CNT Dispersion Research Articles

Enhanced thermoelectric properties of CNT dispersed and Na-doped Bi2Ba2Co2Oy composites

The thermoelectric properties of Bi2Ba2Co2Oy and Bi1.975Na0.025Ba2Co2Oy+xwt% carbon nanotubes (CNT; x=0.00, 0.05, 0.10, 0.15, 0.5, and 1.0) ceramic samples synthesised by the solid-state reaction method were investigated from 300K to 950K. Na doping with a small amount played an important role in reducing resistivity and slightly reduced the Seebeck coefficients and the thermal conductivity. The CNT dispersant increased resistivity, but the thermal conductivity was reduced remarkably. In particular, the Bi1.975Na0.025Ba2Co2Oy+1.0wt% CNT sample exhibited an ultralow thermal conductivity of 0.39WK−1m−1 at 923K. This was attributed to the point defects caused by Na doping and the interface scattering caused by the CNT dispersant. The combination of Na doping and CNT dispersion had better effects on thermoelectric properties. The Bi1.975Na0.025Ba2Co2Oy+0.5wt% CNT sample exhibited a better dimensionless figure of merit (ZT) value of 0.2 at 923K, which was improved by 78.2%, compared with the undoped Bi2Ba2Co2Oy sample.

Migration Behavior of Carbon Nanotube in Capillary Electrophoresis with Sodium Dodecyl Sulfate and Water-Soluble Nonionic Polymer

Single-walled carbon natobube (SWCNT) was dispersed in an aqueous surfactant solution, and the dispersion of CNT was analyzed by capillary electrophoresis (CE). The dispersion was evaluated through a broad peak of the electropherograms, while the aggregation of the CNT was attributed to the shot signals in the electropherograms. Water-soluble nonionic polymer was also added in the separation buffer to examine the dispersion in the surfactant solution as well as to control the migration behavior. Polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone were examined. The electrophoretic mobility of the broad peak got smaller with increasing concentrations of the polymer examined. The theoretical number of plates of the broad peak was improved by the addition of the polymer. Moderately broad peak was preferable for the dispersion of the SWCNT in the surfactant solution.

Functionalized carbon nanotube (CNT) membrane: progress and challenges

Various approaches have been investigated to functionalize CNT for achieving a high dispersion of CNT as well as high compatibility between CNT and polymer matrix which lead to improvement of membrane properties and performances.

Quenching performance of AISI 1010 in CNT nanofluids

In this paper, the effect of a low carbon steel on microstructural and mechanical properties during quenching in CNT Nanofluids has been investigated. CNT nanofluids have been prepared and used as quenchants to study the effect of CNT dispersion, its concentrations and agitation on the heat transfer rate during quenching. However, the microstructure and mechanical properties of the steel that is being quenched in CNT Nanofluids were not yet analyzed. Hence in this research, a low carbon steel of grade AISI 1010 was chosen and quench probes of diameter 20 mm and length 50 mm were machined. They were then quenched in three different quench mediums namely distilled water (D.I), water based CNT nanofluids with and without surfactant. After quenching, the microstructure, surface roughness and hardness of the quenched probes were investigated and found high surface roughness on probes quenched in CNT nanfluids. Also, probes quenched in CNT nanofulid prepared with surfactant had higher hardness and the microstructure of probes quenched in different quenching mediums varied.

Dynamics of FG-CNT reinforced composite cylindrical panel subjected to moving load

Present study deals with the dynamic response of a functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylindrical panel subjected to moving load on the panel surface. Panel is formulated within the framework of first order shear deformation shell theory. Formulation is restricted to be geometrically linear. Distribution of CNTs across the panel thickness is considered to be uniform or functionally graded. Effective properties of the composite media are estimated using a refined rule of mixtures approach with introduction of efficiency parameters. The matrix representation of dynamic equations is obtained according to the Ritz method whose orthogonal shape functions are obtained according to the Gram-Schmidt process. The resulting dynamic equations are traced in time following the Newmark time marching scheme. Parametric studies are given to explore the characteristics of CNTs as reinforcements and influences of boundary conditions. It is shown that, increasing the volume fraction of CNT as reinforcements decreases the dynamic response of the panel. Furthermore, in comparison to other patterns of CNT dispersion, in FG-X pattern of CNT distribution, panel becomes more stiff and dynamic deflection decreases.

Multiscale benzoxazine composites: The role of pristine CNTs as efficient reinforcing agents for high-performance applications

Abstract A convenient and efficient approach is presented in this study for developing advanced thermosetting composite laminates reinforced or not with 0.5 wt% of pristine CNTs. A highly aromatic benzoxazine monomer was selected as the matrix for the preparation of carbon fiber composites due to its strong intrinsic affinities with CNTs. Fine CNT dispersion was achieved within the whole composite after fabric impregnation leading to a considerable increase of the glass transition temperature of about 50 °C. The resulting multiscale composite exibits an improved thermomechanical stability, up to 300 °C and its room temperature flexural strength is enhanced from 520 to 700 MPa. Moreover, the confinement of neat CNTs within the whole composite is also found to have a beneficial effect on the fire properties and the water sensitivity of the composite. These promising results highlight that when neat CNTs are able to develop strong interactions with the aromatic resin, the resulting system can provide a new and efficient way to design and improve the properties of composite laminates.

Effect of functionalized CNTs and liquid crystalline polymer on thermo-oxidative stability of polyethylene-based hybrid composites

Hybrid composites based on polyethylene (PE) filled with thermotropic liquid crystalline polymer (LCP) and pristine or hydroxyl- or carboxylic-functionalized CNTs were prepared using melt extrusion process. Thermo-oxidative decomposition under dynamic and isothermal conditions was investigated using thermogravimetric analysis (TG). From TG profiles and activation energy analysis, the highest thermo-oxidative stability revealed from both dynamic and isothermal investigations was clearly observed for the PE-based hybrid composite filled with LCP and small amount of carboxylic-functionalized CNT. The melt rheological investigation showed that the effect of LCP and CNTs loading on viscoelastic characteristics of the composites was clearly pronounced at low frequency and the viscous part was found as a dominant factor. Complex viscosity, storage and loss moduli of the hybrid composite containing carboxylic-functionalized CNT showed the highest values compared among all samples examined. The morphological results observed using scanning electron microscopy and transmission electron microscopy indicated the improved dispersion of both LCP and carboxylic-functionalized CNT fillers. The obtained results indicated the importance of LCP-assisted dispersion of carboxylic-functionalized CNT through interface interaction, resulting in the remarkable improvement in thermo-oxidative stability of the composite.

Dispersion of multi-walled carbon nanotubes and its effects on the properties of cement composites

In this study, two types of multi-walled carbon nanotubes (pristine, p-CNT and functionalized, f-CNT) were dispersed in water by sonication and then added to cement mortar. The purpose of this study was to characterize the dispersion degree of the CNTs in aqueous suspension and to investigate whether achieving dispersion in water would also result in dispersion inside mortar. Dispersion of the CNTs in water was investigated by means of UV–vis spectroscopy, using different CNT concentrations and sonication durations. Dispersion of the CNTs in cement mortar was investigated by measuring the compressive and flexural strength and fracture toughness as well as the microstructural characterizations of scanning electron microscopy and mercury intrusion porosimetry. The effects of the CNT addition on drying shrinkage and cement hydration were also investigated for cement pastes. The results of UV–vis spectroscopy showed that by increasing the sonication time to 120 min, the dispersion degree of the f-CNT suspension increased progressively, while for p-CNT, a maximum was reached with 60 min of sonication. The compressive and flexural strength and fracture toughness of mortars containing f- and p-CNTs were not significantly improved either by increasing the amount of CNT or imposing sonication in mixing water. High CNT dispersion in cement matrix was not equally obtained by utilizing highly dispersed CNT suspension. Sonication of f- and p-CNT led to a remarkable deceleration of cement hydration in the first hour of hydration and drying shrinkage of the cement composites was found to be reduced by f- and p-CNT addition.

Influence of polyamide ratio on the CNT dispersion in polyamide 66/6 blends by dilution of PA66 or PA6-MWCNT masterbatches

Nanocomposites with 3wt.% multi-walled carbon nanotubes (MWCNTs) are produced by melt dilution technique using two commercial masterbatches where MWCNTs are pre-dispersed in PA66 and PA6. As polymer matrix, two blends (polyamide 66 (PA66)/polyamide 6 (PA6)) are assessed with different PA66/PA6 ratio (25/75 and 50/50). The influence of both masterbatch and polyamide ratio on microstructure of CNT composites and the relations between microstructure and physical properties (dielectrical properties, crystallinity and rheology) are analysed.Though all nanocomposites are rheologically percolated, those prepared from PA6 masterbatch show higher stiffness. The highest conductivity value corresponds to the nanocomposites with 50/50 PA66/PA6 ratio, possibly because the nanotubes form well-distributed big agglomerates in co-continuous blend morphology. Comparing the different masterbatches, the best electrical results are obtained with PA6 masterbatch, probably due to the fact that its lower melt-viscosity encourages CNT dispersion during extrusion and subsequent re-agglomeration during compression moulding.

용매를 이용한 에폭시 희석 조건이 CNT 에폭시 복합재료 내 CNT 분산도에 미치는 영향

용매를 이용한 에폭시 희석 조건이 CNT 에폭시 복합재료 내 CNT 분산도에 미치는 영향

Combined microfluidization and ultrasonication: a synergistic protocol for high-efficient processing of SWCNT dispersions with high quality

High-efficient and large-scale production of high-quality CNT dispersions is necessary for meeting the future needs to develop various CNT-based electronic devices. Herein, we have designed novel processing protocols by combining conventional ultrasonication process with a new microfluidization technique to produce high-quality SWCNT dispersions with improved processing efficiency. To judge the quality of SWCNT dispersions, one critical factor is the degree of exfoliation, which could be quantified by both geometrical dimension of the exfoliated nanotubes and percentage of individual tubes in a given dispersion. In this paper, the synergistic effect of the combined protocols was systematically investigated through evaluating SWCNT dispersions with newly developed characterization techniques, namely preparative ultracentrifuge method (PUM) and simultaneous Raman scattering and photoluminescence spectroscopy (SRSPL). The results of both techniques draw similar conclusions that as compared with either of the processes operated separately, a low-pass microfluidization followed by a reasonable duration of ultrasonication could substantially improve the processing efficiency to produce high-quality SWCNT dispersions with averaged particle length and diameter as small as ~600 and ~2 nm, respectively.

Determination of nonlinear behavior of multi-walled carbon nanotube reinforced polymer: Experimental, numerical, and micromechanical

In this investigation, nonlinear behavior of Multi Walled Carbon Nanotube reinforced epoxy resin is determined using experimental, numerical and micromechanical methods. Standard nanocomposite samples containing various weight fractions of MWCNTs were prepared and were tested. Experimental results show significant improvement in tensile and compressive mechanical properties of epoxy resin as a result of CNT addition. Compressive modulus of elasticity initially increased with nanotube content up to 0.45wt.%. At higher CNT weight fractions, compressive modulus decreased slightly. In addition, Field Emission Scanning Electron Microscope was used to obtain images of the samples' fracture surface. These images suggested a good CNT dispersion in the matrix. Numerical simulations are conducted to evaluate the nanocomposite elastic moduli using two different interface models. Numerical results suggest that the connector model predicts values lower than the thin shell interface model. Also, the elastic-plastic behavior of nanocomposites was estimated using a combination of micromechanical and numerical methods. To achieve this goal, micromechanical methods based on Mori–Tanaka and Halpin–Tsai models were used to predict the tensile stress-strain curves for the nanocomposites. In addition, nanocomposite compressive behavior was predicted using a combination of numerical and micromechanical methods. Finally, the numerical and micromechanical results showed good agreement with experimental measurements.

Construction of a cathode using amorphous FePO4 nanoparticles for a high-power/energy-density lithium-ion battery with long-term stability

Using amorphous FePO4 (a-FePO4) nanoparticles with a high purity, a narrow size distribution and good dispersion, we successfully developed a new strategy to generate a uniformly dispersed a-FePO4-CNT nano-composite using the interface interaction between surface-modified a-FePO4 and CNT dispersion under mild sonication. The uniformly dispersed a-FePO4-CNT nano-composite exhibited the best performance and long-term stability as a cathode material in a lithium-ion battery compared to previously reported results. The developed nano-composite could deliver a theoretical specific capacity at 0.1 C, 162 mAh g−1 at 1 C and 117 mAh g−1 at 5 C. No capacity fading was observed at 1 C after 500 cycles, and nearly 90% of the initial discharge capacity could be retained at 5 C after 2000 cycles. This study confirms the validity of the proposed strategy to construct a cathode structure, and also describes the potential of a-FePO4 for building high-power energy-storage and conversion systems.

Microwave-induced hierarchical iron-carbon nanotubes nanostructures anchored on polypyrrole/graphene oxide-grafted woven Kevlar® fiber

Iron-carbon nanotube (Fe-CNT) nanostructures were synthesized in 15–30 s through the microwave irradiation of woven Kevlar® fibers (WKFs) deposited with either polypyrrole (PPy) or polypyrrole/graphene oxide (GO). Microwave-induced growth of Fe-CNT on the base fibers is a simple technique and has not been previously reported using WKF as a substrate. This method of forming composites avoids the difficulties associated with obtaining a homogeneous dispersion of CNT in a surrounding matrix material. Iron-decorated CNTs were synthesized on WKF and polyester resin (PES) via vacuum-assisted resin transfer molding. Substantial improvements in tensile strength (upto 122.57%) and moduli (upto 89.82%) were observed for Fe-CNTs grown on the WKF/PES composites. The impact response and in-plane shear strength were also significantly enhanced compared to bare WKF/PES composites. In situ polymerization of pyrrole on WKF altered the electrically insulating behavior of Kevlar, creating a conductive material. Fe-CNT/PPy-coated WKF/PES exhibited the highest electrical conductivity. This proposed approach for growing Fe-CNTs constitutes a novel and economical means of developing high-performance WKF/CNT composites with enhanced mechanical properties and electrical conductivity.

Recent Advances in Biocathodes Based on Conductive 3D Structures for Biofuel Cells

Owing to their high conductivity, inertness and electroactive surface area, graphene and carbon nanotube are widely used for the design of biosensors and biofuel cells [1,2]. Concerning the bioconversion of energy, an example of biofuel cell based on carbon nanotube/enzyme compressions, employing glucose oxidase for glucose oxidation, and laccase for oxygen reduction will be reported as well as its one-year stability [3]. Recent advances in the elaboration of enzyme electrodes based on carbon nanotube coatings functionalized by electropolymerized films or pi-stacked compounds will be presented for the design of biocathodes. In particular, anthraquinone-functionalized reduced oxide graphene nanosheets were thus stacked on carbon nanotube electrodes and successfully used for the non-covalent attachment of laccase and its electrical wiring [4]. In addition, the efficient immobilization and orientation of bilirubin oxidase on multi-walled carbon nanotube electrodes by using pi-stacked porphyrins as a direct electron transfer promoter will be reported. Different types of porphyrins were investigated to identify some effects of the porphyrin structure on the immobilization and wiring of the enzyme [5]. Another alternative concerns the non-covalent functionalization of carbon nanotube electrode with biomimetic model of the horseradish peroxidase active site. The electrogeneration of a polypyrrole film N-substituted by imidazole group on nanotube coating allows the coordination of protoporphine IX iron(III) and its use for the electroreduction of hydrogen peroxide [6]. The combination of carbon nanotube coating and an electropolymerized polypyrrole film of a protein: concanavalin A is also an original strategy for the non-covalent immobilization of glycoproteins via specific interactions with polymerized concanavalin A. This approach was exploited for the biofunctionalization of buckypapers obtained by cross-linking of carbon nanotubes by bis pyrene derivative [7]. Increased attention has been also given to the combination of carbon nanotubes with polynorbornene films. Owing to the conductivity of carbon nanotubes, the formation of BP obtained by filtration of CNT dispersion, represents an attractive way of creating a new kind of electrode or membrane. Flexible bucky paper electrodes were thus easily produced by mixing polynorbornene polymers bearing pyrene groups and multi-walled carbon nanotubes both dispersed in dimethylformamide and then filtering the mixture through a PTFE membrane [8]. In addition, the flexibility and mechanical resistance of these buckypapers were modulated by changing the length of the linear polynorbornene polymers. These bucky paper electrodes were modified by enzymes and applied to the electroenzymatic reduction of oxygen in phosphate buffer (pH 5). References M. Holzinger, A. Le Goff, S. Cosnier. Electrochim. Acta, 82 (2012) 179-190.S. Cosnier, A. Le Goff, M. Holzinger. Electrochem. Commun, 38 (2014) 19-23B. Reuillard, C. Abreu, N. Lalaoui, A. Le Goff, M. Holzinger, O. Ondel, F. Buret, S. Cosnier. Bioelectrochemistry, 106 (2015) 73-76.N. Lalaoui, A. Le Goff, M. Holzinger, M. Mermoux, S. Cosnier. Chem. Eur. J., 21 (2015) 3198-3201.N. Lalaoui, A. Le Goff, M. Holzinger, S. Cosnier. Chem. Eur. J.,21 (2015)16868-16873.B. Reuillard, S. Gentil, M. Carrière, A. Le Goff, S. Cosnier. Chem. Sci., 6 (2015) 5139-5143.K. Elouarzaki, M. Bourourou, M. Holzinger, A. Le Goff , R. S. Marks, S. Cosnier. Energy Environ.Sci.. 8 (2015) 2069-2074.S. Cosnier, R. Haddad, D. Moatsou, R. K. O'Reilly. Carbon, 93 (2015) 713-718.

Composites of Carbon Nanotubes with the Blend of Poly(vinylidene fluoride)/Poly(vinyl acetate)

Poly(vinylidene fluoride)/poly(vinyl acetate)/carbon nanotubes, PVDF/PVAc/CNT, composite films were prepared at various compositions via a solution casting method. The amorphous PVAc formed a miscible blend with PVDF and drastically improved dispersion of CNT in PVDF/CNT composites. Combination of ductile PVAc and rigid CNT had favorable effects on mechanical properties of PVDF. The elongation of PVDF increased from 8% to 300% with addition of 40 wt% PVAc and 0.5 wt% CNT and the modulus at 1.5 wt% CNT was almost 2.3 fold of that of the neat PVDF while retaining high ductility and tensile strength. XRD and FTIR results showed that CNT favored formation of β-crystalline phase in PVDF. Also DSC results showed that the addition of CNT resulted in higher melting temperatures, TSUBm/SUB, and higher crystallinity. Electrical conductivity of the composite films increased sharply by addition of only 1 wt% CNT that attributed to development of CNT network morphology in PVDF/PVAc matrix.

Forming CNT-guided stereocomplex networks in polylactide-based nanocomposites

Grafting a nanoparticle surface using a polymer similar to the matrix has been widely applied to control the spatial organization of nanoparticles. However, the fabrication of target materials with well-defined nanoparticle arrangement remains fundamentally difficult because of the absence of specific interactions between the matrix and the graft. In this study, the self-networking structure of poly(d-lactide)-grafted carbon nanotubes (CNT-g-PDLA) in poly(l-lactide) (PLLA) matrix was investigated. Specific interactions between enantiomeric pairs not only promoted CNT dispersion, but also contributed to the regular phase-separation-like CNT self-networking. Furthermore, the grafted PDLA chains preferably formed stable stereocomplex crystallites with the PLLA matrix, and the CNT self-networking resulted in the self-assembly of 3D continuous stereocomplex scaffold. It was demonstrated that the CNT-guided stereocomplex network endows polylactide-based nanocomposites with significantly improved mechanical strength, heat-resistance, and electrical conductivity at low CNT concentrations.

3D RVE Models Able to Capture and Quantify the Dispersion, Agglomeration, and Orientation State of CNT in CNT/PP Nanocomposites

The focus of this study is to investigate the capabilities of 3D RVE models in predicting the tensile modulus of carbon nanotube polypropylene (CNT/PP) composites which differ slightly in the dispersion, agglomeration and orientation states of CNT within the PP matrix. The composites are made using melt mixing followed by either injection molding or melt spinning of fibers. The dispersion, agglomeration and orientation of CNT within the PP are experimentally altered by using a surfactant and by forcing the molten material to flow through a narrow orifice (melt spinning) that promotes alignment of CNT along the flow/drawing direction. An elaborate image analysis technique is used to quantify the CNT characteristics in terms of probability distribution functions (PDF). The PDF are then introduced to the 3D RVE models which also account for the CNT-PP interfacial interactions. It is concluded that the 3D RVE models can accurately distinguish among the different cases (dispersion, distribution, geometry and alignment of CNT) as the predicted tensile modulus is in good agreement with the experimentally determined one.

An approach to identify complex CNT reinforcement effect on the interlaminar shear strength of prepreg composites by Taguchi method

Several factors affect the interlaminar shear strength of carbon nanotube reinforced carbon fiber composites in multi-scale. A combined route of CNT toughening through manufacturing a custom made prepreg system with CNT dispersion in epoxy and integrating vertically aligned CNTs as nanofibers to bridge in between prepreg plies is applied to achieve enhanced interlaminar shear strength (ILSS). Depending on the CNT loading, effectiveness of dispersion and CNT bridging between prepreg plies, the mechanical enhancement is achieved up to 15%. A new approach of identifying the critical parameters of nano-engineered and nano-reinforced composites through Taguchi method is a novel route for investigating the combined effects of several factors in a complex mechanical enhancement problem with reduced number of experiments as studied in here. Taguchi L8 orthogonal array is used to obtain maximum ILSS by short beam shear (SBS) test. The parametric study has shown that the most significant parameters affecting the ILSS results are type of epoxy, fabrication procedure and CNT loading.

The relationship between microstructure and mechanical properties of carbon nanotubes/polylactic acid nanocomposites prepared by twin-screw extrusion

Twin-screw extrusion was applied to prepare the carbon nanotubes/polylactic acid (CNT/PLA) nanocomposites. Five different extruded plates were produced under variation of CNT concentrations. The internal microstructures were also observed by optical microscope to examine the distribution and dispersion of CNT in the PLA. Besides, the crystallinity of the CNT/PLA nanocomposites was investigated by differential scanning calorimetry (DSC) and density method. The effects of the CNT concentrations on the mechanical and electrical properties of the nanocomposites were investigated. Scanning electron microscope (SEM) was performed to observe the CNT dispersion in the nano-scale. These results suggested that the crystallinity was increased with the increase of CNT concentrations, demonstrating that CNT played a role as a nucleating agent in PLA. Moreover, the mechanical and electrical properties of PLA have been improved by a proper incorporation of CNTs due to a good distribution and dispersion of the CNTs.