Increasing Multi-walled Carbon Nanotubes Content Research Articles

Influence of NR/MWCNT Blending on Rotor Metal Friction and Wear during Mixing Process.

Mixing involves blending raw rubber or masticated rubber with additives using a rubber mixer, which is the most critical process in rubber production. The internal mixer, as the most important mixing equipment, experiences rotor wear during prolonged operation, affecting the gap between the mixer rotor and the chamber wall. This wear reduces mixing effectiveness, weakens filler dispersion, and ultimately impacts rubber performance. In recent years, as research on multi-walled carbon nanotubes (MWCNTs) and nanomaterials has deepened, their broad application prospects have become increasingly apparent. The objective of the present study is to understand and quantify rotor wear in rubber blends during the mixing process as influenced by multi-walled carbon nanotubes. This study found that with the increase in MWCNT content, the proportion of abrasive wear rises, while the proportion of corrosive wear decreases, leading to reduced overall wear. Compared to rubber without MWCNTs, the Payne effect decreased by 6.78%, 9.57%, 13.03%, 20.48%, and 26.06% with the addition of 1 phr, 3 phr, 5 phr, 7 phr, and 9 phr of MWCNTs, respectively. The friction coefficients between the rubber and metal increased by 6.31%, 8.57%, 25.43%, 39.31%, and 47.61%, while the metal wear rate decreased by 9.08%, 10.73%, 13.41%, 17.46%, and 25%. Conversely, the friction coefficients were reduced by 19.39%, 22.42%, 33.94%, 66.06%, and 76.36%.

Epsilon‐negative materials with lower percolation threshold derived from segregated structures

AbstractEpsilon‐negative materials (ENM) at radio frequency, usually designed based on percolation theory, recently drew much attention because of their potential applications in capacitors, transistors, and antennas. However, randomly distributed conductive functional materials cannot achieve directional long‐range electron transportation within the material, resulting in decreased utilization efficiency. The morphology design of the substrate material can change the distribution state and electron transfer pathway of conductive fillers. By controlling the size of the polystyrene (PS) and the content of multi‐walled carbon nanotubes (MWCNTs), PS/MWCNTs composites with random structures and segregated structures were designed, both of which exhibited negative permittivity with increasing MWCNTs content. Further investigation revealed that negative permittivity behavior is due to the establishment of the conductive network and the plasma oscillation of free electrons. Moreover, components with segregated structures have lower percolation thresholds, as directional electron transport is achieved and conductive fillers are efficiently utilized. This work provides a new method for guiding the electron transport pathway and effectively changing the distribution state of conductive fillers in ENM.Highlights Negative permittivity is achieved by plasma oscillation at radio frequency. The segregated structure leads to a decrease in the percolation threshold. Epsilon‐negative materials have good prospects in inductive components.

Preparation and characterization of PVA/MWCNT nanocomposites: a composition dependence study of structural, optical and mechanical properties

This work investigates the properties of polyvinyl alcohol (PVA) nanocomposite films with varying multi-walled carbon nanotube (MWCNT) content, ranging from 2 to 8 wt.%. The films were prepared using a solution casting method and characterized using UV-visible spectroscopy, optical microscopy, X-ray diffraction, and tensile tests. The prepared PVA/MWCNT nanocomposite films exhibited optical band gap values ranging from 3.5 eV to 5.3 eV. XRD analysis confirmed the semi-crystalline nature of these nanocomposites. Mechanical properties, including hardness, yield strength, ultimate tensile strength, and Young’s modulus, were enhanced by increasing MWCNT content by up to 8%. Contact angle measurements showed an increase in hydrophobicity with increasing MWCNT content. Optical microscopy images revealed uniform dispersion of MWCNTs in the PVA matrix. These findings suggest potential applications of PVA-MWCNT nanocomposites in various fields, including photosensors, UV shielding, adjustable band gap devices, and flexible optoelectronic devices.

Enhancing Photovoltaic Performance with BaTiO3/MWCNTs Composite Photoelectrodes in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have attracted renewed research interest as a potential low-cost substitute for conventional silicon photovoltaics. This work aims to improve the photovoltaic performance of the DSSCs by incorporating multi-walled carbon nanotubes (MWCNTs) into the BaTiO3 photoelectrode. The pure BaTiO3 and BaTiO3/MWCNT nanocomposites were sensitized with N719 dye and fabricated into solar cell devices for testing. The structural characterization confirmed the successful formation of the nanocomposite with an optimal dispersion at 6% of MWCNT incorporation, beyond which agglomeration effects manifested. The optical analysis verified the modulation of defect states and bandgap engineering induced by the MWCNT network. The morphological studies revealed irregular nanoparticle clusters with embedded nanotubes. Solar cell testing under AM1.5G-simulated sunlight demonstrated a peak power conversion efficiency of 4.044% for 6% of MWCNT doping, constituting a 6-fold increment versus pure BaTiO3 (0.693%). It originated from the simultaneous enhancements in the open-circuit voltage and short-circuit current enabled by the favorable band structure alterations and percolation-assisted charge transport. However, further increasing MWCNT content deteriorated the device metrics, owing to emerging limitations like trapping. The rational integration of multi-walled carbon nanotubes with lead-free ferroelectric metal oxides can contribute to the development of emerging organic-inorganic hybrid solar platforms.

CoFe2O4/PANI/MWCNTs ternary hybrid composites. Synthesis, characterization, the effect of MWCNTs ratio and dye removal capability.

We have synthesized cobalt ferrite (CoFe2O4) using the sucrose auto-combustion method and subsequently employed the in situ polymerization technique to fabricate ternary composites comprising CoFe2O4, polyaniline (PANI), and multi-walled carbon nanotubes (MWCNTs). In this novel investigation, we explored the influence of varying MWCNTs ratios on these composites' structural, magnetic, thermal, and electrical properties. The crystal structures of the synthesized composites were analyzed using X-ray diffraction (XRD), while Fourier transform infrared (FT-IR) spectroscopy revealed changes in bonding patterns, including the disappearance of ferrite bonds and the emergence of new ones. Transmission electron microscopy (TEM) images illustrated a complete coating of PANI on both MWCNTs and CoFe2O4 particles, resulting in a substantial reduction in magnetization compared to pure CoFe2O4 ferrite due to PANI's nonmagnetic nature. Vibrating sample magnetometer (VSM) measurements confirmed this reduction, indicating a decrease to 7.3 emu.g-1. Thermal analysis demonstrated an enhancement in thermal stability with increasing MWCNTs content, as evidenced by an increase in the temperature equivalent for half decomposition (T50) from 486 to 522°C for composites with 40% MWCNTs. Moreover, the electrical conductivity showed a corresponding rise with MWCNTs content, increasing from 3.1 × 10-3 Ω-1.cm-1 to 2.2 × 10-2 Ω-1.cm-1, possibly indicating charge transfer from PANI to MWCNTs. To assess practical applications, we investigated the ability of the composite with 40% MWCNTs to remove phenol red (PR) dye from aqueous solutions. Through a systematic study of adsorption parameters and kinetics, we determined optimal conditions for effective dye removal and elucidated the underlying adsorption mechanism. Our results demonstrated the composite's efficiency in dye removal, with a 6.4mg·g-1 capacity for PR dye, highlighting its potential for environmental remediation efforts.

Experimental investigation and comparison of PBI/MWCNT and PSF/MWCNT membranes for recovering water from RO reject of brackish water by FO

The performances of polybenzimidazole (PBI) and polysulfone (PSF) membranes for recovering water from reverse osmosis (RO) reject of brackish water through forward osmosis (FO) were assessed and compared. Non-functionalised multi-walled carbon nanotubes (MWCNT) were added to the membrane casting solutions, with concentrations ranging from 0 to 3 wt%. The experiment was conducted for eight samples using RO reject of brackish water as the feed solution (FS) and 2 M analytical grade MgCl2 as the draw solution (DS). The hydrophilicity, water permeability, salt rejection rate (Rs), water flux (WF) and porosity of the membranes improved with increasing MWCNT content up to 2 wt%. Also, the structural parameter, salt permeability and reverse solute flux decreased. PBI/MWCNT2 wt% exhibited the best performance among the membranes tested compared with porosity of 70 ± 4 %, structural parameter of 0.36 ± 0.2 μm, and Rs of 93.5 %. In contrast with the pristine PBI membrane, an average water flux enhancement of 15 % and 49 % was observed for the FS and DS sides, respectively, for PBI/MWCNT2 wt%. It is evident from the results that including MWCNT improves the performance of both membranes, with better relative performance for PBI membranes than PSF membranes.

Tailoring Optoelectronic Properties of ZnO Nanoparticles via Incorporation of Multiwalled Carbon Nanotube Contents on of ZnO/MWCNT Nanocomposites

The present study demonstrates the tailoring of optoelectronic properties of ZnO nanoparticles (NPs) by adding multi-walled carbon nanotubes (MWCNTs) at different weight ratios. ZnO/MWCNT nanocomposites were successfully prepared using the solution blending method, and the optical spectra of all samples were determined using a UV–vis spectrometer. An increase in the optical absorption coefficient (α) and extinction coefficient (k) was observed with an increase in MWCNT content, resulting in the significant ability to attenuate incident light in ZnO/MWCNT nanocomposites compared to pure ZnO NPs. The optical band gap of pure ZnO NPs decreased from 3.26 eV to 2.58 eV in the ZnO/50 wt% MWCNT nanocomposite. The refractive index values ranged from 1.66 to 1.61 as the wavelength varied between 400 nm and 700 nm. Furthermore, the incorporation of MWCNTs in the ZnO/MWCNT nanocomposite had an impact on various dispersion parameters related to the refractive index. With increasing MWCNT content, the dielectric constant (ε 0) decreased from 2.40 to 1.96, while the mean oscillator wavelength (λ 0) increased from 157.7 nm to 164.2 nm and the oscillator strength (S0) decreased from 5.93 × 10−5 nm−2 to 3.70 × 10−6 nm−2. The localized density of state (N/m*) increased from 7.45 × 1057 to 20.8 × 1057 (m3 Kg) −1, and the long wavelength refractive index (ε ∞) rose from 3.683 to 4.745. Moreover, the plasma frequency (ω p) of the electron exhibited an increase from 2.15 × 1031 to 6.01 × 1031 Hz. These findings highlight the potential of tailoring the optoelectronic properties of ZnO NPs through the incorporation of MWCNTs, paving the way for the development of novel materials with improved optoelectronic characteristics for a wide range of applications.

Investigating the effects of MWCNTs on sustainable alkali-activated mortar: physical, rheological, and mechanical analysis

Alkali-activated material (AAM) is a potential sustainable substitute for normal Portland cement-based concrete, but the composition of the material and the design of the mixture has a significant impact on fresh and hardened properties. This research describes the formulation and mechanical behavior of a multi-walled carbon nanotube (MWCNT)-reinforced-based alkali-activated nanocomposite. MWCNTs were incorporated into the fly ash/hydrated lime-based alkali-activated material at concentrations of 0.1%, 0.2%, 0.3%, and 0.35% by weight of the binder. The significant dispersion of MWCNTs within the matrix was achieved in an aqueous solution of surfactant and superplasticizer by employing both magnetic stirring and sonication procedures. The fresh-state characteristics of the MWCNT-based AAM were evaluated in terms of setting time and rheology parameters. Notably, samples containing 0.3% and 0.35% MWCNTs exhibited setting times of 26 and 25 min, respectively. The rheological behavior of the nanocomposite adhered to Modified Bingham's model, displaying shear-thinning properties. Moreover, an increase in MWCNT content led to an augmentation in yield stress, with the highest enhancement of 11.1% and 13.1% in yield stress and plastic viscosity, respectively, observed for mortar samples with 0.3% MWCNTs. Mechanical assessments were performed at 7, 14, and 28 days to investigate the compressive and flexural strengths of the specimens. The addition of approximately 0.3% MWCNTs resulted in an impressive boost of up to 14% in compressive strength and an even more remarkable increase of 28% in flexural strength. Furthermore, after exposure to acid and sulfate attacks, the ACN3 samples (0.3% wt. of MWCNTs) exhibited minimal strength loss, with only 5.1% and 3.9% decrease in compressive strength after acid and sulfate attacks, respectively. According to these results, the MWCNTs can function as effective bridges to reduce and limit the progression of microcracks through the AAM-based nanocomposite under the circumstances of homogeneous distribution and good adhesion between both the MWCNTs and the adjacent AAM paste.

Unveiling thereinforcement potentiality of MWCNTs architecture towards the improvement of microstructural vis-a-vis mechanical and thermo-mechanical properties of pressureless sintered MgAl2O4 spinel ceramic composite

The study presented in this work focuses on the preparation of composites made of multi-walled carbon nanotubes (MWCNTs) and magnesium aluminate spinel through a pressureless sintering technique. The effects of sintering temperature and MWCNTs content on the densification behavior and mechanical properties of the composite were investigated in detail. The results revealed that the composite exhibited improved densification behavior, enhanced mechanical performance and decent control at the microstructural refinement with increasing MWCNTs content up to 0.75 wt%. The superior mechanical properties obtained in case of sintered composite were attributed to the synergetic toughening mechanisms involving the fiber pull out, cracks bridging and cracks deflection effects of reinforcing phases, observed as a resultant effect of strong interfaces with the matrix phase. The crystalline structural arrangement obtained from the XRD and Raman spectral analysis of the composites structure also satisfies the attainment of the promising reinforcement potential of the nanotubular structure. Most importantly, the study also exemplified the subsidiary interference of a surface decorative coating on the MWCNTs structure with the MgAl-binary oxide network. The strategic grafting of the oxide protective shell and the consequent development of a robust interfacial bridging network between the matrix and reinforcement phase regulated the energy dissipation characteristic for fiber debonding. This, in turn, restricted the crack growth phenomenon during mechanical loading, and thereby ultimately contributing to the enhanced fracture toughness, reduced thermal expansion co-efficient and augmented thermo-mechanical performance of the evolved spinel-based composite structure

Mechanical characterization of multifunctional highly porous carbon nanotube‐reinforced foams

AbstractIn recent years, novel features of ultra‐flexible nanocomposite foams have drawn tremendous attention toward these materials to be utilized in a variety of engineering applications. Since Young's modulus of nanocomposite foams is related to their mechanical strength and directly affects their applications, in this study, this property was evaluated experimentally and theoretically. In this regard, polydimethylsiloxane (PDMS)/multiwalled carbon nanotube (MWCNT) nanocomposite foams with different filler contents (e.g., 0.1, 0.25, and 0.5 wt%) and different porosities (e.g., 60%, 70%, and 80%) were fabricated by solvent casting and particulate leaching methods. The results suggested that the optimum value for foam porosity and MWCNT content is required to elevate Young's modulus of nanocomposite foams. The experimental data indicated that in the samples with 60% porosity increasing MWCNT content improved Young's modulus of the samples; however, in the samples with 70% porosity Young's modulus was elevated when the filler content was up to 0.25 wt%. Moreover, using the experimental data, a theoretical approach was successfully extended to predict Young's modulus of nanocomposite foams with the combination of different void fractions and CNT contents.

COMPARING THE PERFORMANCE OF USING NANOFLUIDS IN TWO DIFFERENT TYPES OF HEAT EXCHANGERS WITH THE SAME HEAT TRANSFER AREA

Using multi-wall carbon nanotubes (MWCNTs) based on distilled water with varied volume concentrations, experimental research was conducted. The performance of two distinct heat exchangers with the same heat transfer area was assessed. A tubular heat exchanger (THE) and a shell-and-tube heat exchanger (STHE) with a heat transfer area of 20,000 mm<sup>2</sup> were employed. A tubular heat exchanger (HT31) and a shell-and-tube heat exchanger (HT33) are available from Armfield for use with the heat exchange service unit (HT30X). Three volume concentrations of nanomaterials are used to create nanofluids (0.5%, 1%, 2%). While the rate of flow was the same in the heat exchangers, the Reynolds number of the flow inside the tube ranged from 1600 to 7800 for THE and from 2500 to 12,500 for STHE due to different inside diameters. The measured variables determine the coefficient of heat transfer, friction factor, Nusselt number, and effectiveness. The heat transfer coefficient in both heat exchangers was boosted with increasing MWCNT content, according to the experimental data. Because of the nanoparticle concentration, the heat transfer coefficient of STHE is 7-43% greater than that of THE. With the increase of nanofluid concentration, the Nusselt numbers were enhanced for the two heat exchangers. The increase in the Nu number for THE is higher than in its value for STHE within a range of 28.5-40%. Correlations between the Reynolds number and MWCNT volume concentration are proposed for each heat exchanger to compute the Nusselt number and friction factor. The results of the current study have been compared with previous studies and acceptable agreement can be found.

Effect of multi‐walled carbon nanotubes on rheological behavior and electrical conductivity of poly(ethylene‐co‐vinyl acetate)/acrylonitrile‐butadiene rubber/multi‐walled carbon nanotubes nanocomposites

AbstractIn this work, the effect of multi‐walled carbon nanotubes (MWCNTs) on electrical conductivity and rheological behavior of poly(ethylene‐co‐vinyl acetate) (EVA)/acrylonitrile‐butadiene rubber (NBR) blends containing 0 to 7 wt% MWCNTs are investigated. The theoretical calculations according to the interfacial free energy of the components revealed that the nanofillers had a tendency to locate in NBR domains. However, the rheological, electrical, and morphological studies indicated that the majority of the MWCNTs remained in the EVA phase. Shear creep measurements of the molten materials showed that the creep stability improved steadily with the increase in MWCNTs content. The creep behaviors of the materials, except EVA, were analogous to the Burgers model prediction and all four parameters of the model increased in value with the increase in the nanofillers content in comparison with those of the unfilled blend. The rheological studies indicated that the damping factor (tanδ) for the materials containing small amounts of the nanofillers reached a maximum and subsequently decreased with rising temperature. However, for the materials having 1 wt% MWCNTs and higher, the tanδ values were smaller at the highest temperature (200°C) than those of the lowest temperature (100°C) investigated in this work. The electrical percolation threshold was also found to take place at about 2.80 wt% MWCNTs loading.

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.

Experimental study on physical and mechanical properties and micro mechanism of carbon nanotubes cement-based composites

Carbon nanotubes are considered as a promising material for the development of high performance concrete. In order to study the effects of Multi walled carbon nanotubes (MWCNTs) content, water cement ratio and addition method on the mechanical properties and microstructure of cement-based composites, specimens with MWCNTs content of 0%, 0.05%, 0.08%, 0.10%, 0.15%, 0.20%, and 0.30% were prepared when the water cement ratio was 0.25, 0.3, 0.35, and 0.4, respectively. The physical properties, mechanical properties and microstructure were tested. The test results show that with the increase of MWCNTs content, the flexural strength and compressive strength of cement-based composites increase first and then decrease. The DIC test shows that the displacement and strain of the specimen with MWCNTs are smaller than the blank sample under the same concentrated load, while it is opposite before the failure of sample. The SEM test shows that MWCNTs play the role of bridging and filling in the matrix. The EDS analysis results show that the five main elements of carbon, oxygen, aluminum, silicon, and calcium in the composite are evenly distributed in the cement matrix.

Development of single‐polypropylene composites interleaved with MWCNT‐doped melt‐blown fine fiber mats

AbstractIn this article, we demonstrate fabricating polypropylene (PP)/multiwalled carbon nanotube (MWCNT) nanocomposite fiber veils and use them as interleaves in single‐polymer composites (SPCs) to enhance their thermal and mechanical properties. With this regard, we produced a hierarchical composite structure made of a film, a woven fabric and a fine fiber mat made of the same polymer. The nanocomposite fiber mats were generated by melt‐blowing. Results implied that incorporating MWCNT increased the viscosity of the melt blowing grade PP resin. Increasing MWCNT content increased the average fiber diameter and pore size by 2.1‐fold and 2.5‐fold, respectively. Incorporating MWCNT enhanced the melt‐blown (MB) fiber mat's specific strength by 78% and improved the thermal stability. We generated multiscale SPCs by film‐stacking, for which we applied a PP film as a matrix, a PP‐woven fabric as the primary reinforcement, and the MB fiber mats as interleaves. The SPC's tensile modulus was improved by 37% by the interleaving. Our findings implied that the MWCNT‐doped PP fiber mat interleaving provides a robust interfacial adhesion and higher damage tolerance under tensile load. Master curves were constructed from dynamic mechanical analysis frequency sweep tests based on the time–temperature superposition principle. The storage modulus increased by 33%, while the tanδ decreased around 10% with PP/MWCNT fiber mat interleaving. The developed multiscale SPC with MWCNT fiber mat interleaving veils may be easily integrated into engineering composite applications due to its cost‐efficiency, fair recycling, straightforward processing, enhanced stiffness, and interfacial adhesion.

Morphological and Electrical properties of Polyvinylpyrrolidone/Multi-walled Carbon Nanotubes Nanocomposite with Graphene

The solution casting method was used to prepare a polyvinylpyrrolidone (PVP)/Multi-walled carbon nanotubes (MWCNTs) nanocomposite with Graphene (Gr). Field Effect Scanning Electron Microscope (FESEM) and Fourier Transformer Infrared (FTIR) were used to characterize the surface morphology and optical properties of samples. FESEM images revealed a uniform distribution of graphene within the PVP-MWCNT nanocomposite. The FTIR spectra confirmed the nanocomposite information is successful with apperaring the presence of primary distinct peaks belonging to vibration groups that describe the prepared samples.. Furthermore, found that the DC electrical conductivity of the prepared nanocomposites increases with increasing MWCNT concentration which is due to hopping conduction

A low seepage threshold and super‐toughness of polybutylene succinate‐based composites with double percolation structure: Synergy of multi‐wall carbon nanotubes and polyvinyl butyral

AbstractTo obtain a super‐toughness and low seepage threshold for the conductivity of biodegradable soft polymer material, biodegradable polybutylene succinate (PBS)‐based composites with different contents of polyvinyl butyral (PVB) and multi‐wall carbon nanotubes (MWCNTs) were prepared by melt‐blending method. Synergy effects of different modified MWCNTs and PVB on the morphology, crystallization, and electrical and mechanical properties of MWCNTs/PVB/PBS composites were examined by Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), polarizing microscope (POM), resistance tester, and universal testing machine. Compared with pure PBS, with increasing MWCNT content, the electrical conductivity of the MWCNTs/PBS composites showed an upward trend, and the percolation threshold for electrical conductivity of the MWCNTs/PBS composites reached 0.47%. The electrical conductivity of the PBS composite mixed with 1.0 wt% of surface modified MWCNTs slightly increased by one order of magnitude compared with that of pure PBS. By adding 20 wt% of the PVB and 1 wt% of the unmodified MWCNTs, the electrical conductivity of the MWCNTs/PVB/PBS composite increased by seven orders of magnitude compared with that of pure PBS. The percolation threshold for electrical conductivity of the MWCNTs/PVB/PBS composites decreased to 0.049% owing to the formation of double percolation structure. Furthermore, compared with pure PBS, when the PVB content was 20 wt%, and the MWCNTs was 1 wt%, the elongation at break and V‐notch impact strength of PBS‐based composite dramatically increased by approximately 300% and 12‐fold, respectively.

Dielectric spectroscopy of poly(ethylene oxide)–carbon nanotube nanocomposites

The dielectric properties of poly(ethylene oxide)–multiwalled carbon nanotube (MWCNT) nanocomposites have been studied over a wide range of frequency (0.1–106 Hz) and temperature (180–300 K). Nanocomposites were prepared by both melt mixing and twin-screw extrusion, and the concentration of MWCNTs was varied from 0 to 5 wt. %. Both the real and imaginary parts of the complex permittivity increase with the increasing MWCNT concentration. We observe a percolation transition in the DC conductivity of the composites above a critical MWCNT concentration pc. The data from the twin-screw extruded samples give a very well-defined value of pc and a percolation exponent of 1.9 ± 0.2, in good agreement with theoretical predictions. In contrast, both the percolation threshold and the critical exponent were more poorly defined for the melt-mixed nanocomposites. This indicates that the conductive properties of these materials can strongly depend on the details of sample preparation. Our data suggest that the dc conductivity of the nanocomposites is due to the conduction along the nanotubes, coupled with thermally activated transport of electrons across thin polymer bridges, which separate the nanotubes. The frequency dependence of the dielectric spectrum was studied as a function of temperature and composition. The primary dielectric relaxation process is due to the motions of electric dipoles on the polymer backbone. At low MWCNT concentrations, the relaxation involves the entire polymer chains and is slowed substantially when a low concentration of MWCNT is added. At higher MWCNT concentrations, the relaxation becomes much faster. We attribute this to binding of the polymer chains to the nanotubes, which reduces the length of the chain segments contributing to the dielectric relaxation.

Physico–mechanical properties of poly(ethylene‐co‐vinyl acetate)/acrylonitrile‐butadiene rubber/multi‐walled carbon nanotubes nanocomposites

AbstractThe influence of multi‐walled carbon nanotubes (MWCNTs) on thermal, mechanical and wetting properties as well as rheological behavior of poly(ethylene‐co‐vinyl acetate) (EVA)/acrylonitrile‐butadiene rubber nanocomposites were studied. The solid surface free energy (), work of adhesion (), interfacial free energy (), spreading coefficient () and Girifalco‐Good's interaction parameter () were calculated for the materials fabricated. The results showed that the contact angle and decreased; however, , , , and increased with the increase in MWCNTs content. The maximum tensile strength and toughness were obtained for the nanocomposite containing 1 wt% nanofillers. It was also found that both of the relaxation ratio (Rr) and relaxation rate index (n) decreased with increasing in the carbon nanotubes (CNTs) concentration. The results designated that the values of Rr and n for the nanocomposite containing 7 wt% MWCNTs were 19% and 60% smaller than those of the unfilled blend, respectively. The Casson plot analysis indicated that the yield stress of the molten materials incremented with the increase in MWCNTs loading according to a quadratic equation. The analysis of crystallization exotherms and melting endotherms revealed that CNTs triggered the crystallization process at slightly higher temperature, however, melting point slightly and the rate of nucleation noticeably reduced with the increase in the nanofillers content.

Facile fabrication of carbon nanotube embedded pore filling ion exchange membrane with high ion exchange capacity and permselectivity for high-performance reverse electrodialysis

The harvesting salinity gradient power of reverse electrodialysis is mainly derived from ion-exchange membranes (IEMs). Among IEMs for the assembly of reverse electrodialysis stacks, pore-filling ion exchange membranes (PIEMs) and nanocomposite IEMs have been considered for high performance. In our study, we fabricated multiwall carbon nanotube (MWCNT) nanocomposite PIEMs, in which nanocomposite IEM and PIEM were hybridized by a simple impregnation process using an aqueous MWCNT solution. The MWCNT composition in the PIEM could be precisely controlled by the impregnation times and MWCNT concentration in the solution. Additionally, the MWCNTs in the PIEMs were homogenously dispersed without any aggregation. The ion exchange capacities and permselectivities of the MWCNT nanocomposite PIEMs increased with increasing MWCNT content in the PIEMs due to the formation of an optimized ion pathway by reconstruction of the ion-conducting moiety in the electrolyte polymer by hydrophobic MWCNTs. The open-circuit voltages, currents, and power densities of the reverse electrodialysis stacks made with MWCNT nanocomposite IEMs were better than those of PIEMs without MWCNTs, indicating improved performance. This improvement originated from the high ion exchange capacities and permselectivities of the MWCNT nanocomposite PIEMs.