Conductive Multi-walled Carbon Nanotubes Research Articles

Enhanced dielectric performance of PDMS-based three-phase percolative nanocomposite films incorporating a high dielectric constant ceramic and conductive multi-walled carbon nanotubes

Enhanced dielectric constant of PDMS incorporating chain-ball structured CCTO@MWCNT nanoparticles.

Ultralow-Threshold and Lightweight Biodegradable Porous PLA/MWCNT with Segregated Conductive Networks for High-Performance Thermal Insulation and Electromagnetic Interference Shielding Applications.

Lightweight, biodegradable, thermally insulating, and electrically conductive materials play a vital role in achieving the sustainable development of our society. The fabrication of such multifunctional materials is currently very challenging. Here, we report a general, facile, and eco-friendly way for the large-scale fabrication of ultralow-threshold and biodegradable porous polylactic acid (PLA)/multiwalled carbon nanotube (MWCNT) for high-performance thermal insulation and electromagnetic interference (EMI) shielding applications. Thanks to the unique structure of the microporous PLA matrix embedded by conductive 3D MWCNT networks, the lightweight porous PLA/MWCNT with a density of 0.045 g/cm3 possesses a percolation threshold of 0.00094 vol %, which, to our knowledge, is the minimum value reported so far. Furthermore, the material exhibits excellent thermal insulation performance with a thermal conductivity of 27.5 mW·m-1·K-1, which is much lower than the best value of common thermal insulation materials. Moreover, it also shows outstanding EMI shielding performance characterized by its high shielding effectiveness (SE) values and absorption-dominated shielding feature. More importantly, its specific EMI SE is as high as 1010 dB·cm3·g-1, which is superior to those of other shielding materials reported so far. Thus, this novel multifunctional material and its general fabrication methodology provide a promising way to meet the growing demand for high-performance multifunctional materials in sustainable development.

Improved dielectric behaviour of graphene oxide-multiwalled carbon nanotube nanocomposite

We have prepared graphene oxide (GO)-multiwalled carbon nanotube (MWCNT) composite film through vacuum filtration method. In this work, we carried out the dielectric behaviour of GO-MWCNT composite film in the frequency range of 100 Hz to 1 MHz and temperature range of 30–200 °C. The GO-MWCNT composite film showed significantly higher dielectric constant as 6021 than the GO (5031) which was even very high compared to conventional dielectric materials. The enhancement of dielectric constant is attributed to the strong interaction between sp2 MWCNT fillers and sp3 GO matrix as well as the formation of microcapacitors by highly conductive MWCNT segregated by GO sheets. Furthermore, we found interesting transition between semiconductor to conductor was attained at 165 °C. It is suggested that the temperature dependent transition of electrical properties of GO-MWCNT composite film is closely related with the ion mobility, removal of water molecules and reduction of GO in the composite. The effect of interfacial polarization and relaxation process were studied. The redox peak current has increased significantly for the GO-MWCNT composite electrode than the GO and MWCNT where the highly conducting MWCNT provide the necessary conduction pathways on the electrode surface. These flexible, high dielectric constant nanocomposites are potential flexible dielectric materials for use in high frequency capacitors and in electronic devices.

Thermal conductivity, morphology and mechanical properties for thermally reduced graphite oxide-filled ethylene vinylacetate copolymers

Systematic variation of copolymers (Poly (ethylene-covinylacetate)) composition provide an opportunity to change matrix polarities and thus explore their effects on the polymer/filler interactions and composite properties. The main objective of this work is to study the effect of vinyl acetate (VA) content on the extent of exfoliation and dispersion of thermally reduced graphite oxide (TrGO), as well as its impact on the thermal conductivity and mechanical properties of the resultant composites. The use of ethylene vinyl-acetate (EVA) copolymers of different (0–40 wt%) vinyl acetate content with similar melt viscosities allowed us to keep the processing conditions constant and quantitatively compare the thermal conductivity and mechanical properties of composites with different matrix polarities. Composites with conductive graphite (GT) and multiwalled carbon nanotubes (MWCNT) were also prepared and examined for comparison. Melt dispersion of TrGO in EVA copolymers was quantified using a range of characterization techniques: transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray scattering measurements. Electron microscopy and X-ray diffraction revealed highly exfoliated morphology of TrGO throughout the entire matrix, while GT remained multi-layer even after melt processing. Nanocomposites reinforced with TrGO showed significantly improved thermal conductivities and mechanical properties combined with low rheological percolation thresholds comparable to those achieved using MWCNT and GT. We propose a formalism to assess the thermal conductivity and mechanical properties of graphene nanocomposites based upon the interfacial excess energies of EVA copolymers.

Synthesis of core-shell covalent organic frameworks/multi-walled carbon nanotubes nanocomposite and application in lithium-sulfur batteries

A novel core-shell covalent organic frameworks/multi-walled carbon nanotubes nanocomposite (TpPa-COF@MWCNTs) was prepared via growing the porous TpPa-COF on conductive multi-walled carbon nanotubes (MWCNTs) under a facile solvothermal condition. The resultant TpPa-COF@MWCNTs showed a high initial discharge capacity of 1242.2 mAh g−1 at current density 0.05 C and an outstanding capacity retaining ability (an ultralow capacity fade rate of 0.099% per cycle for 450 cycles with coulombic efficiency over 99% at 0.5 C), excellent cycling stability and long cycle life for lithium-sulfur batteries.

A rationally designed polysulfide-trapping interface on the polymeric separator for high-energy Li–S batteries

A coating layer consisting of a layer of graphene oxide (GO) inserted in between two layers of multi-walled carbon nanotubes (MWCNT) forms a multifunctional polysulfide-trapping triple-interface on the polymeric separator for lithium–sulfur (Li–S) batteries. The top and bottom highly conductive MWCNT interfaces are able to physically inhibit polysulfide diffusion and effectively reutilize the trapped active material during cycling. The inserted ultrathin GO layer with negatively charged carboxyl groups, on the other hand, electrostatically repels the migrating polysulfide anions. The stacked GO sheets also extensively prolong the migration routes of the polysulfides. Additionally, the “buffer zones” interspersed within the triple-interface accommodate the migrating polysulfides. Thus, the sandwiched separators enable Li–S cells with a high-sulfur-loading (10 mg cm−2), high areal capacity (10.9 mA h cm−2), and stable cycling ability even though the coating layer is ultra-thin (∼17 μm) and light-weight (∼0.23 mg cm−2).

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.

Mussel-Inspired Dopamine and Carbon Nanotube Leading to a Biocompatible Self-Rolling Conductive Hydrogel Film.

We report a novel self-rolling, conductive, and biocompatible multiwall carbon nanotube (MWCNT)-dopamine-polyethylene glycol (PEG) hydrogel film. The gel can self-fold into a thin tube when it is transferred from a glass slide to an aqueous environment, regardless of the concentrations of the MWCNT. The film presents a highly organized pattern, which results from the self-assembly of hydrophilic dopamine and hydrophobic carbon nanotubes. By exploring the biomedical potential, we found that MWCNT-included rolled film is nontoxic and can promote cell growth. For further functional verification by qPCR (quantitative polymerase chain reaction), bone marrow derived mesenchymal cells present higher levels of osteogenic differentiations in response to a higher concentration of CNTs. The results suggest that the self-rolling, conductive CNT-dopamine-PEG hydrogel could have multiple potentials, including biomedical usage and as a conductive biosensor.

A Clean and Facile Synthesis Strategy of MoS2 Nanosheets Grown on Multi-Wall CNTs for Enhanced Hydrogen Evolution Reaction Performance

Unique hybrid nanostructure, which consists of multi-wall carbon nanotube (MWCNT) stems and MoS2 nanosheet (NS) leaves, are prepared by a hydrothermal method. The fabricated material can be potentially used as an electrocatalyst for the hydrogen evolution reaction (HER). To our knowledge, as the reaction medium, water is firstly utilized to the synthesis of the 1T phase MoS2 NSs which uniformly grow on the carbon-based materials. As a result, a nanohybrid catalyst with excellent HER electrocatalytic properties, which included an onset potential of as low as 50 mV, a Tafel slope of 43 mV dec−1, and remarkable cycling stability, is produced. The observed outstanding catalytic performance can be attributed to the uniform distribution of the metallic 1T phase of the MoS2 NSs, which are characterized by the presence of multiple active edges as well as the effective electron transport route provided by the conductive MWCNT substrate. This work demonstrates the high potential of the synthesized HER catalyst and proposes a novel, efficient, environmentally friendly, and inexpensive method for its fabrication.

Constructing conductive multi-walled carbon nanotubes network inside hexagonal boron nitride network in polymer composites for significantly improved dielectric property and thermal conductivity

With the rapid development of high performance capacitors for energy storage, materials with both giant dielectric constant and low dielectric loss are urgently needed. Adding conductive filler could largely enhance the dielectric constant of polymer matrix but also greatly increase the dielectric loss. In this study, we provide a new strategy by using hybrid fillers to construct a segregated double network, where conductive multi-walled carbon nanotubes (MWCNT) network is wrapped by insulating hexagonal boron nitride (h-BN) network to destroy the continuity of embedded MWCNT network. To do this, pre-fabricated micron-sized PS/MWCNT particles were completely coated by h-BN through π-π interaction. As a result, the MWCNT network inside h-BN network provides good conductivity while h-BN network provides the isolation effect but do not increase the distance between two adjacent MWCNT agglomerations, which together can maintain the high dielectric constant and decrease the dielectric loss. Therefore, a high dielectric constant of 123 is achieved while a relatively low dielectric loss is also kept as 0.36. More importantly, this special structure of segregated double network also leads to obviously enhanced thermal conductivity which is 2.23-fold of that of the composites with randomly dispersed hybrid fillers. This high thermal conductivity is ascribed to the high synergistic efficiency between segregated h-BN network and dense MWCNT network. We believe that these good comprehensive performances promise this structure to offer a unique and effective way to prepare high-performance dielectric materials with not only high dielectric constant and low dielectric loss, but also good capability of heat dissipation.

Ultrarapid sonochemical synthesis of enzyme-incorporated copper nanoflowers and their application to mediatorless glucose biofuel cell

We have developed a mediatorless glucose biofuel cell based on hybrid nanoflowers incorporating enzymes including glucose oxidase (GOx), laccase, or catalase with copper phosphate, which were further mixed and compressed with conductive multi-walled carbon nanotube (CNT). The nanoflowers were simply synthesized within 5min at room temperature using sonication method but yielded greatly improved stability as well as highly retained activity by the proper incorporation of enzyme molecules inside the flower-like structure. With glucose as biofuel, GOx and laccase nanoflowers were applied to form enzyme anode and cathode, respectively, and catalase nanoflowers were additionally employed to catalyze the decomposition of hydrogen peroxide, which may be deleterious for GOx, into oxygen and water. Using the enzyme nanoflowers-based biofuel cell system without any involved mediator, a high power density up to 200μWcm−2 were obtained, which was approximately 80% to that from the biofuel cell system prepared with the corresponding free enzymes. Importantly, the enzyme nanoflowers-based biofuel cell maintained their initial power density over 90% during storage for two months at 4°C, while most of the glucose biofuel cells in the literature present meaningful stability only in the range of one or two weeks. Based on this result, we expect that this simple but efficient strategy to prepare highly stable glucose biofuel cell using the rapidly-synthesized enzyme-inorganic hybrid nanoflowers can be readily extended to diverse applications in medical and environmental chemistry.

Probe Sensor Using Nanostructured Multi-Walled Carbon Nanotube Yarn for Selective and Sensitive Detection of Dopamine.

The demands for electrochemical sensor materials with high strength and durability in physiological conditions continue to grow and novel approaches are being enabled by the advent of new electromaterials and novel fabrication technologies. Herein, we demonstrate a probe-style electrochemical sensor using highly flexible and conductive multi-walled carbon nanotubes (MWNT) yarns. The MWNT yarn-based sensors can be fabricated onto micro Pt-wire with a controlled diameter varying from 100 to 300 µm, and then further modified with Nafion via a dip-coating approach. The fabricated micro-sized sensors were characterized by electron microscopy, Raman, FTIR, electrical, and electrochemical measurements. For the first time, the MWNT/Nafion yarn-based probe sensors have been assembled and assessed for high-performance dopamine sensing, showing a significant improvement in both sensitivity and selectivity in dopamine detection in presence of ascorbic acid and uric acid. It offers the potential to be further developed as implantable probe sensors.

Electrical double layer ion transport with cell voltage-pulse potential coupling circuit for separating dilute lead ions from wastewater

Continuous separation of dilute Pb2+ from wastewater was demonstrated by using a membrane containing highly conductive multiwalled carbon nanotubes (MWCNTs) in an electrochemically switched ion permselective (ESIP) process, with a cell voltage–pulse potential coupling circuit. The membrane with high selectivity for Pb2+ separation was fabricated by pressure filtering MWCNT solution through a polytetrafluoroethylene (PTFE) film. In the separation system, the directional uptake and release of Pb2+ were realized by modulating the positive and negative charge densities on the electrical double layer (EDL) of the membrane, together with the application of an external electric field. The effects of the operating parameters on the flux of Pb2+ and membrane permselectivity were investigated. The highest Pb2+ flux across the membrane occurred with considerable permselectivity at a cell voltage of 0.8V, a pulse width of 40s, and a membrane MWCNT content of 30mg. The system reduced the Pb2+ concentration in the solution from 30 to 0.36ppm with a current efficiency of 46.1%. Such a novel EDL membrane-based ESIP system could be used for wastewater treatment.

Designing, modeling and manufacturing of lightweight carbon nanotubes/polymer composite nanofibers for electromagnetic interference shielding application

Lightweight conductive multi-walled carbon nanotubes (MWCNTs)/polyvinyl alcohol (PVA) composite nanofibers were prepared by electrospinning process with an aim to investigate the potential of such nanofibers as an effective electromagnetic interference (EMI) shielding material. The influence of MWCNTs content, thickness, and frequency on the EMI shielding of conductive MWCNTs/PVA composite nanofiber has been investigated. These experiments were designed by response surface methodology (RSM) and quadratic model was used to calculation of the responses. The predicted responses were in good agreement with the experimental results according to RSM model. The RSM analysis confirmed that MWCNTs content and thickness were the main significant variables affecting the absorption shielding effectiveness. Moreover, the sample thickness has no significant influence on the reflection shielding effectiveness. The RSM model predicted the 31.5 dB value of the highest absorption with low reflection (8.8 dB) at conditions of 7.7 wt% MWCNTs content, 3 mm of the sample thickness, and 12 GHz of incident EM wave frequency. The obtained RSM results confirmed that the selected RSM model presented suitable performance for evaluating the involved variables and prediction of EMI shielding parameters.

A flexible nanostructured paper of MnO NPs@MWCNTs/r-GO multilayer sandwich composite for high-performance lithium-ion batteries

Designing a high capacity and long cycle life MnO-based composite material for lithium ion batteries (LIBs) is still a great challenge because of the intrinsically low electrical conductivity and dramatic volume variations during lithiation/delithiation. In this paper, the MnO nanoparticles (MnO NPs) are recombined with multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (r-GO) to rationally construct a novel MnO NPs@MWCNTs/r-GO multilayer sandwich structure via electrostatic interaction self-assembly and vacuum filtration processes. As a result, the MnO NPs are closely attracted in the conductive MWCNTs network, and the MWCNTs adsorbed on the surface of MnO NPs can be served as a soft and flexible carbon coating layer to self-adapt the huge volume expansion. For another, the r-GO between two MnO NPs@MWCNTs layers is the cause to form a free-standing paper, enhancing the transverse conductivity of the whole electrode simultaneously. These features will contribute to achieve excellent cycling stability and improved rate capability.

Multidimensional Thin Film Hybrid Electrodes with MoS2 Multilayer for Electrocatalytic Hydrogen Evolution Reaction.

Hybrid electrodes are widely used in various energy storage and conversion devices. However, conventional fabrication methods like simple mixing allow only limited control over the internal electrode structure, and it is often difficult to elucidate the structure-property relationship among the electrode components. Taking advantage of the versatile layer-by-layer (LbL) assembly method, herein we report the preparation of electrocatalytic thin film electrodes for hydrogen evolution reaction (HER), highlighting the importance of nanoscale composition in multidimensional hybrid electrodes. The fabrication utilized the electrostatic interaction between the two components: catalytically active two-dimensional MoS2 nanosheets and conductive, one-dimensional multiwalled carbon nanotube (MWNT) support. The electrocatalytic activity was found to be highly tunable by adjusting the thickness of the electrode, suggesting structural dependence of electron transfer and mass transport between the electrolyte and electrode, which is otherwise difficult to investigate in electrodes fabricated by simple conventional methods. Furthermore, the detailed mechanism of HER on the hybrid electrode was also investigated, revealing the fine balance between the catalytic activity of MoS2 and conductivity of MWNT. We anticipate that this unique approach will offer new insights into the nanoscale control of electrode architecture and the development of novel electroactive catalysts.

Facile preparation of rapidly electro-active shape memory thermoplastic polyurethane/polylactide blends via phase morphology control and incorporation of conductive fillers

Rapidly electro-active thermoplastic polyurethane (TPU)/polylactide (PLA) shape memory polymer (SMP) blends via phase morphology control and incorporation of conductive multi-walled carbon nanotubes (MWCNTs) were achieved by simple and efficient melt blending in this work. Binary TPU/PLA blends with various composition ratios were firstly prepared, and the effect of phase morphology on shape memory behavior was studied. The optimum shape memory behavior was observed for TPU50/PLA50 blends with co-continuous phase morphology. Then a small number of MWCNTs were selectively incorporated into TPU phase of TPU50/PLA50 and TPU60/PLA40 blends to realize electro-active shape memory effect. The formation of double percolation network imparted TPU/PLA/MWCNT conductive polymer composites with high electrical conductivities in low percolation thresholds, thus realized rapidly electro-active shape memory behaviors. Additionally, the mechanical properties of TPU/PLA blends (50/50, 60/40) can be enhanced by the addition of MWCNTs even at high temperature. Therefore, our work provides a simple way to fabricate polymer blends with rapid electro-active shape memory performances, good mechanical properties as well as good processing capability but low cost.

Processing, characterisation and electromechanical behaviour of elastomeric multiwall carbon nanotubes-poly (glycerol sebacate) nanocomposites for piezoresistive sensors applications

Highly stretchable elastomeric multiwall carbon nanotubes – poly (glycerol sebacate) (MWCNT-PGS) nanocomposites were prepared by mixing conductive multiwall carbon nanotubes (MWCNTs) with PGS prepolymer and curing at 120 °C. The incorporation of conductive filler increases the matrix crosslinking density and mechanical stiffness without loss of the flexibility and elasticity of the polymeric network with low mechanical hysteresis behaviour. The percolation threshold for the electrical conductivity was found to be ∼1 wt% of MWCNTs. The piezoresistive behaviour of the prepared samples shows a negative gauge factor (GF) between −0.5 and −0.8 under uniaxial tensile stress, probably due to geometrical factors, whilst under 3-point bending the calculated GF values were positive and a maximum GF = 42 was achieved for the samples with 2 wt% MWCNTs. Overall, the unique property combination between the MWCNTs and the PGS make them potentially suitable for the development of large deformation piezoresistive sensors, especially for biomedical engineering applications, flexible and wearable devices.

Molecular dynamics simulations of flame propagation along a monopropellant PETN coupled with multi-walled carbon nanotubes

Reactive molecular dynamics simulations were conducted to study the flame speed enhancement phenomenon of a solid mono-propellant, Pentaerythritol Tetranitrate (PETN), when coupled to highly conductive multi-walled carbon nanotubes (MWCNTs). The simulations were based on the first-principles derived reactive force field, ReaxFF, which includes both the physical changes such as thermal transport and the chemical changes such as bond breaking and forming. An annular deposition of a PETN layer around the MWCNTs was considered. The thickness of the PETN layer and the diameter of the MWCNT were varied to understand the effect of the MWCNT loading ratio on the flame propagation. Flame speed enhancements up to 3 times the bulk value were observed. An optimal MWCNT loading ratio was determined. The enhancement was attributed to the layering of the PETN molecules around the MWCNT, which increased the heat transport among the PETN molecules near the MWCNT surface, thus causing the flame to travel faster. Furthermore, a stronger ignition source was required for the MWCNT-PETN complex because of the higher thermal transport among the PETN molecules along the MWCNT, which makes the ignition energy dissipate more quickly. Lastly, the MWCNT remained unburned during the PETN combustion process.

Molecular dynamics study of the interfacial thermal conductance of multi-walled carbon nanotubes and van der Waals force induced deformation

Thermal boundary resistance (TBR) plays an important role in the thermal conduction of carbon nanotube (CNT)-based materials and CNT networks (e.g., thin films, arrays, and aerogels). Although individual CNTs have extremely high thermal conductivity, interfacial resistances can dominate the overall resistance and largely influence their thermal performance. Using molecular dynamics simulations, we systematically study the interfacial thermal conductance (ITC, the inverse of TBR) of multi-walled carbon nanotube (MWNT)-substrate interfaces and MWNT-MWNT junctions, and compare the CNT-CNT junctions with graphene-graphene junctions. The results show that for CNTs with the diameter of a few nanometers, the total ITCs first decrease and then stabilize with the increase of the number of walls, mainly due to the changes of mechanical strength and adhesive energy. Increasing the CNT diameter leads to a larger total ITC and it is mainly due to a larger contact area. The area normalized ITC of CNT-CNT junctions increases and then saturates with the number of walls, and it behaves non-monotonically with the diameter. Furthermore, a trapezoidal model of multi-layer graphene-graphene junctions is used to explain the number of wall dependence of ITC. We also find that with the same adhesive energy, total ITCs of CNT-CNT junctions and graphene-graphene junctions are similar, which allows us to roughly estimate ITCs of CNT-CNT junctions without performing numerical simulations.