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.     

通量可控的双壁碳纳米管水分子泵

以双壁碳纳米管作为基本单元设计了一种新型纳米机械水泵, 其内管固定作为水分子通道, 外管做活塞式轴向运动. 分子动力学计算表明, 水分子净通量及管内水分子电偶极矩分布均与外管运动速率有强烈耦合效应. 该设计可以实现水分子的高效单向运输, 且输运效率可以通过外管活塞运动的速率进行调控. 这些发现可为未来实用纳米分子泵器件的设计提供新的思路.     

碳纳米管阵列水渗透性质的研究

碳纳米管阵列组成的碳纳米管分子膜在生物学分子器件等方面有重要应用. 本文利用分子动力学方法计算研究水分子对(11, 11)碳纳米管阵列的渗透过程. 结果发现, 只有当阵列间隙面积大于57.91 Ų时, 水分子才能进入阵列间隙中, 并揭示了碳管内部、阵列间隙内水分子结构随相邻碳管间距变化的演化趋势以及管内外水分子电偶极矩的分布特性.     

形变碳纳米管选择通过性的分子动力学研究

本文采用分子动力学方法, 研究了基团修饰后形变碳纳米管的水分子通过性和离子选择性. 结果表明, 形变碳纳米管的短径与修饰基团的种类、修饰率及修饰位置有关. 不同粗细碳纳米管均存在临界短径, 小于临界短径的形变碳纳米管具有对氯离子和钠离子的选择性, 同时水分子通过速率与本征碳纳米管相比未明显变小. 分析系统平均力势表明, 离子选择性来源于不同短径碳纳米管管口的通过势垒. 对于实际制备中较宽孔径分布的碳纳米管, 可以通过基团修饰等方法调控其短径, 提高其离子选择性.     

硅基材料界面石墨烯片层运动行为及其摩擦特性

应用从头算分子动力学方法,模拟了在挤压剪切作用下石墨烯片层作为润滑剂添加于硅基材料界面的摩擦过程,研究了水分子和石墨烯表面氧化对石墨烯片层运动行为的影响.干燥环境下,压强较大时单纯石墨烯片层才会出现滑移,而氧化石墨烯片层在低压强下就开始滑移.潮湿环境下,界面结构影响水分子的整体分布和运动状态,而水分子的运动状态又影响氧化石墨烯片层的运动行为.由于二氧化硅表面羟基取向角较大,使得水分子在挤压剪切作用下偶极矩角变大,从而导致其与氧化石墨烯片层之间的结合强度削弱,二者之间出现相对滑移.石墨烯片层运动行为的改变引起了剪切面的转变.通过对石墨烯片层沿滑移方向上的速度波动幅度的分析,发现其与摩擦系数之间存在正相关性.     

乙醇水混合物在碳纳米管中的吸附与结构性质

用分子动力学模拟研究乙醇水混合物在碳纳米管中的结构与吸附．在(6,6)到(10,10)碳纳米管内,几乎总是充满乙醇分子,很少有水分子．在更粗的碳纳米管中有一些水分子,管内的乙醇质量分数远远高于体相值．对管内外的分子进行了径向、轴向、角向的密度和取向的分布以及氢键数目的分析．管外第一溶剂化层中分子的角向密度分布指出乙醇分子的甲基和碳壁有最强的作用,被钉扎在碳纳米管的六角形中心位置．基于对这些现象微观机制的理解,推测碳纳米管在甲醇和乙醇中更倾向吸附乙醇,通过对乙醇甲醇混合物与碳纳米管的分子动力学模拟验证了这个预测．     

水流在旋转黑磷纳米管内轴向驱动特性

运用分子动力学方法模拟研究了旋转的黑磷纳米管对管内水流的轴向驱动特性,研究结果表明:手性黑磷纳米管在旋转时会驱动管内水分子沿轴向运动,运动方向由纳米管转向决定;管内水流的流速和驱动力会随着黑磷管转速的提高而增大.采用黑磷双壁Couette模型计算分析了水-黑磷界面的摩擦系数及滑移特性,阐明了黑磷表面天然的各向异性微结构是旋转黑磷管轴向驱动水流的本质原因.构建了在双层黑磷纳米管间填充水分子的模型,发现内外黑磷管同时旋转时,管间水分子的轴向运动会增强.纳米管半径也会对水分子的定向运动产生影响,具体表现为在相同转速下,随着纳米管半径的增大,管内水分子在轴向上的运动速度会减小,而受力则会增大;双壁黑磷纳米管在旋转时管内水分子的轴向运动情况和单壁黑磷纳米管模型差异很小,证明黑磷管层数对水流驱动效果的影响不明显;温度对水流驱动效果的影响规律取决于管内压强和温度对流固界面摩擦系数的耦合作用,当温度低于常温时水分子在轴向上的速度和受力会随着温度的升高而增大,当温度达到常温时则趋于平稳.研究结果可为基于黑磷纳米管的流体传动器件的设计和应用提供理论基础.     

Rh在单壁碳纳米管上吸附的密度泛函理论研究

本文利用密度泛函理论研究了Rh原子在（6,6）单壁碳纳米管内外的吸附行为. 通过对Rh在单壁碳纳米管上不同吸附位的吸附构型与吸附能的研究发现: Rh吸附在管内、外的洞位最稳定, 且管外吸附比在管内强. 这是由于单壁碳纳米管的卷曲效应使得管外电荷密度比管内大造成的. 态密度分析表明, 吸附在管内外的Rh原子的5s电子均转移到了4d轨道上; Rh原子4d轨道上的电子转移到了（6, 6）碳管上, 使Rh带正电, 碳管带负电. 结合能带分析表明, Rh原子吸附在管内磁性较弱, 而吸附在管外较强. 关键词： 密度泛函理论 单壁碳纳米管 Rh原子 吸附     

水分子链受限于单壁碳纳米管结构的密度泛函理论研究

本文采用第一性原理的密度泛函理论,主要以(6,6)Armchair型,(11,0)Zigzag型单壁碳纳米管为研究对象,研究了水分子链在碳纳米管内部吸附的稳定结构,以及结合能随其结构的变化.结果表明:当水分子链受限于碳纳米管内部时,引起碳纳米管直径收缩,这主要是由于水分子链与碳纳米管之间的氢键作用以及范德华弱相互作用所引起的.随着碳纳米管半径的增加,两种单体之间的结合能逐渐减小,但当碳纳米管半径增加至6.78时,其结合能又有所增加,这是由于在优化过程中,水分子链单体之间的氢键作用大于水分子链与碳纳米管之 关键词： 水分子链/单壁碳纳米管 密度泛函理论 结构稳定性     

界面氢键对受限水结构和动态特性的影响

应用反应力场分子动力学方法, 模拟了水限制在全羟基化二氧化硅晶体表面间的弛豫过程, 研究了基底表面与水形成的界面氢键, 及其对受限水结构和动态特性行为的影响. 当基底表面硅醇固定时, 靠近基底表面水分子中的氧原子与基底表面的氢原子形成强氢键, 这使得靠近表面水分子中的氧原子比对应的氢原子更靠近基底表面, 从而水分子的偶极矩远离表面. 当基底表面硅醇可动时, 靠近基底表面水分子与基底表面原子形成两种强氢键, 一种是水分子中的氧原子与表面的氢原子形成的强氢键, 数量较少, 另一种是水分子中的氢原子与表面的氧原子形成的强氢键, 数量较多, 这使得靠近表面水分子中的氢原子比对应的氧原子更靠近表面, 从而水分子的偶极矩指向表面. 在相同几何间距下, 当基底表面硅醇可动时, 表面的活动性使得几何限制作用减弱, 导致了受限水分层现象没有固定表面限制下的明显. 此外, 固定表面比可动表面与水形成的界面氢键作用较强, 数量较多, 导致了可动表面限制下水的运动更为剧烈.     

Characterization of the radiation from single-walled zig-zag carbon nanotubes at terahertz range

This paper investigates the radiation characteristics of metal single-walled zig-zag carbon nanotubes as a dipole antenna at terahertz wave range. The current distribution, input impedance and mutual impedance are calculated for various geometrical parameters of vertically-aligned carbon nanotubes. The numerical results demonstrate the properties of the antenna depending strongly on the geometrical parameters such as the radius, the lengths of carbon nantobues, and the spacing between nanotubes. It is found that the zig-zag carbon nanotubes exhibit very high input impedance and the mutual impedances for antenna array applications. These unique high impedance properties are different from the conventional metal thin wire antenna. The far-field patterns and gain of antenna array are also calculated. The maximum gain of array of 100-element array is up to 20.0~dB, which is larger than the gain of 0.598~dB of single dipole antenna at distance d = 0.5\lambda .     

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.     

Quantum walk transport on carbon nanotube structures

We study source-to-sink excitation transport on carbon nanotubes using the concept of quantum walks. In particular, we focus on transport properties of Grover coined quantum walks on ideal and percolation perturbed nanotubes with zig-zag and armchair chiralities. Using analytic and numerical methods we identify how geometric properties of nanotubes and different types of a sink altogether control the structure of trapped states and, as a result, the overall source-to-sink transport efficiency. It is shown that chirality of nanotubes splits behavior of the transport efficiency into a few typically well separated quantitative branches. Based on that we uncover interesting quantum transport phenomena, e.g. increasing the length of the tube can enhance the transport and the highest transport efficiency is achieved for the thinnest tube. We also demonstrate, that the transport efficiency of the quantum walk on ideal nanotubes may exhibit even oscillatory behavior dependent on length and chirality.     

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.     

Pumping of confined water in carbon nanotubes by rotation-translation coupling

Bidirectional single file water transport in a carbon nanotube is known to occur in "bursts" in short nanotubes. Here we show that in long carbon nanotubes, when the orientation of the water molecules is maintained along one direction, a net water transport along that direction can be attained due to coupling between rotational and translational motions. The rotations of the water molecules are correlated more with the translation of the neighboring water molecule with the acceptor oxygen than the neighbor with the donor hydrogen. This mechanism can be used to pump water through nanotubes.     

Optical absorption of graphite and single-wall carbon nanotubes

A review of the electronic dipole transitions in graphite and single-wall carbon nanotubes is presented. Because of its singular electronic structure, the optical absorption matrix element as a function of wave vector has a node in the two-dimensional Brillouin zone of graphite, which depends linearly on the optical polarization direction. In the case of the single-wall carbon nanotubes, the dipole selection rule and the van Hove singularity in the joint density of states will give a characteristic behavior, which is observed by luminescence and resonance Raman spectroscopy. PACS 78.30.Na; 78.20.Bh; 78.66.Tr; 63.22.+m; 36.20.Kd; 36.20.Ng     

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.