Grand canonical Monte Carlo simulations of phase equilibria of pure silicon tetrachloride and its binary mixture with carbon dioxide

Grand canonical histogram-reweighting Monte Carlo simulations were used to obtain the phase behaviour of pure silicon tetrachloride and its binary mixture with carbon dioxide. Two new potential models for pure silicon tetrachloride were developed and parametrized to the vapour-liquid coexistence properties. The first model, with one exponential-6 site and fixed electrostatic charges on atoms, does not adequately reproduce the experimental phase behaviour due to its inability to represent orientational anisotropy in the liquid phase. The second potential model, with five exponential-6 sites for the repulsive and dispersive interactions plus partial charges, accurately reproduces experimental saturated liquid and vapour densities as well as vapour pressures and the second virial coefficient for pure silicon tetrachloride. This model was used in simulations of the phase behaviour of the binary mixture carbon dioxide-silicon tetrachloride. Two sets of combining rules (Lorentz-Berthelot and Kong [1973, J. chem. Phys., 59, 2464]) were used to obtain unlike-pair potential parameters. For the binary system, the predicted phase diagram is in good agreement with experiment when the Kong combining rules are used. The Lorentz-Berthelot rules significantly overestimate the solubility of carbon dioxide in silicon tetrachloride.     

On the Viscoelastic and Dielectric Behavior of Some Organic Compounds and Their Binary Mixtures

The dependence of dielectric relaxation time on the viscosity of the medium is being extensively used to draw certain quantitative conclusions regarding molecular motion and inter-molecular forces in liquids, liquid mixtures, dilute solutions, and multi-component polar solutes in dilute solution. In the absence of proper empirical or theoretical equations for the variation of dielectric relaxation time with viscosity, only the experimental investigations on different systems can give an insight. In the present study, the results of dielectric measurements carried out on pure samples of bromohexane, bromooctane and bromodecane in dilute solutions in different mixed solvents (benzene + paraffin) and on binary mixtures (1 : 1) of (bromohexane + bromodecane); (bromodecane + propyl alcohol) and (propyl alcohol + methyl alcohol) are reported. For comparison, the results of bromodecane + propyl alcohol and propyl alcohol + methyl alcohol are chosen as they form examples of mixture of non-associative + associative and associative + associative liquids, respectively. Different parameters determined using these dielectric measurements are also presented using different models. These studies indicate that the dielectric behavior at microwave frequencies favor the concept of dynamic viscosity and a single viscoelastic relaxation time for the systems under study.     

Dielectric constants of binary mixtures of propylene carbonate with dimethyl carbonate and ethylene carbonate from molecular dynamics simulation: comparison between non-polarizable and polarizable force fields

Using non-polarizable and polarizable molecular dynamics simulations, binary mixtures of propylene carbonate?+?dimethyl carbonate and propylene carbonate?+?ethylene carbonate with various compositions were investigated. The polarizable model produces more reasonable estimation of dielectric constants than the non-polarizable model; however, combining the electronic continuum model with the non-polarizable MD improves the comparison between the two models. Fair agreement was found between the results from these simulations and available experimental data. In addition, for a better understanding of the mixing behaviour, the excess dielectric constants over the entire composition were calculated. By comparison of the two mixtures in various mole fractions, distinctive mixing behaviours of propylene carbonate?+?dimethyl carbonate (poorly symmetric mixture) and propylene carbonate?+?ethylene carbonate (highly symmetric mixture) were observed.     

Calculation of the rate constant for the ultrasonic degradation of aqueous solutions of polyvinyl alcohol by viscometry

Ultrasonic degradation of polyvinyl alcohol (PVA) was carried out in aqueous solution at 25 degrees C. In this experiment, the effect of solution concentration on the rate of degradation was investigated. Kinetics of degradation was studied by viscometry method. The calculated rate constants indicate that degradation rate of PVA solutions decreases with increasing of solution concentration (C= g lit(-1)). The calculated rate constants correlated in terms of reverse concentration and relative viscosity of PVA solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. With increasing solution concentration, viscosity increases and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased.     

Dielectric permittivity, density, viscosity and refractive index of binary mixtures of anisole with methanol and 1-propanol at different temperatures

Static dielectric permittivity, density, viscosity, and refractive index of anisole (AN), methanol (MeOH), 1-propanol (1-PrOH) and binary mixtures of AN with MeOH and 1-PrOH at nine different concentrations, were measured at 303, 313 and 323 K temperatures. Measured properties of pure AN, MeOH and 1-PrOH were compared with literature values and they were found in good agreement. The investigation of binary mixtures showed a systematic change in static dielectric permittivity, density and viscosity with change in concentration of anisole in the mixture. Measured properties of liquid samples were used to calculate Kirkwood correlation factor and excess parameters such as excess dielectric permittivity, excess molar volume and excess viscosity. Determined parameters have been interpreted in terms of molecular interaction among the molecular species of the binary mixtures.     

Understanding the molecular interaction and relaxation findings in amphiphilics on solution state using TDR

The dielectric behavior of stearic acid in 1,4-dioxane medium at various temperature 303 K–288 K and frequency regime (10 MHz–30 GHz) determined from the complex dielectric permittivity spectra obtained by Time Domain Reflectometry(TDR). In this frequency range, the dielectric study gives the electrostatic interaction as well as orientational polarizability of complex mixtures of long chain molecules significantly. Dielectric parameters were calculated from the complex spectra of the binary mixture by non linear least square fit method. The excess permittivity (ε^E), correlation factors were calculated for the binary system. Thermal parameters(ΔH-enthalpy, ΔS-entropy and ΔG-Gibbs free energy) were calculated and the direction of reaction is determined. The FTIR spectrum of the binary system recorded and the assignments are discussed. The FTIR spectral assignments confirm the molecular interactions.     

Dielectric relaxation in aqueous solutions and suspensions I. Solutions and suspensions

The dielectric constants and dielectric loss factors of aqueous solutions and suspensions are measured as a function of the specific electrical conductivity, temperature, and electric field frequency. The dispersion of the dielectric constant and the dielectric loss factor in solutions is explained by the formation of a electric double layer at the electrodes and the redistribution of the electric field between the region adjoining the electrodes and the remaining volume of the measuring cell. An equivalent-circuit calculations for suspensions displays acceptable agreement with experiment.     

Dielectric spectroscopy and viscosity studies of aqueous poly(ethylene oxide) and poly(vinyl pyrrolidone) blend

The complex dielectric function, electric modulus, impedance and ac electrical conductivity behaviour of aqueous solutions of 5 wt% poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) and their different volume percent blends were investigated in the frequency range 20 Hz to 1 MHz at 15, 30 and 45 °C. It is found that the real part of dielectric function of these blends at 1 MHz decreases with the increase of PEO concentration and their dc electrical conductivity has strong correlation with the electrode polarization relaxation time. The static permittivity, ionic conductivity, electrode polarization relaxation time and apparent viscosity have linear behaviour with temperature variation at fixed volume concentration of the aqueous polymers blend. The viscosity of these aqueous polymeric blends increases with the increase of PEO concentration. The behaviour of hydrogen bond interactions between the polar segments of PEO and PVP were explored from the comparative change in dielectric parameters and viscosity of the two phase aqueous polymeric systems.     

液晶在电场和剪切耦合作用下的流变学行为

本文通过理论和实验对液晶 5CB在剪切和电场耦合作用下流变行为进行了研究. 采用液晶连续理论, 建立了包括界面锚定能, 弹性自由能, 介电自由能和流动能在内的系统 Gibbs自由能公式, 通过最小化系统自由能的方法求解液晶在剪切和电场耦合作用下的取向分布及其黏度变化, 从分子基础模型上揭示了液晶在耦合作用下的流变行为、微观机理及其影响规律, 并通过流变测试对此进行验证. 对比分析了理论和试验结果的误差和原因, 发现界面锚定效应对于液晶分子的取向和黏度具有重要影响. 理论和试验结果均表明, 液晶在电场作用下具有明显的电黏效应, 表现出非牛顿流变行为, 其黏度值由剪切和电场的竞争和耦合作用共同决定. 在外电场作用下液晶的黏度可以增加到初始值的 4倍左右, 液晶这种其自身黏度可随着外场 (例如运动速度) 改变的特性在一定的条件下可以自适应地满足不同工况对黏度的要求, 这对实现智能摩擦润滑具有重要的意义. 关键词： 液晶 流变行为 电黏效应 耦合作用     

Structural study of aqueous solutions of tetrahydrofuran and acetone mixtures using dielectric relaxation technique

The complex permittivity, static dielectric constant and relaxation time for tetrahydrofuran-water and acetone-water mixtures have been determined at 0°, 10°, 25° and 35°C using time domain reflectometry technique (TDR). The behaviour of relaxation time of the mixture shows a maxima for the mixture with 30% of water by volume. This suggests that the tendency to form cluster between water and solute molecule is maximum for this mixture. The excess permittivity for both tetrahydrofuran-water mixture and acetone-water mixtures, are found to be negative. The Kirkwood correlation factor has been determined at various concentrations of water. Static dielectric constant for the mixtures have been fitted well with the modified Bruggeman model. The values of the Bruggeman parametera for tetrahydrofuran is found to be more than the corresponding value for acetone.     

Topological transition in aqueous nonionic micellar solutions

We have studied the topological transition of the nonionic micelles of a penta-ethyleneglycol mono n-dodecyl ether (C12E5)/DL-alpha-phosphatidylcholine Dimyristoyl (DMPC) mixture in water by light scattering and viscosity measurements. The topological transition concentration decreases with an increase of the mixing ratio of DMPC to C12E5. The topological transition point is strongly affected by defect energies of the end cap (epsilon(1)) and a threefold junction (epsilon(3)) and is compared with a recent theoretical study. This experimental study shows the first clear evidence for the topological transition in a nonionic micellar system resulting from balancing the defect energies.     

Modeling the electrical transfer in a mixture of disperse dielectric and finely disperse solid- or liquid-phase conductor

The dependence of the electrical conductivity of a mixture of finely disperse graphite with quartz sand and moist quartz sand on the composition is investigated. It is shown that, in the region of critical and near-critical concentrations of the conducting component, the dependence is satisfactorily described by two power-law equations of flow theory with two different threshold values of the conducting-phase concentration. In this concentration range, the conductivity of the sandgraphite system is satisfactorily modeled by a lattice bond problem. The electrical transfer in the sand-KCl solution system may be modeled by a lattice point problem in the representation of the moist system as a mixture of dielectric particles coated with an electrolyte film (conducting particles) and dry dielectric particles (nonconducting particles).Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 29–35, November, 1984.     

涂层球体混合体系的等效介电常数计算及应用

采用一定的包覆工艺制备了炭黑包覆发泡型聚苯乙烯(EPS)颗粒，用包覆的颗粒作为填料制备了环境适应性强的吸波材料. 将涂层球体混合体系作为密实整体考虑，计算了炭黑含量1%时的等效介电常数，并用计算结果预测了吸波性能. 与实验值对比表明，计算值是基本准确的，可以应用于新型微波暗室用吸波材料的设计和优化. 关键词： 炭黑 吸波材料 等效介电常数 吸波性能     

激光触发SF6-N2混合气体开关的数值模拟

 在气体放电物理的基础上，对SF₆和N₂采用双光子电离模型，对碳氢化合物的光电离采用3能级模型，并考虑了混合气体的热电离和激光对气体的欧姆加热作用，建立了激光触发SF₆-N₂混合气体开关的数值模型，模拟了激光触发SF6-N2混合气体多级间隙开关实验。激光触发延迟时间的计算值与实验结果符合较好。理论计算表明：激光触发SF₆-N₂混合气体间隙开关的延迟时间随SF₆含量的增加呈上升趋势，而随激光脉冲能量、充气压力等的上升呈下降趋势。     

Rotational Diffusion of Coumarins in Aqueous DMSO

The rotational dynamics of four structurally similar polar molecules viz., coumarin 440, coumarin 450, coumarin 466 and coumarin 151 has been studied in binary mixtures comprising of dimethyl sulphoxide and water at room temperature using the steady state fluorescence depolarization method and time correlated single photon counting technique. The binary mixtures are characterized by the fact that at a particular composition the viscosity (η) of the solution reaches a maximum value that is higher than the viscosities of either of the two co-solvents. The dielectric properties of the solution change across the composition range and the qualitative features of the solvent relaxation dynamics in complex systems are known to differ from those in simple solutions. A hook type profile of rotational reorientation time (τ _r ) vs viscosity (η) is obtained for all the solutes in dipolar aprotic mixture of dimethyl sulphoxide-water, with the rotational reorientation times being longer in organic solvent-rich zone, compared to the corresponding isoviscous point in water-rich zone due to strong hydrogen bonding. Fluorescence lifetimes as well as rotational reorientation times are sensitive to the composition of the binary solvent system under study than to the viscosity suggesting the importance of local structure. The results are discussed in the light of hydrodynamic and dielectric friction models. Dedicated to Professor M.I. Savadatti on his 77^th Birthday.     

CuS纳米粒子在太赫兹波段的光电性质研究

关键词： 太赫兹 CuS纳米粒子 Lorentz理论 Drude-Smith模型     

An assessment of techniques for predicting radiation transfer in aqueous media

Five methods of determining radiative transfer in aqueous suspensions have been compared on the basis of their ability to predict radiative flux and absorption profiles within the suspension, as well as overall absorption and reflection by the suspension. They include the forward scattering technique, the delta-Eddington method, a three-flux technique, the six-flux model, and the more rigorous method of discrete ordinates. Calculations have been performed for a planar aqueous suspension over a wide range of independent parameters which include the scattering albedo, bottom reflectance, overall optical depth, and directional distribution of the incident radiation. Reasonable agreement is obtained between the three-flux, six-flux and discrete ordinate results for the range of conditions. In contrast suspension absorption effects are consistently underpredicted and overpredicted, respectively, by the forward scattering and delta-Eddington methods.     

Alignment of polarizable dipoles on a lattice

The alignment average of polar molecules may be derived from their NMR spectrum, when a strong electric field is applied to the liquid. The Kerr effect can likewise be related to the alignment.In this paper the alignment has been calculated for a rigid-lattice model, previously developed by Van Vleck in the theory of dielectric polarization and extended by others. A series expansion of the alignment for a system of isotropically polarizable dipoles is presented up to second-order terms in the dipolar interaction. The result for a continuum has been compared with those calculated on the basis of the Lorentz and Onsager model of the liquid.An explicit expression for the total electrostatic energy of a binary mixture of polar and non- polar molecules with a symmetric polarizability tensor has also been calculated; it has been obtained from a generalization of a formalism, developed by Mandel and Mazur for the pure polar liquid.     

Dynamically evaluating mixture effects on multi-channel reactions in flames: A case study for the CH3 + OH reaction

Complex-forming reactions, whose rate constants depend on pressure and collisional energy transfer characteristics of the surrounding bath gas, play a major role in the kinetics of combustion. In most realistic combustion environments, multiple species of distinct collisional energy transfer characteristics are present in significant quantities and thus contribute to collisional energy transfer involved in such systems. Recent studies have indicated that certain representations of multi-component pressure dependence (i.e. “mixture rules”) and/or a failure to implement a mixture rule can result in errors reaching an order of magnitude, whereas recently proposed mixture rules yield errors less than 10%. The present study compares the performance of various mixtures rules for representing multi-component pressure dependence of the multi-channel CH₃ + OH reaction in flames, using a novel dynamic procedure for evaluating mixture effects as a function of reaction progress (viz. local temperature, pressure, and mixture composition). This procedure enables mixture effects to be simulated in current combustion codes despite codes not yet having functional forms intended to capture these mixture dependence effects. Results from this procedure, combining master equation simulations and kinetic-transport simulations, indicate that recently proposed mixture rules based on the reduced pressure provide a considerably more accurate representation of mixture effects for CH₃ + OH than previous mixture rules based on the absolute pressure. Furthermore, the present results demonstrate that mixture effects for the CH₃ + OH reaction, which are not accounted for in many models, have a significant effect on predictions of the laminar flame speed – of comparable magnitude to differences motivating parameter adjustments in model development studies.