Electrical Conductivity Of Carbon Nanotubes Research Articles

A multiscale modeling framework for predicting strain‐dependent electrical conductivity of carbon nanotube‐incorporated nanocomposites considering the electron tunneling effect

AbstractThe present work proposes a multiscale modeling framework for predicting the strain‐dependent electrical conductivity of carbon nanotube (CNT)‐incorporated nanocomposites considering the electron tunneling effect. A micromechanical model taking into account the waviness of the CNTs is utilized and molecular dynamics simulations estimating changes in distance between CNTs in the polymer matrix are conducted in an attempt to incorporate the electron tunneling effect. A series of numerical parametric studies are carried out to examine the influence of model parameters (e.g., CNT length, number of CNT segments, and intrinsic interfacial resistivity) on the strain‐dependent electrical conductivity of the nanocomposites. In addition, CNT/polydimethylsiloxane samples are fabricated and their strain‐dependent electrical conductivity is experimentally evaluated. Finally, to verify the predictive capability of the proposed modeling framework, the present predictions are compared with experimental results.Highlights A multiscale modeling framework of CNT‐incorporated nanocomposites is proposed. A micromechanics model and molecular dynamics simulations are used. The study includes a numerical parametric investigation. The present predictions are compared with those obtained experimentally.

PAM/CNTs-Au microcrack sensor with high sensitivity and wide detection range for multi-scale human motion detection

As the quintessential material for flexible sensors, conductive hydrogels face an inherent sensitivity-sensing range paradox and electrical-mechanical balance, which significantly curtail its applicability in multiscale motion detection. Inspired by the spider slit sensor, PAM/CNTs-Au hydrogel microcrack sensor is obtained by depositing conductive gold film on the surface of PAM/CNTs hydrogel using magnetron sputtering. By modulating the cross-linking density of conductive hydrogels and the content of carbon nanotubes (CNTs), it is possible to tailor the mechanical properties and adhesion of PAM/CNTs-Au hydrogel crack-based sensors. This self-adhering flexible sensor aids in minimizing detection errors arising from mechanical mismatch between flexible sensors and human tissues. Moreover, the exceptional electrical conductivity of CNTs, coupled with their unique one-dimensional structure, facilitates the formation of an interconnected conductive network "bridge" within the hydrogel. The harmonization of electrical and mechanical attributes in the PAM/CNTs flexible substrate is achieved by finely tuning the crosslinking density of the PAM hydrogel and the content of carbon CNTs. Simultaneously, the high-conductivity "islands" formed by the Au conductive layer during stretching ensures elevated sensitivity (gauge factor (GF) = 54.89) over an extensive detection range (>1200%). The distinctive "island-bridge" configuration of the PAM/CNTs-Au hydrogel microcrack sensor effectively suppresses crack propagation, thereby markedly augmenting the sensor's stability. Successful monitoring of physiological and motion signals across various scales attests to the potential of the PAM/CNTs-Au hydrogel microcrack sensor in wearable biosensor.

Analytical modeling of the electrical conductivity of CNT-filled polymer nanocomposites

Electrical conductivity of most polymeric insulators can be drastically enhanced by introducing a small volume fraction [Formula: see text] of conductive nanofillers. These nanocomposites find wide-ranging engineering applications from cellular metamaterials to strain sensors. In this work, we present a mathematical model to predict the effective electrical conductivity of carbon nanotubes (CNTs)/polymer nanocomposites accounting for the conductivity, dimensions, volume fraction, and alignment of the CNTs. Eshelby’s classical equivalent inclusion method (EIM) is generalized to account for electron-hopping—a key mechanism of electron transport across CNTs, and is validated with experimental data. Two measurements, namely, the limit angle of filler orientation and the probability distribution function, are used to control the alignment of CNTs within the composites. Our simulations show that decreasing the angle from a uniformly random distribution to a fully aligned state significantly reduces the transverse electrical conductivity, while the longitudinal conductivity shows less sensitivity to angle variation. Moreover, it is observed that distributing CNTs with non-uniform probability distribution functions results in an increase in longitudinal conductivity and a decrease in transverse conductivity, with these differences becoming more pronounced as the volume fraction of CNTs is increased. A reduction in CNT length decreases the effective electrical conductivity due to the reduced number of available conductive pathways while reducing CNT diameter increases the conductivity.

Single walled carbon nanotubes band gap width measurement and the influence of nitrogen doping research.

The adjustment and measurement of the band gap width of single-walled carbon nanotubes are crucial for optimizing the design and enhancing the performance of carbon-based devices. This study utilizes the relationship between the band gap and temperature of semiconductor-based carbon nanotubes. The electrical conductivity of carbon nanotubes was obtained at various temperatures, and the corresponding band gap width (0.57 eV) was determined. The introduction of nitrogen results in a reduction of the band gap width and an increase in current flow between the device source and drain electrodes. Theoretical calculation demonstrated that nitrogen doping not only increases the conductivity of carbon nanotubes but also effectively inhibits the Schottky barrier between carbon nanotubes and metal electrodes. The Schottky barrier and the internal electric field can be effectively modulated via nitrogen doping in carbon nanotubes, which enhances the performance of carbon-based devices.

Acid-base engineered strategy of HKUST-1 dopants for high electrical conductivity of single-walled carbon nanotubes films

The improvement of electrical conductivity of carbon nanotubes is still a challenge via tuning the carrier concentration and mobility with organic or inorganic dopants due to low doping efficiency. In this paper, single-walled carbon nanotubes (SWCNTs) have been doped with Cu3(BTC)2·(H2O)3 (HKUST-1) as metal organic frameworks via simple mixing and vacuum filtration method. With fine acid or base post-treatment, the crystal structure of HKUST-1 was broken into fragments with more active sites and provided plenty of carriers injecting into SWCNTs. The electrical conductivity of SWCNTs/HKUST-1 films was increased by almost 2.5 times compared to pristine SWCNTs at room temperature. The defect tuning of dopants on SWCNTs surface is an effective carrier injection strategy, which provides a way to improve the electrical conductivity of SWCNTs.

Fluorinated bamboo-structure carbon nanotubes: as attractive substrates for the cathodes of lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have gained considerable attention for high theoretical specific capacity and energy density. However, their development is hampered by the poor electrical conductivity of sulfur and the shuttle of polysulfides. Herein, the acidified bamboo-structure carbon nanotubes (BCNTs) were mixed with polyvinylidene difluoride and pyrolyzed at high-temperature to obtain the fluorinated bamboo-structure carbon nanotubes (FBCNTs), which were compounded with sulfur as the cathode. The prepared S@FBCNTs with sulfur loading reaching 74.2 wt.% shows a high initial specific capacity of 1407.5 mAh·g−1 at the discharge rate of 0.1 C. When the discharge rate was increased to 5 C, the capacity could be maintained at 622.3 mAh·g−1. The electrical conductivity of carbon nanotubes is effectively improved by semi-ionic C–F bonds formed by the doped F atoms and carbon atoms. Simultaneously, the surface of the F-containing carbon tubes exhibits strong polarity and strong chemisorption effect on polysulfides, which inhibits the shuttle effect of Li–S batteries.

Efficiency Enhancement of Biophotovoltaic Solid‐State Solar Cells

Biophotovoltaic solid‐state solar cells are new environmentally friendly solar cells inspired by photosynthesis phenomena. Photosystem I, a complex protein located in the chloroplast of the plant leaves that has a principal role in light absorption, is the most common light absorber used in biophotovoltaic solid‐state solar cells. Low efficiency and low current density are the main challenges in this kind of solar cell. Herein, to vacillate the motion of electrons and holes, carbon nanotubes and tyrosine are used as transfer layers and to increase light absorbance, a solution of Photosystem I with silver nanoparticles as an absorber layer is used. It is shown that the short circuit current density and the efficiency can be enhanced to 6.61 mA cm−2 and 0.83%, respectively which are the highest values for current density and efficiency reported for this kind of solar cell. These enhancements are due to the high electrical conductivity of carbon nanotubes, proper porosity of tyrosine, and the localized surface plasmon resonance of silver nanoparticles induced under light irradiation. The results can illuminate hopes and dreams for biophotovoltaic solid‐state solar cells with higher current density and higher efficiency.

Different carbonization temperature effect on Mo2C/MWCNT hybrid structure formation for enhanced supercapacitor performance

Various forms of energy used in our daily lives prevail in contemporary society. Application requirements have expanded from high power density to sustainable long term energy density for energy storage devices. The present study signifies effect of carbonization temperature role (700 °C, 800 °C, 900 °C) on electrochemical studies of MoO3 as electrode in supercapacitor devices. The prepared electrodes were characterized by electrochemical studies such as cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS) and basic characterizations like X-ray diffraction, Raman, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM). Different carbonization temperatures with the addition of carbon precursors produced MoO2/MWCNT and α-Mo2C/MWCNT. The areal capacitance of MoO2–700 °C, MoO2–800 °C, α-Mo2C-900 °C electrode were found to be delivered as 0.45 F/cm2, 0.54 F/cm2, 0.96 F/cm2 at 0.003 A/cm2. The substantial increase in specific capacitance for α-Mo2C-900 °C was attributed to improve charge transport, faradic redox development occurring at electrode surface, and high electrical conductivity of carbon nanotubes.

A novel CNTs/QCS/BiOBr composite membrane with electron–ion transfer channel for Br- recovery in ESIX process

Based on the superior selectivity of bismuth oxybromide (BiOBr) for Br-, the excellent electrical conductivity of carbon nanotubes (CNTs), and the ion exchange capacity of quaternized chitosan (QCS), a three-dimensional network composite membrane electrode CNTs/QCS/BiOBr was constructed, in which BiOBr served as the storage space for Br-, CNTs provided the electron transfer pathway, and QCS cross-linked by glutaraldehyde (GA) was used for ion transfer. The CNTs/QCS/BiOBr composite membrane exhibits superior conductivity after the introduction of the polymer electrolyte, which is seven orders of magnitude higher than that of conventional ion-exchange membranes. Furthermore, the addition of the electroactive material BiOBr improved the adsorption capacity for Br- by a factor of 2.7 in electrochemically switched ion exchange (ESIX) system. Meanwhile, the CNTs/QCS/BiOBr composite membrane displays excellent Br- selectivity in mixed solutions of Br-, Cl-, SO42- and NO3–. Therein, the covalent bond cross-linking within the CNTs/QCS/BiOBr composite membrane endows it great electrochemical stability. The synergistic adsorption mechanism of the CNTs/QCS/BiOBr composite membrane provides a new direction for achieving more efficient ion separation.

Review on Molecular Dynamics Simulations of Effects of Carbon Nanotubes (CNTs) on Electrical and Thermal Conductivities of CNT-Modified Polymeric Composites

Due to the unique properties of carbon nanotubes (CNTs), the electrical and thermal conductivity of CNT-modified polymeric composites (CNTMPCs) can be manipulated and depend on several factors. There are many factors that affect the thermal and electrical conductivity of CNTs and CNTMPCs, such as chirality, length, type of CNTs, fabrication, surface treatment, matrix and interfacial interaction between the matrix and reinforcement (CNTs). This paper reviews the research on molecular dynamics (MD) simulations of the effects of some factors affecting the thermal and electrical conductivity of CNTs and CNTMPCs. First, the chirality dependence of the thermal and electrical conductivity of single-walled carbon nanotubes (SWNTs) was analyzed. The effect of chirality on the conductivity of short-length CNTs is greater than that of long-length CNTs, and the larger the chiral angle, the greater the conductivity of the CNTs. Furthermore, the thermal and electrical conductivity of the zigzag CNTs is smaller than that of the armchair one. Therefore, as the tube aspect ratio becomes longer and conductivity increases, while the effect of chirality on the conductivity decreases. In addition, hydrogen bonding affects the electrical and thermal conductivity of the CNTMPCs. The modeling of SWNTs shows that the thermal and electrical conductivity increases significantly with increasing overlap length. MD simulations can be effectively used to design highly conductive CNTMPCs with appropriated thermal and electrical properties. Since there are too many factors affecting the thermal and electrical conductivity of CNTMPCs, this paper only reviews the effects of limited factors on the thermal and electrical conductivity of CNTs and CNTMPCs based on MD simulations, and further detailed studies are required.

Localized Liquid Zones Assisted Highly Crystalline Single-Wall Carbon Nanotube Sheets: Implications for Conducting Shields in Coaxial Cables

The electrical conductivity of carbon nanotube (CNT) macro assemblies can be influenced by their crystallinity. Herein, we present the synthesis of high-quality SWCNT sheets for which an appropriate optimization parametric research of synthesis temperature, precursor flow rate, and H2 flow rate was carried out in this approach. It was found that highly crystalline SWCNT sheet (IG/ID = 180.3) was synthesized by floating catalyst chemical vapor deposition technique at 12 mL/h precursor flow rate and 1000 sccm H2 flow rate. Three distinct Raman laser wavelengths (514, 532, and 785 nm) were used to study the as-synthesized sheet, and the maximum calculated IG/ID ratio was found to be 180.3 (@ λ = 514 nm). Due to high concentration of H2 gas, the number of localized liquid zones or CNT nucleation sites increased which has an impact on both the quality as well as the diameter of CNTs. The I–V characteristics of CNT sheet were studied via four-probe technique, yielding a measured value of electrical conductivity of 9.21 × 106 S/m. Further, the R-T measurement showed the positive temperature coefficient up to the 108 K which indicates the metallicity of as produced CNT sheets. These highly conducting SWCNT sheets are the best solution for a wide range of applications in many fields, including conducting shields in coaxial cables, flexible and nano scale electrical and electronic devices, displays, biosensors, field-effect transistors and gas sensing materials.

Substrate Modification for High‐Performance Thermoelectric Materials and Generators Based on Polymer and Carbon Nanotube Composite

AbstractPolymer and carbon nanotube composites have aroused extensive attention for thermoelectric materials owing to the combination of low thermal conductivity of polymer and high electrical conductivity of carbon nanotubes. Surface properties of the substrate are of great importance for the charge transport behaviors of semiconducting thin films, which are less explored in thermoelectric applications. Herein, self‐assembled monolayers (SAMs) are used to modify the substrate for thermoelectric polymer composites. The trifluoromethyl (CF3)‐terminated SAM is beneficial for an improved electrical conductivity; while the SAM with amino group is found to improve their Seebeck coefficient and decrease the electrical conductivity. As a result, polymer composites on CF3‐SAM‐modified substrate show a high room‐temperature power factor of 285 µW m−1 K−2 and a large output power of 2.36 µW for thermoelectric generator at a temperature gradient of 50 K. This work demonstrates that surface modification by SAMs is a promising strategy for improving performance of thermoelectric materials and devices.

Electrochemical sensor for isoniazid detection by using a WS2/CNTs nanocomposite

This paper presents a new modified electrode that combines the high electrical conductivity of carbon nanotubes (CNTs) with the catalytic sites of WS2 (named WS2/CNTs) for isoniazid detection. Electrochemical and electroanalytical properties of the WS2/CNTs/glassy carbon electrode (GCE)-modified electrodes were investigated by cyclic voltammetry and differential pulse voltammetry (DPV). The composite material was characterized by Raman spectroscopy, X-ray diffractometry (XRD), and scanning electron microscopy . The electrochemical performance of the WS2/CNTs/GCE sensor exhibited a limit of detection of 0.24 μM with a linear range from 10 to 80 μM of isoniazid using DPV. This sensor provided enhanced stability and electrocatalytic activity for isoniazid oxidation reactions. Recoveries ranging from 96.9 to 104.5% were calculated, demonstrating satisfactory accuracy of the proposed method. The improvement of electrochemical activity was assigned to synergic effects obtained by combining the catalytic sites from WS2 and the known electrical conductivity and large surface area of the CNTs, resulting in an anticipation of the oxidation peak of isoniazid in about 400 mV in comparison with bare GCE.

Application of MnO2/MWCNT composite in supercapacitors

Supercapacitors have attracted tremendous attention due to high power density, high rate capability, long cycling life and safety. The article presents the comparison of electrochemical performance of multi-walled carbon nanotubes (MWCNTs), MnO2 and MnO2/MWCNT nanocomposite as electrode mass in supercapacitor. Materialswere characterized by X-ray diffraction, scanning electron microscopy, low temperature nitrogen adsorption and cyclic voltammetry. The specific capacitance was found to increase in the row MWCNTs < MnO2 < MnO2/MWCNT achieving 32, 90 and 140 F · g−1 at 5 mV · s−1, respectively. The outstanding improvement of specific capacitance for MnO2/MWCNT was attributed to the combination of high electrical conductivity of carbon nanotubes enhancing the charge transport and faradic redox reactions occurring on MnO2 surface.

Electrical conductivity of a single parallel contact between carbon nanotubes.

Interfacial resistance plays a critical role in the transport properties of nanomaterial-based assemblies. However, understanding of them remains limited due to the difficulty of experimental approaches. Here we report in situ measurements of the electrical resistance of a single parallel contact between carbon nanotubes. By varying the contact length systematically, we derive the electrical conductivities of carbon nanotubes and interfaces. The interface between nanotubes exhibits conductivity intermediate between those of pyrolytic and single-crystal graphite. The threshold contact length between interface- and bulk-dominant electrical transport is quantitatively estimated.

Monte Carlo analytical-geometrical simulation of piezoresistivity and electrical conductivity of polymeric nanocomposites filled with hybrid carbon nanotubes/graphene nanoplatelets

Piezoresistivity and electrical conductivity of carbon nanotube (CNT)/graphene nanoplatelet (GNP)-filled polymer nanocomposites are investigated using a 3D Monte Carlo analytical-geometrical model. GNPs and CNTs are considered as randomly distributed solid thin rectangular cube and cylinder, respectively. After establishment of a random CNT/GNP network, electrical conductivity and relative resistance change with strain is calculated. Model considers effect of CNT and GNP deformation on filler separation distance as the dominant factor for percolation tunneling. Comparing model results with experimental data of hybrid nanocomposites showed a good agreement for electrical conductivity and piezoresitivity. Analytical model is developed on the basis of geometrical tunneling percolation theory to consider the effect of several parameters like height of barrier potential, GNP side length, CNT orientation and dimensions on electric behavior of nanocomposites. Results revealed that CNT dispersion state and GNP dimensions have significant effects on the percolation threshold and resistivity change ratio of nanocomposites with strain.

Development of an advanced Takayanagi equation for the electrical conductivity of carbon nanotube-reinforced polymer nanocomposites

Currently available models for the conductivity of nanocomposites commonly disregard the roles of interphase and tunneling sections. Here, the interphase and tunneling parts are considered to yield an expanded Takayanagi equation to express a model for the electrical conductivity of carbon nanotubes (CNTs)-reinforced polymer nanocomposites (PCNTs). Invoking the interphase section, the operative filler loading and percolation onset are shown to control the volume fraction of networks. Application of the advanced model allows calculation of the conductivity over disparate ranges of various factors and estimation of the conductivity for real specimens. Experimental data for several examples show good matching with the predictions. Straighter CNTs, a dense interphase region, large nets, large tunneling diameter, low polymer tunneling resistivity, and short tunnels give rise to high conductivity. Conductivity is increased to 3.5 S/m at a CNT radius (R) of 5 nm and a CNT length of 20 μm, whereas an insulating sample is observed at R > 8 nm. A percolation onset (ϕp) below 0.0012 results in a conductivity of 0.13 S/m, but it decreases to 0.1 S/m at ϕp> 0.0044. A high CNT volume fraction of 0.02 raises the conductivity to 0.35 S/m, whereas a low CNT volume fraction of 0.005 lowers it to 0.05 S/m.

Immobilization of multicopper oxidase from Pyrobaculum aerophilum onto an electrospun‐aligned single‐walled carbon nanotube surface via a carbon‐nanotube‐binding peptide for biocathode

AbstractBiofuel cells (BFCs) that produce electrical energy from organic resources through enzymatic reactions have been attracting significant attention. Owing to the high electrical conductivity of carbon nanotubes (CNTs), their modification on the electrode surface of a BFC is expected to increase the current, and their high specific surface area may be useful in increasing the power output. Previously, we constructed a biocathode by immobilizing multicopper oxidase from Pyrobaculum aerophilum (McoP) with a carbon nanotube binding peptide (CBP) sequence on the CNTs. This resulted in higher current densities than when using enzymes without CBP sequences. However, owing to the randomly stacked CNTs on the surface of the electrodes, their conductive properties were impaired and performance as biocathodes was poor. Herein, we constructed a biocathode in which single‐walled CNTs (SWCNTs) were oriented one‐dimensionally and McoP is immobilized on the surface of an SWNCT via CBP. The current density was successfully increased by two‐fold by orienting the CNTs and orienting and immobilizing McoP on their surfaces. This technology provides insights into the development of biodevices with controlled orientation of both the SWCNTs and enzymes immobilized on their surfaces.

Development and simplification of a micromechanic model for conductivity of carbon nanotubes-reinforced nanocomposites

In the current paper, Hui-Shia model for composite’s modulus is simplified and advanced to evaluate the electrical conductivity of carbon nanotubes (CNT)-reinforced nanocomposites (PCNT) by CNT aspect ratio, CNT network part, interphase district and tunnels between adjacent CNT. CNT loading, CNT magnitude and interphase depth suggest the proportion of networked CNT. In addition, CNT and tunneling intrinsic resistances express the entire conductivity of included components in nanocomposites. The reasonable roles of all factors in the conductivity and the proper matching between trial data and predictions approve the established model. Both dense interphase and long CNT improve the conductivity; however, reedy interphase or short CNT induces an insulated sample. The polymer tunneling resistivity negatively affects the conductivity, while CNT conductivity is an unsuccessful term. Furthermore, both short and wide tunnels desirably control the nanocomposite’s conductivity.

Electrically conductive and light-weight branched polylactic acid-based carbon nanotube foams

Abstract In spite of the high electrical conductivity of carbon nanotube (CNT), its tendency to aggregate and expensive cost in fabricating aerogel, foams, and porous materials remains a problem. Therefore, we described a simple and feasible way to design light-weight, high electrically conductive, and cost-efficient polylactic acid (PLA)/CNT foams. The branched PLA (BPLA) resin with excellent melt elasticity and foamability was induced by nucleophilic ring-opening reaction of epoxy-based acrylic/styrene copolymer and PLA. After that, BPLA/CNT composites and foams were prepared by melt-mixing and supercritical carbon dioxide foaming technology, respectively. The thermal, electrical, and foaming properties were studied. The resultant BPLA/CNT foam possessed a low density of 0.174 g/cm3 and high crystallinity of 3.03%. An improvement of the oriented structure of CNT induced by cell growth in BPLA matrix increased the conductivity of the foam up to 3.51 × 104 Ω/m. The proposed foaming materials provided a way for designing and preparing high performance CNT products.