Effects of combination modes of favorable growth unit of Al(OH)_3 crystals precipitating on Van der Waals and chemical bond force

The dipole moment, total energy, atomic charge, orbital population and orbital energy of four representative combination models of the favorable growth unit Al6（OH）18（H2O）6 of Al（OH）3 crystals precipitating are calculated by ab initio at RHF/STO-3G, RHF/3-21G, RHF/6-31G levels and DFT at RB3LYP/STO-3G, RB3LYP/3-21G, RB3LYP/6-31G levels with Dipole & Sphere solvent model. The effect of various combination models on Van der Waals force is analyzed using dipole moment and molecular radius, and that on chemical bond force is analyzed using total energy, orbital population and orbital energy.

A Revisited Definition of the Three Solute Descriptors Related to the Van der Waals Forces in Solutions

It is currently admitted that the intermolecular forces implicated in Gas Liquid Chromatography (GLC) can be expressed as a product of parameters (or descriptors) of solutes and of parameters of solvents. The present study is limited to those of solutes, and among them the three ones are involved in the Van der Waals forces, whereas the two ones involved in the hydrogen bonding are left aside at this stage. These three studied parameters, which we call δ, ω and ε, respectively reflect the three types of Van der Waals forces: dispersion, orientation or polarity strictly speaking, and induction-polarizability. These parameters have been experimentally obtained in previous studies for 121 Volatile Organic Compounds (VOC) via an original Multiplicative Matrix Analysis (MMA) applied to a superabundant and accurate GLC data set. Then, also in previous studies, attempts have been made to predict these parameters via a Simplified Molecular Topology procedure (SMT). Because these last published results have been somewhat disappointing, a promising new strategy of prediction is developed and detailed in the present article.

Updated Definition of the Three Solvent Descriptors Related to the Van der Waals Forces in Solutions

Innovative viewpoint on the older topic of the van der Waals forces, is of interesting and significant issue to be concerned in both the fields related to the fundamental investigation and thus valuable in guiding the new physiochemical phenomena and processes for both academic research and practical applications. The intermolecular Van der Waals forces involved in solutions have been recently deeply reconsidered as far as the solute side is concerned. More precisely, the solute descriptors (or parameters) experimentally established, have been accurately related to molecular features of a Simplified Molecular Topology. In the present study, an equivalent result is reached on the solvent side. Both experimental parameters have been obtained simultaneously in previous Gas Liquid Chromatographic studies for 121 Volatile Organic Compounds and 11 liquid stationary phases, via an original Multiplicative Matrix Analysis. In that experimental step, five groups of forces were identified, two of hydrogen bonding and three of Van der Waals: 1) dispersion (London), 2) orientation or polarity strictly speaking (Keesom), and 3) induction-polarizability (Debye). At this stage, an attempt of characterization the solvent parameters via the SMT procedure has been limited to those related to the Van der Waals forces, those related to the hydrogen bonding being for now left aside.

Interest of Splitting the Enthalpies of Vaporization in Four Distinct Parts Reflecting the Van der Waals and the Hydrogen Bonding Forces

An experimental characterization of the Van der Waals forces involved in volatile organic compounds (VOC) dissolved into stationary phases of gas liquid chromatography (GLC) has been started at the beginning of the seventies. This field has been reactivated from 1994 thanks to a fruitful cooperation between our CNRS team and the group of Ervin Kováts at the Federal Polytechnic School of Lausanne. The applied strategy can be summarized, in the first instance, as the experimental measurement of accurate and superabundant mutual affinities of a limited number of VOC and stationary phases and their processing using an original tool named Multiplicative Matrix Analysis (MMA). Then, in the second stage, the obtained results have been compared with molecular properties well established, as the Van der Waals molecular volume, the refraction index and the polar surface area (PSA), in order to get generalized values for any compound. The present study summarizes the positive results developed in our three last papers on this topic (2013, 2016 and 2018), as well as the attempt to overcome the negative ones using enthalpies of vaporization.

Van der Waals力场中束缚态粒子能级的数值方法和波函数

利用近似情况下Van der Waals力场中束缚态粒子的定态Schrodinger方程,研究束缚态粒子能级的数值方法和波函数,并讨论不同能量状态粒子的概率密度分布情况,计算经典禁区粒子出现的概率,产生了隧道效应。

动力学压缩真空中的Van der Waals力

基于参数动力学过程产生的压缩效应 ,利用Millonni源理论方法研究了动力学压缩真空中VanderWaals力的性质及其与真空压缩的关系。所得结果表明 :VanderWaals力的性质依赖于真空压缩的程度 ;在一定的临界条件下 ,VanderWaals力由通常的吸引性作用转化为排斥性作用。当压缩系数为零时 ,所得结果与通常文献完全一致。

Van der Waals力量子性分析

本文用量子力学的方法对两个谐振子的电偶极模型进行研究，得到ＶａｎｄｅｒＷａａｌｓ力的量子性结果．

Numerical Analysis of the Adhesive Forces in Nano-Scale Structure

Nanohairs, which can be found on the epidermis of Tokay gecko＇s toes, contribute to the adhesion by means of van der Waals force, capillary force, etc. This structure has inspired many researchers to fabricate the attachable nano-scale structures. However, the efficiency of artificial nano-scale structures is not reliable sufficiently. Moreover, the mechanical parameters related to the nano-hair attachment are not yet revealed qualitatively. The mechanical parameters which have influence on the ability of adhesive nano-hairs were investigated through numerical simulation in which only van der Waals force was considered. For the numerical analysis, finite element method was utilized and van der Waals force, assumed as 12-6 Lennard-Jones potential, was implemented as the body force term in the finite element formulation.

Influence of atomic force microscope(AFM) probe shape on adhesion force measured in humidity environment

In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope （AFM） tips and substrate. The analysis shows that the precise tip geometry plays a critical role on humidity depen- dence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt （paraboloid） tip, the adhesion force versus humidity curves tends to the apparent contrast （peak-to-valley corrugation） with a broad range. This paper demonstrates that the abrupt change of the adhesion force has high correla- tion with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines （triple point） on the probe profiles. The study provides insights for further under- standing nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.

INVESTIGATION OF THE DYNAMIC BUCKLING OF DOUBLEWALLED CARBON NANOTUBE SUBJECTED TO AXIAL PERIODIC DISTURBING FORCES

The dynamic response of a double_walled carbon nanotube embedded in elastic medium subjected to periodic disturbing forces is investigated. Investigation of the dynamic buckling of a double_walled carbon nanotube develops continuum model. The effect of the van der Waals forces between two tubes and the surrounding elastic medium for axial dynamic buckling are considered. The buckling model subjected to periodic disturbing forces and the critical axial strain and the critical frequencies are given. It is found that the critical axial strain of the embedded multi_walled carbon nanotube due to the intertube van der Waals forces is lower than that of an embedded single_walled carbon nanotube. The van der Waals forces and the surrounding elastic medium affect region of dynamic instability. The van der Waals forces increase the critical frequencies of a double_walled carbon nanotube. The effect of the surrounding elastic medium for the critical frequencies is small.

A Comparative Study of Force Measurements in Solution Using Micron and Nano Size Probe

Atomic force microscopy (AFM) is a device that is used for not only high-resolution imaging but also used for measuring forces. It is possible to quantify the surface density change for both colloid and nano probe as well as silica surface. By changing the quantity of ions within a potassium chloride solution, it then becomes possible to evaluate the quantity of ions that attach themselves to AFM colloid probe, nano probe and silica samples. In this study, the force was measured between AFM probes and silica surface in different ionic concentrations. Two different types of AFM probe were used: a colloid probe with a radius of 500 nano-meters and a nano probe with a radius of 10 nano-meters. This study is focused on measuring how the force magnitude, especially electrical double layer force, varied between the two types of probes by changing ionic concentrations. For all test trials, the results agreed with the electrical double layer theory. Although the micron probe was almost an exact match for all ranges, the nano probe was closest within its short-range forces. This is attributed to the formula use when analyzing the electrical double layer force. Because the formula was originally calculated for the micron probe, the shape and size of the nano probe created too many variables for an exact match. Along with quantifying the forces, this experiment allowed for an observation of Van der Waals force making it possible to calculate the Hamaker constant. Conclusively, all results show that the obtained surface charge density increases as the ionic concentration increases. In addition, through the comparison of the results obtained from the nano-sized probe and the micron-sized probe, it was concluded that nano size probe mapped higher surface charge density above the silica surface than the micron-sized probe under the same conditions.

Quantitative Evaluation of the Lifshitz-Type Temperature Effect on the Casimir Force

We consider the extension of the Casimir effect to finite temperatures in the ideal case of perfectly reflecting plates. We apply Lifshitz’s theory in its Dzyaloshinskii version, and calculate the resulting force numerically for various plate distances. We show that the limiting expression found in the literature corresponds to unrealistic values of the parameters for which the force is too small to be measurable. Preliminary remark: There exists a huge literature on the Casimir effect both theoretical and experimental. In this note we concentrate on a particular point of the subject, quoting only references directly related to this point.

Detecting van der Waals forces between a single polymer repeating unit and a solid surface in high vacuum

Ubiquitous van der Waals(vdW)forces are very importa nt for nano structures.Although the vdW forces between two surfaces(or two layers)have been measured for several decades,a direct detection at the single-molecule level is still difficult.Herein,we report a novel method to solve this problem in high vacuum by means of AFM-based sin gle-molecule force spectroscopy(SMFS).Solve nt molecules and surface adsorbed water are removed thoroughly under high vacuum so that the situation is greatly simplified.A constant force plateau can be observed when a polymer chain is peeled off from a substrate in high vacuum.Accordingly,the vdW forces between one polymer repeating unit and the substrates can be obtained.The experimental results show that the vdW forces(typical range:21-54 pN)are dependent on the species of substrates and the size of polymer repeating unit,which is in good accordance with the theoretical results.It is expected that this novel method can be applied to detect other non-covalent interactions(such as hydrogen bond andπ-πstacking)at the single-molecule level in the future.

结合布朗力与范德华力的磁流变液沉降模拟

为提升磁流变液沉降稳定性的研究效率,改善只能通过实验检测磁流变液沉降性能的现状,本文通过动力学方法模拟磁性颗粒的微观力学模型,提出了无磁场条件下的磁流变液沉降模拟方法,并以基于电感的沉降检测实验验证了模拟方法的有效性。磁流变液的沉降过程是在无磁场环境下进行的,因此,文章在磁场条件下磁流变液微观力学模型的基础上,引入布朗力与范德华力的作用,去除了磁场对磁性颗粒的影响,并提出了考虑布朗力与范德华力的磁流变液沉降模拟方法;将磁流变液的各项参数代入到前文提出的磁流变液沉降模拟方法中,并与基于电感的磁流变液沉降检测实验数据进行对比,以验证所提方法的有效性。结果表明,引入布朗力与范德华力的磁流变液沉降模拟方法可以较为准确地预测磁流变液的沉降速率,有效解决当前磁流变液沉降稳定性研究耗时较长的缺点。

基于二项熵和邻域节点间范德华力的关键节点识别方法

对节点重要性进行排序是复杂网络中识别关键节点的一种常用分析方法,分析网络中节点的重要性,有助于深入了解网络特性。在现有方法上为进一步提升节点评估精准度,引入二项熵概念来量化节点在网络中的重要性,通过邻域相似度衡量节点间的相互影响力,同时采用范德华力抽象节点之间的相互作用关系,提出一种基于二项熵和邻域节点间范德华力的关键节点识别方法,该方法从网络的整体信息流和相邻节点之间的位置和交互关系,综合考虑节点的局部和全局特征,并选取3个同类算法通过3个评价指标验证性能优劣,实验结果表明该算法对重要节点的判断具有良好的性能。

A kinematic model describing particle movement near a surface as effected by Brownian motion and electrostatic and Van der Waals forces

Nanoparticle movement near a surface is greatly influenced by electrostatic and Van der Waals forces between the particle and the surface,as well as by Brownian motion.In this paper,several precise equations are derived to describe the Van der Waals and electrostatic forces between a particle and a surface when the particle is removed from the surface.These include an equation for particle displacement under the electrostatic force,and a numerical calculation for particle displacement under the Van der Waals force.Finally,a kinematic model is constructed to describe the particle distribution under the effects of the electrostatic and Van der Waals forces,as well as the particle’s Brownian motion.The results show that increasing the multiply of the particle and surface zeta potential values and decreasing the ionic strength of the detergent can prevent a particle from redepositing onto a surface.

NONLINEAR DYNAMIC INSTABILITY OF DOUBLE-WALLED CARBON NANOTUBES UNDER PERIODIC EXCITATION

A multiple-elastic beam model based on Euler-Bernoulli-beam theory is presented to investigate the nonlinear dynamic instability of double-walled nanotubes. Taking the geometric nonlinearity of structure deformation, the effects of van der Waals forces as well as the non- coaxial curvature of each nested tube into account, the nonlinear parametric vibration governing equations are derived. Numerical results indicate that the double-walled nanotube （DWNT） can be considered as a single column when the van der Waals forces are sufficiently strong. The stiffness of medium could substantially reduce the area of the nonlinear dynamic instability region, in particular, the geometric nonlinearity can be out of account when the stiffness is large enough. The area of the principal nonlinear instability region and its shifting distance aroused by the nonlinearity both decrease with the increment of the aspect ratio of the nanotubes.

Distinct element method investigation on mechanical behavior within shear bands in granulates under the Earth and the Moon conditions

This letter mainly aims to investigate the mechanical behavior within shear bands in regolith both under the Earth and the Moon conditions via the distinct element method, in which a novel contact model considering interparticle van der Waals forces and rolling resistance is employed. The results show that for regolith under both conditions the stress paths are almost identical inside and outside the shear bands but void ratio, average pure rotation rate, and strain paths are rather distinct with dilation, particle rotation and the second invariant of strain tensor mainly occurring within the bands. However, the regolith under the Moon condition has higher peak strength and more significant strain localization than those under the Earth condition.

Axisymmetric compressive buckling of multi-walled carbon nanotubes under different boundary conditions

The paper studies the axisymmetric compressive buckling behavior of multi-walled carbon nanotubes （MWNTs） under different boundary conditions based on continuum mechanics model. A buckling condition is derived for determining the critical buckling load and associated buckling mode of MWNTs, and numerical results are worked out for MWNTs with different aspect ratios under fixed and simply supported boundary conditions. It is shown that the critical buckling load of MWNTs is insensitive to boundary conditions, except for nanotubes with smaller radii and very small aspect ratio. The associated buckling modes for different layers of MWNTs are in-phase, and the buckling displacement ratios for different layers are independent of the boundary conditions and the length of MWNTs. Moreover, for simply supported boundary conditions, the critical buckling load is compared with the corresponding one for axial compressive buckling, which indicates that the critical buckling load for axial compressive buckling can be well approximated by the corresponding one for axisymmetric compressive buckling. In particular, for axial compressive buckling of double-walled carbon nanotubes, an analytical expression is given for approximating the critical bucklingload. The present investigation may be of some help in fur- ther understanding the mechanical properties of MWNTs.

月壤颗粒间的范德华力作用研究进展

当前中国嫦娥工程“绕、落、回”三期任务已经圆满完成,为保持中国月球探测技术的领先地位,对月壤的力学特性进行研究具有重要意义。月表所处环境高真空、低重力和强辐射等特点使月壤表现出不同于地面砂土的性质,导致这一现象最主要的原因之一是月壤颗粒间的范德华力作用。本文对当前有关范德华力的研究进行总结,分别从分子/原子间的范德华力计算、范德华力的迟滞性、理想条件下宏观物体间的范德华力计算和真实条件下范德华力的计算四个方面对目前已有的研究进行分析,给出当前宏观颗粒间范德华力研究的不足,为今后月壤颗粒间范德华力的进一步研究提供参考。