碳纳米管受限空间对共轭高分子聚(9,9-二辛基芴-2,7-二基)链段运动行为的影响

在纳米受限空间中,高分子往往会表现出与本体状态不同的性质,如异常的链段运动特性及晶相间转变行为等,这些性质对于研究和开发新型高分子材料具有重要的意义,因此针对受限环境下高分子的物理化学特性研究也一直是高分子界关注的焦点.本文通过化学气相沉积法制备垂直取向排列的多壁碳纳米管阵列,借助溶剂润湿–收缩法获得规整的高密度阵列结构,其取向排列的碳纳米管间隙形成了准一维的纳米受限空间,尺寸在5—50 nm尺度下可调.进一步将共轭高分子聚(9,9-二辛基芴-2,7-二基)(PFO)填充到碳管间隙的纳米空间中,制备PFO与取向多壁碳纳米管阵列复合膜.结果发现在碳纳米管形成的纳米受限空间中,PFO的链段热运动行为与本征态PFO薄膜相比受到了明显的抑制,不同晶型间转变速度大大减缓,提高了构象的热稳定性,同时取向排列的碳纳米管对PFO分子链取向排列分布具有明显的诱导作用,有利于获得高性能的PFO晶体.这种高密度取向排列的碳纳米管阵列结构未来可以用于制备优良发光性能及高稳定性的PFO光电器件.     

石墨烯碳纳米管复合结构渗透特性的分子动力学研究

采用经典分子动力学方法研究了压力驱动作用下水在石墨烯碳纳米管复合结构中的渗透特性.研究结果表明,水分子渗透通过石墨烯碳纳米管复合结构的渗透率明显高于石墨烯碳纳米管组合结构.水在石墨烯碳纳米管复合结构中的渗透率随着压强的升高而增大,随着电场强度的增大而减小.考虑了温度和复合结构中双碳管轴心距对水渗透性的影响规律.系统温度越高,水的渗透率越高;随着双碳管轴心距的增加,水的渗透率逐渐降低.通过计算分析水流沿渗透方向的能障分布,解释了各参数变化对水在石墨烯碳管复合结构中渗透特性的影响机理.研究结果将为基于石墨烯碳管复合结构的新型纳米水泵设计提供一定的理论依据.     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用.本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为,即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响.结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用.分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化;同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用. 本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为, 即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响. 结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用. 分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化; 同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

碳纳米管组成二维光子晶体的有效介电常数FDTD数值模拟

把有序排列的碳纳米管看做二维光子晶体,引入平均场方法,先计算单根纳米碳管的有效介电常数,再用时域有限差分方法(FDTD)计算碳管阵列的有效介电常数,其结果与Maxwell-Garnett(MG)法结果相比,更接近实验数据.     

含有Stone-Wales缺陷的碳纳米管的热导率模拟

本文以Stone-Wales(SW)缺陷对碳纳米管热导率的影响为研究内容,采用非平衡态分子动力方法,模拟计算存在一个或多个SW缺陷的碳纳米管的轴向温度分布和热导率,并与无缺陷完整碳纳米管进行比较,开展缺陷效应分析,考察了缺陷浓度、碳管长度、碳管手性以及环境温度等因素的影响。模拟结果表明,由于缺陷存在,碳管轴向温度分布在缺陷处产生非线性的间断性跳跃,局部热阻增大。相对完整无缺陷碳管,含有SW缺陷的碳管热导率显著下降;随着缺陷数目的增加,碳管热导率下降的幅度增大。无论是否存在缺陷,锯齿型碳管的热导率通常小于扶手椅型的碳管,而长碳管的热导率通常大于短碳管;相对于锯齿型/长碳管,扶手椅型碳管/短碳管对SW缺陷更为敏感。     

纳米碳管阵列场发射电流密度的理论数值优化

以纳米碳管阵列为研究对象,利用镜像悬浮球模型及Fowler-Nordheim电流密度公式,对纳米碳管阵列的场发射电流密度进行计算,进而综合考虑场发射增强因子及场发射电流密度对纳米碳管阵列场发射性能进行定量优化.参考碳管阵列场发射电流密度最大值及场发射增强因子,表明当纳米碳管阵列间距为碳管高度十分之一时,纳米碳管阵列的场发射性能得到优化.与以前的理论估算结果相比,优化的阵列间距进一步减小.当纳米碳管间距过大,场发射增强因子增加,而场发射电流密度会在更大程度上减小;当纳米碳管密度较大时,场发射增强因子受到静电 关键词： 纳米碳管 场发射 增强因子 电流密度     

单壁碳纳米管的振动频率

将修正的分子结构力学方法(MMSMM)扩展用来分析单壁碳纳米管的动态特性. 应用MMSMM方法分析了悬臂单壁碳纳米管的振动特性，对计算得到的单壁碳纳米管振动的基频进行了讨论. 发现单壁碳纳米管振动的基频与碳管的直径和长度有关，呈现出一定的尺度依赖性，当管径很小的时候，单壁碳纳米管的振动基频可以达到GHz.并尝试用有限元方法模拟碳管的振动问题. 两种方法得到的结果表明，在常用的原子模拟方法(如分子动力学方法)解决碳纳米管振动问题遇到困难时，通过扩展修正可以简单的处理这类问题，并可以保持很好的精度.     

碳纳米管阵列拉曼光谱的对比研究

利用热化学气相沉积技术制备碳纳米管阵列,并对不同工艺下获得的一系列定向碳纳米管阵列进行了拉曼光谱的对比研究。研究发现：碳纳米管阵列一阶拉曼光谱的G峰中心和D峰中心都会向低波数方向发生红移。并且阵列中碳管的一致性、准直性越好,红移的波数就越多。除了谱峰以外,D线和G线的积分强度比I_D / I_G也能够反映所研究的碳材料的有序度和完整性。I_D / I_G越低,说明该碳纳米管阵列的石墨化越好,无定形碳杂质越少。     

单壁碳纳米管端口结构的热稳定性

利用紧束缚势分子动力学模拟方法,研究了温度在1000 K-3000 K之间单壁碳纳米管端口结构的变化趋势.计算表明,温度对整个管端口结构有重要影响,温度升高容易使理想单壁碳管端口封闭.温度在3000 K下碳管端口达到封闭,而且端口封闭导致碳管系统能量的降低.碳纳米管长度越长,端口封闭越快,且扶手型碳纳米管比锯齿型碳纳米管更容易形成端口封闭的结构.     

单壁碳纳米管受限空间内水的分布

碳纳米管管腔作为分子物质的纳米通道,其储存或输送水的能力具有重要研究价值.为了研究碳纳米管管腔受限空间对水分子团簇结构和分布的影响,本文采用分子动力学方法探究了管径、手性和温度对单壁碳纳米管管腔内水的结构和分布的影响.结果表明:在常温下,管径尺寸范围为1.018—1.253 nm的单壁碳纳米管管内易形成有序的多元环水结构,此范围以外碳纳米管管内难以形成水的有序结构;且随着管径尺寸增大,多元环水呈现由三元环至六元环的结构变化;范德瓦耳斯势分布分析表明,在上述管径范围内,水分子趋向于贴近碳纳米管管壁分布而形成水的有序结构.对比管径尺寸差别较小的碳纳米管,其手性对多元环水结构影响不大.多元环水结构的稳定性表现出温度依赖性,管径较大的碳纳米管内的多元环水的有序结构更易随温度升高而消失.     

Structures of water molecular nanotube induced by axial tensile strains

Five well-ordered nano-ice structures embedded in carbon nanotubes are obtained in this study. These five nano-ice phases all exhibit single walled tubular morphologies, including the pentagon, hexagon ice nanotubes whose structures are quite different from bulk ice. Our simulation results indicate that water molecules tend to rearrange into surface ring structures to reduce the number of free OH groups. The structural behavior of these ice nanotubes inside CNTs subject to axial stress is also investigated. The ice nanotubes tend to be drawn to ice nanorings or ice nanospring during the mechanical stretching. The distribution function exhibits typical order-to-disorder transition of the water network confined in carbon nanotube during the stretching. By analysis, we suggest that it is unlikely that additional water molecules will enter the tubes because of the increased volume available if the tubes are stretched at contact with a water reservoir.     

Control of the motion of nanoelectromechanical systems based on carbon nanotubes by electric fields

A new method is proposed for controlling the motion of nanoelectromechanical systems based on carbon nanotubes. In this method, a single-walled nanotube acquires an electric dipole moment owing to the chemical adsorption of atoms or molecules at open ends of the nanotube. The electric dipole moments of carbon nanotubes with chemically modified ends are calculated by the molecular orbital method. These nanotubes can be set in motion under the effect of a nonuniform electric field. The possibility of controlling the motion of nanoelectromechanical systems with the proposed method is demonstrated using a nanotube-based gigahertz oscillator as an example. The operating characteristics of the gigahertz oscillator are analyzed, and its operation is simulated by the molecular dynamics method. The controlling parameters and characteristics corresponding to the controlled operating conditions at a constant frequency for the system under investigation are determined.     

Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches

The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.     

Water alignment and proton conduction inside carbon nanotubes

First-principles molecular dynamics simulations have been carried out to investigate the structure, electronic properties, and proton conductivity of water confined inside single-walled carbon nanotubes. The simulations predict the formation of a strongly connected one-dimensional hydrogen-bonded water wire resulting in a net electric dipole moment directed along the nanotube axis. An excess proton injected into the water wire is found to be significantly stabilized, relative to the gas phase, due to the high polarizability of the carbon nanotube.     

Effect of molecular structure on fluid transport through carbon nanotubes

We perform molecular dynamics simulations to study the transport of geometrically modified water models through channels of carbon nanotube (CNT) membranes. We use two modifications to an existing water model (extended simple point charge SPC/E) as representative surrogates of molecular fluids: (1) bent model (model B) in which the HOH angle is varied while keeping the dipole moment constant by adjusting the OH bond length and (2) modified bent model (model MB) in which the HOH angle changes without any change in OH bond length thereby changing the dipole moment. Interestingly, we find that the fluid transport is a nonmonotonic function of the bond angle for both fluid models. This observed trend is not anticipated based on the fluid density as a function of the bond angle inside and outside of the nanotube channel. However, the average residence time of transmitted molecules through the channel provides an approximately inverse linear correlation with the observed flux, independent of the fluid model. Based on these correlations, we have developed an empirical design parameter connecting fluid transport through CNTs as a function of average occupancy (number of fluid molecules inside the nanotube) and the average residence time. Our results suggest that transport through carbon nanotubes can be sensitive to small changes in the structure of fluid molecules that can potentially be utilised for mixture separation.     

Modeling on ion rejection using membranes comprising ultra-small radii carbon nanotubes

In this paper, we investigate the complete ion rejection using carbon nanotube membranes comprising ultra-small radii nanotubes. Three acceptance radii for a water molecule, a sodium ion and a chloride ion are determined assuming the continuous approximation. Given the acceptance radii, we may confine the scope of the nanotube radius so that only water molecules can pass through but the heavier sodium and chloride ions are repulsed from the nanotube ends. We assume that the collective motion of water molecules inside a sufficiently long nanotube is driven by atomic vibrations so that classical phonon theory might be used to deduce the average water transit time inside the nanotube for ion rejection. We predict that for carbon nanotube membranes comprising nanotubes of radii lying between 3.4 and 3.9 ?, only water molecules will pass through, and sodium and chloride ions will not, which together using phonon theory, we deduce that the smaller the nanotube radius, the lower the average water transit time and the higher the efficiency of the membrane for ion rejection purposes. The present theoretical approach has the merit of rapid computational times and indicates those nanotube radii where future experimental work might be focussed.     

铁镍合金纳米管阵列的模板制备和磁性

"在阳极氧化铝模板的孔洞中利用模板浸润的方法成功制备出了铁镍合金纳米管阵列．通过改变所用模板的参数和沉积纳米管的的制备条件,所制备的纳米管的长度、内径和外径的尺寸都可以得到有效控制．利用扫描电子显微镜和透射电子显微镜对所制备的纳米管及其阵列的形貌进行了表征．对铁镍合金纳米管阵列的宏观磁性测量表明样品具有磁各向异性,沿纳米管长轴方向样品更容易被磁化．对纳米管的磁化反转机制和磁矩在纳米管中的静态分布进行了讨论．铁镍合金纳米管的这些性质都是由纳米管的独特结构造成的．"     

Control of the motion of nanoelectromechanical systems based on carbon nanotubes

A new method is proposed for controlling the motion of nanoelectromechanical systems based on carbon nanotubes. In this method, a single-walled nanotube acquires an electric dipole moment owing to the chemical adsorption of atoms or molecules at open ends of the nanotube and, then, the electric dipole moment thus induced can be set in motion under the effect of a nonuniform electric field. The electric dipole moments of chemically modified nanotubes are calculated for the first time. The possibility of controlling the motion of nanotube-based nanoelectromechanical systems with the proposed method is demonstrated using a gigahertz oscillator as an example. The operating characteristics of the gigahertz oscillator and the controlling electric field are calculated.     

The structure and dynamics of water inside armchair carbon nanotube

In this paper we present some simulation results about the behaviour of water molecules inside a single wall carbon nanotube (SWNT). We find that the confinement of water in an SWNT can induce a wave-like pattern distribution along the channel axis, similar phenomena are also observed in biological water channels. Carbon nanotubes(CNTs) can serve as simple nonpolar water channels. Molecular transport through narrow CNTs is highly collective because of tight hydrogen bonds in the protective environment of the pore. The hydrogen bond net is important for proton and other signal transports. The average dipoles of water molecules inside CNTs (7,7), (8,8) and (9,9) are discussed in detail. Simulation results indicate that the states of dipole are affected by the diameter of SWNT. The number of hydrogen bonds, the water--water interaction and water--CNT interaction are also studied in this paper.