The effect of density on the properties of short chain fluids

We incorporate density dependence into continuum Born-Green-Yvon (BGY) theory through calculation of the end-to-end intramolecular correlation function. Whereas in previous studies we had only performed this calculation for the case of an isolated (zero-density) square-well chain of m segments (3相似文献   

Studies on fluids and their mixtures using the Born-Green-Yvon integral equation technique

We have developed the Born-Green-Yvon (BGY) integral equation theory for investigating the equilibrium properties of fluids and their mixtures both on the lattice and in the continuum. Using the continuum theory we have studied hard sphere fluids over a range in density having chain lengths between one and fifty sites. We have also investigated the collapse transition of a square well chain and a square well ring, each having up to four hundred sites, and have predicted the theta temperature for these systems. Turning to the case of a dilute (hard-sphere) solution we have been able to show the effect of solvation on a hard sphere chain, and captured the dependence of this effect on the ratio of hard sphere diameters of the solvent and chain segments. In all the continuum studies we have found good to excellent agreement with simulation results. We have also derived a lattice BGY theory which, while less sophisticated than the continuum version, has the advantage of producing simple closed-form expressions for thermodynamic properties of interest. This theory is capable of exhibiting the full range of miscibility behaviour observed experimentally, including upper and lower critical solution temperatures and closed-loop phase diagrams. We find that the theory does an excellent job of fitting to different kinds of experimental data and, making use of the parameters derived from fits to pure component data alone, we have been able to predict properties ranging from pure fluid vapour pressures and critical temperatures to changes in the volume and enthalpy on mixing as well as coexistence curves for solutions.     

Wetting behavior of mixtures of water and nonionic polyoxyethylene alcohol

Five binary water + C4Ej mixtures, water + n-C4E0, water + 2-C4E0, water + iso-C4E0, water + n-C4E1, and water + iso-C4E1, were chosen to perform the surface/interfacial tension measurements over the experimental temperature range from 10 to 85 degrees C at the normal pressure by using a homemade pendent drop/bubble tensiometer. The symbol CiEj is the abbreviation of a nonionic polyoxyethylene alcohol CiH(2i+1)(OCH2CH2)jOH. The wetting behavior of the CiEj-rich phase at the interface separating gas and the aqueous phase is systematically examined according to the wetting coefficient resulting from the experimental data of surface/interfacial tensions measurements. For those systems with a lower critical solution temperature, for example, water + n-C6E2, water + n-C4E1, and water + iso-C4E1, a wetting transition from partial wetting to nonwetting is always observed when the system is brought to close to its lower critical solution temperature. On the other hand, to start with a partial wetting CiEj-rich phase, a wetting transition from partial wetting to complete wetting is always observed when the system is driven to approach its upper critical solution temperature. The effect of hydrophobicity of CiEj on the wetting behavior of the CiEj-rich phase at the interface separating gas and the aqueous phase was carefully investigated by using five sets of mixtures: (1) water + n-C4E0, water + n-C5E0, and water + n-C6E0; (2) water + 2-C4E0 and water + 2-C5E0; (3) water + 2-C4E0 and water + n-C4E0; (4) water + n-C4E1, water + n-C5E1, and water + n-C6E1; (5) water + n-C4E0 and water + n-C4E1. The CiEj-rich phase would tend to drive away from complete wetting (or nonwetting) to partial wetting with an increase in the hydrophobicity of CiEj in the binary water + CiEj system. All the wetting behavior observed in the water + CiEj mixtures is consistent with the prediction of the critical point wetting theory of Cahn.     

Structures, electron affinities, and harmonic vibrational frequencies of the simplest alkyl peroxyl radicals and their anions

The molecular structures and electron affinities of the R-OO/R-OO(-) (R = CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, i-C3H7, t-C4H9) species have been determined using seven different density functional or hybrid Hartree-Fock density functional methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s-type and p-type functions, denoted DZP++. The geometries are fully optimized with each density functional theory method. Harmonic vibrational frequencies were found to be within 3.1% of available experimental values for most functionals. Two different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity and the vertical detachment energy. The most reliable adiabatic electron affinities obtained at the DZP++ BP86 level of theory are 1.150 (CH3OO), 1.124 (C2H5OO), 1.146 (n-C3H7OO), 1.173 (n-C4H9OO), 1.184 (n-C5H11OO), 1.145 (i-C3H7OO), and 1.114 eV (t-C4H9OO). Compared with the experimental values, the average absolute error of the BPW91 method is 0.05 eV.     

Continuum formulation of the Scheutjens-Fleer lattice statistical theory for homopolymer adsorption from solution

Homopolymer adsorption from a dilute solution on an interacting (attractive) surface under static equilibrium conditions is studied in the framework of a Hamiltonian model. The model makes use of the density of chain ends n(1,e) and utilizes the concept of the propagator G describing conformational probabilities to locally define the polymer segment density or volume fraction phi; both n(1,e) and phi enter into the expression for the system free energy. The propagator G obeys the Edwards diffusion equation for walks in a self-consistent potential field. The equilibrium distribution of chain ends and, consequently, of chain conformational probabilities is found by minimizing the system free energy. This results in a set of model equations that constitute the exact continuum-space analog of the Scheutjens-Fleer (SF) lattice statistical theory for the adsorption of interacting chains. Since for distances too close to the surface the continuum formulation breaks down, the continuum model is here employed to describe the probability of chain configurations only for distances z greater than 2l, where l denotes the segment length, from the surface; instead, for distances z < or = 2l, the SF lattice model is utilized. Through this novel formulation, the lattice solution at z = 2l provides the boundary condition for the continuum model. The resulting hybrid (lattice for distances z < or = 2l, continuum for distances z > 2l) model is solved numerically through an efficient implementation of the pseudospectral collocation method. Representative results obtained with the new model and a direct application of the SF lattice model are extensively compared with each other and, in all cases studied, are found to be practically identical.     

Effect of lattice topology on geminate recombination

The molecular theory of geminate recombination is applied to the simple cubic lattice, and the results compared to those obtained previously for the face-centered cubic lattice. The results demonstrate that, for corresponding molecular parameters, lattice topology is a strong determinant of recombination/dissociation efficiency. The implications of this fact for interpretation of experimental data in terms of the Onsager and other continuum approximations are noted.     

Allowing for Intermolecular Vibrations in the Thermodynamic Functions of a Liquid Inert Gas

Russian Journal of Physical Chemistry A - Ways of calculating interatomic vibrations in a fluid are considered using the example of an inert gas. Discrete continuum theory in the lattice gas model...     

柔性高分子/小分子液晶混合物的自洽场理论

发展了柔性高分子/小分子液晶混合物连续自洽场理论，将小分子液晶模型化 为取向与位置无关的单体分子，小分子液晶间存在各向异性的Maier-Saupe相互作 用，该理论可还原成高分子和各向同性小分子组成的Flory-Huggins溶液理论和纯 液晶的Maier-Squpe液晶理论，通过数值解自洽场方程组，还将理论用于研究柔性 高分子/小分子液晶混合物相分离开界面性质，得到的结果与用Helfand格子界面理 论和MOnte Carlo模拟的结果一致。     

Molecular simulation and macroscopic modeling of the diffusion of hydrogen, carbon monoxide and water in heavy n-alkane mixtures

The self-diffusion coefficient of hydrogen (H(2)), carbon monoxide (CO) and water (H(2)O) in n-alkanes was studied by molecular dynamics simulation. Diffusion in a few pure n-alkanes (namely n-C(8), n-C(20), n-C(64) and n-C(96)) was examined. In addition, binary n-C(12)-n-C(96) mixtures with various compositions as well as more realistic five- and six-n-alkane component mixtures were simulated. In all cases, the TraPPE united atom force field was used for the n-alkane molecules. The force field for the mixture of n-alkanes was initially validated against experimental density values and was shown to be accurate. Moreover, macroscopic correlations for predicting diffusion coefficient of H(2), CO and H(2)O in n-alkanes and mixtures of n-alkanes were developed. The functional form of the correlation was based on the rough hard sphere theory (RHS). The correlation was applied to simulation data and an absolute average deviation (AAD) of 5.8% for pure n-alkanes and 3.4% for n-alkane mixtures was obtained. Correlation parameters vary in a systematic way with carbon number and so they can be used to provide predictions in the absence of any experimental or molecular simulation data. Finally, in order to reduce the number of adjustable parameters, for the n-alkane mixtures the "pseudo-carbon number" approach was used. This approach resulted in relatively higher deviation from MD simulation data (AAD of 18.2%); however, it provides a convenient and fast method to predict diffusion coefficients. The correlations developed here are expected to be useful for engineering calculations related to the design of the Gas-to-Liquid process.     

The addition of hydrogen atoms to diacetylene and the heats of formation of i-C4H3 and n-C4H3

In this article, we discuss in detail the addition of hydrogen atoms to diacetylene and the reverse dissociation reactions, H + C(4)H(2)<==>i-C(4)H(3) (R1) and H + C(4)H(2)<==>n-C(4)H(3) (R2). The theory utilizes high-level electronic structure methodology to characterize the potential energy surface, Rice-Ramsperger-Kassel-Marcus (RRKM) theory to calculate microcanonical/J-resolved rate coefficients, and a two-dimensional master-equation approach to extract phenomenological (thermal) rate coefficients. Comparison is made with experimental results where they are available. The rate coefficients k1(T, p) and k2(T, p) are cast in forms that can be used in chemical kinetic modeling. In addition, we predict values of the heats of formation of i-C(4)H(3) and n-C(4)H(3) and discuss their importance in flame chemistry. Our basis-set extrapolated, quadratic-configuration-interaction with single and double excitations (and triple excitations added perturbatively), QCISD(T), predictions of these heats of formation at 298 K are 130.8 kcal/mol for n-C(4)H(3) and 119.3 kcal/mol for the i-isomer; multireference CI calculations with a nine-electron, nine-orbital, complete-active-space (CAS) reference wavefunction give just slightly larger values for these parameters. Our results are in good agreement with the recent focal-point analysis of Wheeler et al. (J. Chem. Phys. 2004, 121, 8800-8813), but they differ substantially for DeltaH0(f 298)(n-C(4)H(3)) with the earlier diffusion Monte Carlo predictions of Krokidis et al. (Int. J. Chem. Kinet.2001, 33, 808-820).     

载铂铝交联蒙脱土的烷烃芳构化特性──Ⅰ．载铂铝交联蒙脱土对烷烃的择形芳构化作用

对比考察了Ｐｔ／ＫＬ沸石，Ｐｔ／Ａｌ２Ｏ３和载铂铝交联蒙脱土（Ｐｔ／Ａｌ－ＣＬＭ）催化剂对不同碳原子数烷烃的芳构化特性．脉冲微反的评价结果表明：Ｐｔ／Ａｌ－ＣＬＭ比Ｐｔ／Ａｌ２Ｏ３和Ｐｔ／ＫＬ具有较高的转化ｎ－Ｃ８，ｎ－Ｃ９为其对应芳烃的选择性，在转化ｎ－Ｃ８时，产物中的间、对位二甲苯收率很高，而转化ｎ－Ｃ９时有高的正丙苯收率．采用１２９Ｘｅ－ＮＭＲ、ＸＲＤ和孔分布测定考察了Ｐｔ／Ａｌ－ＣＬＭ和Ｐｔ／ＫＬ、Ｐｔ／Ａｌ２Ｏ３之间孔结构的差异．结果表明：由于ｎ－Ｃ８，ｎ－Ｃ９在反应过程中其过渡态的极限尺寸与Ｐｔ／Ａｌ－ＣＬＭ０．９ｎｍ左右的层间域相匹配，因而它对ｎ－Ｃ８，ｎ－Ｃ９具有择形芳构化作用．     

ZnO超微粒子光催化氧化降解n-C7H16的研究

利用ZnO光催化氧化技术对气相n-C7H16进行了降解研究，考察了氧气、水燕气体积分数等因素对n-C7H16光催化氧化的影响，利用气相色谱－质谱联用仪和气相色谱仪对气相光催化反应过程中的气体组成进行了定性分析，并对主要中间产物丙醛进行了定量分析，结果发现，ZnO超微粒子光催化氧化n-C7H16的降解率较高，n-C7H16绝大部分被完全氧化成CO2，探讨了n-C7H16光催化氧化反尖的动力学行为及机理。     

An Improved Approximation for the Primitive Model of the Electric Double Layer

Abstract

The primitive model for the one sided electrode interface consists of an electrode which is perfectly smooth and flat, and an electrolyte formed by charged hard spheres, all immersed in a dielectric continuum.

The early work of Gouy,¹ Chapman² and Stern³ is based on such a model, and in recent times it has received considerable attention by a number of researchers. Extensive computer simulations have been performed by Torrie, Valleau and coworkers.⁴ The approximate integral equations which have been used to compute the density and voltage profiles and differential capacitance can be divided into four groups. Mean Spherical Approximation (MSA) and its generalization (GMSA),^5,6 the Hypernetted Chain (HNC) and derived equations,^7,8 the Modified Poisson-Boltzmann's (MPB)⁹ and the Born-Green-Yvon (BGY)^10,11 type theories.     

Experimental and theoretical study of hydrogen atom abstraction from n-butane by lanthanum oxide cluster anions

Lanthanum oxide cluster anions are prepared by laser ablation and reacted with n-C(4)H(10) in a fast flow reactor. A time-of-flight mass spectrometer is used to detect the cluster distribution before and after the reactions. (La(2)O(3))(m=1-3)OH(-) and La(3)O(7)H(-) are observed as products, which suggests the occurrence of hydrogen atom abstraction reactions: (La(2)O(3))(m=1-3)O(-) + n-C(4)H(10) → (La(2)O(3))(m=1-3)OH(-) + C(4)H(9) and La(3)O(7)(-) + n-C(4)H(10) → La(3)O(7)H(-) + C(4)H(9). Density functional theory (DFT) calculations are performed to study the structures and bonding properties of La(2)O(4)(-), La(3)O(7)(-), and La(4)O(7)(-) clusters. The calculated results show that each of La(2)O(4)(-) and La(4)O(7)(-) contains one oxygen-centered radical (O(-?)) which is responsible for the high reactivity toward n-C(4)H(10). La(3)O(7)(-) contains one oxygen-centered radical (O(-?)) and one superoxide unit (O(2)(-?)), and the O(-?) is responsible for its high reactivity toward n-C(4)H(10). The O(-?) and O(2)(-?) can be considered to be generated by the adsorption of an O(2) molecule onto the singlet La(3)O(5)(-) with electron transfer from a terminally bonded oxygen ion (O(2-)) to the O(2). This may help us understand the mechanism of the formation of O(-?) and O(2)(-?) radicals in lanthanum oxide systems. The reaction mechanisms of La(2)O(4)(-) + n-C(4)H(10) and La(3)O(7)(-) + n-C(4)H(10) are also studied by the DFT calculations, and the calculated results are in good agreement with the experimental observations.     

On the model dependence of kinetic shifts in unimolecular reactions: the dissociation of the cations of benzene and n-butylbenzene

Statistical adiabatic channel model/classical trajectory (SACM/CT) calculations have been performed for transitional mode dynamics in the simple bond fission reactions of C(6)H(6)(+) --> C(6)H(5)(+) + H and n-C(6)H(5)C(4)H(9)(+) --> C(7)H(7)(+) + n-C(3)H(7). Reduced-dimensionality model potentials have been designed that take advantage of ab initio results as far as available. Average anisotropy amplitudes of the potentials were fitted by comparison of calculated specific rate constants k(E,J) with measured values. The kinetic shifts of the calculated k(E) curves and the corresponding bond energies E(0)(J=0), derived as 3.90 +/- 0.05 eV for C(6)H(6)(+) and 1.78 +/- 0.05 eV for n-C(6)H(5)C(4)H(9)(+), were in good agreement with literature values from thermochemical studies. Kinetic shifts from fixed tight activated complex Rice-Ramsperger-Kassel-Marcus (RRKM) theory, which also reproduces the measured k(E), were larger than the present SACM/CT results as well as earlier results from variational transition state theory (for C(6)H(6)(+)). The approach using RRKM theory was found to underestimate E(0)(J=0) by about 0.2-0.3 eV. A simplified SACM/CT-based method is also proposed which circumvents the trajectory calculations and allows derivation of E(0)(J=0) on the basis of measured k(E) and which provides similar accuracy as the full SACM/CT treatment.     

Novel superstructure of nondiscoid mesogens: uneven-parallel association of half-disk molecules, 3,4,5-trialkoxybenzoic anhydrides, to a columnar structure and its one-directionally geared interdigitation

Compact and simple nondiscoid mesogens, trialkoxybenzoic anhydrides 2-11 ((RO)(3)C(6)H(2)-CO-O-CO-C(6)H(2)(OR)(3), R = C(2)H(5), n-C(3)H(7), n-C(4)H(9), n-C(6)H(13), n-C(8)H(17), n-C(10)H(21), n-C(12)H(25), n-C(14)H(29), n-C(16)H(33), and (S)- and (R)-3,7-dimethyloctyl) were designed and synthesized, and their superstructures were investigated by polarized light microscopy, differential scanning calorimetry, calculation (MM2 and AM1), circular dichroism spectroscopy, and X-ray diffraction. As the result, in the cases of 5-9 and 11, the half-disk molecules in the liquid crystal phases were self-assembled by the dipole-dipole interaction between their carbonyl groups to a column in which the molecules were piled up in an alternately antiparallel manner, and the columns were interdigitated each other. The observed interdigitations were highly directional in the perpendicular direction to the column axis. In the case of compound 11 which has (S)- or (R)-3,7-dimethyloctyl groups, a helical organization of the molecules in the column was estimated from the peaks in the circular dichroism spectra. This is the first report of a one-directionally interdigitated columnar phase, and these compounds are the first liquid crystalline acid anhydrides. It was demonstrated that a -CO-O-CO- moiety is useful as a polar junction in liquid crystalline compounds.     

Deformability of adsorbents during adsorption and principles of the thermodynamics of solid-phase systems

A microscopic theory of adsorption, based on a discrete continuum lattice gas model for noninert (including deformable) adsorbents that change their lattice parameters during adsorption, is presented. Cases of the complete and partial equilibrium states of the adsorbent are considered. In the former, the adsorbent consists of coexisting solid and vapor phases of adsorbent components, and the adsorbate is a mobile component of the vapor phase with an arbitrary density (up to that of the liquid adsorbate phase). The adsorptive transitioning to the bound state changes the state of the near-surface region of the adsorbent. In the latter, there are no equilibrium components of the adsorbent between the solid and vapor phases. The adsorbent state is shown to be determined by its prehistory, rather than set by chemical potentials of vapor of its components. Relations between the microscopic theory and thermodynamic interpretations are discussed: (1) adsorption on an open surface, (2) two-dimensional stratification of the adsorbate mobile phase on an open homogeneous surface, (3) small microcrystals in vacuum and the gas phase, and (4) adsorption in porous systems.     

Surface tensions of linear and branched alkanes from Monte Carlo simulations using the anisotropic united atom model

The anisotropic united atoms (AUA4) model has been used for linear and branched alkanes to predict the surface tension as a function of temperature by Monte Carlo simulations. Simulations are carried out for n-alkanes ( n-C5, n-C6, n-C7, and n-C10) and for two branched C7 isomers (2,3-dimethylpentane and 2,4-dimethylpentane). Different operational expressions of the surface tension using both the thermodynamic and the mechanical definitions have been applied. The simulated surface tensions with the AUA4 model are found to be consistent within both definitions and in good agreement with experiments.     

Atmospheric chemistry of n-C(x)F(2)(x)(+1)CHO (x = 1, 2, 3, 4): fate of n-C(x)F(2)(x)(+1)C(O) radicals

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C(x)F(2)(x)(+1)C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O(2)/N(2) diluent at 298 +/- 3 K. A competition is observed between reaction with O(2) to form n-C(x)()F(2)(x)()(+1)C(O)O(2) radicals and decomposition to form n-C(x)F(2)(x)(+1) radicals and CO. In 700 Torr O(2)/N(2) diluent at 298 +/- 3 K, the rate constant ratio, k(n-C(x)F(2)(x)(+1)C(O) + O(2) --> n-C(x)F(2)(x)(+1)C(O)O(2))/k(n-C(x)F(2)(x)(+1)C(O) --> n-C(x)F(2)(x)(+1) + CO) = (1.30 +/- 0.05) x 10(-17), (1.90 +/- 0.17) x 10(-19), (5.04 +/- 0.40) x 10(-20), and (2.67 +/- 0.42) x 10(-20) cm(3) molecule(-1) for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O(2) accounts for 99%, 50%, 21%, and 12% of the loss of n-C(x)F(2)(x)(+1)C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C(x)F(2)(x)(+1)C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.     

Studies of gas-phase fragmentation reactions of [Pd(PPh3)2(OCOR)]+ by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Gas-phase fragmentation reactions of [Pd(PPh3)2(OCOR)]+ (R = H, CH3, CD3, C2H5, n-C3H7, n-C6H13 and C6H5) were studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). In sustained off-resonance irradiation collision-activated dissociation (SORI-CAD) experiments, the complexes all dissociated to yield the same product ion at m/z 629.1. We propose that the fragmentation pathway occurs through the elimination of RCOOH and a palladium(IV) hydride intermediate. Semi-empirical (PM3) calculations shed light on the mechanism for the fragmentation reactions of these compounds. The results of deuterium-labeling experiments indicate that the protons of RCOOH lost from [Pd(PPh3)2(OCR)]+ originate from the phenyl in the triphenylphosphine ligand. [Pd(PPh3)2(OCOH)]+ undergoes two competitive pathways in SORI-CAD experiments, one of which is similar to that of [Pd(PPh3)2(OCOR)]+ (R = CH3, CD3, C2H5, n-C3H7, n-C6H13 and C6H5), and the other involves decarboxylation. The present study demonstrates that MS could play an important role in studying the gas-phase chemistry of palladium hydrides.