Volumetric coefficients,internal pressure,and cohesion energy density of <Emphasis Type="Italic">n</Emphasis>-alcohols

Changes in the thermal expansion coefficient and isothermal compressibility in homological series of n-alcohols at 298 K are discussed. It is shown that only methanol exhibits abnormal behavior. Volumetric coefficients of hypothetical solvents such as pseudo-water and pseudo-methanol are determined. Internal pressure values of liquids are calculated. The internal pressure of pseudo-water exceeds that of water, whereas the situation is opposite for the cohesion energy density.     

A new regularity for internal pressure of dense fluids

In this paper, we derive a new regularity for dense fluids, both compressed liquids and dense supercritical fluids based on the Lennard-Jones (12-6) potential function and using speed of sound results. By considering the internal pressure by modeling the average configurational potential energy, and then taking its derivative with respect to volume, we predict that isotherm [(partial differential E/partial differential V)(T)/rhoRT]V(2) is a linear function of rho(2), where E is the internal energy, (partial differential E/partial differential V)(T)) is the internal pressure, and rho = 1/V is the molar density. The regularity is tested with experimental data for ten fluids including Ar, N(2), CO, CO(2), CH(4,) C(2)H(6), C(3)H(8), C(4)H(10), C(6)H(6), and C(6)H(5)CH(3). These problems have led us to try to establish a function for the accurate calculation of the internal pressure based on speed of sound theory for different fluids. The results of the fitting show limited success of the pure substances. The linear relationship appears to hold from the lower density limit at the Boyle density and from the triple temperature up to about double the Boyle temperature. The upper density limit appears to be reached at 1.4 times the Boyle density. The results are likely to be useful, although they are limited.     

Relationship between the internal pressure and cohesive energy density of liquids

The concepts of internal pressure and cohesive energy density of liquids are considered. Conditions of equality between the internal pressure and the cohesive energy density are revealed.     

Intermolecular forces and the internal pressure of liquids

The problem of the introduction of the term internal pressure from the standpoint of intermolecular forces is solved. It is shown that internal pressure is created by the macrosystem average force field of the structural units of a liquid. Internal pressure is shown to be not an energy characteristic, but a macrosystem average force parameter of the interaction between the structural units of a liquid phase system, although it has the energy density dimension, [J/m³].     

Prediction of the thermodynamic properties of {ammonia + water} using cubic equations of state with the SOF cohesion function

The SOF cohesion function for cubic equations of state is based on the behavior of the residual energy of pure fluids. It contains two adjustable parameters for each component, which have been obtained for over 800 substances by regression of pure-fluid saturation pressures, and correlated in terms of a four-parameter corresponding states principle. In the present work, we compare the performance of this function and of the original Soave cohesion function with the Redlich-Kwong and Peng-Robinson equations of state in the prediction of vapor-liquid equilibria and enthalpy-composition diagrams for the polar system {ammonia + water}. We use simple van der Waals one-fluid mixing rules, linear for the covolume and quadratic for the cohesion parameter with one (symmetric) and two (asymmetric) binary interaction parameters. The non-linear least squares minimization algorithm lsqnonlin, in Matlab^®, is used to adjust the interaction parameters to phase equilibrium and enthalpy data taken from the IAPWS fundamental formulation. Upper and lower bounds of the optimized interaction parameters are obtained using Matlab^®bootstrap with 95% confidence of a normal distribution sampling. The validity of the parameters as functions of temperature is between the triple point of water and the critical point of ammonia. At lower temperatures, a rapid increase of statistical uncertainties is observed that can be attributed to the scarcity of phase equilibrium data.The two-parameter SOF cohesion function and the cubic equations of state are shown to give accurate predictions of the VLE and enthalpies of {ammonia + water}. Both equations of state give very similar results. Statistical analysis of the interaction parameters shows that their values (within the range of validity mentioned above) are effectively the same for both cohesion functions. At higher temperatures, however, extrapolation of the two cohesion functions gives different results, and correspondingly requires different interaction parameters.     

Thermodynamic perturbation theory of simple liquids. A hierarchy of equations for expansion coefficients

The properties of an expansion of the statistical sum of a simple liquid with respect to the potential in thermodynamic perturbation theory are analyzed. The coefficients of this expansion are determined by the unperturbed potential, depend on temperature and density, and can be calculated by means of mathematical modeling. It is shown here that the derivatives of these coefficients with respect to temperature and density are expressed through the higher expansion coefficient (these relations are usually called a hierarchy of equations). These coefficients determine the expansion of the Helmholtz free energy and RDF with respect to the perturbation potential. The thermodynamic characteristics of the system (entropy, internal energy, pressure) are expressed through both the differential relations for the Helmholtz free energy and the integral expressions containing RDF. It is found that the hierarchy of equations obtained in this work makes these different methods equivalent. This is important for the application of thermodynamic perturbation theory because it becomes unnecessary to model any other equilibrium properties of the system apart from the expansion coefficients.     

Calculating thermodynamic properties from perturbation theory: Part III. The mixtures of square-well chain fluid

A completely analytic perturbation theory has been developed to calculate the Helmholtz energy, compressibility factor, internal energy and constant-volume heat capacity for square-well chain fluid mixtures. This theory is based on the improved Barker–Henderson macroscopic compressibility (mc) approximation proposed by Zhang, the first-order perturbation theory of Wertheim in which Zhang’s analytic monomer radial distribution function as the function of temperature and monomer density is used, and a simple mixing rule similar to that of Hino–Prausnitz. The validity of the perturbation theory is evaluated by comparing the calculated compressibility factor, internal energy and constant-volume heat capacity for the freely jointed square-well chain mixtures from the theory to MC simulation data. The results show that the theory predicts results in good agreement with simulation results.     

Synthesis and adhesion property of waterborne polyurethanes with different ionic group contents

In this study, a series of waterborne polyurethanes (WPUs) with different ionic group contents were synthesized by varying the amount of the internal emulsifier 2,2-dimethylolpropionic acid (DMPA). The effects of the ionic group content on the stability and adhesion behavior of WPUs were investigated in terms of particle size, viscosity, surface tension, interfacial tension, contact angle, and adhesion performance. It was found that stable WPUs could be obtained when the DMPA content was larger than 3.5 wt% (with respect to the total solid content). Adhesion performance of WPUs to substrates was mainly affected by the wetting of WPUs on the substrates and the molecular interactions between them. With the increase of DMPA content, the surface tension of WPUs as well as the interfacial tension and contact angle between WPUs and polyethylene terephthalate (PET) films increased. Moreover, the adhesion strength of the WPUs firstly increased and then gradually decreased. The type of debonding failure of all the synthesized WPUs on PET films was cohesion failure due to their lower cohesion strength, which was theoretically testified by the comparison between the adhesion energy and cohesion energy.     

聚合物内压测定及对应状态模型

实验测定了PEG(M~n=200),PEG(M~n=300),PEG(M~n=400),PDMS(M~w=15000)和PDMS(M~w=20000)在20-90℃温度范围的热压力系数和密度,它们的热压力系数和内压几乎与分子量无关。据此还建立了一个聚合物内压的对应状态模型,它只含一个可调参数,能满意地适用于各种聚合物。     

Design of experimental routes and data processing for the determination of the depth-distribution of energy in real solids

No adequate thermodynamic definition of non-equilibrated solids is available at present. In this paper a method is suggested for the energetic characterization of solids by estimation of the distribution of the differential molar internal energies — as they appear during the breakdown of sample e.g. by chemical reaction, i.e. the ‘depth distribution of differential energies’ (DDE) of samples. Thermodynamic considerations are presented for approximating this quantity — and experimental possibilities proposed to attain the needed input information by thermoanalytical methods. Application of the suggested procedure is supposed to contribute to the better understanding of structure — energy — reactivity relations in real solids.     

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.     

A model for energy transfer in inelastic molecular collisions applicable at steady state or non-steady state and for an arbitrary distribution of collision energies

A new model for energy exchange between translational and internal degrees of freedom in atom-molecule collisions has been developed. It is suitable for both steady state conditions (e.g., a large number of collisions with thermal kinetic energies) and non-steady state conditions with an arbitrary distribution of collision energies (e.g., single high-energy collisions). In particular, it does not require that the collision energies be characterized by a quasi-thermal distribution, but nevertheless it is capable of producing a Boltzmann distribution of internal energies with the correct internal temperature under quasi-thermal conditions. The energy exchange is described by a transfer probability density that depends on the initial relative kinetic energy, the internal energy of the molecule, and the amount of energy transferred. The probability density for collisions that lead to excitation is assumed to decrease exponentially with the amount of transferred energy. The probability density for de-excitation is obtained from microscopic reversibility. The model has been implemented in the ion trap simulation program ITSIM and coupled with an Rice-Rampsberger-Kassel-Marcus (RRKM) algorithm to describe the unimolecular dissociation of populations of ions. Monte Carlo simulations of collisional energy transfer are presented. The model is validated for non-steady state conditions and for steady state conditions, and the effect of the kinetic energy dependence of the collision cross-section on internal temperature is discussed. Applications of the model to the problem of chemical mass shifts in RF ion trap mass spectrometry are shown.     

Au-MgB2-Au纳米结点的负微分电阻效应

运用密度泛函理论结合非平衡格林函数的方法对MgB2直线原子链与两半无限Au（100）电极构成纳米结点的电子输运特性进行了第一性原理计算．在模拟Au-MgB2-Au纳米结点的拉伸过程中,计算了结点在不同距离下的结合能与电导．结果发现结点的Au-B键长为1．90A,B-Mg键长为2．22A时,结合能最大,结构最稳定,此时结点平衡电导为0．51G0（G0=2e^0／h）．通过计算投影态密度发现电子通过结点时主要是通过B、Mg原子的px和py电子轨道形成的π键进行传输的．在-1．5～1．5V的电压范围内,结点的电流-电压近似为线性关系,表现出类似金属的导电性质,而当正负电压高于15V时,电流对称性逐渐减小,即存在负微分电阻效应,从不同电压下透射谱的变化对负微分电阻现象进行了分析与讨论．     

New regularities and an equation of state for liquids

Three regularities have been introduced for liquids (T < T_C and ρ > ρ_C) based on average potential energy. The experimental data have been used to show the validity of the regularities. First, there exists near-linearity relation between and ρ for all isotherms of a liquid, where P_i and ρ are internal pressure and density, respectively. Second, changes linearly with ρ for each isotherm of any liquid, where Z and V_m are compressibility factor and molar volume, respectively. Third, a new regularity using the definition of bulk modulus and our new equation of state between reduced bulk modulus and density has been introduced, that is versus ρ must be linear for all isotherms of a liquid where B_r is the reduced bulk modulus.

A new equation of state has been also derived. The density of some liquids in the extensive ranges of temperature and pressure has been calculated using the new equation of state. The densities calculated from this equation agree with experiment to better than 0.3%. The new equation of state can predict internal pressure, thermal expansion coefficient, and isothermal compressibility of liquids within experimental error.     

聚1,2-丁二烯的内聚能密度和玻璃化温度

本工作用环己烷-甲苯混合溶剂测定了不同1,2-链节含量的无定形聚1,2-丁二烯的溶解度参数,进而得到它们的内聚能密度,另外测定了它们的玻璃化温度。发现1,2-链节提高了聚1,2-丁二烯的玻璃化温度,同时稍稍降低了它们的内聚能密度。认为这是1,2-链节降低了聚1,2-丁二烯分子链柔顺性的缘故。     

A theoretical investigation on the honeycomb potential fluid

A local self-consistent Ornstein-Zernike (OZ) integral equation theory (IET) is proposed to provide a rapid route for obtaining thermodynamic and structural information for any thermodynamically stable or metastable state points in the bulk phase diagram without recourse to traditional thermodynamic integration, and extensive NVT-Monte Carlo simulations are performed on a recently proposed honeycomb potential in three dimensions to test the theory's reliability. The simulated quantities include radial distribution function (rdf) and excess internal energy, pressure, excess chemical potential, and excess Helmholtz free energy. It is demonstrated that (i) the theory reproduces the rdf very satisfactorily only if the bulk state does not enter deep into a two phases coexistence region; (ii) the excess internal energy is the only one of the four thermodynamic quantities investigated amenable to the most accurate prediction by the present theory, and the simulated pressure is somewhat overestimated by the theoretical calculations, but the deviation tends to vanish along with rising of the temperature; (iii) using the structural functions from the present local self-consistent OZ IET, a previously derived local expression, due to the present author, achieves even a higher accuracy in calculating for the excess chemical potential than the exact virial pressure formula for the pressure, and the resulting excess Helmholtz free energy is in surprisingly same with the simulation results due to offset of the errors. Based on the above observations, it is suggested that it may be a good procedure to integrate the theoretical excess internal energy along the isochors to get the excess Helmholtz free energy, which is then fitted to a polynomial to be used for calculation of all of other thermodynamic quantities in the framework of the OZ IET.     

An application of the linear isotherm regularity (LIR)

The linear isotherm regularity (LIR) for dense fluids is used to derive another regularity which is the isotherm [(partial differentialE/partial differentialv)T/rhoRT]v2 as a linear function of rho2, where E is the molar internal energy, (partial differentialE/partial differentialv)T is the internal pressure, and rho is the molar density (inverse of the molar volume v). The analytical expressions for the parameters of the latter regularity are obtained in terms of LIR parameters and reported for argon.     

High pressure study on the phonon spectra and thermal properties in hafnium nitride and zirconium nitride

We report ab initio calculations of the thermal properties for transition metal nitrides, hafnium and zirconium nitride at ambient and high pressures. The assessment of thermodynamical properties like lattice specific heat, vibrational energy, internal energy and entropy for two nitrides has been carried out. The basic calculations of ingredient phonon density of states for the determination of thermal properties have been done using density functional perturbation theory including external perturbations like strains and electric fields in periodic systems. The ground state properties such as equilibrium lattice constants and bulk modulus obtained for two nitrides are in good agreement with the available experimental value. The calculated pressure variation of the phonon density of states shows trend similar to the experimental pressure dependent Raman spectra. The lattice specific heat, internal energy, entropy and Helmholtz energy increases with pressure.     

Relation between characteristic adsorption energy and internal pressure in the theory of volume filling of micropores

An equation for the internal pressure acting on an adsorbate in micropores was obtained on the basis of the assumption that the chemical potential of an adsorbate in micropores is equal to that in an equilibrium gas phase and using the Dubinin-Radushkevich equation. The empirical relation between the characteristic adsorption energy and the half width of pores was expressed in terms of internal pressure and diameter of adsorbate molecules. The two-dimensional pressure was calculated for micropores with plane-parallel walls, where the width of a micropore coincides with the diameter of an adsorbate molecule. The results obtained were compared with the two-dimensional pressure of a monolayer on a free planar surface for an adsorbate and adsorbent of the same nature.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1928–1930, October, 1995.     

New insights into the multiple minima problem

Minima distribution of thorough conformational searches of three peptides of different length ranging from five to nine residues, were compared with the density of states of a flexible molecule derived from the rotational isomeric approximation. It is observed that minima distributions generated from the conformational searches exhibit the same characteristics as the density of states derived from the rotational isomeric model: an asymmetric distribution with a maximum. These results together with a more profound understanding of the characteristics of the energy landscapes of polypeptides, provide new insights into the multiple minima problem. The implications in devising more robust conformational search strategies are discussed.