单壁碳纳米管力学性质的分子动力学模拟

用分子动力学方法研究了在"拉伸"和"悬臂梁"两种模型下单壁碳纳米管的力学性质。通过对扶手椅形式的单壁碳纳米管进行分子动力学计算,得出半径在0.35nm~0.69nm之间的碳纳米管的杨氏模量在1.32623Tpa~1.03947TPa范围内波动。从模拟结果可以看出,在"拉伸"和"悬臂梁"两种模型下得到的单壁碳纳米管的杨氏模量不但在数值上有所差异,而且随其半径的变化趋势相反。     

金纳米线拉伸行为的分子动力学模拟

采用分子动力学方法模拟了不同截面尺寸金纳米线的拉伸力学行为。计算结果表明:相同长度的金纳米线弹性模量随着截面尺寸的减小而减小,而其屈服强度随着截面尺寸的减小而增大,并且发生屈服推迟现象。应力—应变曲线与形变过程相对应。在弹性变形阶段,纳米线形变不显著;随着应变量的增加,发现纳米线出现大量堆垛层错。     

纳米尺度拉伸变形行为的分子动力学模拟

为了研究单晶面心立方材料在纳米尺度下的拉伸变形机理,采用分子动力学方法模拟了单晶Cu的拉伸变形过程,并研究了不同温度、不同应变速率对其拉伸变形行为的影响.结果表明:不同温度对单晶Cu屈服强度影响明显,温度越高,屈服强度越低;不同应变速率对拉伸过程的弹性变形和屈服机理没有影响,但对塑性变形影响大,应变速率越大,屈服强度越大.     

碳纳米管受介电泳作用三维运动仿真

利用溶于介电液中的碳纳米管在外加交变电场作用下极化产生介电泳力和液体粘滞阻力的共同作用,建立了碳纳米管受力和运动模型;对碳纳米管的运动过程进行了仿真,得到了碳纳米管从特定初始点开始的三维运动轨迹和可以实现组装的碳纳米管初始点分布区域.计算了碳纳米管运动过程中所受介电泳力和速度的变化规律,距离电极间隙越近,碳纳米管受力和速度越大,最大分别能达到10^-9 N和10⁵μm/s的数量级.仿真结果为碳纳米管介电电泳组装提供指导.     

镍单晶纳米丝单向拉伸的分子动力学模拟

应用分子动力学方法模拟了金属镍单晶纳米丝在无热激活状态下的轴向拉伸变形过程，得出
纳米尺度下单晶镍丝的应力-应变演化关系、能量和原子构型变化以及损伤初始化与扩展过程。通过与宏
观拉伸过程的比较，模拟结果表明表面原子使纳米丝在无外荷载作用时存在系统初始应力，自由表面张力
的作用使纳米丝横截面上存在与轴向应力变化趋势一致的正交等值应力，自由表面发射位错和滑移并形成
堆垛层错和原子台阶导致纳米丝变形；表面原子偏离理想位置形成的空穴和孔洞及其连接是纳米丝损伤破
坏过程的几何特征。模拟获得镍单晶纳米丝的断裂强度为22.96 GPa。     

多壁纳米碳管环的成环机理研究

利用连续介质模型和弹性能理论,分析了多壁纳米碳管环的形成过程.发现弯曲纳米碳管成形自由能为零的条件决定了多壁纳米碳管环的形成;并存在使直纳米碳管变弯的阈值条件,纳米碳管环是诸多弯曲构型中的一种稳定构型.此模型导出的多壁纳米碳管环半径与实测值符合.说明了连续介质弹性能理论在原子尺度下仍能使用及多壁纳米碳管环的形成是一个成形自由能为零的自组织过程.     

碳纳米管结构的模拟计算

碳纳米管具有着奇异的物理和化学性质，这与其几何结构是密切相关的.为了生动形象地揭示其结构，用分子静力学方法对碳纳米管结构进行了模拟计算.首先从二维石墨片晶体坐标出发，通过坐标变换，得到碳纳米管上碳原子的三维坐标.在此基础上给出了扶手椅型、锯齿型和螺旋型三种单壁碳纳米管的三维立体结构.利用单壁碳纳米管的模拟结果，对多壁碳纳米管和管束的构型进行了组合模拟.模拟效果形象、逼真，为碳纳米管的性能和应用的模拟计算提供了必要的基础.     

氧化钆掺杂氧化铈的分子动力学模拟

为了研究氧化钆掺杂的氧化铈( GDC)在不同掺杂浓度下的晶格变化情况及工作机理,以牛顿第二定律为基础,建立了GDC的微观原子模型,采用分子动力学模拟的方法系统计算了工作状态下的GDC.计算结果显示:随掺杂浓度的增加,GDC 晶格常数、O2--O2 -最近邻距离不断增加,Ce4+ -O2 -、Gd3+-O2-最近邻距离却不断减小,且由当前常用的4种势函数计算的晶格构型并无太大差异.在模拟过程中,O2-的扩散系数随掺杂浓度的增加先增大后减小,当氧化钆浓度为8％左右时,扩散系数达到最大.     

Molecular dynamics simulation of hydrogen enhancing dislocation emission

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金刚石薄膜热导率的分子动力学模拟

采用非平衡分子动力学法(NEMD),利用Tersoff势能函数,通过固定边界模型和常热流法,模拟了金刚石薄膜的微尺度导热过程.根据薄膜内的温度梯度和通过薄膜的热流,采用Fourier定律计算某一给定状态下的薄膜热导率.计算结果表明:厚度在2~8 nm,温度在400 K状态下,金刚石薄膜的热导率与厚度成近似线性变化;薄膜厚度和热流一定,温度400~1 200 K时,金刚石薄膜的热导率随温度的升高,温度增至1200 K时热导率趋近于一个常数.     

Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

Currently, because of the thermal instability of nanocrystalline (NC) materials, there is little report on their thermal properties. Thus, for the NC, the study on their thermal sta- bility has been an urgent issue from the view of practical application and theoretical re- search. The difficulty for investigating the growth of NC material is to determine the crystal grain size precisely. Crystal grain size is generally determined by electronic mi- croscopes or X-ray diffraction[1]. Experime…     

模型流体扩散系数与温度关系的分子动力学模拟

采用分子动力学(MD)模拟的方法,计算了模型流体氩及氩/氪溶液的自扩散系数和互扩散系数,及其与温度的关系.计算结果表明:对不同状态下氩的自扩散系数的计算与实验结果符合较好,误差在10%左右;采用Green-Kubo法和Einstein法计算的扩散系数相等;扩散系数与温度的关系均服从D=D0-e E/RT的关系,对A r/K r体系自扩散系数和互扩散系数的M D模拟结果进行拟合,得到Ar、Kr自扩散系数及互扩散系数的活化能分别为1278J/mol、1340J/mol和1296J/mol.     

多壁纳米碳管的压力储氢研究

采用催化热解法制备了多壁纳米碳管，并对其进行酸化、灼烧、掺杂等一系列预处理后，在室温及氢气的压力分别为9，12MPa的条件下研究了多壁纳米碳管的储氢性能。通过对纳米碳管的不同处理可以提高纳米碳管储氢容量，掺杂金属锂后，纳米碳管的储氢量增加最大。     

碳纳米管的电学性质

依据碳纳米管中电子-声子相互作用的原理,采用哈密顿量、量子化理论推导了二聚化对应能隙和相变温度,在紧束缚近似、量子理论和能带理论的基础上,利用周期性边界条件对碳纳米管Π电子进行了分析,讨论了碳纳米管的导电性,预测了室温下碳纳米管碳管中载流子输运方向.     

Residual Tensile Strength of Plain Concrete Under Tensile Fatigue Loading

The functional relation between the residual tensile strength of plain concrete and number of cycles was determined. 99 tappered prism specimens of plain concrete were tested under uniaxial tensile fatigue loading. Based on the probability distribution of the residual tensile strength, the empirical expressions of the residual tensile strength corresponding to the number of cycles were obtained. The residual tensile strength attenuating curves can be used to predict the residual fatigue life of the specimen under variable-amplitude fatigue loading. There is a good correlation between residual tensile strength and residual secant elastic modulus. The relationship between the residual secant elastic modulus and number of cycles was also established.     

Molecular dynamics simulation of Ni3Al melting

With the Voter-Chen version of embedded-atom model (EAM) potential and molecular dynamics, the melting of Ni3Al alloy was simulated by one-phase (conventional) and two-phase approaches. It is shown that the simulated melting point is dependent on the potential and the simulation method. The structures of the melts obtained by different simulation methods were analyzed by the pair correlation function, the coordination number, and the distribution of atom pair type (indexed by the Honeycutt-Andersen pair analysis technique). The results show that the structures are very similar.     

Molecular dynamics simulation of ion transport in a nanochannel

A molecular dynamics (MD) model of the fluidic electrokinetic transport in a nano-scale channel with two bulk sinks was presented, and the process of ion transport in the nanochannel was simulated in this paper. The model consists of two water sinks at the two ends and a pump in the middle, which is different from a single pump model in previous MD simulations. Simulation results show that the charged surfaces of the nanochannel result in the depletion of co-ions and the enrichment of counterions in the nanochannel. A stable current is induced because of the motion of ions when an external electric field is applied across the nanochannel, and the current in the pump region is mainly induced by the motion of counterions. In addition, the ion number in the pump region rapidly decreases as the external electric field is applied. In the equilibrated system, the electrically neutral character in the pump region is destroyed and this region displays a certain electrical character, which depends on the surface charge. The ion distribution is greatly different from the results predicted by the continuum theory, e.g. a smaller peak value of Na⁺ concentration appears near the wall. The transport efficiency of counterions (coions) can be effectively increased (decreased) by increasing the surface charge density. The simulation results demonstrate that the ion distribution in the electric double layer (EDL) of a nanochannel cannot be exactly described by the classical Gouy-Chapman-Stern (GCS) theory model. The mechanism of some special experimental phenomena in a nanochannel and the effect of the surface charge density on the ion-transport efficiency were also explored to provide some theoretical insights for the design and application of nano-scale fluidic pumps. Supported by the National Basic Research Program of China (Grant No. 2006CB300404), the National Natural Science Foundation of China (Grant Nos. 50475077, 50676019, 50506008), the Natural Science Foundation of Jiangsu Province (Grant No. BK2006510), and the Foundation of Education Ministry of China (Grant No. 20050286019). The author Y. Chen also acknowledges the financial support from the Program for New Century Excellent Talents in University (NCET-04-0470).     

高强钢纤维碳纳米管混凝土单轴受压本构关系

为了改善高强素混凝土的脆性破坏行为,通过钢纤维与碳纳米管的混掺试验,分别进行了空白试样和高强钢纤维碳纳米管混凝土的立方体和轴心抗压试验,得到了单轴受压应力-应变关系曲线,并由此建立了本构方程。试验结果表明:HSPC的棱柱体试件破坏形态为典型的脆性破坏;HSSFCNRC属于典型的塑性破坏。其次,两者的轴压比(轴心与立方体抗压强度之比)均随强度提高而提高,但HSPC的峰值应变、弹性模量和泊松比均比HSSFCNRC小;第三,由于HSPC的脆性和压力试验机的局限性,所采集到的下降段曲线上数据点远较后者少得多,而且后者也较前者的曲线平缓得多。这些特征指标,均说明了钢纤维与碳纳米管已有效改善了HSPC的脆性破坏行为,可为相关工程应用奠定基础。     

支链烷基苯磺酸盐在油水界面的分子动力学模拟

采用分子动力学的方法研究了阴离子表面活性剂十六烷基苯磺酸盐在正十六烷-水界面上的聚集结构,研究了苯环在碳氢链上的取代位置对油水界面性质的影响。由界面生成能和界面层厚度的计算结果可知,苯磺酸盐接在十六烷第2个碳上体系从能量上最稳定,界面厚度最大;不同体系的分子占有面积和分子构象参数决定了不同表面活性剂界面单层膜排列情况。研究结果表明,对于较大碳数烷烃,支链烷基苯磺酸盐结构的影响主要来自于尾链的构象排布,苯环的取代位置越靠近碳链端点,分子占有面积越小,在界面上的吸附能力越强。表面活性剂分子的伸展性和有序性的增加使界面排布更紧密,更容易达到低界面张力,利于驱油。     

Development of supercapacitors based on carbon nanotubes

Block-type electrodes made of carbon nanotubes were fabricated by different processes. The volumetric specific capacitance based on such electrodes reached 107 F/cm3, which proves carbon nanotubes to be ideal candidate materials for supercapacitors. The composite electrodes consisting of carbon nanotubes and RuO2 ·xH2O were developed by the deposition of RuO2 on the surface of carbon nanotubes. Supercapacitors based on the composite electrodes show much higher specific capacitance than those based on pure carbon nanotube ones. A specific capacitance of 600 F/g can be achieved when the weight percent of RuO2· xH2O in the composite electrodes reaches 75% . In addition , supercapacitors based on the composite electrodes show both high energy density and high power density characteristics.