Numerical algorithms for prediction of mechanical properties of single-walled carbon nanotubes based on molecular mechanics model

The objective of this paper is to develop the numerical algorithms for the prediction of mechanical properties of single-walled carbon nanotubes (SWCNTs). By using the energy method, the analytical expressions are obtained and the five independent variables algorithm is developed for the prediction of the elastic properties of SWCNTs via a molecular mechanics model in which the geometrical relationship of carbon nanotube is introduced. It can be found that due to the introduction of the geometrical approximate conditions some errors may exist in the calculation of mechanical properties of SWCNTs in terms of the five independent variables algorithm. Therefore, two improved algorithms, i.e., eigenvalues modified method (EMM) and eigenvalues and eigenvectors modified method (EEMM) are proposed to analyze the possible errors in the numerical results. It is found that the results obtained by the three kinds of algorithms are almost consistent with one another, but EMM and EEMM are preferred to be used because they have properties similar to those of the finite element method, where the consistent equation works just as the constraint condition to void the singularity of the element stiffness matrix. The computational results also reveal that both the surface Young’s modulus and Poisson’s ratio depend on the diameter of carbon nanotubes, and finally converge to the values of the graphite sheet with an increase in the tube diameter in the inverse trends. For SWCNTs with approximately the same diameters, the surface Young’s modulus is in direct and Poisson’s ratio is in inverse proportion to chiral angles, respectively.     

多壁碳纳米管增强水泥基复合材料的纳米力学性能

采用纳米压痕技术探讨了多壁碳纳米管(MWCNTs)对有骨料水泥基复合材料纳米尺度上力学性能的影响,分别对压痕模量(M)小于50 GPa和压痕硬度(H)小于4.0 GPa的数据进行了统计,对其频率分布进行了Gaussian函数(PDF)的解卷积分峰处理,并对低密度水化硅酸钙凝胶(LD C-S-H)和高密度水化硅酸钙(HD C-S-H)凝胶进行了定量的体积分数计算。结果表明,除LD C-S-H、 HD C-S-H、 Ca(OH)2(CH)外,还出现了一个假相。MWCNTs降低了水化产物中LD C-S-H的体积分数,提高了HD C-S-H的体积分数,提高了C-S-H凝胶的压痕模量,但利用压痕模量和压痕硬度统计结果计算出的各相体积分数存在一定的差异。MWCNTs作为一种纳米晶核,对HD C-S-H凝胶形成起到了一定的诱导作用,从纳观尺度阐释了MWCNTs对水泥基材料的改性机制。     

添加纳米碳管对高密度聚乙烯力学行为和结晶过程的影响

利用熔融法制备了一系列具有不同纳米碳管含量的纳米碳管(Q盯)／高密度聚乙烯(HDPE)复合材料。对其拉伸性能的研究结果表明，添加质量分数分别为2％，5％和10％的纳米碳管使HDPE的拉伸模量分别提高了7．4％，27．0％和28．6％，屈服强度分别提高了3．3％，14．4％和18．5％，但是会降低HDPE的断裂强度和断裂伸长率。同时，对复合材料中HDPE结晶过程的研究表明，纳米碳管可以提高HDPE的开始结晶温度，降低结晶活化能，但是会使HDPE的结晶速率下降，结晶度降低。     

碳纳米管/丁苯橡胶复合材料的电学性能

采用喷雾干燥法可制备不同配比的碳纳米管（Carbon nanotubes,CNTs）/粉末丁苯橡胶复合材料,观察CNTs在橡胶基体中的分散情况,检测复合材料的导电性能及介电性能,并进行了简要的理论分析。结果表明:CNTs在橡胶基体中获得了充分均匀的分散,有利于CNTs改性补强作用的发挥。与纯胶样品及填充炭黑（Carbon black,CB）样品相比, 填充CNTs样品在8~18GHz下具有较高的介电常数及低介电损耗。随着CNTs加入量的增加,CNTs/粉末丁苯橡胶复合材料的电导率逐渐升高,当CNTs加入量为60phr（per hundred rubber）时,与纯胶样品及添加60phr CB样品相比,电导率提高近10个数量级;复合材料内部导电同时存在隧道导电机制和渗逾导电机制。采用喷雾干燥法制备的CNTs/粉末丁苯橡胶复合材料,将是一种综合性能良好的新型纳米复合材料,有望在抗静电橡胶、电磁屏蔽及介电材料等领域获得应用。      

机械混炼对碳纳米管/丁苯橡胶复合材料的影响

为研究机械混炼对碳纳米管(CNTs)/粉末丁苯橡胶(SBR)复合材料性能的影响,从而获得性能优异的CNTs/SBR复合材料,联合采用喷雾干燥法和机械混炼法,制备高填充量CNTs/SBR复合材料.将喷雾干燥法制备的CNTs/粉末SBR复合材料在开炼机上机械混炼,对比分析混炼前后试样的物理和力学等相关性能,并对其微观形貌进行检测.结果表明,机械混炼使CNTs获得进一步的分散,与SBR基体间作用力得到增强,与混炼前相比,混炼后试样的玻璃化转变温度、交联度和常规力学性能均得到提高,当CNTs加入量为50phr时,混炼后复合材料的拉伸强度和撕裂强度分别为13.1MPa和39.8kN/m,比混炼前试样分别提高了约80%和20%.     

Impact and after-impact properties of carbon fibre reinforced composites enhanced with multi-wall carbon nanotubes

The goal of the present study was to investigate the influence of multi-wall carbon nanotubes (MWCNTs) on the impact and after impact behaviour of carbon fiber reinforced polymer (CFRP) laminates. About 0.5% per weight MWCNTs were dispersed via a high shear device in the epoxy matrix (Bisphenol A) of carbon reinforced quasi-isotropic laminates. Subsequently, the modified CFRPs were subjected to low-energy impact and directly compared with unmodified laminates. In previous studies, the beneficial effect of the MWCNT inclusion to the fracture properties of CFRPs has been demonstrated. In terms of the CFRP impact performance, enhanced performance for the CNT doped specimens was observed for higher energy levels. However, the after-impact properties and more specifically compression after impact were improved for both the effective compression modulus and the compression strength. In addition, compression–compression fatigue after impact performance of the CNT modified laminates was also improved, by extending the fatigue life.     

Effect of solidification on microstructures and mechanical properties of carbon nanotubes reinforced magnesium matrix composite

A novel approach was successfully developed to fabricate bulk carbon nanotubes (CNTs) reinforced Mg matrix composites. The distribution of CNTs in the composites depends on the solidification rate. When the solidification rate was low, CNTs were pushed ahead of the solidification front and will cluster along grain boundaries. When the solidification rate was high, CNTs were captured by the solidification front, so the CNTs remained inside the grain. Moreover, good interfacial bonding was achieved in the composite under high solidification rate. Meanwhile, compared with the matrix alloy, the ultimate tensile strength (UTS) and yield strength (YS) of the composite were significantly improved. The mechanical properties of the composite under higher solidification rate are better than composite under low solidification rate and the alloy. Moreover, most CNTs on the fracture surfaces were directly pulled out from the matrix. The Kelly–Tyson formula agreed well with the experimental tensile value in the composite under higher solidification rate, and the load-transfer efficiency is almost equal to 1.     

碳纳米管/橡胶复合材料的界面性能:碳纳米管的比表面积的影响

橡胶大分子和无机纳米填料由于相互作用形成的界面是决定弹性体复合材料性能的重要因素.利用原子力显微镜的峰值力定量纳米力学映射模式(AFM-QNM)建立了碳纳米管/溶聚丁苯橡胶(CNT/SSBR)复合材料的界面纳米力学性能和界面厚度的定量表征方法,研究揭示了CNT的比表面积对CNT/SSBR复合材料的界面纳米力学性能和界面...     

Synthesis and properties of magnetic multi-walled carbon nanotubes loaded with Fe4N nanoparticles

High saturation magnetization (>90 emu/g) multi-walled carbon nanotubes (MWCNTs) and Fe₄N nanoparticles composite were successfully synthesized by gas nitriding at 550 °C. Almost all Fe₄N nanoparticles were evenly distributed inside the carbon nanotubes and formed a special composite microstructure. This composite microstructure shows excellent soft magnetic property, structural stability, and chemical stability at room temperature. The investigations of electromagnetic and microwave absorption performances indicate that microwave absorbing capacity of low frequency band of MWCNTs were greatly improved by addition of Fe₄N nanoparticles.     

全氟辛基季胺碘化物改性碳纳米管对天然橡胶胶乳性能的影响

用水溶性的阳离子表面活性剂全氟辛基季胺碘化物FC-134对碳纳米管进行非共价键改性,并用液相法制备改性碳纳米管/天然橡胶复合材料,研究了改性碳纳米管对天然橡胶复合材料的影响。结果表明,改性碳纳米管在水介质中具有很好的稳定性。佩恩效应表明,碳纳米管经过表面修饰增强了与橡胶的相互作用,降低了碳纳米管之间的相互作用。橡胶加工分析仪的结果表明,碳纳米管均匀地分散到复合材料中。与未改性碳纳米管/天然橡胶胶乳复合材料相比,改性碳纳米管/天然橡胶胶乳复合材料硫化胶的撕裂强度提高了65%,拉伸强度提高了29%。     

Catalyst nanocomposites templates of carbon nanoribbons, nanospheres and nanotubes

Several attractive types of amorphous or crystalline carbon nanostructure were obtained by a single catalytic process, during natural gas decomposition using different nanostructured catalysts as template. The nanostructured catalyst templates were based on transition metal nanoparticles embedded in carbon matrixes and nanoceramic supports which consist of magnesium oxide doped with ceria rare earths, prepared by the high-energy mechanical milling. The yield and the nature of the nanostructured carbon are strongly influenced by the preparation method of the template and the chemical composition of the catalysts.     

Density functional theory investigation of the mechanical properties of single-walled carbon nanotubes

We detail the results of our first-principles study based on density functional theory on the elastic properties of (6, 6) single-walled carbon nanotubes (SWCNTs) in both periodic and non-periodic systems. The Young’s modulus and the shear modulus of nanotubes were evaluated through applying axial and torsion strains on periodic, H-, and C-capped nanotubes. Based on our first-principles calculations, the Young’s modulus of the periodic nanotube tens to increase as the nanotube’s length increases, and finally approaches a constant value at long tube lengths. It was found that the Young’s modulus characteristic of H- and C-capped nanotubes exhibit contradictory behaviors during compression with the periodic nanotube. Our calculations also predict that the Young’s and Shear moduli of C-capped nanotubes are larger than those of other types of nanotubes.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

Correlation between the acoustic and dynamic mechanical properties of natural rubber foam: Effect of foaming temperature

Acoustic absorbing foam materials are produced from dry natural rubber (NR) with the addition of sodium bicarbonate as a blowing agent. The acoustical efficiencies of NR foams were studied, and the results show a significant influence of the viscoelastic and damping properties of the base matrix. Both of these properties are governed by the average cell size, relative density, crosslink density and number of cells per unit volume. The lowest foaming temperature, 140 °C, yielded the NR foam (NR 140) with the highest relative density, crosslink density, smallest average cell size and greatest number of cells per unit volume. Consequently, these foam cell characteristics resulted in a superior sound absorption coefficient and a high storage modulus, which indicates that the NR 140 foam exhibits a better elastic behavior. On the other hand, the NR foam that expanded at 160 °C (NR 160) exhibited great potential for insulating sound and possessed good damping properties, which was characterized by its high transmission loss and tan δ values.     

Influence of shape and size on the alignment of multi-wall carbon nanotubes under magnetic fields

The influence of the shape and size of carbon nanotubes (CNTs) on the alignment of multi-wall CNTs was investigated. A CNT suspension with polyethylenimine (PEI) added as a dispersant showed stable dispersion. Stable CNT dispersion had a relatively high zeta potential value compared with poor dispersion. In addition, a strong magnetic field of 12 T was applied to the CNT suspension to investigate the alignment behavior of the CNTs. Good alignment of the CNTs according to the direction of the magnetic field was obtained. The degree of alignment depended on the shape and size of the CNTs, with the thick, straight CNTs showing better alignment than the thin, curved CNTs.     

Effect of addition of carbon nanofibers and carbon nanotubes on properties of thermoplastic biopolymers

This paper presents the properties of nano-bio-composites of solvent cast polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactone (PCL) containing carbon nanofiber or carbon nanotubes as a function of filler content. It is found that carbon nanotubes and nanofibers can be used to enhance the conductivity, thermal, mechanical and to enhance gas barrier properties of thermoplastic biopolyesters.     

Self-assembled natural rubber/silica nanocomposites: Its preparation and characterization

A novel natural rubber/silica (NR/SiO₂) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO₂ nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO₂ loading is less than 6.5 wt%. At low SiO₂ contents (4.0 wt%), the NR latex (NRL) and SiO₂ particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO₂ are observed. When more SiO₂ is loaded, secondary aggregations of SiO₂ nanoparticles are gradually generated, and the size of SiO₂ cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO₂ nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO₂ nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO₂ has great potential to manufacture medical protective products with high performances.     

Molecular dynamic simulations on tensile mechanical properties of single-walled carbon nanotubes with and without hydrogen storage

Using a bond order potential, molecular dynamics (MD) simulations have been performed to study the mechanical properties of single-walled carbon nanotubes (SWNTs) under tensile loading with and without hydrogen storage. (10,10) armchair and (17,0) zigzag carbon nanotubes have been studied. Up to the necking point of the armchair carbon nanotube, two deformation stages were identified. In the first stage, the elongation of the nanotube was primarily due to the altering of angles between two neighbor carbon bonds. Young's Modulus observed in this stage was comparable with experiments. In the second stage, the lengths of carbon bonds are extended up to the point of fracture. The tensile strength in this stage was higher than that observed in the first stage. Similar results were also found for the zigzag carbon nanotube with a lower tensile strength. Hydrogen molecules stored in the nanotubes reduced the maximum tensile strength of the carbon nanotubes, especially for the armchair type. The effect may be attributed to the competitive formation between the hydrogen–carbon and the carbon–carbon bonds.     

Effect of functionalized carbon nanotubes on the mechanical properties of epoxy-based composites

Abstract

In this research, composites reinforced with multi-walled carbon nanotubes (MWCNTs) in terms of their capability of absorbing energy during ballistic impact and tensile test were investigated. In order to investigate the effect of functional groups on mechanical properties of multi-wall carbon nanotubes composites, multi-walled carbon nanotubes were functionalized by COOH and NH₂. In order to investigate the penetration resistance of produced composites, the ballistic impact test with the high velocity was used. Results of the ballistic impact test imply that composites which benefit from carbon nanotubes with the carboxylic functional group have the highest value of the energy absorption. Results of the tensile test indicate, the interaction between carbon nanotubes with the carboxylic agent and the polymer matrix is much better. The ultimate stress for the sample containing nanotubes with hydroxyl functional group is 55% higher compared with the sample which does not contain any nanotubes. Reinforced composite samples which contain carbon nanotubes with the carboxylic functional group absorb 57.63% of the projectile energy and represent a better performance compared to the sample without nanotubes and the sample which consists of nanotubes with the amine functional group. The results of this study show that, uniform dispersion of nanotubes in the polymer matrix can profoundly affect mechanical properties especially the tensile strength. By functionalizing nanotubes and creating suitable functional groups, the cohesion between nanotubes and the matrix can be improved.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.