电化学界面处离子分布、静电势和ζ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamental-measure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent     

带电硬哑铃流体的分子热力学

Chemical potentials of charged hard-dumbbell fluids are obtained by Monte Carlo simulations using Widom‘s test-particle method, corresponding compressibility factors are achieved by integration of chemical potentials at different densities. A molecular thermodynamic model is also developed for these charged hard-dumbbell fluids where the residual Helmholtz function is composed of two terms: a reference term responsible for the charged hard spheres and a bonding contribution measuring the sticky interactions between positive and negative hard ions.Model predictions are in good agreement with simulation results.     

硬球链流体在狭缝中密度分布的Monte Carlo模拟

Covering a wide range of bulk densities, density profiles for hard-sphere chain fluids (HSCFs) with chain length of 3,4,8,20,32 and 64 confined between two surfaces were obtained by Monte Carlo simulations using extended continuum configurationai-bias (ECCB) method. It is shown that the enrichment of beads near surfaces is happened at high densities due to the bulk packing effect, on the contrary, the depletion is revealed at low densities owing to the configurationai entropic contribution. Comparisons with those calculated by density functional theory presented by Cai et al. indicate that the agreement between simulations and predictions is good. Compressibility factors of bulk HSCFs calculated using volume fractions at surfaces were also used to test the reliability of various eauations of state of HSCFs by different authors.     

喹啉和异喹啉热解机理的密度泛函理论研究

The pyrolysis mechanisms of quinoline and isoquinoline were investigated using the density functional theory of quantum chemistry, including eight reaction paths and a common tautomeric intermediate 1-indene imine. It is concluded that the conformational tautomerism of the intermediate decides the pyrolysis products (C6H6, HC C C N, C6H5C N and HC CH) to be the same, and also decides the total disappearance rates of the reactants to be the same, for both original reactants quinoline and isoquinoline during the pyrolysis reaction. The results indicate that the intramolecular hydrogen migration is an important reaction step, which often appears in the paths of the pyrolysis mechanism. The activation energies of the rate determining steps are obtained. The calculated results are in good agreement with the experimental results.     

离子在电解质溶液-荷电膜界面的分配平衡

Ionic partition equilibrium in charged membrane immersed in solution of single electrolyte with monovalence or multi-valence is systematically investigated and several expressions are established for determination of partition coefficients. On this basis, the effects of the ratio of membrane charge density to hulk electrolyte solution concentration, the charge sign and valence of electrolyte ions and the type of membrane on the partition equilibrium were analyzed and simulated with in chosen parameters. It is revealed that ion partition is not related solely withthe respective concentrations but also definitely with the concentration ratio of fixed group to bulk solution in addition to the charge sign and the valence. For a counterion, the partition coefficient increases with this ratio and the valence; while for a coion, the partition coefficient decreases with this ratio and the valence. The theoreticalcal culations were compared with the experimental data and a good agreement was observed.     

密度泛函理论在非极性纯流体表面性质研究中的应用

The density functional theory, simplified by the local density approximation and mean-field approximation, is applied to study the surface properties of pure non-polar fluids. A reasonable long rang correction is adopted to avoid the truncation of the potential. The perturbation theory is applied to establish the equation for the phase equilibrium, in which the hard-core chain fluid is as the reference fluid and the Yukawa potential is used as the perturbation term. Three parameters, elk, d and ms, are regressed from the vapor-liquid equilibria, and the surface properties, including density profile, surface tension and local surface tension profile are predicted with these parameters.     

循环硫化床上升管中动态行为的拟流体模拟

The kinetic theory of granular flow (KTGF) is modified to fit the Einstein′s equation for effective viscosity of dilute flow. A pseudo-fluid approach based on this modified KTGF is used to simulate the dynamic formation and dissipation of clusters in a circulating fluidized bed riser. The agglomeration of particles reduces slip velocity within particle clusters, and hence results in two reverse trends: discrete particles are lifted by air while particle clusters fall down along the wall. The dynamic equilibrium of these two types of motion leads to the characteristic sigmoid profile of solid concentration along the longitudinal direction. The predicted solid velocity, lateral and longitudinal profiles of solid volume fraction and annulus thickness are in reasonable agreement with experimental results.     

The Effect of Sparger Geometry on Gas Bubble Flow Behaviors Using Electrical Resistance Tomography

By electrical resistance tomography （ERT） the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is revealed by applying a sensitivity conjugated gradients reconstruction method （SCG）. Experimental results show that overall hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.     

基于一种改进的自适应遗传算法估算环已烷自催化氧化反应动力学参数

A modified genetic algorithm of multiple selection strategies, crossover strategies and adaptive operator is constructed, and it is used to estimate the kinetic parameters in autocatalytic oxidation of cyclohexane. The influences of selection strategy, crossover strategy and mutation strategy on algorithm performance are discussed. This algorithm with a specially designed adaptive operator avoids the problem of local optimum usually associated with using standard genetic algorithm and simplex method. The kinetic parameters obtained from the modified genetic algorithm are credible and the calculation results using these parameters agree well with experimental data. Furthermore, a new kinetic model of cyclohexane autocatalytic oxidation is established and the kinetic parameters are estimated by using the modified genetic algorithm.     

Tao-Mason状态方程扩展用于重正烷烃(英文)

In our previous paper we extended the Tao and Mason equation of state (TM EOS) to refrigerant fluids, using the speed of sound data. This is a continuation for evaluating TM EOS in predicting PVT properties of heavy n-alkanes. Liquid density of long-chain n-alkane systems from C 9 to C 20 have been calculated using an analytical equation of state based on the statistical-mechanical perturbation theory. The second virial coefficients of these n-alkanes are scarce and there is no accurate potential energy function for their theoretical calculation. In this work the second virial coefficients are calculated using a corresponding state correlation based on surface tension and liquid density at the freezing point. The deviation of calculated densities of these alkanes is within 0.5% from experimental data. The densities of n-alkanes obtained from the TM EOS are compared with those calculated from Ihm-Song-Mason equation of state and the corresponding-states liquid densities (COSTALD). Our results are in favor of the preference of the TM EOS over other two equations of state.     

The behavior of salt-free polyelectrolyte solutions at charged surfaces

The properties of polyelectrolytes at oppositely charged surfaces are studied using Monte Carlo (MC) simulations and integral equation theory. The polymer molecules are modeled as chains of charged spheres, the counterions and co-ions are charged spheres, and the surface is smooth and uniformly charged. The polymer concentration in the simulations is strongly peaked at the surface, and this is accompanied by a depletion of polymers at larger distances from the surface. The thickness of the adsorbed layer decreases with increasing polymer concentration or surface charge density, but the total adsorbed amount displays a non-monotonic dependence on polymer concentration. The integral equation theory predictions are in qualitative agreement with the MC results.     

A CONSISTENT ALTERNATIVE TO THE DLVO THEORY

An overview of a new theory of repulsions between charged surfaces is given. The theory is based on consistent Maxwellian electrostatics with linear distribution laws, which predict the existence of co-ion exclusion boundaries. The theory covers interactions from infinity to contact in terms of three electrostatic models: the low potential (LP) model, the co-ion exclusion (CX) model, and the high potential (HP) model. The new theory predicts short-range electrostatic forces that are much stronger than those derived from the nonlinear DLVO theory; no universal Van der Waals adhesion at short distances is predicted. For planar charged surfaces, these short-range electrostatic forces decay according to the inverse square of separation in accordance with experimental observations.     

A consistent alternative to the dlvo theory

An overview of a new theory of repulsions between charged surfaces is given. The theory is based on consistent Maxwellian electrostatics with linear distribution laws, which predict the existence of co-ion exclusion boundaries. The theory covers interactions from infinity to contact in terms of three electrostatic models: the low potential (LP) model, the co-ion exclusion (CX) model, and the high potential (HP) model. The new theory predicts short-range electrostatic forces that are much stronger than those derived from the nonlinear DLVO theory; no universal Van der Waals adhesion at short distances is predicted. For planar charged surfaces, these short-range electrostatic forces decay according to the inverse square of separation in accordance with experimental observations.     

The Electrostatic Potential Above the 100 Surface Plane of a f.c.c. Ionic Crystal with a Continuous Electron Chargè Distribution

The electrostatic potential above the 100 surface plane of a f.c.c. ionic crystal has been calculated using a point charge distribution for the positive nuclei and a continuous charge density distribution for electrons. The continuous electron charge distribution has been obtained from the known results of a Fourier crystal structure analysis. The results for the electric field and its different gradients are compared with those obtained from the Lennard-Jones and Dent model (point charge distributions for both the positive and negative ions). It has been found that the two models lead to significant differences of the electrostatic potentials and their derivatives.     

Experimental Study of Electrostatic Aerosol Filtration at Moderate Filter Face Velocity

Aerosol collection efficiency was studied for electrostatically charged fibrous filters (3M Filtrete?, BMF-20F). In this study, collection efficiencies at moderate filter face velocities (0.5–2.5 m/s) representative of some high volume sampling applications was characterized. Experimental data and analytical theories of filter performance are less common in this flow regime since the viscous flow field assumption may not be representative of actual flow through the filter mat. Additionally, electrostatic fiber charge density is difficult to quantify, and measurements of aerosol collection efficiency are often used to calculate this fundamental parameter. The purpose of this study was to assess the relative influence of diffusion, inertial impaction, interception, and electrostatic filtration on overall filter performance. The effects of fiber charge density were quantified by comparing efficiency data for charged and uncharged filter media, where an isopropanol bath was used to eliminate electrostatic charge. The effects of particle charge were also quantified by test aerosols brought into the equilibrium Boltzmann charge distribution, and then using an electrostatic precipitator to separate out only those test particles with a charge of zero. Electrostatically charged filter media had collection efficiencies as high as 70–85% at 30 nm. Filter performance was reduced significantly (40–50% collection efficiency) when the electrostatic filtration component was eliminated. Experiments performed with zero charged NaCl particles showed that a significant increase in filter performance is attributable to an induction effect, where electrostatic fiber charge polarizes aerosol particles without charge. As filter face velocity increased the electrostatic filtration efficiency decreased since aerosol particles had less time to drift toward electrostatically charged fibers. Finally, experimental data at 0.5 m/s were compared to theoretical predictions and good agreement was found for both electrostatic and nonelectrostatic effects.

© 2013 American Association for Aerosol Research     

Electrostatic and Entropic Interactions between Parallel Interfaces Separated by a Glassy Film

A simple classical density functional model is set up to describe the electrostatic and entropic interactions between two parallel planar charged interfaces separated by a thin film of a phase (the glass) containing a distribution of charged ions. The total charge in the system is zero. Three cases are treated: (1) the two interfaces carry a fixed surface charge; (2) the first interface carries a fixed surface charge, simulating a ceramic, while the second is held at zero potential, simulating a metal; and (3) both interfaces are held at zero potential. A discretized form of the nonlinear Poisson–Boltzmann equation is derived and solved by a Newton–Raphson method. The continuum approximation is compared with a model in which the ions are only allowed to occupy discrete planes. The effect of correlation among the ions is included within the local density approximation. Inserting parameters appropriate to the copper–alumina interface, we find that the attractive image force between the ceramic and metal dominates the entropic (DLVO) repulsive force in the 1–2 nm range.     

基于静电作用选择性吸附染料的超分子凝胶剂

设计并合成了一系列季铵盐型凝胶剂，仅通过调控季铵盐烷基侧链的长度，可得到两种自组装模式不同的凝胶剂。通过FTIR、XRD研究了甲苯干凝胶的自组装模式。这两种干凝胶具有相反的表面Zeta电位，通过静电作用实现了对阴阳离子染料的选择性吸附。在二元阴阳离子混合染料水溶液中，表面带有负电荷的干凝胶可优先捕获阳离子染料，而表面带有正电荷的干凝胶可捕获阴离子染料。特别是表面带有负电荷的干凝胶对龙胆紫表现出优异的吸附性能，在60 min左右的平衡吸附量高达1313.16 mg/g。将凝胶剂负载于三聚氰胺海绵骨架表面，得到的改性海绵吸附染料种类与对其改性的干凝胶保持一致，且对染料的吸附量均明显高于干凝胶的吸附量，尤其是对龙胆紫的吸附量提升至2488.22 mg/g。     

Zeta Potential Measurement in Catalyst Preparations

Oxide surfaces are covered with hydroxyl groups. In contact with water, positive or negative surface charges can be developed. The surface charge of oxide particles can be fine‐tuned by changing the calcination temperature of the oxides before dispersion in water or by variation of the suspension pH. Strong negative or positive surface charges stabilize a suspension and avoid particle aggregation. Nano‐structured catalysts suspended in water show surface charges different from those of compact TiO₂. For spray drying, the cationic or anionic additives used have to be strongly attached via electrostatic forces to the surface of the suspended oxide particles. When noble metal complexes have to be brought to the support surface, the positively or negatively charged complexes must have an opposite charge relative to the surface charge. Zeta potential measurements can solve these problems.     

Adhesion of charged particles

The adhesion properties of charged particles are of considerable importance in the electrophotographic process. Measurements on irregularly-shaped, pigmented particles, called toner in the electrophotographic industry, show that adhesion increases with toner charge but that the magnitude is much larger than expected from a simplified electrostatic image force model. An enhanced electrostatic adhesion is also seen in electric field detachment measurements on spherical charged particles. In both cases, this unexpected large adhesion can be attributed to a nonuniform distribution of charge on the surfaces of the particles.