Homogeneous Dispersion Of Carbon Nanotubes Research Articles

A tough, stretchable, adhesive and electroconductive polyacrylamide hydrogel sensor incorporated with sulfonated nanocellulose and carbon nanotubes

Recently, hydrogel sensors have been widely applied in wearable and portable electronics, but the low mechanical property, intolerance of fatigue, and low sensitivity and adhesion limit their further applications. In this study, sulfonated nanocellulose (SCNF) with dual functionality was blended into polyacrylamide (PAM) hydrogel matrix to reinforce the mechanical strength and facilitate the homogeneous dispersion of carbon nanotubes (CNTs). The SCNF-CNT/PAM hydrogel was designed through free radical polymerization to achieve commendable mechanical, electrical, and multifunctional properties. The environmental-friendly SCNF serves as bio-templates to facilitate the assembling of CNT into integrated SCNF-CNT structures with good dispersity, thus enabling the establishment of an integrated conducting and reinforcing network. The fabricated SCNF-CNT/PAM hydrogel exhibited outstanding compressive strength (∼0.45 MPa at 50 % strain), tensile strength (∼169.12 kPa), and antifatigue capacity under cyclic stretching and pressing. Furthermore, the multifunctional sensors assembled using this hydrogel demonstrated high strain sensitivity (gauge factor ~ 3.7 at 100–400 % strain) and effectively detected human motions. This design principle provides promising prospects for constructing next-generation multifunctional flexible sensors, and the integration of these distinctive properties enables the prepared composite hydrogels to find potential applications in various areas, such as implantable soft electronic devices, electronic skin, and human movement monitoring.

Aging behavior, microstructure and mechanical properties of Al-Cu-Mg alloy matrix composites reinforced with carbon nanotubes

High-strength Al-Cu-Mg alloys are good matrix candidates for fabricating strong and tough Al matrix composites reinforced with carbon nanotubes (CNTs). In this study, an element mechanical alloying method was used to achieve homogeneous CNT dispersion in hard Al-Cu-Mg matrix. A comprehensive transmission electron microscopy study was applied on peak-aged CNTs/Al-Cu-Mg composites and referential Al-Cu-Mg alloy. It was found that the ex-situ CNTs increased the dislocation density and hindered the recrystallization of the Al-Cu-Mg matrix. Thus, larger local stress and strain were detected in CNTs/Al-Cu-Mg composites. The precipitation in CNTs/Al-Cu-Mg composites was accelerated, which brought extra 12 % improvement to tensile yield strength of the composite. The distribution of precipitates in CNTs/Al-Cu-Mg composites were nonuniform due to the element mechanical alloying process, which was probably beneficial to the high ductility of the CNTs/Al-Cu-Mg composite. With the synergetic strengthening effect of CNTs and fine precipitates, CNTs/Al-Cu-Mg composites exhibited well-balanced strength and ductility.

From Nanoscale to Macroscale Characterization of Sulfur-Modified Oxidized Carbon Nanotubes in Styrene Butadiene Rubber Compounds.

The homogeneous dispersion of carbon nanotubes (CNTs) in a rubber matrix is a key factor limiting their amazing potential. CNTs tend to agglomerate into bundles due to van der Waals interactions. To overcome this limitation, CNTs have been surface-modified with oxygen-bearing groups and sulfur. Using atomic force microscopy (AFM) techniques, a deep nanoscale characterization of the morphology, the degree of dispersion of the CNTs in the styrene butadiene rubber (SBR) matrix, and the thickness of the interfacial layer was carried out in this study. In this context, the results from nanoscale characterization showed that the thermal oxidation-sulfur treatment leads to a composite with better dispersion in the matrix, as well as a thicker interfacial layer, indicating a stronger filler-rubber interaction. The second part of this work focused on the macroscale results, such as the Payne effect, vulcanization curves, and mechanical properties. The Payne effect, vulcanization curves, and mechanical properties confirmed the lower reinforcing effect observed in the case of the chemical oxidation treatment because, on the one hand, this composite showed the highest agglomeration of CNTs after the acid treatment. On the other hand, the presence of acid residues provoked the absorption of basic accelerators on the surface of the CNTs.

Development of an Electroactive and Thermo-Reversible Diels-Alder Epoxy Nanocomposite Doped with Carbon Nanotubes.

The manufacturing of Diels-Alder (D-A) crosslinked epoxy nanocomposites is an emerging field with several challenges to overcome: the synthesis is complex due to side reactions, the mechanical properties are hindered by the brittleness of these bonds, and the content of carbon nanotubes (CNT) added to achieve electroactivity is much higher than the percolation thresholds of other conventional resins. In this work, we develop nanocomposites with different D-A crosslinking ratios (0, 0.6, and 1.0) and CNT contents (0.1, 0.3, 0.5, 0.7, and 0.9 wt.%), achieving a simplified route and avoiding the use of solvents and side reactions by selecting a two-step curing method (100 °C-6 h + 60 °C-12 h) that generates the thermo-reversible resins. These reversible nanocomposites show ohmic behavior and effective Joule heating, reaching the dissociation temperatures of the D-A bonds. The fully reversible nanocomposites (ratio 1.0) present more homogeneous CNT dispersion compared to the partially reversible nanocomposites (ratio 0.6), showing higher electrical conductivity, as well as higher brittleness. For this study, the nanocomposite with a partially reversible matrix (ratio 0.6) doped with 0.7 CNT wt.% was selected to allow us to study its new smart functionalities and performance due to its reversible network by analyzing self-healing and thermoforming.

Morphology and selected properties of NR/BR/CNT nanocomposites effect of ethanol-assisted mixing

Carbon nanotubes (CNT) and ethanol-assisted mixing were used to obtain composites based on a mixture of natural rubber and butadiene rubber (NR/BR 80/20). The structure of the composites was determined by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermal aging tests were also carried out and the vulcanization process was characterized. SEM confirmed the homogeneous dispersion of CNTs in the polymer matrix. Improvements in tensile and tear strength as well as thermal stability were also achieved.

In Situ Filler Addition for Homogeneous Dispersion of Carbon Nanotubes in Multi Jet Fusion-Printed Elastomer Composites.

The dispersibility of fillers determines their effect on the mechanical properties and anisotropy of the 3D-printed polymeric composites. Nanoscale fillers have the tendency to aggregate, resulting in the deterioration of part performance. An in situ filler addition method using the newly developed dual-functional toughness agents (TAs) is proposed in this work for the homogeneous dispersion of carbon nanotubes (CNTs) in elastomer composites printed via multi jet fusion. The CNTs added in the TAs serve as an infrared absorbing colorant for selective powder fusion, as well as the strengthening and toughening fillers. The printability of the TA istheoretically deduced based on the measured physical properties, which aresubsequently verified experimentally. The printing parameters and agent formulation areoptimized to maximize the mechanical performance of the printed parts. The printed elastomer parts show significant improvement in strength and toughness for all printing orientations and alleviation of the mechanical anisotropy originating from the layer-wise fabrication manner. This in situ filler addition method using tailorable TAs is applicable for fabricating parts with site-specific mechanical properties and is promising in assisting the scalable manufacturing of 3D-printed elastomers.

Development and Investigation of Repair Self-Sensing Composites Using S-CNT

This study analyzed the mechanical and electrical characteristics of repair self-sensing composites. In order to ensure homogeneous dispersion of carbon nanotubes (CNTs) in the repair mortar, porous powder was impregnated with the liquid MWCNT, dried, and then pulverized. This CNT powder was named S-CNT, and a repair self-sensing cement composite was fabricated using it with different dosages, by weight, of 3, 6, and 9%. Mechanical and electrical performances of the developed materials were investigated through flexural, compressive, and bonding strengths, dry shrinkage, porosity, and fractional change in resistance (FCR) tests. There was little difference in terms of strength, between the three different composites made with the different dosages of S-CNT. The strength of the composite with 9% of S-CNT was even higher than that of the plain specimen. As a result of measuring drying shrinkage, conducted to evaluate the effect of improving dispersion, the length change rate decreased as the amount of S-CNT increased. As a result of the porosity results of the specimens incorporating the same mass of CNT as S-CNT, it was confirmed that the dispersibility was clearly improved. In addition, as an electrical characteristic, when the S-CNT mixed specimen was repeatedly loaded with a bending load, FCR appeared, confirming the self-sensing performance.

Intelligent Sensing System of the Car Seat With Flexible Piezoresistive Sensor of Double-Layer Conductive Network

A highly sensitive and flexible piezoresistive sensor is fabricated by Spacial Confined Forced Network Assembly (SCFNA) method in this paper. Polydimethylsiloxane (PDMS)/ short carbon fiber (SCF)/ carbon nanotube (CNT) composite with a V-shaped groove microstructure on surface is prepared as the flexible sensitive components. Because the size of SCF is larger than the microstructure mold, SCF is hard to enter the microstructure. So a double-layer conductive network is constructed by spacial confined assembly of microstructure mold, so that pure CNT network is in the layer of microstructure and the SCF/CNT network is in the layer of non-microstructure. As SCF is more effective in enhancing the conductivity of PDMS than CNT due to its larger aspect ratio and more compact network, the conductivity of SCF/CNT network is higher than CNT network. But the stability and sensitivity of CNT network is higher than SCF/CNT network because the smaller size and more homogeneous dispersion of CNT. Therefore the laminating of SCF/CNT network and CNT network with microstructure on surface could have synergistic effect to improve both the conductivity, stability and the sensitivity of sensor. The accuracy rate of the sensing system can reach 91.1%, which provide the relevant basis for the intelligent control of the car seats.

Nanocomposite block copolymer membranes with enhanced permeance and robustness by carbon nanotube doping

Block copolymers (BCPs) have received extensive attention in the preparation of advanced membranes for precise separations. However, BCP-derived membranes usually suffer from insufficient mechanical robustness, especially for the most extensively studied polystyrene-based ones. Herein, carbon nanotubes (CNTs) are incorporated into polystyrene-block-poly (2-vinyl pyridine) (S2VP) membranes to enhance the mechanical robustness and water permeance. It is found that mild oxidation is enough to enable the homogeneous dispersion of CNTs in the S2VP solution. The CNT/S2VP mixture is directly coated on macroporous substrates, followed by selective swelling-induced pore generation to produce the CNT-doped S2VP nanocomposite membranes. The as-prepared membranes are featured with two sets of pores: swelling-induced pores and incompatibility-induced nanoscale gaps between CNTs and the S2VP matrix, leading to improved permeances without any decrease of the retention performances. Also, owing to the presence of CNTs in the polymer matrix, the membranes show excellent mechanical robustness and exhibit better pressure resistance than neat S2VP membrane without CNT doping. This work demonstrates a simple yet efficient strategy to prepare BCP-based nanocomposite membranes with enhanced permeance and robustness at no expense of retention.

Fabrication of High-Performance CNT Reinforced Polymer Composite for Additive Manufacturing by Phase Inversion Technique.

Additive Manufacturing (AM) of polymer composites has enabled the fabrication of highly customized parts with notably mechanical properties, thermal and electrical conductivity compared to un-reinforced polymers. Employing the reinforcements was a key factor in improving the properties of polymers after being 3D printed. However, almost all the existing 3D printing methods could make the most of disparate fiber reinforcement techniques, the fused filament fabrication (FFF) method is reviewed in this study to better understand its flexibility to employ for the proposed novel method. Carbon nanotubes (CNTs) as a desirable reinforcement have a great potential to improve the mechanical, thermal, and electrical properties of 3D printed polymers. Several functionalization approaches for the preparation of CNT reinforced composites are discussed in this study. However, due to the non-uniform distribution and direction of reinforcements, the properties of the resulted specimen do not change as theoretically expected. Based on the phase inversion method, this paper proposes a novel technique to produce CNT-reinforced filaments to simultaneously increase the mechanical, thermal, and electrical properties. A homogeneous CNT dispersion in a dilute polymer solution is first obtained by sonication techniques. Then, the CNT/polymer filaments with the desired CNT content can be obtained by extracting the polymer’s solvent. Furthermore, optimizing the filament draw ratio can result in a reasonable CNT orientation along the filament stretching direction.

Influence of carbon nanotube reinforcement on the heat transfer coefficient, microstructure, and mechanical properties of a die cast Al-7Si-0.35Mg alloy

Al-7Si-0.35Mg or A356 alloy is most widely used in aircraft and automobile industries owing to its high strength to weight ratio. This alloy has been reinforced with a 1 wt% carbon nanotube (CNT) to improve its properties in this investigation. First, A356/1 wt% CNT powders were ball milled in the presence of ethanol and subsequently consolidated using gravity die casting. Ball milling was effective in achieving homogeneous dispersion of CNT. The microstructural study revealed the segregation of the Al4C3 phase at the grain boundary. This mechanism is known as grain boundary precipitation. Also, the grain size has decreased by ~44%. Next, the casting-die interfacial heat transfer coefficient (IHTC) has been evaluated using Beck's inverse heat transfer algorithm. With the reinforcement, the IHTC has increased by ~2.5%, which indicates the rise in heat transfer rate during solidification. Then, the experimental and theoretical tensile properties of A356 were correlated using simulation software. The experimental results showed the synergistic effect of grain size, Al4C3, and IHTC improving yield strength by ~19.8%, ultimate tensile strength by ~14.13%, elongation by 7%, and hardness ~22%. Therefore, a meagre 1 wt% CNT has improved the heat transfer rate of the melt as indicated by IHTC values. This effect was further corroborated by evaluating the thermal conductivity of the sample. The thermal conductivity has improved by 10% that resulted in finer grain size of the sample. Therefore, such reinforced alloys are expected to display higher strength demanded in various industrial applications.

Influence of crystallinity and chain interactions on the electrical properties of polyamides/carbon nanotubes nanocomposites

AbstractThis work evaluates the effects of the crystallinity degree and π–π interactions between nanoparticles and a polymeric matrix on the electrical properties of polyamides and carbon nanotubes (CNT) nanocomposites. Two polymeric matrices were chosen; polyamide (PA) 6.6, a semi‐crystalline polymer, and PA 6I‐6T (here called aPA), a semi‐aromatic and amorphous polyamide. The PA 6.6 crystallinity degree did not significantly change. Both lamellar thicknesses, amorphous (La) and crystalline (Lc), were estimated through Small‐angle X‐ray scattering. La increased significantly when CNTs were added. Both nanocomposites presented almost the same percolation threshold. In aPA nanocomposites, the π–π interaction between aromatic groups of CNTs and aPA is not only responsible for a homogeneous CNT dispersion, but also creates a direct path, parallel to the electrodes, for electron conduction after the percolation limit. In the PA 6.6 nanocomposites, the CNTs preferably disperse in the amorphous regions, forming a conductive network.

The Study of the Preliminary Forming Process of the Highly-Homogeneous Mixture Consisting of the Aluminum Powder – CNT in the Production Technology of Composite Materials

The issue of the nanocomposites’ synthesis using of aluminum matrixes, reinforced with carbon nanotubes, with high physical and mechanical performance capabilities, as related to achieving of the homogeneous dispersion of carbon nanotubes in the composite’s aluminum matrix has been considered. Basics of the preparation technology have been developed and requirements for parameters of the so-called «normalized» mixture (highly-homogeneous in terms of volume of the dry mixture «aluminum powder – single-walled carbon nanotubes), intended for the efficient synthesis of composite granules by the mechanical alloying have been determined.

INFLUENCE OF CARBON NANOTUBES REINFORCEMENT ON CHARACTERISTICS OF THERMALLY SPRAYED CERAMIC COATINGS

The influence of reinforcement of carbon nanotubes (CNTs) on microstructural features and mechanical properties of thermally sprayed Al2O3–3[Formula: see text]wt.%TiO2and WC–20[Formula: see text]wt.%Co coatings was investigated. Alumina–Titania coatings were deposited by Air Plasma Spraying (APS) and Tungsten Carbide–Cobalt coatings were deposited by High-Velocity Oxy-Fuel (HVOF) spraying process. The coatings obtained with reinforcement of CNTs were characterized to interpret the microstructural changes and also to evaluate the variation in their mechanical properties. The percentage composition of CNTs in both APS and HVOF coatings systems were varied in the order of 2, 4, and 6[Formula: see text]wt.%. It has been found that homogenous dispersion of carbon nanotubes in the coating systems results in increased microhardness and reduced surface roughness. Also, the microstructural features of the coating systems clearly showed that the coatings are denser with fewer pores due to the presence of CNTs.

Properties of Carbon Nanotubes-Calcium Carbonate Hybrid Filled Epoxy Composites

Carbon nanotubes (CNTs) have a great potential to be used as filler to enhance the mechanical properties of polymer composites due to excellent properties. However, CNTs have limitation of difficult to disperse in polymer matrix. The hybridization of CNTs and inorganic fillers can improve the dispersion and combine their properties in polymer composites. In the present work, the properties of the epoxy composites filled with carbon nanotube-calcium carbonate (CNTs-CaCO3) hybrid, at various filler loading (i.e., 1-5 wt.%) were studied. The CNTs-CaCO3 hybrid fillers were prepared by physically mixing (PHY) method and chemical vapor deposition (CVD) method. The tensile properties and hardness of both composites were investigated at different weight percentages of filler loading. The CNTs-CaCO3 CVD hybrid composites showed higher tensile strength and hardness than the CNTs-CaCO3 PHY hybrid composites. This increase was associated with the homogenous dispersion of CNT–CaCO3 particle filler. The morphological studies of fracture surfaces after tensile test by means of SEM showed homogenous dispersion of CNTs-calcium carbonate CVD hybrid in epoxy matrix. The result shows that the CNTs-calcium carbonate CVD hybrid composites are capable in increasing tensile strength by up to 116.4%, giving a tensile modulus of 40.3%, and hardness value of 39.2% as compared to a pure epoxy.

Carbon nanotube-collagen@hydroxyapatite composites with improved mechanical and biological properties fabricated by a multi in situ synthesis process.

A novel carbon nanotube-collagen@hydroxyapatite (CNT-Col@HA) composite with good mechanical and biological properties was fabricated successfully by a multi in situ synthesis process, which can be used to repair or replace the damaged bone tissues. The carbon nanotube (CNT)/hydroxyapatite (HA) composite powders were firstly synthesized by the in situ chemical vapor deposition method. After the acidification of CNTs, the collagen (Col) molecules were covalently grafted onto the surface of CNTs in situ by the formation of amide linkages, obtaining Col-encapsulated CNTs powders. And then, a HA layer was deposited in situ onto the Col-encapsulated CNTs to form HA- and Col-encapsulated CNTs, consequently the ideal CNT-Col@HA composite was fabricated by the powder metallurgy method, and its mechanical and biological properties were investigated. The results showed that, the multi in situ synthesis process ensured the homogeneous dispersion of CNTs in HA matrix, and via the intermediate layer of Col, the close chemical bonding between CNT reinforcements and HA matrix was obtained, thereby the flexural strength and fracture toughness of the in situ synthesized 3wt.% CNT-Col@HA composite were increased by approximately 74.2% and 274.6% compared with those of pure HA bulk, and better cell adhesion, spreading and proliferation were also observed on the in situ synthesized CNT-Col@HA composites. Therefore, the obtained composites in this work have great potential to be applied as implant material in clinic.

Synergistic strengthening effect of carbon nanotubes (CNTs) and titanium diboride (TiB2) microparticles on mechanical properties of copper matrix composites

Synergistic strengthening is increasingly explored for developing high-performance metal matrix composites. In the present work, copper matrix composites reinforced with carbon nanotubes (CNTs) and TiB2 microparticles were fabricated via electroless deposition, powder metallurgy, hot extrusion, and water quenching. The synergistic strengthening effect of the nano-and micro-reinforcements was elaborated and analyzed based on experimental investigation and theoretical calculation. (1CNT-4TiB2)/Cu composite exhibited a better combination of the tensile strength of 375MPa with elongation of 32.4% than other composites, representing 86.3%, 71.5%, and 22.8% strength increment in comparison with pure Cu, 4TiB2/Cu composite, and 1CNT/Cu composite, respectively. The strengthening efficiency of CNTs in (1CNT-4TiB2)/Cu composite is markedly higher than that in 1CNT/Cu composite (126.7 and 82.3, respectively), confirming the synergistic strengthening effect in enhancing the mechanical properties. Quantitative analysis and experimental characterization indicated that the thermal mismatch and load transfer mechanism of CNTs were the main factors contributing to the tensile strength enhancement of the composite. The synergistic strengthening effect was attributed to that TiB2 microparticles improved the homogeneous dispersion of CNTs, promoting the proportion of thermal mismatch and load transfer mechanisms. The present work may provide a new sight into improving the synergistic strengthening effect in metal matrix composites.

Composite of medium-chain-length polyhydroxyalkanoates-co-methyl acrylate and carbon nanotubes as innovative electrodes modifier in microbial fuel cell.

A microbial fuel cell is a sustainable and environmental-friendly device that combines electricity generation and wastewater treatment through metabolic activities of microorganisms. However, low power output from inadequate electron transfer to the anode electrode hampers its practical implementation. Nanocomposites of oxidized carbon nanotubes and medium-chain-length polyhydroxyalkanoates (mcl-PHA) grafted with methyl acrylate monomers enhance the electrochemical function of electrodes in microbial fuel cell. Extensive polymerization of methyl acrylate monomers within mcl-PHA matrix, and homogenous dispersion of carbon nanotubes within the graft matrix are responsible for the enhancement. Modified electrodes exhibit high conductivities, better redox peak and reduction of cell internal resistance up to 76%. A stable voltage output at almost 700mV running for 225H generates maximum power and current density of 351mW/m2 and 765mA/m2 , respectively. Superior biofilm growth on modified surface is responsible for improved electron transfer to the anode hence stable and elevated power output generation.

Evaluation of the Mechanical Properties of Carbon Nanotube (CNT) Reinforced Aluminum (6061) Composites Using Closed Die Forging

In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

Planting carbon nanotubes within Ti-6Al-4V to make high-quality composite powders for 3D printing high-performance Ti-6Al-4V matrix composites

We developed a novel process of planting carbon nanotubes (CNTs) within spherical Ti-6Al-4V powder to fabricate a CNTs/Ti-6Al-4V composite powder. The new powder addressed the issues of spherical morphology maintaining and homogenous dispersion of CNTs, and thereby exhibited good printability. After printing, a relative density of 99.9% was obtained. Microstructurally, some CNTs were retained, while the remaining formed TiC nanoparticles and nanoplatelets via interfacial reaction and dissolution-precipitation mechanisms, respectively. The printed composites had tensile yield strength of 1162 MPa and elongation of 3.2% due to synergistic effect of bridge enhancement of TiC nanoplatelets and load transfer from matrix to CNTs.