct a network like entanglement structure. The active groups of PDA layer on GF surface generated chemical/hydrogen bonding interactions with UF matrix, while rough CNTs network structure promoted the mechanical interlocking between GF and UF resin. Such multiple interfacial enhancement improved the stress transmission ability of the interface, exhibiting “supporting” on the cell wall and “cracks bridging” effect of GF. Compared with neat UF foam, the composite foam exhibited smaller cell size, narrower cell size distribution, higher cell density, more complete closed cell structure, while compressive strength and modulus of the composite foam increased by 78.7% and 90.08%, respectively. Moreover, the composite foam showed improved thermal stability and excellent flame retardancy with V‐0 rating of UL‐94 tests.

Magnetically aligned CNT/magnetite heterogeneous composite membranes for electromagnetic wave shielding and heat dissipation

The miniaturization and integration of next-generation electronic devices are accompanied by a substantial increase in electromagnetic interference (EMI) and heat generation, which requires light and thin EMI shielding materials. Herein, we attempt to tackle this challenge by designing a heterogeneous membrane using carbon nanotubes (CNTs) and magnetite (Fe3O4) nanorods. The polymer-coated Fe3O4 uniformly adsorbs on the surface of the polyaniline (PANi) coated CNTs, forming a self-supporting composite membrane with vertical CNTs under a magnetic field. Due to the entanglement of the CNTs, the vertical alignment is more effective in the top region of the membrane than in the bottom, resulting in an asymmetric structure that is beneficial to EMI absorption. When electromagnetic waves are incident from the top surface, high-absorption electromagnetic shielding is obtained due to multiple attenuations and absorption-reflection losses. The vertical orientation and heterogeneous CNTs network structure of the membrane also enable stable heat dissipation.

Enhanced thermal conductivity with ultralow filler loading via constructing branch-type heat transfer network

The rapid growth of modern electronic has put forward higher requirements for the design of thermal management materials. The construction of composites with low filler loading and high thermal conductivity has always been a bottleneck in the research field. Herein, the carbonized melamine sponge (MSC) with in-situ growth carbon nanotubes (CNTs) in MSC@CNTs/EP was prepared to achieve the κ⊥ and κ∥ of 0.51 W/(m K) and 0.48 W/(m K) at ultralow filler loading, respectively. This result showed that the expanded network structure of CNTs converted from ZIF-67 on the MSC maximized isotropic heat transfer efficiency through branch-type thermal conductive pathways. The lightweight structure endowed the skeleton with elasticity and ensured the excellent mechanical properties of the composite. The outstanding performance of the as-obtained composites demonstrates a promising prospect of tackling contemporary electronic devices thermal management issues.

Dual‐Responsive Soft Actuators with Integrated Sensing Function Based on 1T‐MoS2 Composite

Developing a multiresponsive and multifunctional soft actuator that can output mechanical deformation is crucial to the fields of soft robotics and wearable devices. Herein, a 2D metallic molybdenum disulfide (MoS2)‐based soft actuator with dual‐response and self‐sensing function is designed and fabricated. By using the outstanding photothermal property of 1T phase MoS2, good electrical property and network structure of carbon nanotubes (CNTs), hygroscopic expansion of paper, and thermal expansion of polyimide (PI), the MoS2‐based actuator can respond to external voltage and light stimulation and produce rapid and large bending deformation. In addition, the actuator can be used as a flexible strain sensor to realize real‐time sensing of bending deformation by using piezoresistive property of the MoS2–CNT composite film. Based on this soft actuator, a flexible mechanical gripper that can manipulate soft objects with irregular shape and intelligent wearable gloves that can automatically close to block the light irradiation are made. Furthermore, combined with the sensing feature of this MoS2‐based actuator, the gripper with integrated sensing function is also developed. These results indicate the great prospect of the MoS2‐based actuator in intelligent soft mechanical devices, robots, and wearable systems.

Electro-thermal and mechanical performance of multi-wall carbon nanotubes buckypapers embedded in fibre reinforced polymer composites for ice protection applications

Several ice protection strategies have been developed to overcome the icing hazards in the aerospace industry. The electro-thermal method is one of the popular approaches to prevent ice accretion and accumulation on aircraft surfaces. Given the increasing requirement of composites on aircraft structures, metal frameworks/fibre-reinforced composites have been developed as a de-icing solution for the new generation aircraft. The present work aimed to fabricate self-heating multi-wall carbon nanotubes based composites for ice protection and to study their electro-thermal and mechanical characteristics. Carbon nanotube buckypapers (CNPs) were prepared and embedded in fibre reinforced polymer composites by two methods: pre-preg and resin impregnation. The influence of the carbon nanotube network structure on the mechanical properties and electrical characteristics of the composites was evaluated. Mechanical tests, three-point flexural test and interlaminar shear strength test demonstrated improved mechanical characteristics of the CNP based composites. De-icing performance of the composites was conducted through a heating test in a climate chamber at −20℃. The results indicated that the CNP-based composite is a promising self-heating material candidate for ice protection systems.

Enhanced thermal stability, toughness, and electrical conductivity of carbon nanotube-reinforced biodegradable poly(lactic acid)/poly(ethylene oxide) blend-based nanocomposites

Carbon nanotube (CNT) was incorporated into the miscible poly(lactic acid)/poly(ethylene oxide) (PLA/PEO) blend to successfully fabricate biodegradable nanocomposites. Scanning electron microscope images revealed the well dispersion of as-received CNT within the blend through the melt-mixing process. Thermogravimetric analysis showed that the CNT significantly improved the thermal stability of the blend (up to 68 °C increase at 3-phr CNT addition compared to the blend at 10 wt% loss) in air. Differential scanning calorimetry data showed the nucleation effect of CNT on the crystallization of individual PLA and PEO; the presence of CNT increased the melting temperature of PLA crystals. Measurement of rheological behavior confirmed the formation of CNT (pseudo-)network structure in the composites. The impact strength of the composite with 3-phr CNT loading was three times higher than that of the blend. The electrical resistivity of the blend reduced by up to nine orders of magnitude at 3-phr CNT loading. The electrical and rheological percolation thresholds were both achieved at 1-phr CNT loading for the nanocomposites.

Enhanced arc erosion resistance of TiB2/Cu composites reinforced with the carbon nanotube network structure

The continuous network structure induced by carbon nanotubes (CNTs) was introduced to TiB2/Cu composites by electroless deposition, slurry dispersion and powder metallurgy to enhance arc erosion resistance. The arc erosion characteristics of the TiB2/Cu-CNT composites at a current ranging from 10 A to 20 A were investigated. The mechanisms of enhanced arc erosion resistance by the CNT network structure were elaborated based on microstructure and physical characteristics as well. The results show that with the introduction of continuous CNT network structure, arc energy was reduced by more than 83%, there were almost no fluctuation of arc energy and the welding force was relatively low at current above 15 A for TiB2/Cu-1.2 vol% CNT composite in comparison with the CNT unreinforced TiB2/Cu composite. The continuous network structure facilitated the cathode arc motion and dispersed the cathode arc, mitigating the concentrated deterioration of arc erosion. Simultaneously, CNTs could float much easily at the surface of molten pool to weaken the Cu splashing. The CNT network structure delayed the formation of the deeper crater on the cathode and the protrusion with a sharper tip on the anode. Furthermore, it could prevent the formation of cracks and fracture of anode protrusion.

Ceramic-Based Composite Membrane with a Porous Network Surface Featuring a Highly Stable Flux for Drinking Water Purification.

Highly efficient drinking water purification is still an important challenge for membrane techniques where high flux, high rejection, and low fouling are highly emphasized. In the present work, a porous network surface with carbon nanotubes (CNTs) was in situ constructed on hierarchically-structured mullite ceramic membranes. Interestingly, such a composite structure was demonstrated to effectively remove bacteria from drinking water with a highly stable long-term flux. After membrane structure characterizations, separation performance, such as flux and rejection, was assessed by the purification of bacteria-contaminated drinking water. The results confirmed that the mullite-CNT composite membrane claimed a complete removal of two model bacteria (100% rejection of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus)), driven by a trans-membrane pressure of 0.1 MPa, where a surface sieving mechanism was dominant. A highly stable long-term flux for the 24 h filtration process was achieved, which can be attributed to the porous membrane surface with a special randomly-oriented CNTs network structure, featuring very high three-dimensional open porosity, allowing water to rapidly transport. The bacteria were only trapped on the CNTs network surface via surface filtration, without pore plugging, endowing the mullite-CNT membrane with unprecedentedly low fouling propensity to keep high flux with long-term operation time.

Simplified Calculation of the Electrical Conductivity of Composites with Carbon Nanotubes

The electrical conductivity of two groups of polymer nanocomposites filled with the same NC7000 carbon nanotubes (CNTs) beyond the percolation threshold is described with the help of simple formulas. Different manufacturing process of the nanocomposites led to different CNT network structures, and, as a consequence, their electrical conductivity, at the same CNT volume, differed by two orders of magnitude. The relation between the electrical conductivity and the volume content of CNTs of the first group of composites (with a higher electrical conductivity) is described assuming that the CNT network structure is close to a statistically homogeneous one. The formula for this case, derived on the basis of a self-consistent model, includes only two parameters: the effective longitudinal electrical conductivity of CNT and the percolation threshold (the critical value of CNT volume content). These parameters were determined from two experimental points of electrical conductivity as a function of the volume fraction of CNTs. The second group of nanocomposites had a pronounced agglomerative structure, which was confirmed by microscopy data. To describe the low electrical conductivity of this group of nanocomposites, a formula based on known models of micromechanics is proposed. Two parameters of this formula were determined from experimental data of the first group, but the other two — of the second group of nanocomposites. A comparison of calculation and experimental relations confirmed the practical expediency of using the approach described.

Two-dimensional plasmons in lateral carbon nanotube network structures and their effect on the terahertz radiation detection

We consider the carrier transport and plasmonic phenomena in the lateral carbon nanotube (CNT) networks forming the device channel with asymmetric electrodes. One electrode is the Ohmic contact to the CNT network and the other contact is the Schottky contact. These structures can serve as detectors of the terahertz (THz) radiation. We develop the device model for collective response of the lateral CNT networks which comprise a mixture of randomly oriented semiconductor CNTs (s-CNTs) and quasi-metal CNTs (m-CNTs). The proposed model includes the concept of the collective two-dimensional (2D) plasmons in relatively dense networks of randomly oriented CNTs (CNT “felt”) and predicts the detector responsivity spectral characteristics exhibiting sharp resonant peaks at the signal frequencies corresponding to the 2D plasmonic resonances. The detection mechanism is the rectification of the ac current due the nonlinearity of the Schottky contact current-voltage characteristics under the conditions of a strong enhancement of the potential drop at this contact associated with the plasmon excitation. The detector responsivity depends on the fractions of the s- and m-CNTs. The burning of the near-contact regions of the m-CNTs or destruction of these CNTs leads to a marked increase in the responsivity in agreement with our experimental data. The resonant THz detectors with sufficiently dense lateral CNT networks can compete and surpass other THz detectors using plasmonic effects at room temperatures.

Toughening modification of polycarbonate/poly(butylene terephthalate) blends achieved by simultaneous addition of elastomer particles and carbon nanotubes

Small quantities of maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MAH) copolymer and carbon nanotubes (CNTs) were introduced into polycarbonate (PC)/poly(butylene terephthalate) (PBT) blends. The results demonstrated that simultaneously adding SEBS-g-MAH and CNTs greatly enhanced the fracture toughness of the samples and the impact strength increased with increasing CNT content. The morphologies, the dispersion of CNTs, the relaxation behaviors and the crystallization behaviors of samples were systematically investigated. SEBS-g-MAH formed the dispersed particles in the system. The particle diameter was decreased in the blend composites. CNTs exhibited homogeneous dispersion in the blend composites and they also formed a percolated network structure at relatively high content. The transesterification between PC and PBT components was suppressed by SEBS-g-MAH, and the crystallization ability of the PBT component was greatly enhanced. The toughening mechanisms were mainly related to the suppressed transesterification, the decreased elastomer particle size, and the formation of a CNT network structure.

Effects of lithium doping on hydrogen storage properties of heat welded random CNT network structures

This paper presents the effects of lithium doping on the hydrogen storage capability of heat welded random carbon nanotube (CNT) network structures having different cross-link densities at room temperature. Cluster based and atom based doping strategies are taken into consideration in the current simulations. Moreover, different doping ratios are used in our calculations to clarify the effect of doping ratio on hydrogen uptake behavior of CNT networks. The network structures are generated by using a cyclic stochastic algorithm and covalently bonded couplings are created by applying the heat welding method via molecular dynamic simulations. Hydrogen storage capacity of the Li-doped CNT networks is investigated using Grand Canonical Monte Carlo (GCMC) simulations. The simulation results show that hydrogen storage capacity is appreciably enhanced with the presence of lithium atoms and increases as the doping ratio increases. Besides, atom based doping method is found to be more efficient in hydrogen uptake than cluster based doping method under the same doping ratio. Furthermore, our results also show that the cross-link density is a critical parameter and hydrogen storage capability of Li-doped CNT network material can be improved with the appropriate choice of cross-link density.

Damage of single-wall carbon nanotube network structure under electric current loading

Damage of single-wall carbon nanotube network structure under electric current loading

The Evolution of Carbon Nanotube Network Structure in Unidirectional Nanocomposites Resolved by Quantitative Electron Tomography.

Carbon nanotube (CNT) reinforced polymers are next-generation, high-performance, multifunctional materials with a wide array of promising applications. The successful introduction of such materials is hampered by the lack of a quantitative understanding of process-structure-property relationships. These relationships can be developed only through the detailed characterization of the nanoscale reinforcement morphology within the embedding medium. Here, we reveal the three-dimensional (3D) nanoscale morphology of high volume fraction (V(f)) aligned CNT/epoxy-matrix nanocomposites using energy-filtered electron tomography. We present an automated phase-identification method for fast, accurate, representative rendering of the CNT spatial arrangement in these low-contrast bimaterial systems. The resulting nanometer-scale visualizations provide quantitative information on the evolution of CNT morphology and dispersion state with increasing V(f), including network structure, CNT alignment, bundling and waviness. The CNTs are observed to exhibit a nonlinear increase in bundling and alignment and a decrease in waviness as a function of increasing V(f). Our findings explain previously observed discrepancies between the modeled and measured trends in bulk mechanical, electrical and thermal properties. The techniques we have developed for morphological quantitation are applicable to many low-contrast material systems.

MoS2 nanolayers grown on carbon nanotubes: an advanced reinforcement for epoxy composites.

In the present study, carbon nanotubes (CNTs) wrapped with MoS2 nanolayers (MoS2-CNTs) were facilely synthesized to obtain advanced hybrids. The structure of the MoS2-CNT hybrids was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements. Subsequently, the MoS2-CNT hybrids were incorporated into EP for reducing fire hazards. Compared with pristine CNTs, MoS2-CNT hybrids showed good dispersion in EP matrix and no obvious aggregation of CNTs was observed. The obtained nanocomposites exhibited significant improvements in thermal properties, flame retardancy and mechanical properties, compared with those of neat EP and composites with a single CNT or MoS2. With the incorporation of 2.0 wt % of MoS2-CNT hybrids, the char residues and glass transition temperature (Tg) of the EP composite was significantly increased. Also, the addition of MoS2-CNT hybrids awarded excellent fire resistance to the EP matrix, which was evidenced by the significantly reduced peak heat release rate and total heat release. Moreover, the amount of organic volatiles from EP decomposition was obviously decreased, and the formation of toxic CO was effectively suppressed, implying the toxicity of the volatiles was reduced and smoke production was obviously suppressed. The dramatically reduced fire hazards were generally ascribed to the synergistic effect of MoS2 and CNTs, containing good dispersion of MoS2-CNT hybrids, catalytic char function of MoS2 nanolayers, and physical barrier effects of MoS2 nanolayers and CNT network structure.