纯流体在临界区内外的表面张力研究

An equation of state(EOS)applicable for both the uniform and non-uniform fluids was established by using thedensity-gradient expansion,in which the influence parameter к[p(r),T] was obtained by the use of direct correlationfunction.The density functional theory(DFT)provides a framework under which both the phase equilibria and in-terfacial properties can be investigated within a single set of molecular parameters.The phase equilibria inside thecritical region can be improved by the renormalization group theory(RGT).However,the correction of interracialproperties by DFT and RGT is computationally difficult.In the present work,the density gradient theory(DGT)inwhich к[p(r),T] is treated as a constant is used to combine with the RGT for interfacial properties inside the criticalregion.     

STUDIES ON THE MECHANICAL PROPERTIES AND CRYSTALLIZATION BEHAVIOR OF POLYETHYLENE COMPOSITES

The effects of inter facial modifier on the mechanical, dynamic mechanical properties andcrystallization behavior of the polyethylene composites were investigated in the present paper.It was found that the interfacial modifer significantly improved the mechanical properties,influenced the dynamic mechanical spectra and slightly changed the crystallization behavior.The results showed that the interfacial modifier changed the dispersion state of dispersedphase of the composites, resulting in different phase structure, which was the major reasonIeading to different mechanical and crystallization properties.     

Quantum chemical study on excited states and charge transfer of oxazolo[4,5-b]-pyridine derivatives

The excitedstate intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The sub-stituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.     

Preparation and Characterization of High-quality α-Al2O3/Al4.59Si1.41O9.7/Al2TiO5 Multiphase Material

The α-Al2O3/Al4.59Si1.41O9.7/Al2TiO5 multiphase material with high performance was prepared by reaction sintering. The influence of different formulas on the structures and properties of multiphase material was investigated to determine the optimal formula. Crystalline structure and cell parameters of sintered samples were characterized by XRD. Microstructure of all samples was observed by SEM. The properties of sintered samples were investigated. The results show that corundum phase (α-Al2O3 ), mullite solid solution phase (Al4.59Si1.41O9.7 ) and aluminium titanate phase (Al2TiO5 ) were formed in the sintered samples. Different formulas would not change the symmetry of each crystalline phase, but caused slight change in their cell parameters. The optimal formula was determined to be coarse corundum of 36%, fine corundum of 21%, total amount of three kinds of clay of 33%, and TiO2 of 12%, which possessed a comparatively ideal microstructure and optimal properties.     

EFFECT OF DRAWING ON MORPHOLOGY,STRUCTURE AND MECHANICAL PROPERTIES OF BLENDS OF A LIQUID CRYSTALLINE POLYMER AND MODIFIED POLY(PHENYLENE OXIDE)

Polymer strands with various draw ratios of a thermotropic liquid crystalline polymer(LCP) and modified poly(phenylene oxide) were prepared by drawing the melts leaving aslit die in open air. The morphology, structure and mechanical properties of the resultingstrands were studied as a function of LCP content and draw ratio. It was found that thethermal and mechanical properties of the matrix phase did not change dramatically withthe amount of LCP and draw ratio, but the orientation of LCP phase could be increasedwith draw ratio. The mechanical properties of the strands could be improved by moderatelydrawing the melts. Wide angle X-ray diffraction suggested that the improvement in tensilestrength of the strands was due to the resultant fibrillation of LCP phase and enhancedmolecular orientation. Morphological observation indicated that excessive drawing of thestrands could lead to the break down of the microfibrils of LCP and thus resulted in thedecrease of mechanical strength.     

Phase separation in mixtures of thermotropic liquid crystals and flexible polymers

The spinodal equation and the concentration-induced anisotropic-isotropic transition equation of the mixtures of thermotropic liquid crystals and flexible polymers have been studied by using the molecular field theory The calculations of the phase diagrams of this system show that,besides the isotropic classic spinodal curve,there ex ists an anisotropic spinodal curve which has not been reported in literature.These two spinodal curves can be linked up by the concentration-induced anisotropic-isotropic transition line.In the various phase regions,demixing may take place due to different phase separation mechanisms.The phase equilibrium curve cannot always join the.spinodal curve at a critical point.These results are considered very meaningful for the understanding of the special properties of liquid crystal/polymer composites and very useful for controlling the morphology and the performance of PDLC materials     

Phase behavior and structure analysis of the middle mixed layer for ASP flooding system at low surfactant concentration

The phase behavior and interfacial tension of alkali/surfactant/polymer (ASP) flooding system and simulative crude oil were investigated, and the size distribution and structure analysis of the middle mixed layer (MML) were also studied by size analyzer and freeze-fracture TEM. It was found that there were some rules between the volume of MML and the concentration of each component, and the interfacial tension between MML and the oil phase or water phase could reach an ultra-low value. Especially, the freeze-fracture TEM micrographs of MML were firstly obtained, and the new viewpoint was put forward that there coexist the structures of micelle, microemulsions and emulsions in MML and the structure of microemulsion is dominant. This would make an important effect on the research of surfactant theory and ASP flooding mechanism.     

Surfactant-free oil/water and bicontinuous microemulsion composed of benzene, ethanol and water

<正>Generally,a microemulsion consists of oil,water,surfactant and sometimes cosurfactant.Herein,we report a novel suffactant-free microemulsion(denoted as SFME) composed of benzene,water and ethanol without the amphiphilic molecular structure of traditional surfactant.The phase behavior of the ternary system was investigated,finding that there were a single-phase region and a two-phase region in ternary phase diagram.The electrical conductivity measurement was employed to investigate the microregion of the single-phase region,and a bicontinuous microregion and a benzene-in-water(O/W) microemulsion microregion were identified,which was confirmed by freeze-fracture transmission electron microscopy(FF-TEM) observations.The sizes of the microemulsion droplets are in the range of 20-50 nm.     

Electronic and Optical Properties of KNbO3,NaNbO3 and K0.5 Na0.5 NbO3 in Paraelectric Cubic Phase：a Comparative First-principles Study

The structural,electronic and optical properties of KNbO 3 (KN),NaNbO3(NN)and K05 Na0.5NbO3(KNN) in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density functional theory (DFT).The calculated electronic structures of the three crystals show similar features in the valence bands and the lower conduction bands.However,the structures in higher conduction bands differ markedly due to the effect of Na and K atoms.The calculated optical properties reveal that the features of optical spectrum at low energy are dominated by the transitions from O2p valence bands to Nb 4d conduction bands and those at high energy are related to the transitions to K 4s4p and/or Na 3s3p states.Moreover,the optical constants of KNN are approximately the average of KN and NN at high energy.Therefore,the optical properties of KNN in high energy region can probably be altered by changing the ratio of Na/K.     

Morphology and Mechanical Properties of Nylon 6/PBT Blends Compatibilized with Styrene/Maleic Anhydride Copolymer

The mechanical properties and dynamic mechanical properties of blends composed of Nylon 6 and poly(butylenes terephthalate)(PBT),with styrene/maleic anhydride(SMA)as compatibilizer,were studied.The observation on the morphologies of the etched surfaces of the cryogenically fractured specimens via scanning electron microscopy(SEM)demonstrated that in the compatibilized Nylon 6/PBT blends,there exists a finer and more uniform dispersion induced by the in-situ interfacial chemical reactions during the preparation than that in the corresponding uncompatibilized blends.On the other hand,the overall mechanical properties of the compatibilized blends could be remarkably improved compared with those of the uncompatibilized ones.Moreover,increasing the amount of the compatibilizer SMA leads to a more efficient dispersion of the PBT phase in Nylon 6/PBT blends.Furthermore,there exists an optimum level of SMA added to achieve the maximum mechanical properties.As far as the mechanism of this reactive compatibilization is concerned,the enhanced interfacial adhesion is necessary to obtain improved dispersion,stable phase morphology,and better mechanical properties.     

由L-J流体的FMSA状态方程计算流体的PVT性质

运用Tang等提出的Lennard-Jones (L-J)流体两参数的一阶平均球形近似(FMSA)状态方程, 计算了流体的汽液共存相图和饱和蒸汽压曲线, 以及非饱和区的PVT性质, 并与文献数据进行比较. L-J参数由Tr＜0.95的汽液相共存数据回归得到. 计算结果表明, 对于分子较接近球形的流体, 除临界点附近外, 该方程可以在较大的温度和压力范围内计算真实流体的PVT性质, 结果满意. 对于球形分子, 该方程的精确度随分子尺寸的变大基本保持稳定. 该方程不适用于强极性物质. 在高密度区, 该方程的计算结果明显优于P-R方程. 对于分子偏离球形较远的流体, 该方程的适用性变差, 此时要考虑分子形状的影响, 可采用三参数的FMSA状态方程进行计算.     

受限于纳米狭缝中的四缔合Lennard-Lones流体的相平衡和界面张力研究

分别用改进的基础测量理论和平均球近似理论表达短程作用和长程作用对四缔合Lennard-Jones流体的过剩自由能的贡献. 在密度函泛理论的框架下, 研究了平均密度等温线, 密度分布, 未缔合分子在平衡汽相和液相中的分布, 相平衡以及平衡时的界面张力等热力学性质. 分析了缔合能量, 流体-固体作用和孔宽对受限于纳米狭缝中的四缔合Lennard-Jones流体相行为的影响.     

Prediction of global vapor-liquid equilibria for mixtures containing polar and associating components with improved renormalization group theory

Our recently improved renormalization group (RG) theory is further reformulated within the context of density functional theory. To improve the theory for polar and associating fluids, an explicit and complete expression of the theory is derived in which the density fluctuation is expanded up to the third-order term instead of the original second-order term. A new predictive equation of state based on the first-order mean spherical approximation statistical associating fluid theory (FMSA-SAFT) and the newly improved RG theory is proposed for systems containing polar and associating fluids. The calculated results for both pure fluids and mixtures are in good agreement with experimental data both inside and outside the critical region. This work demonstrates that the RG theory incorporated with the solution of FMSA is a promising route for accurately describing the global phase behavior of complex fluids and mixtures.     

First-order mean-spherical approximation for interfacial phenomena: a unified method from bulk-phase equilibria study

The recently proposed first-order mean-spherical approximation (FMSA) [Y. Tang, J. Chem. Phys. 121, 10605 (2004)] for inhomogeneous fluids is extended to the study of interfacial phenomena. Computation is performed for the Lennard-Jones fluid, in which all phase equilibria properties and direct correlation function for density-functional theory are developed consistently and systematically from FMSA. Three functional methods, including fundamental measure theory for the repulsive force, local-density approximation, and square-gradient approximation, are applied in this interfacial investigation. Comparisons with the latest computer simulation data indicate that FMSA is satisfactory in predicting surface tension, density profile, as well as relevant phase equilibria. Furthermore, this work strongly suggests that FMSA is very capable of unifying homogeneous and inhomogeneous fluids, as well as those behaviors outside and inside the critical region within one framework.     

Bulk and Interfacial Properties for CO2-SO2 Binary Mixtures

The perturbed‐chain statistical associating fluid theory (PC‐SAFT) and density‐gradient theory (DGT) were used to construct an equation of state (EOS) for the phase behaviors of carbon dioxide (CO₂)‐sulfur dioxide (SO₂) binary mixtures. The p‐x diagrams at 263 and 333 K, and the p‐T diagrams corresponding to x=0.8871 and 0.6213 were satisfactorily calculated as compared to the experimental data. With the influence parameters of pure components and the equilibrium bulk properties of mixtures as input, the interfacial properties of CO₂‐SO₂ binary mixtures in a wide temperature range were predicted, and the influences of temperature, pressure and bulk properties on the surface tension were discussed.     

用密度梯度理论研究缔合流体的汽液成核性质

在密度梯度展开的基础上,将影响参数k 表达成温度的函数,建立了一个适用于均相和非均相缔合流体的状态方程。应用流体的蒸汽压和液相密度实验数据关联分子参数。在密度梯度理论的框架下,计算了水,重水,甲醇,乙醇,正丙醇,正丁醇,正戊醇和正己醇的成核速率并与实验数据进行了对比,计算结果令人满意。结果表明,密度梯度理论与密度泛函理论一样,可研究液核的结构和性质,但通过调整影响参数k, 可获得更为准确的成核速率。     

Criticality of a liquid-vapor interface from an inhomogeneous integral equation theory

A microscopic theory is developed to study the liquid-vapor interfacial properties of simple fluids with ab initio treatment of the inhomogeneous two-body correlation functions, without any interpolation. It consists of the inhomogeneous Ornstein-Zernike equation coupled with the Duh-Henderson-Verlet closure and the Lovett-Mou-Buff-Wertheim equation. For the liquid-vapor interface of the Lennard-Jones fluid, we obtained the density profile and the surface tension, as well as their critical behaviour. In particular, we identified non-classical critical exponents. The theory accurately predicts the phase diagram and the interfacial properties in a very good agreement with simulations. We also showed that the method leads to true capillary-wave asymptotics in the macroscopic limit.     

An improved renormalization group theory for real fluids

On the basis of White's theory, an improved renormalization group (RG) theory is developed for chain bonding fluids inside the critical region. Outside the critical region, the statistical associating fluid theory based on the first-order mean sphere approximation [Fluid Phase Equilibria 171, 27 (2000)] is adopted and all the microscopic parameters are taken directly from its earlier application of real fluids. Inside the critical region, the RG transformation for long-range density fluctuation is derived in the k space, which illustrates explicitly the contributions from the mean-field term, the local density fluctuation, and the nonlocal density fluctuation. The RG theory is applied to describe physical behavior of ten n alkanes (C1-C10) both near to and far from the critical point. With no additional parameters for chain bonding fluids, good results are obtained for critical specific heat and phase coexistence curves and the resulting critical exponents are in good agreement with the reported nonclassic values.     

Evaluation of site-site bridge diagrams for molecular fluids

The presence of bridge functions in formally exact integral equation theories is the primary obstacle preventing the extraction of exact fluid structure from these theories. The bridge functions are typically neglected but in many fluids their impact may be significant. Each bridge function can be subdivided into bridge diagrams, which are well defined but difficult to evaluate. The calculation of bridge diagrams for the Chandler-Silbey-Ladanyi (CSL) integral equation theory is the subject of this paper. In particular, we evaluate the diagrams required to yield an exact theory up to the first power in density [O(rho(1))] and provide algorithms that remain feasible for any molecule. Further, the bridge diagrams are evaluated and compared with the f-bond and h-bond formulations. Exact bridge diagrams are numerically evaluated for several chiral molecules, for two polar dimers, and for SPC/E water. The quality of the diagrams is assessed in two ways: First, the predicted interatomic distributions are compared with those obtained from Monte Carlo simulations. Second, the connectivity constraints are evaluated and the errors in satisfying these exact relationships are compared for the f-bond and h-bond formulations. For apolar fluids, a clear improvement in CSL theory is evident with the inclusion of O(rho(0)) and O(rho(1)) diagrams. In contrast, for polar fluids, the inclusion of bridge diagrams does not lead to improvement in the structural predictions.