Degradation of physicomechanical properties of epoxy nanocomposites with carbon nanotubes upon heat and humidity aging

The dependence of the physicomechanical properties of epoxy nanocomposites subjected to heat and humidity aging on the type of covalently functionalized carbon nanotubes and on the uniformity of their distribution in the epoxy matrix was studied. Two types of carbon nanotubes were used: those modified with carboxy and amide groups. The elastic modulus, bending deflection, and ultimate bending strength for the initial epoxy nanocomposites with carbon nanotubes and for those subjected to heat and humidity aging were determined. The epoxy binders modified with carboxylated carbon nanotubes are more resistant to the action of aging factors. The presence of aggregates of carboxylated carbon nanotubes in the epoxy matrix positively influences the preservation of physicomechanical properties of the composite subjected to heat and humidity aging. Microscopic examination revealed structural features of the epoxy nanocomposite and their effect on the resistance of the composite to the heat and humidity aging.     

Multiwall carbon nanotubes and their applications

The chemical, electrophysical, magnetic, tribological, and physicomechanical properties of multiwall carbon nanotubes (MWCNTs), as well as the characteristics of new nanocomposites and instruments thereof were discussed. These MWCNTs are produced by unique technology and are free from impurities of other carbon modifications. Advantages of multiwall over single-wall carbon nanotubes were demonstrated for applications in electronic devices and preparation of nanocomposites (as filling agents).     

Effect of the initial state of carbon nanotubes on their ability to be dispersed in polar solvents upon liquid-phase oxidative treatments

Effect of the structural defectiveness of carbon nanotubes on the influence exerted on these nanotubes by their liquid-phase treatments with oxidizing agents (hydrogen peroxide, concentrated nitric acid, and its mixture with sulfuric acid) was studied. It was found that this factor affects changes in the structure of oxidized carbon nanotubes, their hydrophilicity, high-quality arrays of these tubes, and their ability to form stable dispersions in water, ethanol, isopropanol, and acetone.     

Synthesis and characterization of monolithic carbon aerogel nanocomposites containing double-walled carbon nanotubes

We report the synthesis and characterization for the first examples of monolithic low-density carbon aerogel (CA) nanocomposites containing double-walled carbon nanotubes. The CA nancomposites were prepared by the sol-gel polymerization of resorcinol and formaldehyde in an aqueous surfactant-stabilized suspension of double-walled carbon nanotubes (DWNTs). The composite hydrogels were then dried with supercritical CO 2 and subsequently carbonized under an inert atmosphere to yield monolithic CA structures containing uniform dispersions of DWNTs. The microstructures and electrical conductivities of these CA nanocomposites were evaluated for different DWNT loadings. These materials exhibited high BET surface areas (>500 m (2)/g) and enhanced electrical conductivities relative to pristine CAs. The details of these results are discussed in comparison with theory and literature.     

Fabrication of super-macroporous nanocomposites by deposition of carbon nanotubes onto polymer cryogels

Electrically conducting super-macroporous carbon nanotube/polymer cryogel nanocomposites were fabricated by a novel approach based on deposition of carbon nanotubes (CNTs) onto the inner surface of pre-formed cryogels assisted by cryogenic treatment. Stable aqueous dispersions of multi-walled and single-walled carbon nanotubes were firstly obtained by non-covalent modification of pristine nanotubes with either pyrene containing polydimethylacrylamide or poly(ethylene oxide)₂₆-b-poly(propylene oxide)₄₀-b-poly(ethylene oxide)₂₆ copolymers and, then, exploited for the preparation of nanocomposites. The mechanical and electrical properties of nanocomposite materials were measured and compared to similar materials prepared by established method. The novel approach provided super-macroporous nanocomposites with high electrical conductivity (>10^?2 S/m) at much lower nanotube content (0.12 wt.%).     

Effects of processing conditions on rheological,thermal, and electrical properties of multiwall carbon nanotube/epoxy resin composites

We report on the effect of processing conditions on rheology, thermal and electrical properties of nanocomposites containing 0.02–0.3 wt % multiwall carbon nanotubes in an epoxy resin. The influence of the sonication, the surface functionalization during mixing, as well as the application of external magnetic field (EMF) throughout the curing process was examined. Rheological tests combined with optical microscopy visualization are proved as a very useful methodology to determine the optimal processing conditions for the preparation of the nanocomposites. The Raman spectra provide evidence for more pronounced effect on the functionalized with hardener compositions, particularly by curing upon application of EMF. Different chain morphology of CNTs is created depending of the preparation conditions, which induced different effects on the thermal and electrical properties of the nanocomposites. The thermal degradation peak is significantly shifted towards higher temperatures by increasing the nanotube content, this confirming that even the small amount of carbon nanotubes produces a strong barrier effect for the volatile products during the degradation. The ac conductivity measurements revealed lower values of the percolation threshold (pc) in the range of 0.03–0.05 wt %. CNTs for the nanocomposites produced by preliminary dispersing of nanotubes in the epoxy resin, compared to those prepared by preliminary functionalization of the nanotubes in the amine hardener. This is attributed to the higher viscosity and stronger interfacial interactions of the amine hardener/CNT dispersion which restricts the reorganization of the nanotubes. The application of the EMF does not influence the pc value but the dc conductivity values (σ_dc) of the nanocomposites increased at about one order of magnitude due to the development of the aforementioned chain structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Oligoaniline assisted dispersion of carbon nanotubes in epoxy matrix for achieving the nanocomposites with enhanced mechanical,thermal and tribological properties

A critical challenge for initiating many applications of the carbon nanotubes (CNTs) is their dispersion in organic solvent or in polymer melt. In the present study, we described a novel strategy for fabricating carbon nanotubes (CNTs)-reinforced epoxy nanocomposite by utilizing aniline trimer (AT) as the noncovalent dispersant. Tensile testing showed that the tensile modulus of the CNTs-reinforced epoxy composites was considerably improved by adding a small amount of AT functionalized CNTs. Additionally, the as-prepared CNTs-epoxy nanocomposites exhibited superior tribological properties with much lower frictional coefficients and wear rates compared to those of neat epoxy resin. The well dispersed AT-functionalized CNTs in epoxy matrix played an important role in enhancing the mechanical properties, as well as acting as a solid lubricant for improving the tribological performance of epoxy/CNTs nanocomposite.     

Broadband radio-absorbing materials based on porous composites with carbon nanotubes

The reflection coefficient of an electromagnetic wave has been theoretically studied as a function of the thickness of a material and its dielectric properties. Samples based on spheroplastics with noncovalently modified carbon nanotubes have been obtained. The radio-engineering and electrophysical properties of these composites are discussed as well. The prospects for applying porous nanocomposites with carbon nanotubes in the fabrication of radio-absorbing materials are also shown.     

碳纳米管及碳纤维增强环氧树脂复合材料研究进展

碳纳米管与碳纤维具有优异的力学、电学等性能,广泛用做复合材料增强体,但目前碳纳米管/碳纤维/环氧树脂复合材料的研究具有一定的局限性,只考虑了两相材料间的作用,即仅对单一相进行处理而忽略了另一相的改性。本文从碳纳米管/碳纤维协同增强环氧树脂基体复合材料的思路入手,结合自己的研究成果,综述了国内外相关研究进展。从研究结果可以看出,将三相材料之间完全有效地联系起来,发挥三者间的协同效应,复合材料的性能可以发生质的飞跃。     

碳纳米管改性环氧树脂的导热和阻燃性能

以双酚A二缩水甘油醚(DGEBA)环氧树脂(Epoxy Resin,EP)为基体、甲基六氢苯酐(MHHPA)为固化剂、以多壁碳纳米管(MWCNTs)为添加剂制备了环氧树脂/碳纳米管纳米复合材料。通过对微观结构、玻璃化转变温度(Tg)、热失重、热导率和锥形量热测试结果分析,研究了质量分数少于1.5%的MWCNTs对环氧树脂的导热和阻燃性能影响,结果表明,MWCNTs质量分数为1.5%时,复合材料发生团聚;纳米复合材料随着MWCNTs质量分数的增加Tg值先增加后降低;失重5%时,对应的温度先增加后降低,残炭量增加;样品的热导率呈现先升高后降低的趋势,当MWCNTs质量分数为1%时,复合材料的热导率最大;MWCNTs加入后环氧树脂的总释热量减少,释烟量增加,阻燃性得到一定程度的提高。     

Reinforcement effect of carbon nanofillers in an epoxy resin system: Rheology,molecular dynamics,and mechanical studies

The reinforcing effect of carbon nanoparticles in an epoxy resin has been estimated with different approaches based on rheology, molecular dynamics (evaluated by differential scanning calorimetry, dielectric relaxation spectroscopy, and thermally stimulated depolarization current), and dynamic mechanical analysis. Carbon particles aggregate as the volume increases and form a fractal structure in the matrix polymer. The dispersion microstructure has been characterized by its viscoelastic properties and relaxation time spectrum. The scaling of the storage modulus and yield stress with the volume fraction of carbon shows two distinct exponents and has thus been used to determine the critical carbon volume fraction of the network formation (Φ*) for the carbon/epoxy dispersions. At nanofiller concentrations greater than Φ*, the overall mobility of the polymer chains is restricted in both dispersions and solid nanocomposites. Therefore, (1) the relaxation spectrum of the dispersions is strongly shifted toward longer times, (2) the glass‐transition temperature is increased and (3) the relaxation strength of both the secondary (β) and primary (α) relaxations increases in the nanocomposites, with respect to the pure polymer matrix. The dispersion microstructure, consisting of fractal flocs and formed above Φ*, is proposed to play the main role in the reinforcement of nanocomposites. Moreover, the network structure and the interface polymer layer (bond layer), surrounding nanoparticles, increases the relaxation strength and slows the cooperative α relaxation, and this results in an improvement of the mechanical properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 522–533, 2005     

Preparation and Characterization of Electrodes Modified with Pyrrole Surfactant,Multiwalled Carbon Nanotubes and Metallophthalocyanines for the Electrochemical Detection of Thiols

Our aim was to prepare hybrid electrodes active towards the electrooxidation of thiols by the co‐immobilization of native carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc) from aqueous solutions. This strategy was adopted to avoid the oxidation of CNTs that can induce a modification of their exceptional properties. To do so, a hydrosoluble pyrrole surfactant was used to get homogeneous aqueous dispersions of CNTs and CoPc and to trap both materials on the electrode via the electropolymerization of the pyrrole surfactant. The hybrid electrodes exhibit a good electrocatalytic activity towards the oxidation of L ‐cysteine and glutathione. Their performances in terms of limit of detection (0.01 mM) are compatible with the detection of these thiols in biological samples.     

Analysis of stability of nanotube dispersions using surface tension isotherms

In this paper, we present the analyses of surface tension of surfactant-stabilized dispersions of carbon nanotubes. This method allows one to study interactions of carbon nanotubes with surfactants at different levels of nanotube loading when optical methods fall short in quantifying the level of nanotube separation. Sodium dodecyl sulfate was used as a stabilizing agent to uniformly disperse single-walled carbon nanotubes in an aqueous media. We show that surface tension is very sensitive to small changes of nanotube and surfactant concentrations. The experimental data suggest that, at moderate concentrations, surfactant displaces carbon nanotubes from the air-water interface and the nanotubes are mostly moved into the bulk of the liquid. By analyzing the surface tension as a function of surfactant concentration, we obtained the dependence of critical micelle concentration on nanotube loading. We then constructed the adsorption isotherm for dodecyl sulfate on carbon nanotubes and bundles of carbon nanotubes. The results of these experiments enabled us to extend the phase diagram of the produced dispersions to a broader range of surfactant and nanotube concentrations.     

The effect of different treatment methods of multiwalled carbon nanotubes on thermal and flexural properties of their epoxy nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were oxidized using four different acid‐treatment methods followed by their functionalization with 3‐aminopropyltriethoxysilane (3‐APTES). Diglycidyl ether of bisphenol A (DGEBA) nanocomposites with unmodified and silanized MWCNTs (0.2 wt %) were prepared by a cast molding method. The effect of functionalization of MWCNTs on thermal, flexural, and morphological properties of the epoxy nanocomposites were studied. The epoxy/MWCNTs nanocomposites were characterized by thermogravimetric analysis, flexural testing, and field emission electron microscopic analysis. The results showed that the silanization of MWCNTs which were oxidized by a two‐step process using nitric acid and hydrochloric acid showed better thermal and flexural properties due to good interfacial adhesion between MWCNTs and the epoxy matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1175–1184, 2010     

Epoxy Nanocomposites

The formation and physical properties of epoxy nanocomposites with carbon (nanotubes, graphene, and graphite), metal-containing, and aluminosilicate (montmorillonite and halloysite) fillers are considered. The mutual effect of both a matrix and nanoparticles on the composite structure is discussed. The role of the interfacial layer in the mechanical properties of nanocomposites is revealed. It is found that the concentration dependence of electrical and thermal conductivities of the composites is related to the percolation phenomenon.     

Toughening of Epoxy Nanocomposites: Nano and Hybrid Effects

In this paper, we review recent progress made in the field of epoxy-based binary and ternary nanocomposites containing three-, two-, and one-dimensional (i.e., 3D-, 2D-, and 1D) nano-size fillers with a special focus on their fracture behaviors. Despite investigations conducted so far to evaluate the crack-resistance of epoxy nanocomposites and attempts made to clarify the controlling toughening mechanisms of these materials, some questions remain unsolved. It is shown that silica nanoparticles can be as effective as rubber particles in improving the fracture toughness/energy; but incorporation of carbon nanotubes (CNTs) or clay platelets in epoxy matrices delays crack growth only modestly. The “nano” effects of silica (<25 vol.%) and rubber (>10 wt.%) nanoparticles in toughening epoxy resin are confirmed by comparison with silica and rubber micro-particles of the same loading. There is clear evidence of both synergistic and additive toughening effects in the silica/rubber/epoxy ternary nanocomposites. In addition, positive hybrid toughening effect has been observed in the nano-rubber/CNT/epoxy composites; however, a negative hybrid effect is predominant in nano-clay/nano-rubber/epoxy ternary nano-composites. Future research directions for epoxy-based nanocomposites towards multi-functional applications are discussed.     

Colloidal chemistry as a guide to design intended dispersions of carbon nanomaterials

In this review, some established concepts from Colloidal Science and their application to graphene and carbon nanotubes dispersions in organic or aqueous media are highlighted to rationalize alternatives for some issues in terms of colloidal properties. Recent applications for carbon-based dispersions are presented, as well as van der Waals interactions in carbon materials and strategies to overcome these interactions, such as increasing electrostatic repulsion between dispersed particles, surface functionalization, or adsorption of passivation agents such as macromolecules, which are the basis of many dispersion and exfoliation procedures. The demonstration of how knowledge and fine control of colloidal interactions have been used to overcome several limitations, such as the preparation of stable and concentrated dispersions of carbon materials and keeping appreciable electrical conductivity, is presented. It is also showed that the same knowledge can help the development of more environmentally friendly carbon-based colloids as well as the improvement of similar systems as dispersions of two-dimensional materials.     

Fabrication of carbon microcapsules containing silicon nanoparticles-carbon nanotubes nanocomposite by sol-gel method for anode in lithium ion battery

Carbon microcapsules containing silicon nanoparticles (Si NPs)-carbon nanotubes (CNTs) nanocomposite (Si-CNT@C) have been fabricated by a surfactant mediated sol-gel method followed by a carbonization process. Silicon nanoparticles-carbon nanotubes (Si-CNT) nanohybrids were produced by a wet-type beadsmill method. To obtain Si-CNT nanocomposites with spherical morphologies, a silica precursor (tetraethylorthosilicate, TEOS) and polymer (PMMA) mixture was employed as a structure-directing medium. Thus the Si-CNT/Silica-Polymer microspheres were prepared by an acid catalyzed sol-gel method. Then a carbon precursor such as polypyrrole (PPy) was incorporated onto the surfaces of pre-existing Si-CNT/silica-polymer to generate Si-CNT/Silica-Polymer@PPy microspheres. Subsequent thermal treatment of the precursor followed by wet etching of silica produced Si-CNT@C microcapsules. The intermediate silica/polymer must disappear during the carbonization and etching process resulting in the formation of an internal free space. The carbon precursor polymer should transform to carbon shell to encapsulate remaining Si-CNT nanocomposites. Therefore, hollow carbon microcapsules containing Si-CNT nanocomposites could be obtained (Si-CNT@C). The successful fabrication was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These final materials were employed for anode performance improvement in lithium ion battery. The cyclic performances of these Si-CNT@C microcapsules were measured with a lithium battery half cell tests.     

The effect of nanoparticles on structural morphology, thermal and flammability properties of two epoxy resins with different functionalities

The effect of layered silicate nanoclays, nano-silica and double-walled carbon nanotubes (DWNTs) on the thermal stability and fire reaction properties of two aerospace grade epoxy resins (a high temperature curing tetra-functional and a low temperature curing bi-functional resin) has been investigated using thermal analysis, cone calorimetry, LOI and UL-94 techniques. The morphology of the polymer-clay nanocomposites, determined by X-ray diffraction and transmission electron microscopy indicated intercalated structures. The addition of nanoclays (5-wt%) to both resins had a thermal destabilisation effect in the low temperature regime (<400 °C), but led to higher char yield at higher temperatures. The inclusion of nano-silica at 30-wt% significantly improved the thermal stability of the resins while DWNTs had an adverse effect due to their poor dispersion in the matrix. The nanoclays and carbon nanotubes significantly increased the fire resistance of the tetra-functional epoxy resin while a minimal effect was observed for the bi-functional resin.     

Thermal properties enhancement of epoxy resins by incorporating polybenzimidazole nanofibers filled with graphene and carbon nanotubes as reinforcing material

Enhancement of thermal properties of epoxy resins was achieved by incorporation of polybenzimidazole (PBI) fibermats filled with carbon nanomaterials, prepared by the solution electrospinning technique. Different type of carbon nanostructures (carbon nanotubes, graphite flakes, graphene nanoplatelets and carbon black) were compared as fillers in polybenzimidazole fibers. The carbon-PBI-fibermats showed remarkable thermal transport properties and therefore, they were studied as thermal reinforcement material for epoxy composites. Mechanical and thermal properties of produced composites were evaluated and the effectiveness of different types of carbon fillers examined. Results showed that the produced carbon filled fibermats can be used effectively as a thermal reinforcing material in epoxy resins, offering several advantages.