Carbon nanotube (CNT)–epoxy nanocomposites: a systematic investigation of CNT dispersion

A systematic investigation of the dispersion of carbon nanotubes (CNTs), 1–6 nm in diameter and a few microns in length, in a bisphenol F-based epoxy resin has been presented. Several dispersing techniques including high-speed dissolver, ultrasonic bath/horn, 3-roll mill, etc. have been employed. Optical microscopy has been extensively used to systematically characterise the state of CNT dispersion in the epoxy resin during the entire processing cycle from mixing CNT with resin to adding and curing with hardener. Complimentary viscosity measurements were also performed at various stages of nanocomposite processing. A method to produce a good CNT dispersion in resin was established, but the state of CNT dispersion was found to be extremely sensitive to its physical and chemical environments. The cured nanocomposites were further tested for their thermo-mechanical properties by dynamic mechanical thermal analysis (DMTA), and for flexural and compressive mechanical properties. The measured properties of various nanocomposite plates were then discussed in view of the corresponding CNT dispersion.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Resonant Raman spectroscopy and spectroelectrochemistry characterization of carbon nanotubes/polyaniline thin film obtained through interfacial polymerization

Thin, transparent, and self‐assembled films of neat polyaniline and polyaniline/carbon nanotube nanocomposites were deposited over glass substrates by interfacial polymerization. The effect of the carbon nanotubes on the structure and conformation of the polyaniline, and the type of interaction between the polymer and the nanotubes, have been studied by resonant Raman spectroscopy and UV–Vis and Raman spectroelectrochemistry. The results indicate clearly that the carbon nanotubes induce important changes in the electronic structure of the polymer, resulting in a more polaronic organization. Additionally, an effective interaction between the polymer and the nanotube, based on a polyaniline‐to‐nanotube charge transfer, is proposed in this work. Copyright © 2012 John Wiley & Sons, Ltd.     

A preservation study of carbon nanotubes in alumina-based nanocomposites via Raman spectroscopy and nuclear magnetic resonance

Raman spectroscopy was used to study the preservation of the carbon nanotube structure in nanotube-reinforced alumina nanocomposites consolidated via spark plasma sintering (SPS). A series of Raman spectroscopy experiments was used to identify the thermal breakdown temperature of single-walled carbon nanotubes (SWCNTs) embedded in nanocrystalline alumina. It was found that the carbon nanotube structure remains intact after sintering at 1150 °C, but almost completely breaks down by 1350 °C after only 5 min. Also, ²⁷Al nuclear magnetic resonance (NMR) was used to study the chemical and structural effects of high-energy ball milling (HEBM) and SPS consolidation on pure alumina and SWCNT-alumina nanocomposites. HEBM does not change the mixed coordination number of the as-received alumina, but slight peak shifts indicate residual stresses. No Al₄C₃ was detected in any of the consolidated samples – even up to 1550 °C for 10 min. Thus, it is concluded that consolidation of carbon nanotube-reinforced composites should be completed at temperatures below ∼1250 °C in order to preserve the carbon nanotube structure. PACS 61.18.Fs; 61.46.Fg; 61.82.Rx; 62.25.+g; 76.60.-k     

Carbon nanotube grease with enhanced thermal and electrical conductivities

A stable and homogeneous grease based on carbon nanotubes (CNTs, single-wall and multi-wall) in polyalphaolefin oil has been produced without using a chemical surfactant. For example, for a 11 wt% (7 vol%) single-wall CNT (diameter 1–2 nm, length 0.5–40 μm) loading, the thermal conductivity (TC) of the grease shows a 60–70% increase compared to that for no nanotube loading. In addition, the grease is electrically conductive, has a high dropping point, good temperature resistance, and does not react with copper at temperatures up to 177 °C. The performance of carbon nanotube grease could be much better with the improvement of nanotube quality and purity. A possible explanation for these results is that of a high loading of CNTs (>10 wt%), they become associated with each other by van der Waals forces in the grease to form three-dimensional percolation networks. Time-dependent magnetic results demonstrate that, even under the influence of a strong outside magnetic field, the TC value remains constant. This phenomenon can be attributed to the existence of networks that makes magnetic alignment of nanotubes impossible.     

Effect of hydrogen on the growth and morphology of single wall carbon nanotubes synthesized on a FeMo/MgO catalytic system

Single wall carbon nanotubes were synthesized from thermal pyrolysis of methane on a FeMo/MgO catalyst by radio frequency catalytic chemical vapor deposition (RF-CVD) using argon as a carrier gas. Controlled amounts of hydrogen (H₂/CH₄=0-1 v/v) were introduced in separate experiments along with the carbon source. The properties and morphology of the synthesized single wall carbon nanotubes were monitored by transmission electron microscopy, Raman scattering, and thermogravimetric analysis. The nanotubes with the highest crystallinity were obtained with H₂/CH₄=0.6. By monitoring the Radial Breathing Modes present in the Raman spectra of the single-wall carbon nanotube samples, the variation of the structural and morphological properties of the carbon nanotubes with the flow level of hydrogen, reflect changes of the catalyst systems induced by the presence of hydrogen.     

环氧树脂基碳纳米复合电磁屏蔽材料研究

基于碳纳米材料有序结构优异的结构与功能特点,研究了其在新型电磁防护材料中的应用,结合环氧树脂与碳纳米有序结构在电磁屏蔽效能和力学性能方面表现出的显著优势,论述了环氧树脂基碳纳米管复合电磁屏蔽材料和碳纳米管有序纳米结构研究,通过电磁仿真优化设计构筑三维导电网络结构,得出8~12 GHz电磁波段屏蔽效能≥82.96 dB的理想结构模型,为环氧树脂基碳纳米复合电磁屏蔽材料研究开发提供了指导,有利于该新型电磁屏蔽材料在国防、国民经济各领域的应用。     

Fluorescence spectroscopy of single-walled carbon nanotubes in aqueous suspension

Optical studies of single-walled carbon nanotubes have advanced greatly through the recent discovery of near-infrared band gap photoluminescence from single-walled carbon nanotubes (SWNT) isolated in aqueous surfactant suspensions. This fluorescence emission has enabled the detection of many distinct optical transitions and their assignment to specific (n,m) semiconducting species of SWNT. The resulting set of precise transition energies presents a challenge to current theoretical models of nanotube electronic structure and a guide to nanotube researchers using resonance Raman spectroscopy. In the near future, structure-resolved fluorimetry should prove useful for revealing the quantitative (n,m) composition of mixed SWNT samples through sensitive, rapid, and nondestructive measurements. It will also permit detailed studies of many physical and chemical processes that vary with nanotube structure. PACS 71.35.Cc; 78.67.Ch; 78.67.-n     

Preparation and characterization of large-size halloysite nanotubes particles by a combined technique of interfacial polymerization and condensation polymerization

To granulate halloysite nanotubes (HNTs) into large-size particles, interfacial polymerization and condensation polymerization were combined. The former was used to form surface layer of particles and the latter was used to improve particle strength. Polyethylenimine (PEI) and terephthaloyl chloride were chosen, respectively as hydrophilic monomer and hydrophobic monomer in interfacial polymerization. Condensation polymerization was carried out between PEI and glycerol polyglycidyl ether (GPE). The results show that HNTs particles have sphere shape and its diameters range from 1.7 to 2.5 mm and vary with preparation condition. SEM images show that particles have typical core–shell structure with dense surface layer and porous inner structure and single nanotube is completely encapsulated by polymer material. The characterization of BET shows that because of dense surface layer and encapsulation of nanotubes, the specific surface area of particles determined decreases dramatically.     

Role of Stone–Wales defects on the functionalization of (8,0) single wall carbon nanotubes by the amine group: Ab initio study

Using first-principle calculations, we have investigated the chemical functionalization of (8,0) zigzag single wall carbon nanotubes (SWNTs) by the amine group on Stone–Wales (SW) defects. The binding of NH₂ with the defective (8,0) nanotube was explored and the preferential grafting sites have been identified. On the other hand, the modifications induced by SW defect and functional groups in the structural and electronic properties of (8,0) SWNT have also been investigated. The role of SW defects in the chemical reactivity of carbon nanotubes was well identified.     

Microwave-assisted functionalization of single-walled carbon nanotubes with 3-chloropropene

We have reported a highly efficient approach to functionalize single-walled carbon nanotubes by electrophilic addition polymerization of 3-chloropropene under microwave irradiation. Using Lewis acids as catalysts, 3-chloropropene can undergo polymerization followed by hydrolysis with alkaline methanol, and thus the reaction results in the attachment of polymer chains and hydroxyl groups to the surface of the nanotubes. The resulting nanotubes were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The result shows that 30 min of irradiation time is enough to bring the reaction to the end and a longer time did not improve the degree of functionalization.     

Multiwalled carbon nanotubes effect on the bioavailability of artemisinin and its cytotoxity to cancerous cells

Artemisinin regarded as one of the most promising anticancer drugs can bind to DNA with a binding constant of 1.04 × 10⁴ M⁻¹. The electrochemical experiments indicated that for longer incubation time periods, the reduction peak current of artemisinin on carbon nanotube modified electrode increases. Therefore, the uptake of drug molecules from a solution into CNTs will be achieved automatically by adsorption of 88.7% of artemisinin onto carbon nanotubes surface without alteration in drug properties. Hence, capability of carbon nanotubes to have synergistic effect on the bioavailability of artemisinin was investigated. Experimental tests on K562 cancer cell lines growth by MTT assay proved that multi-walled carbon nanotubes can enhance the cytotoxity of artemisinin to the targeted cancer cells with unprecedented accuracy and efficiency. The IC₅₀ values were 65 and 35 μM for artemisinin and artemisinin loaded on multi-walled carbon nanotubes, respectively; demonstrating that artemisinin loaded on multi-walled carbon nanotubes is more effective in inhibition of cancer cell lines growth.     

Evidence of multi-walled carbon nanotube fragmentation induced by sonication during nanotube encapsulation via bulk-suspension polymerization

The synthesis of multi-walled carbon nanotube/polystyrene composites, with nanotube concentrations of 0.04, 0.08 and 0.16 wt%, was carried out by in situ bulk-suspension polymerization with the assistance of sonication. By using this method both encapsulation and exfoliation of the nanotubes into the polymer host were achieved. Evidence of significant nanotube fragmentation was found by scanning electron microscopy; the cause of such fragmentation was attributed to the induction of strong cavitation due to the application of ultrasound during the synthesis. Infrared spectroscopy showed no evidence of the formation of covalent bonds between the nanotubes and the polystyrene during the process of synthesis. The thermal stability was not improved by the inclusion of the nanotubes, it was attributed to the low nanotube concentrations; however, composites glass transition temperature showed improvements.     

Nature of the adhesion bond between epoxy adhesive and steel

The potential difference that appears in the epoxy resin located between two grade 3 steel plates is studied. One of them is stored in epoxy resin to reach equilibrium, and the second plate is coated with an asprepared mixture of epoxy resin with a hardener. It is found that the potential difference decreases in time because of charge transfer by Fe²⁺ ions through epoxy resin. The luminescence and infrared absorption spectra of the epoxy adhesive on the grade 3 steel surface are recorded. An analysis of these spectra shows that Fe²⁺ ions penetrate into the as-prepared mixture of epoxy resin with the hardener, and interact with CN groups in the mixture, and form coordination compounds. As a result, a diffusion layer saturated by the coordination compounds forms at the interface between the steel and the adhesive.     

Effect of processing temperature on the micro- and macro-interfacial properties of carbon fiber/epoxy composites

Three different temperature schemes were applied on carbon fiber/epoxy composite to elucidate the effect on interfacial shear strength (IFSS) and inter-laminar shear strength (ILSS). It showed that carbon fiber/epoxy IFSS was significantly influenced by the processing temperature, while ILSS was only slightly changed. Moreover, the mechanical properties revealed no necessary relationship between the micro- and macro-interfacial strengths with the properties of epoxy matrix. Among all the temperature schemes, Pro2 (the one-platform curing scheme with relatively rapid heating rate) produced highest IFSS and ILSS. Fourier transform infrared spectroscopy analysis demonstrated that the sizing agent can chemically react itself and also react with epoxy resin at temperature 180?°C. The resin rheological data showed that different temperature schemes can considerably impact diffusion behavior of the resin molecules. Hence, the highest interfacial strengths for Pro2 scheme were ascribed to large extent of chemical reactions and good inter-diffusion between components, at the interface region.     

Synthesis and characterization of thermotropic liquid crystalline polyester/multi-walled carbon nanotube nanocomposites

Thermotropic liquid crystalline polyester (TLCP) was synthesized via low-temperature solution polycondensation from 1,4-Bis(4-Hydroxybenzoyloxy)butane and terephthaloyl dichloride. Polymer nanocomposites based on a small quantity of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization method. The wide-angle X-ray diffraction (WAXD) results suggested that the addition of MWNTs to TLCP matrix did not significantly change the crystal structure of TLCP. The interactions between the molecules of the TLCP host phase and the carbon nanotubes were investigated through Raman spectroscopy investigations. We detected a distinct wave number shift of the radial breathing modes, confirming the carbon nanotubes interacted with the surrounding liquid crystal molecules, most likely through aromatic interactions (π-stacking). The interactions between liquid crystal host and nanotube guests were also evident from a polarizing microscopy (POM) study of the liquid crystal-isotropic phase transition in the proximity of nanotubes. The thermal properties and the morphological properties of the TLCP/MWNTs nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). TGA data demonstrated the addition of a small amount of MWNTs into TLCP matrix could improve the thermal stability of TLCP matrix. DSC results revealed that melt transition temperatures and isotropic transition temperatures of the hybrids were enhanced.     

Growth of carbon nanotubes from C<Subscript>60</Subscript>

Carbon nanotubes can be obtained from a multitude of molecular precursors in chemical vapor deposition (CVD) processes. Here we demonstrate that the use of C₆₀ as the carbon feedstock gas in an iron-catalyzed thermal CVD experiment leads to the formation of films of multi-walled carbon nanotubes. The critical role of the diameter of the catalyst particles in determining the efficiency of nanotube growth is clearly demonstrated. Electron microscopy and Raman spectroscopy were employed for the characterisation of the nanotube material. The structural properties of the individual nanotubes show distinctive differences to acetylene-grown multi-walled nanotubes. PACS 81.07.De; 81.10.Bk     

Plasma treatment of carbon fibers: Non-equilibrium dynamic adsorption and its effect on the mechanical properties of RTM fabricated composites

The effect of oxygen plasma treatment on the non-equilibrium dynamic adsorption of the carbon fabric reinforcements in RTM process was studied. 5-Dimethylamino-1-naphthalene-sulfonylchloride (DNS-Cl) was attached to the curing agent to study the change of curing agent content in the epoxy resin matrix. Steady state fluorescence spectroscopy (FS) analysis was used to study this changes in the epoxy resin at the inlet and outlet of the RTM mould, and XPS was used to study the chemical changes on the carbon fiber surfaces introduced by plasma treatment. The interlaminar shear strength (ILSS) and flexural strength were also measured to study the effects of this non-equilibrium dynamic adsorption progress on the mechanical properties of the end products. FS analysis shows that the curing agent adsorbed onto the fiber surface preferentially for untreated carbon fiber, the curing agent content in the resin matrix maintain unchanged after plasma treatment for 3 min and 5 min, but after oxygen plasma treatment for 7 min, the epoxy resin adsorbed onto the fiber surface preferentially. XPS analysis indicated that the oxygen plasma treatment successfully increased some polar functional groups concentration on the carbon fiber surfaces, this changes on the carbon fiber surfaces can change the adsorption ability of carbon fiber to the resin and curing agent. The mechanical properties of the composites were correlated to this results.     

Fabrication and characterization of suspended single-walled carbon nanotubes

Suspended single-walled carbon nanotubes (SWCNTs) between SiO₂ pillars via a direct lithographic route using a simple mixture of catalyst precursor [Co(III) acetylacetonate, Co(acac)₃] and conventional electron beam resist (ma-N2403) were fabricated. The catalytic electron beam resist (Cat-ER) layer plays dual roles as a catalyst and a resist layer for the growth and alignment of CNTs, respectively. The structure of the grown nanotube was characterized by Raman spectroscopy (633 nm laser excitation). Nanotubes grown from Cat-ER with Co(acac)₃ show the typical Raman spectra of SWCNTs which are characterized by the strong tangential bands near to 1590 cm⁻¹ and radial breathing modes (RBMs) in the low frequency region (<300 cm⁻¹). The calculated diameter of the probed nanotubes individually corresponds to the range 0.86-1.77 nm.     

Comparison of modification of electronic properties of single-walled carbon nanotubes filled with metal halogenide, chalcogenide, and pure metal

In present work, thulium chloride, gallium selenide, bismuth telluride, and silver were encapsulated into the channels of single-walled carbon nanotubes (SWCNTs). The structural properties of obtained nanostructures were studied by high-resolution transmission electron microscopy, and the modification of electronic properties of nanotubes as result of filling their channels with chosen substances was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. It was shown that the electronic properties of filled SWCNTs depend on the chemical nature of incorporated materials. The encapsulation of TmCl₃ and GaSe into the carbon nanotube channels leads to acceptor doping of the SWCNTs, and this effect is more prominent for thulium chloride. The incorporation of bismuth telluride into the nanotube cavities does not result in any modification of their electronic properties. The filling of the nanotube channels with silver leads to donor doping of the single-walled carbon nanotubes.