非氢键型的弱相互作用的可视化

文章以二苯甲酮2个同分异构体为研究例子,采用AIM理论(Atoms in molecules)来描述分子中的非成键部分,使用GAUSSIAN等量子化学程序实现对弱相互作用的可视化,从而获得该相互作用的直接证据,以揭示弱相互作用对化合物性能的影响。     

分子体积对丙烯酸酯单体在PMMA中扩散系数的影响

根据Vrenta Duda自由体积扩散理论的推论 ,说明分子体积对扩散系数有指数性的影响关系 ;利用实验数据验证了该推论 ,得到了分子体积对扩散系数影响的简化模型为lgD2 =ξ2 1lgD1+2 331。这对研究梯度型聚合物光纤折射率梯度形成具有较重要的理论意义     

分子印迹的印迹效率及其评价

随着超分子化学、材料科学和生物医学等学科的发展,分子印迹技术在理论及应用研究方面得到了广泛的关注。在总结大量文献的基础上,提出了印迹效率的概念,讨论了影响分子印迹效率的几个影响因素,初步探讨了印迹效率的评价方法及测定手段。简要介绍了分子印迹发展的两个新方向:分子印迹膜和单分子印迹,指出了提高印迹效率是实现分子印迹技术工业化的重要前提。     

分子印迹聚合物在催化反应中的研究进展

分子印迹技术是将某一特定的目标分子作为模板,运用"锁钥"理论,制备出对该目标分子具有特异选择性聚合物的技术。分子印迹技术应用在诸多领域,如色谱分离、固相萃取、仿生传感等。近年来,分子印迹技术在催化领域的研究取得了重要的进展,本文重点介绍了印迹分子用作催化剂在有机反应中的应用,并对分子印迹聚合物在有机合成的发展方向上进行了展望。     

沥青质分子缔合作用机制、表征、理论计算与应用研究进展

石油中沥青质分子的缔合聚集现象对于石油（尤其是重质油或致密油藏等非常规石油）的开采、储运、加工等具有重要影响，直接决定了原油的体相和界面性质，是矿物或管道器壁表面石油组分吸附沉积、油水（固）乳化、原油高黏等现象的主要成因。系统地综述了沥青质分子间缔合现象及理论发展，从分子间非共价相互作用角度探究了沥青质分子缔合聚集的作用机制，阐述了静电与色散作用主导的非共价相互作用对于沥青质缔合聚集的决定性影响规律。在此基础上，总结了近年来分子模拟等理论计算与界面表征技术在沥青质界面现象研究中的应用现状与发展方向。最后，基于沥青质分子缔合现象与理论，探讨了其在固体表面吸脱附、沉积、分散、破乳技术开发、降黏技术开发等领域的应用与思考。     

价键法融合分子轨道理论及轨道杂化概念对O_3分子结构和性质的阐释

物质性构相依是化学的重要学科思想。根据现代价键理论,并融合轨道杂化的概念及分子轨道理论的处理方法,分析讨论了O_3的分子结构,阐释了该分子各键参数的特点及分子理化性质的内在原因。     

影响共价键键角大小的因素

键角是描述分子立体结构的重要参数,键角也是描述共价键的重要参数[1]。分子的许多性质都与键角有关;键角的大小严重影响分子的许多性质,例如分子的极性,从而影响其溶解性,熔沸点等[2]。影响共价键键角大小的因素是多方面的。针对高中阶段共价键键角大小比较过程中常用的方法,本文结合VSEPR理论从价层电子对数、孤电子对、重键效应、电负性,成键环境五个方面讨论影响键角大小的因素。掌握这些方法,有利于对键角的大小作出正确判断并熟悉VSEPR理论的应用。     

密度泛函理论在高电压电解液设计中的应用

基于密度泛函理论的量子化学计算为高电压电解液的配方设计提供了理论基础。运用Gaussian软件可以有效模拟电解液中某一成分的分子构型和溶剂化状态,计算出化合物的分解路径与分解产物,进而大幅缩短电解液研发周期。本文回顾了近年来该计算方法在锂离子电池电解液研究中的相关进展,并以高电压电解液为例,介绍了该理论在溶剂氧化电位计算方面的应用,结合分子模型的优化,实现了计算值与实验值的基本统一。此外,详细阐述了砜类、氟类、离子液体等几种新型高电压溶剂和磷酸酯类、硼类、腈类等几种成膜添加剂的应用。相信今后随着动力学理论的完善和计算机技术的优化,该方法在高浓度电解液、固液界面作用机理等当前难以实现的理论模拟问题方面的应用指日可待。     

高效毛细管电泳分离机理的研究

应用色谱分离理论,综合考虑了分子扩散、进样量、电能消耗、电泳迁移等因素对高效毛细管电泳分离的影响,建立了高效毛细管电泳分离机理模型.以色氨酸为示踪样品进行实验,研究了电压、溶液浓度、进样量、毛细管管径等因素对理论板高度的影响,并与模型计算结果进行了比较.结果表明,本文所提出的模型能够较好地描述高效毛细管电泳的分离机理,该模型可作为优化操作参数和进行放大设计研究的基础.     

π-桥中引入噻吩对D—A型染料敏化剂光电性质的影响

基于D-π-A型染料ND,在π-桥中引入噻吩基团以增长分子共轭链,设计出ND2T和ND4T两个染料分子。通过密度泛函理论研究噻吩基团引入到染料分子π-桥中对染料本身光电性质的影响。计算结果表明,引入噻吩基团可以缩短染料分子HOMO与LUMO之间的能隙。重要的是,π-桥中引入并噻吩基团形成的ND4T分子表现出最大红移和最强的光谱吸收,这将有利于提高该染料分子运用在染料敏化太阳能电池中的光伏性能。     

葡萄糖水溶液扩散系数的测定与关联

液相扩散系数在化工数据中起着非常重要的作用,由于液体结构及扩散本身的复杂性,至今还没有一个合理的理论模型来预测液相扩散系数,有必要从实验和理论上对不同的体系进行研究.制备了金属膜池,用氯化钾溶液标定了膜池常数,并用已有可靠文献值的蔗糖水溶液验证了装置的可靠性.测定了298.15～328.15 K不同温度下葡萄糖水溶液的积分扩散系数,考察了温度对扩散系数的影响.在实验数据的基础上,提出一个有温度关联项的半经验模型,关联和计算了本实验的数据,结果与实验值吻合很好.     

3种芳香烃在聚乙烯膜中的无限稀释扩散系数

基于Hadj-Romdhane和Danner色谱过程的数学模型 ,采用反相气相色谱法在 348.2～ 36 3.2K温度范围内测定了苯、甲苯和乙苯 3种芳香烃溶剂在聚乙烯膜中的无限稀释扩散系数 .实测数据的关联结果表明 ,采用空穴自由体积替代Vrentas-Duda自由体积理论方程中自由体积项的修正方程 ,能很好地描述溶剂分子的无限稀释扩散系数随温度的变化关系 .同时在修正方程的基础上建立了一般化自由体积方程 ,并对该方程的预测能力进行了探讨     

Molecular transport of esters,aldehydes, aromatic liquids,and a ketone into fluoroelastomer membrane at 30, 40, and 50°C

Molecular transport of esters, aldehydes, substituted aromatic liquids, and a ketone through a fluoroelastomer (FC‐2120) membrane sample was studied at 30, 40, and 50°C. Sorption results were obtained by using a gravimetric method and concentration‐independent diffusion coefficients were calculated using Fick's diffusion equation. Permeability coefficients were calculated from sorption and diffusion data. Concentration profiles of the liquid penetrants were calculated by solving the Fick's equation under appropriate initial and boundary conditions and these plots are displayed to show the variations in liquid concentrations with reference to the nature of liquids chosen, membrane thickness, as well as the time of polymer immersion in the liquids. Arrhenius activation parameters were also estimated from a temperature dependence of diffusion and sorption coefficients. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 840–847, 2003     

Studies on molecular transport of n‐alkanes through poly(tetrafluoroethylene‐co‐propylene) elastomeric membrane

Molecular transport of a series of n‐alkanes through commercial TFE elastomer (FA 150L) has been studied in the temperature range 30–50 °C using sorption‐gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes and temperature. The diffusion coefficients at 30°C varied from 4.53 × 10^?8 cm²/s (n‐heptane) to 0.18 × 10^?8 cm²/s (n‐hexadecane). The liquid concentration profiles have also been computed using analytical solution of Fick's equation with the appropriate initial and boundary conditions and these were presented as a function of penetration depth of molecular migration and time of immersion. These results have been discussed in terms of molecular size of alkanes as well as temperature. In all the liquid penetrants, the transport phenomenon was found to follow the anomalous behavior. From the temperature dependence of diffusion and permeation coefficients, the Arrhenius activation parameters have been estimated. These parameters do not exhibit any systematic variation with the size of the penetrants. The resulting low diffusion coefficients, contribute to the superior barrier performance of the membrane, is due, in part, to the high glass transition temperature of Aflas? TFE elastomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2228–2235, 2006     

Study on the Diffusion Coefficient of Sodium Chloride at Infinite Dilution in Supercritical Water

The molecular dynamics (MD) was employed to simulate the diffusion coefficient of sodium chloride at infinite dilution in supercritical water from 703.2 K to 763.2 K and from 30 MPa to 45 MPa. Based on the simulated data and the Patel-Teja(PT) equation of state and the Liu-Ruckenstein equation, an equation for calculating the diffusion coefficient of NaCl at infinite dilution in supercritical water is proposed. Both the agreement between the simulated and correlated data, and that between the simulated and predicted data of diffusion coefficients for NaCl in supercritical water ranging from 703.2K to 803.2 K and from 25 MPa to 50 MPa show that this equation is applicable for the calculation of diffusion coefficients.     

Determination of the infinite dilution diffusion and activity coefficients of alkanes in polypropylene by inverse gas chromatography

Infinite dilution diffusion and activity coefficients of n‐hexane, n‐heptane, and n‐decane in polypropylene were measured from 373.15 to 393.15 K by inverse gas chromatography. The influences of small molecule solvent and temperature on the infinite dilution diffusion and activity coefficients were investigated. The results showed that the infinite dilution diffusion coefficient decreased but the infinite dilution activity coefficient increased with an increasing number of CH₂ group in the aliphatic solvents. The temperature increase resulted in the increase in the infinite dilution diffusion coefficient and the decrease in the infinite dilution activity coefficient. The graphs plotted according to the results of the infinite dilution diffusion coefficient versus temperature were in agreement with the Arrhenius equation. Diffusion constant and activation energy were obtained from the Arrhenius equation. Also, the interdependence on the infinite dilute activity coefficient and temperature accorded with Gibbs‐Helmholtz equation. From the temperature dependence of the limiting activity coefficients partial molar excess enthalpy at infinite dilution H^E,∞ was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1925–1930, 2006     

异戊二烯在聚苯乙烯高分子膜中的扩散系数测定

为了探讨在反应挤出过程中异戊二烯在聚苯乙烯中的扩散传递机理,采用石英弹簧法测定了298.15K、308.15K和318.15K下异戊二烯在聚苯乙烯膜中的吸收动力学曲线。探讨了温度、压力、分子量对扩散吸收的影响,并对实验结果进行了关联。结果表明异戊二烯在聚苯乙烯膜中的扩散吸收呈S型吸收,由吸收曲线获得了平均扩散系数和平衡溶解度。     

局部组成型的互扩散系数模型

根据局部组成概念建立了混合物中互扩散系数与自扩系数的关系,并以分子集团迁移的概念建立了混合物中组分的自扩散系数的预测方法,由此预测二元系的自扩散系数和互扩散系数与实验结果符合良好,比经典的Ｈａｒｔｌｅｙ模型有了很大地改进。     

MODELING OF ROUGH RICE DRYING IN THIN VERTICAL COLUMNS

ABSTRACT

The solution of classical diffusion equation based on the assumption of average moisture diffusion coefficient did not adequately represent natural convection drying of rough rice in thin vertical columns exposed on both sides to hot air. Instantaneous moisture diffusivity coefficients determined from experimental drying curves decreased continuously with an increase in exposure duration and were linearly related to moisture ratio. The proponionality constant which was called apparent moisture diffusion coefficient was distinctly related to air temperature, relative humidity, and initial moisture content of rough rice. The modified moisture diffusion model using the instantaneous moisture diffusion coefficient was found to best represent the moisture removal from bulk rough rice.     

TWO-STAGE MOISTURE DIFFUSION IN WOOD WITH CONSTANT TRANSPORT COEFFICIENTS

To determine whether transport coefficients in desorption curves for northern red oak are constant, four sets of desorption data were compared against previously established mathematical conditions for infinite-series solution of the non-steady-state diffusion equation. For each data set, when moisture fraction in wood is above a certain value, designated as the first stage, these conditions are satisfied, with the diffusion and surface emission coefficients being positive and finite; below that value, designated as the second stage, these conditions are still satisfied, with the diffusion coefficient taking a smaller positive value but the surface emission coefficient becoming negative and finite. Mathematically, these two pairs of transport coefficients can be used to predict the whole diffusion curve that describes the variation of moisture fraction with time. However, the negative surface emission coefficient in the second stage of the desorption process implies that the moisture gradient has cut the surface at a point below the equilibrium moisture content, which is physically impossible. Alternatively, the second stage can be considered as a new stage with moisture fraction values normalized with respect to the lowest value in the first stage, which is also the starting point of the second stage. The transport coefficents are obtained in the same manner as in the first stage and are found to be positive and finite. The two pairs of transport coefficients can describe the diffusion curve with high accuracy. However, the assumption used in the second stage is that the initial moisture content in wood is uniform, which again is physically impossible. We therefore conclude that the transport coefficients for northern red oak are not constant. Although the two-stage approaches presented in this study can predict the diffusion curves accurately, their physical interaction is difficult to justify.