多壁碳纳米管外壁高温蒸发的分子动力学模拟

采用经典分子动力学（MD）方法,使用EDIP（environment-dependent interatomic potential)势描述C纳米管内C原子之间相互作用,对多壁C纳米管由于Stone-Wales缺陷引起外层管高温剥落蒸发现象进行了计算模拟.研究结果表明,高温下多壁C纳米管外层管Stone-Wales缺陷处C原子剧烈振动导致C—C键断裂形成悬键,并逐渐向四周扩散导致外层管剥落蒸发.利用Lindemann指数作为判据,得出多壁C纳米管外层管出现剥落蒸发的温度为2290 K左右,与Huang Jianyu等实验中观测到多壁C纳米管外层管剥落蒸发现象产生的温度2000 ℃基本一致.     

空位结构缺陷对C纳米管弹性性质的影响

用分子动力学方法对不同空位缺陷的扶手椅型与锯齿型单壁C纳米管杨氏弹性模量进行了计算和分析. 结果表明：扶手椅型（5, 5）, （10,10）和锯齿型（9, 0）, （18, 0） 纳米管在无缺陷时其杨氏模量分别为948,901和804,860 GPa. 随管径的增大,扶手椅型和锯齿型单壁C纳米管弹性模量分别减小和增大,表现出完全不同的变化规律. 随着C纳米管中单点空位缺陷的均匀增加,杨氏模量下降,当缺陷比率增加到一定程度时,杨氏模量下降骤然趋缓,形成一下降平台;双空位缺陷对C纳米管杨氏模量的影响与其分布方向有关;随单点空位缺陷间原子数的增加,在轴向上,杨氏模量下降到某一值小幅波动,而在周向上杨氏模量先下降,然后上升到某一稳定值. 随两单点空位缺陷的空间距离进一步增大,杨氏模量又呈微降趋势. 通过分子间σ键与π键特征及缺陷间近程电子云耦合作用规律与空位缺陷内部5-1DB缺陷的形成特点等理论对上述规律进行了分析. 关键词： 空位缺陷 C纳米管 分子动力学 杨氏模量     

碳纳米管对接成异质结器件的计算模拟

基于Stone-Wales缺陷演变理论与分子动力学、Monte Carlo计算方法, 进行了碳纳米管(CNTs)对接成异质结器件的计算模拟.首先, 提出了一种模拟CNTs端帽位置变化的新算法, 并计算模拟了单根CNT的端帽从开口到闭合的过程. Stone-Wales缺陷演变被设计模拟这些端帽变化的跃变过程, 以模拟C–C键的生成与断裂, 而分子动力学则作为跃变后构型弛豫的渐变模拟. 同时, 研究了不同管型CNTs的端帽打开并对接形成异质结的过程.研究结果显示, 对接初期在对接处先产生大量的缺陷, 以促进反应的发生. 这些缺陷趋向于演变成稳定的六元环结构, 或者五元环/七元环的结构, 使异质结趋于稳定. 关键词： 碳纳米管 Monte Carlo Stone-Wales缺陷 分子动力学     

单、双原子空位缺陷对扶手椅型单层碳纳米管屈曲性能的不同影响

采用分子动力学方法，对完善和含缺陷扶手椅型单层碳纳米管进行轴向压缩的数值模拟，对比研究三种不同的温度环境下单、双原子空位缺陷对碳纳米管轴压变形性能的特殊影响.研究结果表明管壁缺陷显著降低了纳米管低温时的承载能力，由于单原子空位缺陷造成的特殊应力集中效应会引发纳米管过早发生局部屈曲，单原子缺陷管的屈曲强度反而小于双原子管的屈曲强度. 关键词： 分子动力学 碳纳米管 屈曲 缺陷     

缺陷对单壁碳纳米管熔化与预熔化的影响

利用分子动力学模拟研究了具有几种常见缺陷的单壁碳纳米管的熔化与预熔化性质. 研究结果表明, 类似于纳米颗粒和聚合物, 碳纳米管发生熔化时的Lindemann指数为003, 远低于晶体熔化的判据01—015 使用Lindemann指数, 得出标准碳纳米管的熔化温度为4800K左右, 而带缺陷的碳纳米管的熔化总是从缺陷处开始, 并且缺陷会影响碳纳米管局部的熔化温度, 导致局部预熔化. Stone-Wales缺陷在2600K引起碳纳米管的局部熔化,空位缺陷导致的局部熔化温度在3200K, 而具有硅替位缺陷的碳纳米管在3800K以下具有很好的热稳定性. 关键词： 熔化 预熔化 缺陷 碳纳米管     

C60轰击石墨烯的瞬间动力学

采用非平衡分子动力学方法,通过分别控制温度和速度的方式研究了C60轰击石墨烯的瞬间动力学,研究表明,无论温度如何变化,C60在低速轰击石墨烯时都不能击穿石墨烯,但在高速轰击石墨烯时都能击穿石墨烯,并不受温度影响,对于在低速与高速的过渡段,发现C60击穿石墨烯的概率会随着温度的提升而呈现增加的趋势,导致此现象的原因是在高温时C60破坏石墨烯C—C键的概率更高,C60轰击石墨烯的动力学在石墨烯表面清理和纳米孔制备方面有潜在应用。     

单壁氮化硼纳米管压缩特性的分子动力学模拟

采用分子动力学方法,分别模拟完好的和含有缺陷的(7,7)扶手椅型氮化硼纳米管的轴向压缩过程.原子间的相互作用采用Tersoff多体势函数来描述.为验证结果的可靠性,同时针对(7,7)扶手椅型碳纳米管进行对比计算.结果表明,氮化硼纳米管的压缩失效模式同碳纳米管相同,均表现为管壁的局部屈曲.发现纳米管的压缩强度,如临界轴向内力在低温下受温度影响明显,并且和应变率的大小有关.然而,应变率对纳米管的弹性变形没有影响.另外,还发现空位缺陷降低了纳米管的力学性能.与完好的纳米管相比,含有缺陷的纳米管轴向压缩强度对于温度的影响并不敏感.     

含氮SW缺陷对单壁碳纳米管电子结构和光学性质的影响

应用第一性原理密度泛函理论研究了单壁碳纳米管中Stone-Wales(SW)缺陷和氮掺杂情况下的电子结构和光学性质.研究发现,含氮SW缺陷单壁碳纳米管体系的总能降低,结合更稳定,且在费米能级附近出现一条半满的杂质带,并且随着氮掺杂位置的不同,掺杂能态出现显著差异.碳管的吸收和反射明显减弱且吸收峰和反射峰在低能区发生红移现象,在能量小于11eV附近均出现杂质特征峰.本文对计算结果进行了分析研究,可望为含氮SW缺陷碳管在光电材料中的应用提供理论依据. 关键词： 单壁碳纳米管 Stone-Wales缺陷 氮掺杂 光学性质     

AuCu249合金团簇热稳定性的原子尺度计算研究

采用基于嵌入原子法的NVT正则系综分子动力学方法,在原子尺度上计算了包含249个原子的金属间化合物AuCu₂₄₉合金团簇由固态转变为熔体的结构演化过程. 根据对分布函数、原子密度分布函数和主要原子键对数目随温度的变化,发现在温度从低温升到高温的过程中,合金团簇内伴随着原子的连续位置交换,团簇呈现由外及里的分阶段结构转变. 同时还发现在团簇内原子堆积结构转变过程中,Au原子出现由团簇内层向外层运动的趋势,而Cu原子则有由外层向内层运动的趋势. 关键词： 合金团簇 分子动力学 计算机模拟 相变     

碳纳米管和碳化硅纳米管热导率的分子动力学研究

采用Tersoff势测试和研究了反向非平衡分子动力学中的Müller-Plathe法和Jund法在一维纳米管热传导中的应用.在相同的模拟步数中,Müller-Plathe法可以得到很好的结果,热导率在交换频率大于50时对参数的选择并不敏感.然而,Jund法并不能得到良好的线性温度梯度,其热导率在一定程度上依赖于选择的热流大小.在此基础上,运用Müller-Plathe法进一步研究了碳纳米管和碳化硅纳米管的长度、直径和温度对热导率的影响.结果表明,无论是碳纳米管还是碳化硅纳米管,其长度、直径和温度对热导率的影响是一致的.只要长度增加,纳米管的热导率相应增大,但增长速率不断降低.直径对热导率的影响很大程度上还取决于温度,在高温时,直径对热导率几乎没有影响.除此之外,纳米管的热导率随着温度的增加总体上也是不断降低的,但峰值现象的出现还受纳米管长度的影响.     

Mapping the resonance wavelengths of MWCNT as an optical nanoantenna

We investigated the surface plasmon resonances of multi-wall carbon nanotube (MWCNT) for applications as the optical antenna. We calculated the near-field and far-field response of MWCNT using finite integral technique. In addition, the effect of shape and dimensions on the optical response of MWCNT was studied. Also, the dielectric properties of MWCNT obtained from the experimental results in the literature were fitted with a Drude–Lorentz model. Finally, a full mapping of the geometry (length and radius) dependence for MWCNT was presented and discussed.     

碳纳米管端口的场蒸发

将单根多壁碳纳米管(multi-walled carbon nanotube，MWCNT)组装在W针尖上并送入超高真空场发射/场离子显微镜(Ultrahigh Vacuum Field-emission/Field-Ion microscope，UHV-FEM/FIM)进行场蒸发及场发射研究.结果表明，场蒸发可以降低MWCNT的逸出功，从而增强其场发射能力.估算MWCNT的蒸发场低于1.3×10⁸V·cm^-1，且在此场强下的平均蒸发速率为9.4nm·min^-1.定性讨论了MWCNT的蒸发场大大低于C的理论值的原因.首先，通过场解吸获得的清洁端口上有较多悬挂键，平均每个C原子的配位数较小，所以升华热较低.其次，可能存在于MWCNT中的H原子会在强场下碰撞端口的C原子，使其更易蒸发.以上结果显示了利用场蒸发剪短碳纳米管从而改善其场发射特性的可行性. 关键词： 碳纳米管 场蒸发 场发射     

拓扑缺陷对单壁碳纳米管电子结构及其光学光谱的影响

应用密度泛函理论计算了半导体型单壁碳纳米管(7,0)和(8,0)以及其发生镜像对称和非镜像对称Stone-Wales形变、形成异质结(7,0)-(8,0)情况下的能带结构、吸收光谱、反射光谱,并对计算结果进行了比较.研究发现:引入拓扑缺陷态后,碳纳米管的能带结构发生了明显的变化,费米能级在不同缺陷情况下移动方向不一致;碳管的吸收和反射明显减弱且吸收峰和反射峰在低能区发生红移现象;在光子能量约为E=13 eV处各碳管的吸收谱和反射谱中均出现一特征峰,并且在引入缺陷以后该特征峰向高能区移动.文章对计算结果进行了分析和探讨,可望利用这种拓扑缺陷的引入而产生的光电特性来设计碳管光电器件.     

Stone-Wales defect as a dipole of dislocation and anti-dislocation

Stone-Wales defect in a single-walled carbon nanotube has been investigated theoretically by a fully discrete dislocation equation. It is found that Stone-Wales defect as a fundamental structure can be obtained from the basic dislocation equation, which is used to determine the structure of the dislocations. In addition, there are two possible equilibrium configurations for the Stone-Wales defect.     

Assessment of the Microstructure and Mechanical Properties of Polycarbonate (PC)/Acrylonitrile Butadiene Rubber (NBR) Blends Reinforced with Multi-wall Carbon Nanotubes

Abstract

A series of polycarbonate (PC)/acrilonitrile butadiene rubber (NBR)/multi-wall carbon nanotube (MWCNT) nanocomposites were prepared via melt compounding in an internal mixer. The effect of the MWCNT content on the morphology and the thermal and mechanical properties of the prepared nanocomposites were studied. The morphologies of the samples were investigated by field-emission scanning electron microscopy (FESEM) and the thermal properties by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile mechanical results of the nanocomposites showed a decrease in elongation at break with an increase of only 2?wt% of MWCNT content in the PC/NBR blends, and an increasing value in elastic modulus and tensile strength of the nanocomposites. The FESEM images showed that the MWCNTs had good affinity with the polymers and no compatibilizer was needed for making the nanocomposites. The DSC and TGA results showed an increase in thermal stability with addition of MWCNTs because of the more thermally stable carbon nanotubes particles which was uniformly dispersed within the nanocomposites.     

Transport phenomena of carbon nanotubes and bioconvection nanoparticles on stagnation point flow in presence of induced magnetic field

This article is a numerical study of stagnation point flow of carbon nanotubes over an elongating sheet in presence of induced magnetic field submerged in bioconvection nanoparticles. Two types of carbon nanotubes are considered i.e. single wall carbon nanotube and multi wall carbon nanotube mixed in based fluid taken to be water as well as kerosene-oil. The emphasis of present study is to examine effect of induced magnetic field on boundary layer flows along with influence of SWCNT and MWCNT. Physical problem is mathematically modeled and simplified by using appropriate similarity transformations. Shooting method with Runge-Kutta of order 5 is employed to compute numerical results for non-dimensional velocity, induced magnetic field and temperature. The effects of pertinent parameters are portrayed through graphs. Numerical values of skinfriction coefficient and Nusselt number are tabulated to study the behaviors at the stretching surface. It is depicted that induced magnetic field is an increasing function of solid nanoparticles volumetric fraction. Moreover, MWCNT contributes in rising induced magnetic field more as compared to SWCNT for both water and kerosene-oil based fluids.     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

碳纳米管负载矾的第一性原理研究

本文基于密度泛函第一性原理研究了原始和带有缺陷的(Stone-Wales缺陷和单空位缺陷)碳纳米管负载金属V的稳定构型.对于V吸附在原始碳纳米管(CNT)上时,V在内表面的吸附比外表面的吸附有更强的相互作用力,且六元环内表面结构最稳定.当V与Stone-Wales缺陷碳纳米管相互作用时,V原子易吸附在管外七元环C-C键的外表面和内表面处,这说明缺陷位置的有效结合使之局域化加强.而以单空位缺陷碳纳米管为载体时V最易吸附在外缺陷处,相当于碳纳米管的一个C被金属V原子取代,形成了3个V-C_(sur)键,这进一步表明SV管外吸附比管内吸附更容易.我们从上述三种构型载体中发现,金属V吸附在缺陷碳纳米管时的稳定性要优于原始碳纳米管,且SV缺陷对金属V的固定效果最好.