Multi-walled Carbon Nanotubes Network Research Articles

High-Performance Ionanofluids from Subzipped Carbon Nanotube Networks

Investments in the transfer and storage of thermal energy along with renewable energy sources strengthen health and economic infrastructure. These factors intensify energy diversification and the more rapid post-COVID recovery of economies. Ionanofluids (INFs) composed of long multiwalled carbon nanotubes (MWCNTs) rich in sp2-hybridized atoms and ionic liquids (ILs) display excellent thermal conductivity enhancement with respect to the pure IL, high thermal stability, and attractive rheology. However, the influence of the morphology, physicochemistry of nanoparticles and the IL-nanostructure interactions on the mechanism of heat transfer and rheological properties of INFs remain unidentified. Here, we show that intertube nanolayer coalescence, supported by 1D geometry assembly, leads to the subzipping of MWCNT bundles and formation of thermal bridges toward 3D networks in the whole INF volume. We identified stable networks of straight and bent MWCNTs separated by a layer of ions at the junctions. We found that the interactions between the ultrasonication-induced breaking nanotubes and the cations were covalent in nature. Furthermore, we found that the ionic layer imposed by close MWCNT surfaces favored enrichment of the cis conformer of the bis(trifluoromethylsulfonyl)imide anion. Our results demonstrate how the molecular perfection of the MWCNT structure with its supramolecular arrangement affects the extraordinary thermal conductivity enhancement of INFs. Thus, we gave the realistic description of the interactions at the IL-CNT interface with its (super)structure and chemistry as well as the molecular structure of the continuous phase. We anticipate our results to be a starting point for more complex studies on the supramolecular zipping mechanism. For example, ionically functionalized MWCNTs toward polyionic systems─of projected and controlled nanolayers─could enable the design of even more efficient heat-transfer fluids and miniaturization of flexible electronics.

Carbon Nanotube Migration in Melt-Compounded PEO/PE Blends and Its Impact on Electrical and Rheological Properties.

In this work, the effects of MWCNT concentration and mixing time on the migration of multi-walled carbon nanotubes (MWCNTs) within polyethylene oxide (PEO)/polyethylene (PE) blends are studied. Two-step mixing used to pre-localize MWCNTs within the PE phase and subsequently to observe their migration into the thermodynamically favored PEO phase. SEM micrographs show that many MWCNTs migrated into PEO. PEO/PE 40:60 polymer blend nanocomposites with 3 vol% MWCNTs mixed for short durations exhibited exceptional electromagnetic interference shielding effectiveness (EMI SE) and electrical conductivity (14.1 dB and 22.1 S/m, respectively), with properties dropping significantly at higher mixing times, suggesting the disruption of percolated MWCNT networks within the PE phase. PE grafted with maleic anhydride (PEMA) was introduced as a compatibilizer to arrest the migration of MWCNTs by creating a barrier at the PEO/PE interface. For the compatibilized system, EMI SE and electrical conductivity measurements showed a peak in electrical properties at 5 min of mixing (15.6 dB and 68.7 S/m), higher than those found for uncompatibilized systems. These improvements suggest that compatibilization can be effective at halting MWCNT migration. Although utilizing differences in thermodynamic affinity to draw MWCNTs toward the polymer/polymer interface of polymer blend systems can be an effective way to achieve interfacial localization, an excessively low viscosity of the destination phase may play a major role in reducing the entrapment of MWCNTs at the interface.

Unified modeling and experimental realization of electrical and thermal percolation in polymer composites

Correlations between electrical and thermal conduction in polymer composites are blurred due to the complex contribution of charge and heat carriers at the nanoscale junctions of filler particles. Conflicting reports on the lack or existence of thermal percolation in polymer composites have made it the subject of great controversy for decades. Here, we develop a generalized percolation framework that describes both electrical and thermal conductivity within a remarkably wide range of filler-to-matrix conductivity ratios (Yf/Ym), covering 20 orders of magnitude. Our unified theory provides a genuine classification of electrical conductivity with typical Yf/Ym≥1010 as insulator–conductor percolation with the standard power-law behavior and of thermal conductivity with 102≤Yf/Ym≤104 as poor–good conductor percolation characterized by two universal critical exponents. Experimental verification of the universal and unified features of our theoretical framework is conducted by constructing a 3D segregated and well-extended network of multiwalled carbon nanotubes in polypropylene as a model polymer matrix under a carefully designed fabrication method. We study the evolution of the electrical and thermal conductivity in our fabricated composites at different loading levels up to 5 vol. %. Significantly, we find an ultralow electrical percolation threshold at 0.02 vol. % and a record-low thermal percolation threshold at 1.5 vol. %. We also apply our theoretical model to a number of 23 independent experimental and numerical datasets reported in the literature, including more than 350 data points, for systems with different microscopic details, and show that all collapse onto our proposed universal scaling function, which depends only on dimensionality.

Stochastic multiscale multimode interlaminar fracture toughness of buckypaper nanocomposites

Delamination is one of the primary damage mechanisms in laminated composites that affects the lifetime integrity of the composite systems. The present study examines the effects of Buckypaper (BP) nano-reinforcement on the multimodal interlaminar fracture properties of the carbon fiber reinforced polymer (CFRP) composites reinforced with BP membranes. The novelty and the focus of this study is the effects of multi-wall carbon nanotube (MWCNT) network size and interphase in the interlaminar fracture toughness of BP nanocomposites. Dry and pre-infused non-functionalized MWCNT BP were integrated at the mid layer of the composite before laminate curing. The Atomic Force Microscopy Peak Force Quantitative Nanomechanics Mapping (AFM PFQNM) technique and the Weibull model were applied to study the effects of random CNT network size and interphase on mode I, II, and mixed-mode I-II fracture properties. Weibull analysis of 150 dry and pre-infused BP data confirms a high scatter of CNT network size in dry BP compared to pre-infused BP. Weibull modulus of CNT network size (2.33 for large size and 5.18 for small size) and interphase thickness (3.46) show a robust, consistent entangled structure of CNTs in pre-infused BP. Dry BP improves the propagation energy release rate of the CFRP laminates up to 54%. However, it does not provide additional toughening in the initiation crack energy for modes I, II, and I-II. Mode I initiation and propagation, mode II initiation and mixed-mode I/II fracture energy of pre-infused BP nanocomposites are ∼33%, ∼52.5%, ∼14%, and ∼28% higher than the reference. The interlaminar crack either moves exclusively through the BP layer by circumventing the rigid CNT networks or moves forward through the interface of the carbon fiber monofilament above and below the reinforcing BP layer. This saw-like interlaminar crack path triggers numerous toughening mechanisms such as nano-toughened epoxy, nanoscale CNT bridging and pullout, and crack deflection, and it increases the total crack propagation path.

The effect of multi-walled carbon nanotubes on the thermo-physical properties of shape stabilised phase change materials for buildings based on high density polyethylene and paraffin wax

The inherent low thermal conductivity and inferior mechanical properties of polymer based shape stabilised phase change materials (SSPCMs) restrict their wide applications in building sections. Multi-walled carbon nanotubes (MWCNTs) with excellent thermal and mechanical properties were incorporated into SSPCMs based on blends of a low molecular weight HDPE (lv-HDPE) and paraffin waxes by extrusion. Their suitability for latent heat thermal energy storage was evaluated. The MWCNTs were uniformly distributed within the SSPCM matrix and were wetted by the SSPCM. The SSPCMs with MWCNTs had latent heats up to 53 J g−1 with 0.5 wt% MWCNTs. Both the Young's moduli and yield stress of lv-HDPE50H-PW50 with MWCNTs composites were lower than that of unfilled lv-HDPE50H-PW50 at low MWCNT loading (≤1 wt%). They then went up with an increase in MWCNT loading (from 1 wt% to 3 wt%). This is due to the formation of an inter-connected network of MWCNTs. Similar results were obtained for both flexural moduli and stress. However, there is no significant difference of the compression moduli between unfilled lv-HDPE50H-PW50 blend and those MWCNT blends. The thermal conductivity increased with increasing MWCNTs content and the greatest enhancement was 29 % for SSPCM with 3 wt% MWCNTs. It will therefore contribute to the decarbonisation of buildings.

Investigation into a Lightweight Polymeric Porous Sponge with High Magnetic Field and Strain Sensitivity.

Recently, flexible sensors have gained significant attention due to their potential applications in soft robotics and biomimetic intelligent devices. However, the successful production of favorable flexible sensors integrated with high flexibility, sensitivity and excellent environment adaptability toward multiple external stimuli is still an enormous challenge. Herein, a lightweight polymeric porous sponge capable of detecting an external magnetic field and strain excitations is proposed by assembling a sodium alginate/chitosan (SA/CHI) porous sponge with micron carbonyl iron and nanoscale Fe3O4 magnetic particles (MPs). Based on the double network structure, the SA/CHI sponge possesses preferable mechanical strength and hydrophilicity, demonstrating its high flexibility and deformability. More importantly, the electrical response of the SA/CHI sponge sensors can display remarkable variation under external magnetic and mechanical stimuli due to their superior magnetic characteristics and electrical conductivity. Meanwhile, their sensing properties can maintain relatively stable recoverability and repeatability towards the periodic excitations and releases. Additionally, a potential mechanism is provided to investigate their stimuli-sensitive behavior. It is highly dependent on the microstructure variations in MPs and conductive multi-walled carbon nanotube (MWCNTs) networks. Due to its exceptional magnetic controllability and appropriate electrical sensitivity, the proposed sensor shows high potential in wearable multi-sensing electronics and intelligent transport devices.

Facile synthesis of hierarchical Co3O4/MWCNT composites with enhanced acetone sensing property

A facile hydrothermal approach is reported for the preparation of a series of hierarchical cobalt tetraoxide (Co3O4)/multi-walled carbon nanotube (MWCNT) composites with different MWCNT amount. The material characterization reveals that the broccoli-like nano-agglomerates of Co3O4 nanoparticles are anchored to the surface of the intertwined MWCNT network structure in all the Co3O4/MWCNT composites. The optimized Co3O4/MWCNT based chemiresistive sensor has ultralow limit of detection of 0.41 ppm, and up to 5 times greater sensing response than the pristine Co3O4 based sensor while exposed to 100 ppm of acetone gas at 140 °C. The Co3O4/MWCNT based sensor has a short response time of 15 s and a short recovery time of 18 s, respectively. In addition, the Co3O4/MWCNT based sensor presents long-term stability, good reproducibility and high selectivity. The possible mechanisms of the enhanced chemiresistive response of the composite include the formation of the p-p hetero-junctions at the interface between Co3O4 and MWCNT, the increased amount of adsorbed oxygen species on the composite surface, and the mesoporous structure of the composite.

Enhanced thermal conduction of hybrid filler/polydimethylsiloxane composites via a continuous spatial confining process

Owing to the rapid development of the electronics and aerospace industry toward high integration and power, the growing demand for heat dissipation management materials was urgent. However, the continuous fabrication of thin highly thermally conductive polymer composites at a large scale remains challenging, especially requiring control of the filling content of fillers. Herein, the continuous spatial confining forced network assembly (CSNA) method was applied to realize the continuous construction of thermally conductive networks of hexagonal boron nitride (h-BN) and multi-walled carbon nanotubes (MWCNT) in polydimethylsiloxane (PDMS) matrix. The thermal conductive composites presented thickness-dependent in-plane thermal conductivity (K), reaching 4.28 W m−1 K−1 for h-BN (30 wt%)/MWCNT(2 wt%)/PDMS in 0.15 mm thickness. The h-BN/MWCNT/PDMS composite represented a 1543.5% increase compared to the pure PDMS thanks to the CSNA method and the bridging connection of MWCNT. This work provided a facile method to prepare the thin high thermal conductive composites, which might promisingly advance the industrialization of thin thermosetting thermal conductive composite films.

Compare Performance MWCNT-OH Network as a Gas Sensor of Embedded Nanoparticles when Exposed (NH3, NO2) Gases

This study is about gas sensor preparation of hydroxyl functionalized multiwall carbon nanotubes (MWCNTs-OH) network use filtration from suspension (FFS) method. Improve the properties of the sensor use embedded nanoparticles (PANI, Pt-CNT active, Ni). the gas sensor good responce toward Exposure (NH3, NO2) gases at room temperature and at low concentration (1ppm). The sensor was more responsive when exposure to NO2 gas because it is an oxidizing gas(corroded), When exposure NH3 gas for concentration (1ppm ) and embedded Ni NP the sensitivity value (3.41, 3.49, 9.7 and 5.4) % at the temperatures (RT, 50, 100 and 150 ) C˚. The recovery time was decreases at (150)C˚ as it was (5.4)sec , the factors to improve the properties of the sensor was increase temperature and embedded NPs.

Resistance sensing response optimization and interval loading continuity of multiwalled carbon nanotube/natural rubber composites: Experiment and simulation

AbstractTo achieve long‐term and real‐time monitoring of the deformation of isolation bearings, a conductive composite with a natural rubber (NR) matrix modified by multiwalled carbon nanotubes (MWCNTs) is processed by prestrain. The resistance‐strain response of this composite indicates excellent uniformity, linearity, hysteresis, reproducibility and stability due to the prestrain process for the composite before application. To explain the mechanism of the resistance‐strain response for the composite, a theoretical model is developed to analyze the relation between the conductivity and the MWCNT network structure. Mechanical and electrical testing under cyclic loads indicates that the prestrain of the composite could reduce or even eliminate the ‘shoulder peak’ effect of the resistance‐strain curve. Meanwhile, the resistance‐strain response behavior is independent of the prestrain temperature and discontinuous before and after the interval time. Furthermore, the coarse‐grained molecular dynamics simulation and microstructure testing indicate that the resistance‐strain response is induced by the changing orientation of MWCNT molecules in the rubber matrix under tension loading. All of the results and findings provide potential applications of this MWCNT/NR composite for deformation monitoring.

Porous Spinel Magnesium Manganese Oxide/Multiwalled Carbon Nanotubes Composite Synthesized by Electrochemical Conversion as High-Performance Cathode for Aqueous Magnesium Ion Battery

Aqueous magnesium ion batteries (AMIBs) have attracted great interest due to the low manufacture cost and eco-friendliness, but the lack of suitable cathodes with good electrochemical performance obstructs their development. Here, a composite of spinel magnesium manganese oxide (MgMn2O4) and multiwalled carbon nanotubes (MWCNTs) with a porous structure is synthesized by electrochemical conversion method and used as the cathode for the AMIB, which improves the inherent low conductivity for MgMn2O4 and enhanced its specific capacity. The electrochemical conversion method helps preserve the surface integrity and structure stability of the electrode, and the MWCNTs network provides the pathway of Mg ion migration among the MgMn2O4 particles. The obtained MgMn2O4/MWCNTs displays a discharge capacity of 322.3 mAh g−1 at 50 mA g−1, and the capacity retention is 81.8% after 2000 iterations at 1000 mA g−1. Further, the MgMn2O4/MWCNTs//VO2 system is assembled, which displays a capacity retention rate of near 100%. The electrochemical mechanism of Mg ion insertion/extraction is investigated though the ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. This paper extends synthesis method of the high performance cathode material for AIMB system.

Study on the improved electromechanical properties of composited dielectric elastomer by tailoring three-dimensional segregated multi-walled carbon nanotube (MWCNT) network

High permittivity and large actuation strain under low actuation voltage have been the “hotspot” on the development and application of dielectric elastomer actuators (DEAs) for decades. In this work, by coating multi-walled carbon nanotube (MWCNT)/silicon rubber (SR) composite on the surface of nickel foam, after which the nickel foam was etched, the segregated MWCNT network structure was filled and encapsulated by SR. As a result, an isolated three-dimensional (3D) MWCNT network was successfully introduced into the SR elastomer matrix. Studies showed that owing to the large amount of accumulated charge on the large polarization interface between MWCNT and SR, high dielectric constant value as high as 10.39 at 1 kHz under 0.8 wt % MWCNT can be endowed to the composited elastomer. In addition, because discontinuity of adjacent MWCNTs in the 3D MWCNT network, the dielectric loss and elastic modulus of the composited elastomer has been significantly lowered, providing a high actuated strain of about 11.61% at a low electric field of 10.1 V·μm−1 under a filler content of 0.6 wt % to the composites. This finding raises a long-range prospect to readily and reliably prepare high-performance polymer based dielectric materials, and the 3D-MWCNT/SR composite elastomer seizes a great potential to be applicated as high-performance DEAs.

Enhanced interfacial adhesion of CF/PEEK-titanium hybrid laminates via introducing micro-nano layers with multi-walled carbon nanotube networks

An effective and easily-handled strategy for enhancing the interfacial adhesion of CF/PEEK-titanium hybrid laminates was proposed, which was achieved by introducing micro-nano layers with multi-walled carbon nanotube (MWCNT) networks between titanium and PEEK layers via electrophoretic deposition. The optimal deposition condition was explored by setting different concentrations of MWCNTs and times of deposition. Short beam shear tests were conducted at room temperature to characterize the interlaminar shear strength of the hybrid laminates. The results showed that the optimum parameters of deposition were 0.75 mg/mL of MWCNTs concentration and 90 s of deposition time, leading to a 47.8% increase of interlaminar shear strength compared with the sandblasted-only case. The mechanisms for enhancement were explained by micromorphology, apparent contact angle, and roughness analyses, which could be utilized to guide the preparation of CF/PEEK-Ti hybrid laminates with interfacial reinforcement by MWCNTs. Besides, multiple failure modes occurred at the metal-composites interface including a mixed mode of interfacial and cohesive failures, and a large amount of PEEK and carbon fibers remaining on the surface of titanium sheet proved the excellent interlaminar properties of the hybrid laminates.

Flexible Electromagnetic Shielding Material Using Multi-Walled Carbon Nanotube Coated Cotton Fabric

The present work focuses on the development of cotton fabric with multi-walled carbon nanotube coating (CMC) through a dip and dry process. The influence of multi-walled carbon nanotubes (MWCNTs) concentration on transmission, reflection, and absorption properties, which leads to an estimation of electromagnetic interference (EMI) shielding, was also studied. The merits of MWCNTs coating on the cotton fabric were evaluated using field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and surface resistivity. The Fourier transform infrared (FTIR) spectroscopy result supports the bonding between MWCNTs and cotton fabric. The significant increase of 98.9% of EMI shielding for the highest MWCNTs weight percentage (22.23 wt%) was attributed due to the well-interconnected network of MWCNTs. The shielding mechanism in the high wt% MWCNTs samples is dominated by both reflection and absorption properties.

The Role of Phase Migration of Carbon Nanotubes in Melt-Mixed PVDF/PE Polymer Blends for High Conductivity and EMI Shielding Applications.

In this work, the effects of blend ratio and mixing time on the migration of multi-walled carbon nanotubes (MWCNTs) within poly(vinylidene fluoride) (PVDF)/polyethylene (PE) blends are studied. A novel two-step mixing approach was used to pre-localize MWCNTs within the PE phase, and subsequently allow them to migrate into the thermodynamically favored PVDF phase. Light microscopy images confirm that MWCNTs migrate from PE to PVDF, and transmission electron microscopy (TEM) images show individual MWCNTs migrating fully into PVDF, while agglomerates remained trapped at the PVDF/PE interface. PVDF:PE 50:50 and 20:80 polymer blend nanocomposites with 2 vol% MWCNTs exhibit exceptional electromagnetic interference shielding effectiveness (EMI SE) at 10 min of mixing (13 and 16 dB, respectively-at a thickness of 0.45 mm), when compared to 30 s of mixing (11 and 12 dB, respectively), suggesting the formation of more interconnected MWCNT networks over time. TEM images show that these improved microstructures are concentrated on the PE side of the PVDF/PE interface. A modified version of the “Slim-Fast-Mechanism” is proposed to explain the migration behavior of MWCNTs within the PVDF/PE blend. In this theory, MWCNTs approaching perpendicular to the interface penetrate the PVDF/PE interface, while those approaching in parallel or as MWCNT agglomerates remain trapped. Trapped MWCNTs act as barriers to additional MWCNTs, regardless of geometry. This mechanism is verified via TEM and scanning electron microscopy and suggests the feasibility of localizing MWCNTs at the interface of PVDF/PE blends.

Flexible Strain-Sensitive Silicone-CNT Sensor for Human Motion Detection.

This article describes the manufacturing technology of biocompatible flexible strain-sensitive sensor based on Ecoflex silicone and multi-walled carbon nanotubes (MWCNT). The sensor demonstrates resistive behavior. Structural, electrical, and mechanical characteristics are compared. It is shown that laser radiation significantly reduces the resistance of the material. Through laser radiation, electrically conductive networks of MWCNT are formed in a silicone matrix. The developed sensor demonstrates highly sensitive characteristics: gauge factor at 100% elongation −4.9, gauge factor at 90° bending −0.9%/deg, stretchability up to 725%, tensile strength 0.7 MPa, modulus of elasticity at 100% 46 kPa, and the temperature coefficient of resistance in the range of 30–40 °C is −2 × 10−3. There is a linear sensor response (with 1 ms response time) with a low hysteresis of ≤3%. An electronic unit for reading and processing sensor signals based on the ATXMEGA8E5-AU microcontroller has been developed. The unit was set to operate the sensor in the range of electrical resistance 5–150 kOhm. The Bluetooth module made it possible to transfer the received data to a personal computer. Currently, in the field of wearable technologies and health monitoring, a vital need is the development of flexible sensors attached to the human body to track various indicators. By integrating the sensor with the joints of the human hand, effective movement sensing has been demonstrated.

Tensile mechanics of buckypaper: Bridging the disconnect between disordered structure and carbon nanotube properties

Carbon nanotubes (CNTs) are the building blocks of a variety of meso- and macro-scale assemblies. Buckypaper (BP) is a typical mesoscopic material that can possess tensile strength and modulus of up to three to four orders of magnitude lower than constituent CNTs. Identifying the “ruler” that not only predicts the realistic tensile properties of BP but also enables the scaling up of these characteristics with the aid of key CNT and structural parameters remains an open challenge. Herein, we propose a comprehensive theoretical framework to devise detailed tensile mechanics of the highly complex and fundamentally challenging random network of multi-walled carbon nanotubes (MWCNTs). A shell-based analytical model comprising intertube sliding and stretching as key modes of deformation has been constructed that successfully reduced Young's modulus of MWCNTs from 1 TPa to a few hundred megapascals in BP. Further, the tensile strength of BP has been modeled based upon the intertube sliding of MWCNTs at a stress that is well below their individual failure strength. A good agreement between the theoretical and experimental stress-strain curves of BPs justified that the predictive model is sufficiently robust. The parametric analysis on various metrics obtained from the analytical model has also been performed.

Metal–organic framework-derived nitrogen-doped carbon-confined CoSe2 anchored on multiwalled carbon nanotube networks as an anode for high-rate sodium-ion batteries

Nitrogen-doped carbon-coated cobalt selenide anchored on multiwalled carbon nanotube networks was constructed via a chemical method with outstanding sodium storage performance.

Surface Modification of Multiwalled Carbon Nano-Tubes Network Through High Energy Electron Beam and its Implications on Thermoelectric Properties

Surface Modification of Multiwalled Carbon Nano-Tubes Network Through High Energy Electron Beam and its Implications on Thermoelectric Properties

Multiwalled carbon nanotube network connected Mg0.5Ti2(PO4)3 composites to improve sodium storage performance.

The research on sodium-ion batteries (SIDs) has aroused intensive attention. In this work, the Mg0.5Ti2(PO4)3 (MTP) composite material with NASICON structure has been studied as an anode material in SIDs. The sol-gel method is used to synthesize the Mg0.5Ti2(PO4)3 with a conductive network that can be constructed by using carbon nanotubes (CNTs) and phenolic resin as the amorphous source of carbon coating. The CNT network is used not only to improve the outcome of electrolyte penetration and reduce the internal resistance to diffusion but also to create a fast path for electron transport, thereby elevating the level of electronic conductivity. The phenolic resin is generated on the surface of MTP which extends its cycle life. The carbon-coated Mg0.5Ti2(PO4)3 with 0.10 g CNTs (MTP-CNT10) displays optimal performance as an anode material in SIDs, and shows a discharge capacity of 298.8 mA h g-1, 258.3 mA h g-1 and 254.8 mA h g-1 at 0.1C, 0.5C and 1C, respectively. Besides, the capacity retention rate reaches 92% after 300 cycles at 10C. This study contributes an effective solution to improving the electrochemical performance of electrode materials through the introduction of carbon coating and highly conductive materials.