Integral relations for the heat and mass transfer resistivities of the liquid–vapor interface

We derived integral relations for the heat and mass transfer resistivities of the liquid–vapor interface in a one-component system. These relations were obtained assuming the validity of the standard expression for the local entropy production rate as the product of the measurable heat flux times the gradient of the inverse temperature through the surface. The integral relations will be useful to interpret results from nonequilibrium molecular dynamics simulations. We verified in this paper that earlier results obtained using the nonequilibrium van der Waals square gradient model are reproduced. For this case, we calculated the Kapitza length along the coexistence curve.     

Thermodynamics of graphene

The 21st century has brought a lot of new results related to graphene. Apparently, graphene has been characterized from all points of view except surface science and, especially, surface thermodynamics. This report aims to close this gap. Since graphene is the first real two-dimensional solid, a general formulation of the thermodynamics of two-dimensional solid bodies is given. The two-dimensional chemical potential tensor coupled with stress tensor is introduced, and fundamental equations are derived for energy, free energy, grand thermodynamic potential (in the classical and hybrid forms), enthalpy, and Gibbs energy. The fundamentals of linear boundary phenomena are formulated with explaining the concept of a dividing line, the mechanical and thermodynamic line tensions, line energy and other linear properties with necessary thermodynamic equations. The one-dimensional analogs of the Gibbs adsorption equation and Shuttleworth–Herring relation are presented. The general thermodynamic relationships are illustrated with calculations based on molecular theory. To make the reader sensible of the harmony of chemical and van der Waals forces in graphene, the remake of the classical graphite theory is presented with additional variable combinations of graphene sheets. The calculation of the line energy of graphene is exhibited including contributions both from chemical bonds and van der Waals forces (expectedly, the latter are considerably smaller than the former). The problem of graphene holes originating from migrating vacancies is discussed on the basis of the Gibbs–Curie principle. An important aspect of line tension is the planar sheet/nanotube transition where line tension acts as a driving force. Using the bending stiffness of graphene, the possible radius range is estimated for achiral (zigzag and armchair) nanotubes.     

Morphology of nanostructures formed on the van der Waals surface of GaSe layered crystals annealed in sulfur vapor

The morphology of nanostructures, which were grown on the (0001) van der Waals surface of layered GaSe crystals and annealed under thermodynamically equilibrium conditions at high pressures of sulfur vapor, has been investigated using atomic force microscopy. The morphology and phase composition of the nanostructures are determined by the deformation and chemical interactions between the vapor phase and the crystal surface and by the thermodynamic conditions of annealing. Elements of nanostructures are formed as small Ga₂S₃ nanocrystallites, pyramidal quantum dots, and quantum rings on the defective (0001) van der Waals surface that contains nanosized indentations (nanocavities) and liquid gallium.     

论范德瓦尔斯a和b参数与温度的关系

范德瓦尔斯方程中a、b参数是否与温度相关,不但不同文献中的说法互不相同,而且有同一文献前后的结论相互矛盾.本文分析了这个令人迷惑的问题.在热力学中a和b参量被处理为与温度无关,它仅仅在临界点附近有效并可以把范德瓦尔斯方程表述为对应态定律;在更加广泛的温度区间a、b参量和温度有关,但是范德瓦尔斯方程却丧失了其独特性.统计...     

Development of a force field for molecular simulation of the phase equilibria of perfluoromethylpropyl ether

A first step towards the development of a general, realistic potential model for perfluoroether compounds has been to parameterize a united atom model for a short chain perfluoroether perfluoromethylpropyl ether (CF₃CF₂CF₂OCF₃). The potential model takes the usual form in which separate bond bending and torsional terms describe the intramolecular interactions with the addition of van der Waals and electrostatic terms to describe the non-bonded interactions. Ab initio quantum calculations have been carried out to obtain the partial charges and intramolecular torsional and bending potentials. Phase equilibrium data were then used to optimize the van der Waals interaction parameters through Gibbs ensemble Monte Carlo simulations. The resulting model reproduces vapour-liquid equilibrium densities, the critical temperature and the critical density of perfluoromethylpropyl ether, in good agreement with those from experiment.     

Two disks in a box

Exact analytical expressions are derived for the thermodynamic properties of two discs in square and rhomboidal boxes with hard walls, and in a square cell with periodic boundaries. With periodic boundaries the equation of state has a van der Waals loop and a second order cusp. In a box with hard walls there is a third order “glass transition” which seems to capture the essence of the glass transition observed in systems of a few hundred hard spheres.     

Structure of a liquid-vapor interface

The structure of the interface of an argonlike fluid in equilibrium with its own vapor at low temperature is studied using molecular dynamics. The longitudinal pair correlations in the interface are found to be consistent with a simply defined ensemble of local thermodynamic states. However, the transverse correlations exhibit very long-range behavior not predicted by straightforward local thermodynamics. These results strongly suggest that the interface is made up of an ensemble of configurations in each of which the transition from liquid to vapor is locally sharp, but that the transition surface fluctuates strongly in space and time.Supported in part by ERDA, Contract No. EY-76-C-02-3077, and by NSF, Grant DMR-72-03029, through Materials Science Center, Cornell University.The classical theoretical density profile dates back to van der Waals. (1)     

Nonclassical behavior of the van der Waals gas

The partition function of the van der Waals gas is represented by a functional integral which is evaluated by summing the value of the integrand over its absolute and all of its secondary maxima. This leads to a one-to-one correspondence with the Ising model with nearest-neighbor interactions only. Whereas the classical behavior of the van der Waals gas is due to the absolute maximum in function space, the nonclassical behavior is shown to derive from the combined contribution of all the secondary maxima. The relation of this work to inverse range expansions and to the droplet model of condensation is discussed.     

Effect of the attractive forces on the density change melting of 2D LJ fluids

The Weeks-Chandler-Andersen perturbation theory of fluids can be considered as a modern version of van der Waals'. Whereas in the old van der Waals theory the effect of the attractive forces on the thermodynamic properties is introduced through a constant, a, in Weeks-Chandler-Andersen theory this constant is replaced by a function of temperature and density α(β, ϱ). This function has been determined by means of Molecular Dynamics simulation of a two-dimensional Lennard-Jones fluid, and here is used to analyse the effect of attractive forces on the density change in melting. The influence is found to be slightly greater than the predictions of van der Waals theory.     

Van der Waals forces in electrolyte solutions

In this article we study van der Waals forces in electrolyte solutions from a local point of view. It is shown for arbitrary geometry that the classical limit of the force density exerted on the ions, as found in the macroscopic theory of van der Waals forces, is identical with the force density calculated from electrostatics and thermodynamic fluctuation theory. Thus neither retardation, nor the Lorentz force affect the average force density.     

A study on the correlations of supercritical temperature of fluid alkali metals based on the generalised van der Waals equation of state

The supercritical temperature, the inversion temperature and the critical compressibility factor of caesium, rubidium and potassium are correlated through the generalised van der Waals equation of state. This three-parameter equation differs from the known van der Waals equation of state by the introduction of a third parameter in the expression for molecular pressure. For caesium, rubidium and potassium, the ratios of the supercritical temperature to the inversion temperature are estimated. The results of estimation are in agreement with the results from other equations which are based on experimental data. It has been established that caesium, rubidium and potassium obey the single-parameter law of corresponding states with the ratio of the supercritical temperature to the inversion temperature as the thermodynamic similarity parameter.     

Exciton-exciton interaction in coupled quantum wells

The exciton-exciton interaction is investigated for spatially indirect excitons in coupled quantum wells. The Hartree-Fock and Heitler-London approaches are improved by a full two-exciton calculation including the van der Waals effect. Using these potentials for the singlet and triplet channel, the two-body scattering matrix is calculated and employed to derive a modified relation between exciton density and blue shift. Such a relation is of central importance for gauging exciton densities on the way toward Bose condensation.     

NpT-ensemble Monte Carlo calculations for binary liquid mixtures

A Monte Carlo method for the calculation of thermodynamic properties in the isothermal-isobaric ensemble is described. Application is made to the calculation of excess thermodynamic properties (enthalpy, volume and Gibbs free energy) of binary mixtures of Lennard-Jones 12-6 liquids. Comparison is made with the predictions of a number of theories of liquid mixtures; the so-called van der Waals one-fluid model and the variational theory of Mansoori and Leland are both found to give excellent results. The accuracy attainable in estimates of the excess properties is discussed in terms of statistical fluctuations in various calculated quantities and the advantages and disadvantages of the method are examined in relation to calculations by the more familiar constant-volume method.     

On energy transfer and generation of an electric current in the vicinity of an electrode dipped in an electrolyte and strongly heated by a current passing through it

Processes occurring when a metal electrode dipped in an electrolyte is heated by intense evaporation of the electrolyte are considered in terms of a physically rigorous model. Based on the Onsager principle of least energy dissipation rate in nonequilibrium processes, the fractions of thermal energy that are spent on heating and evaporating the electrolyte and on heating the vapor are found. The energy is released within the vapor-gas sheath when an electric current flows between the electrode and electrolyte surface. It is found that the electrolyte vapor temperature exceeds 1300 K. Analytical expressions are derived for the vapor-gas sheath thickness, the electrolyte vapor pressure, and the velocity of the vapor escaping the discharge zone. It is shown that field evaporation of thermally activated negative ions from the electrolyte surface cannot provide an electric current with densities found in experiments but is responsible for the generation of free electrons near the electrolyte surface. These electrons arise when the ions decay via collisions with excited molecules.     

Nonuniform van der Waals theory

The liquid-vapor interface of a confined fluid at the condensation phase transition is studied in a combined hydrostatic/mean-field limit of classical statistical mechanics. Rigorous and numerical results are presented. The limit accounts for strongly repulsive short-range forces in terms of local thermodynamics. Weak attractive longer-range ones, like gravitational or van der Waals forces, contribute a self-consistent mean potential. Although the limit is fluctuationfree, the interface is not a sharp Gibbs interface, but its structure is resolved over the range of the attractive potential. For a fluid of hard balls with –r ^–6 interactions the traditional condensation phase transition with critical point is exhibited in the grand ensemble: A vapor state coexists with a liquid state. Both states are quasiuniform well inside the container, but wall-induced inhomogeneities show up close to the boundary of the container. The condensation phase transition of the grand ensemble bridges a region of negative total compressibility in the canonical ensemble which contains canonically stable proper liquid-vapor interface solutions. Embedded in this region is a new, strictly canonical phase transition between a quasiuniform vapor state and a small droplet with extended vapor atmosphere. This canonical transition, in turn, bridges a region of negative total specific heat in the microanonical ensemble. That region contains subcooled vapor states as well as superheated very small droplets which are microcanonically stable.     

范德瓦尔斯磁性材料CrOCl变磁性相变的磁力显微镜研究

近年来,二维范德瓦尔斯磁性材料因为在自旋电子学的应用前景而吸引了广泛的关注.CrOCl是一种范德瓦尔斯磁性材料,理论预言其单层具有高达160 K的居里温度,因此吸引了广泛的关注。为了更好的理解这一材料的磁性,我们利用磁力显微镜研究了CrOCl变磁性相变中磁畴结构随磁场的变化。实验发现,在2K下CrOCl样品表面出现随磁场变化的方格条纹,给出了变磁性相比中反铁磁相和铁磁相竞争的图样,并通过二维快速傅里叶变换证实了CrOCl磁性的各向异性。我们的结果为后续研究CrOCl薄层的磁性提供了参考依据。     

Connection of Gibbs layer gatherings with rate of mass transfer upon deposition of thin films with presence of impurity

The Gibbs layer gatherings on the condensation front of silver vapor in the presence of water vapor are analyzed. The front of condensation for analyzing the Gibbs concentration excess is calculated with the use of the modified Langmuir’s model of sorption. At a fixed flow of silver vapor and temperature of the substrate, the water-vapor pressure varies. Calculations have shown that the change of the water-vapor pressure changes the structure of the silver condensate, the structure of Gibbs layers, and microroughness on the condensation front. As a consequence, the efficiency of mass transfer varies. With growth of the water-vapor pressure, the condensation efficiency of both vapor components decreases. For obtaining the most equal surface of condensed silver film there is an optimum water-vapor pressure. The results allow the influence of noncondensed gas impurity on growth of thin films to be understood in greater detail and help to choose optimum modes for vacuum deposition. A general conclusion regarding the connection of the Gibbs layers and microroughness of the condensation surface with the intensity of mass transfer, leaving a framework of vacuum deposition processes, is drawn.     

Generalized Gibbs’ approach to the thermodynamics of heterogeneous systems and the kinetics of first-order phase transitions

In the theoretical interpretation of the kinetics of first-order phase transitions, thermodynamic concepts are widely employed that were developed long ago by Gibbs and van der Waals. However, the results of such analysis are partly unsatisfactory and internally contradictory. By generalizing Gibbs’ approach, the existing deficiencies and internal contradictions of these two well-established theories can be removed and a new generally applicable tool for the interpretation of these processes can be developed. The basic ideas of the generalized Gibbs approach and a variety of consequences obtained on its basis with respect to the understanding of the general features of the kinetics of first-order phase transitions are outlined. Dedicated to the memory of Vladimir P. Skripov. The text was submitted by the authors in English.