Effect of Insoluble Surfactants on Drainage and Rupture of a Film between Drops Interacting under a Constant Force

The deformation, drainage, and rupture of an axisymmetrical film between colliding drops in the presence of insoluble surfactants under the influence of van der Waals forces is studied numerically at small capillary and Reynolds numbers and small surfactant concentrations. Constant-force collisions of Newtonian drops in another Newtonian fluid are considered. The mathematical model is based on the lubrication equations in the gap between drops and the creeping flow approximation of Navier–Stokes equations in the drops, coupled with velocity and stress boundary conditions at the interfaces. A nonuniform surfactant concentration on the interfaces, governed by a convection–diffusion equation, leads to a gradient of the interfacial tension which in turn leads to additional tangential stress on the interfaces (Marangoni effects). The mathematical problem is solved by a finite-difference method on a nonuniform mesh at the interfaces and a boundary-integral method in the drops. The whole range of the dispersed to continuous-phase viscosity ratios is investigated for a range of values of the dimensionless surfactant concentration, Peclét number, and dimensionless Hamaker constant (covering both “nose” and “rim” rupture). In the limit of the large Peclét number and the small dimensionless Hamaker constant (characteristic of drops in the millimeter size range) a fair approximation to the results is provided by a simple expression for the critical surfactant concentration, drainage being virtually uninfluenced by the surfactant for concentrations below the critical surfactant concentration and corresponding to that for immobile interfaces for concentrations above it.     

The Dynamics of Marangoni-Driven Local Film Drainage between Two Drops

A study of Marangoni-driven local continuous film drainage between two drops induced by an initially nonuniform interfacial distribution of insoluble surfactant is reported. Using the lubrication approximation, a coupled system of fourth-order nonlinear partial differential equations was derived to describe the spatio-temporal evolution of the continuous film thickness and surfactant interfacial concentration. Numerical solutions of these governing equations were obtained using the Numerical Method of Lines with appropriate initial and boundary conditions. A full parametric study was undertaken to explore the effect of the viscosity ratio, background surfactant concentration, the surface Péclet number, and van der Waals interaction forces on the dynamics of the draining film for the case where surfactant is present in trace amounts. Marangoni stresses were found to cause large deformations in the liquid film: Thickening of the film at the surfactant leading edge was accompanied by rapid and severe thinning far upstream. Under certain conditions, this severe thinning leads directly to film rupture due to the influence of van der Waals forces. Time scales for rupture, promoted by Marangoni-driven local film drainage were compared with those associated with the dimpling effect, which accompanies the approach of two drops, and implications of the results of this study on drop coalescence are discussed. Copyright 2001 Academic Press.     

A Mechanistic Approach to Modeling Single Protein Adsorption at Solid-Water Interfaces

A kinetic model for single component protein adsorption which can be readily extended to adsorption from multi-protein solutions was developed, and used to simulate adsorption of site-directed, structural stability mutants of bacteriophage T4 lysozyme. The model allows for two different adsorbed "states," distinguished by different binding strengths and different occupied areas. The presence of an increasing energy barrier to adsorption was incorporated into the model by formulating the adsorption rate constants as functions of time. Numerical analysis was performed using the Marquardt method. Estimated model parameters were consistent with the effect of structural stability on adsorption. In particular, kinetic parameters were such that adsorption into the more tightly bound, conformationally altered state was favored by less stable variants. Copyright 1999 Academic Press.     

低介电多孔薄膜的制备及形成机制研究

摘要利用硅烷偶联剂KH-570(γ-甲基丙烯酰氧基甲氧基硅烷)水解缩合生成的多面低聚倍半硅氧烷(POSS)溶胶为模板剂, 经热解制备低介电多孔薄膜材料. 使用FTIR对材料制备过程及形成机制进行动态研究, 通过 ²⁹Si NMR、 椭偏仪、 氮气吸脱附曲线和TEM等对材料的介电性质、 孔洞大小和分布情况进行表征. 制备的介电多孔薄膜材料孔洞分布均匀、 孔径约1 nm, 比表面积为384.1 m²/g, 介电常数为2.5的低.     

Shock‐Tube Experiments and Kinetic Modeling of CH3NHCH3 Ignition at Elevated Pressures

Ignition delay times of CH₃NHCH₃/O₂/Ar mixtures are measured with a shock tube in the temperature range of 1040–1604 K. Different pressures (4, 8, and 18 atm) and equivalence ratios (0.5, 1, and 2) are investigated. A recently developed CH₃NHCH₃ kinetic model is examined, and then modified by adding the hydrogen abstractions from CH₃NHCH₃ by HO₂ and NO₂. The rate constants of the hydrogen abstraction by HO₂ are estimated by analogy to the CH₃OH + HO₂ system, and those of the hydrogen abstraction by NO₂ by analogy to the CH₃NH₂ + HO₂ system. The modified model is well validated against the present measurements. Based on this model, sensitivity analysis and reaction pathway analysis are performed to provide insight into the chemical kinetics of CH₃NHCH₃ ignition. CH₃NHCH₃ is mainly consumed by hydrogen abstractions at low temperatures, and its unimolecular decomposition becomes important at higher temperatures.     

Film drainage between two surfactant-coated drops colliding at constant approach velocity

The drainage of the intervening continuous phase film between two drops approaching each other at constant velocity under the influence of insoluble surfactant is investigated. The mathematical model to be solved is a coupled pair of fourth-order nonlinear partial differential equations which arise from the relationships governing the evolution of the film thickness and the surfactant interfacial concentration in the lubrication approximation. We adopt a simplified approach which uses lubrication theory to describe the flow within the drop, marking a departure from the conventional framework in which Stokes flow is assumed. When the model is solved numerically together with the relevant initial and boundary conditions, the results obtained are compared with those found in the literature using the "boundary integral" method to solve for the flow in the drop phase. The close agreement between the results inspires confidence in the predictions of the simplified approach adopted. The analysis on the effect of insoluble surfactant indicates that its presence retards the drainage of the film: The fully immobile interface limit is recovered even in the presence of a small amount of surfactant above a critical concentration; film rupture is either prolonged or prevented. The retardation of the film was attributed to gradients of interfacial tension which gave rise to the Marangoni effect. A study of the influence of various system parameters on the drainage dynamics was conducted and three regimes of drainage and possible rupture were identified depending on the relative magnitudes of the drop approach velocity and the van der Waals interaction force: Nose rupture, rim rupture, and film immobilization and flattening. Finally, the possibility of forming secondary droplets by encapsulating the continuous phase film into the coalesced drop at rupture was examined and quantified in light of these regimes.     

用分子模拟方法研究HIV-1整合酶与咖啡酰基类抑制剂的相互作用

用分子对接和分子动力学(MD)模拟方法研究了一类咖啡酰基和没食子酰基类HIV-1整合酶抑制剂与整合酶之间的相互作用模式, 结果表明该类抑制剂分子上的两个侧链基团(咖啡酰基或没食子酰基)与整合酶的DDE基序之间的相互作用对抑制整合酶活性起到关键作用. 当侧链基团为没食子酰基时, 可以提高该类抑制剂与整合酶的结合能力. 采用线性相互作用能方法(LIE)计算了该类抑制剂与整合酶之间的结合自由能, 预测值与实验值相吻合, 均方根偏差RMSD为1.39 kJ•mol^-1, 以上结果可为基于结构的HIV-1整合酶抑制剂设计提供有用的信息.     

Mathematical Modeling of Drug Release from Microemulsions: Theory in Comparison with Experiments

The topic of this paper is the study of the drug release from a drug-loaded microemulsion by reverting to a new mathematical model overcoming some drawbacks of previously proposed models. In particular, attention is focused on the mathematical expression of the drug fluxes existing between the oil and water phases during drug release. Indeed, not only the drug release kinetics, but also the drug oil-water partition coefficient strongly depend on these fluxes. Two microemulsion are considered: the first is composed by water, Tween80 as surfactant, and Triacetin as oil phase, while the second is composed by water, Tween80 as surfactant, and a Triacetin-benzylic alcohol mixture (1 : 1) as oil phase. Both of them are loaded by Nimesulide, an oil-soluble drug of considerable industrial relevance. The drug release is performed by resorting to a permeation experiment (Franz cells apparatus) as it demonstrated to be the most reliable methodology. The good agreement between the experimental permeation data and the model best-fitting ensures that the most important phenomena ruling this kind of drug release were properly accounted for by the new proposed model. Copyright 2000 Academic Press.     

纳米孔金膜电极：合金化/去合金化法制备及电化学性能

采用合金化/去合金化法在金电极表面制备出一层具有纳米孔结构的金膜，其孔径约为15 nm。该方法首先在金电极表面电沉积一层锌，再通过热处理形成合金层，最后利用化学去合金化法去除合金中的锌。X射线衍射(XRD)结果表明在合金化过程中，锌扩散进入金基体并形成了金-锌合金层。利用场发射扫描电子显微镜(FESEM)对去合金化得到的纳米孔金膜进行了形貌的表征，结果表明合金化条件对样品的纳米结构有明显的影响。电化学测试结果表明，经合金化/去合金化处理的金电极，其表面粗糙度有明显的提高。这种金电极对甲醇具有较高的催化氧化活性，在0.3 mol·L^-1甲醇的KOH溶液中，甲醇的氧化峰电流密度高达2.02 mA·cm^-2。     

低介电常数聚喹啉衍生物薄膜的合成与表征

采用等离子体聚合技术合成了一种新型的低介电常数聚喹啉衍生物薄膜: 聚3-氰基喹啉(PP3QCN)薄膜. 借助于傅里叶变换红外光谱(FT-IR)、紫外-可见(UV-Vis)吸收光谱、X光电子能谱(XPS)和原子力显微镜(AFM)对薄膜结构进行了系统表征. 结果表明, 等离子体聚合条件对沉积膜的化学结构、表面组成、膜形态以及介电性能均有影响. 在较低的等离子体放电功率(10 W)条件下, 可得到具有较高芳环保留率和较大π-共轭体系的高质量聚3-氰基喹啉薄膜材料; 而在较高功率(25 W)条件下, 聚合过程中会出现比较严重的单体分子破碎, 形成较多非π-共轭体系的聚合物, 从而导致聚3-氰基喹啉的共轭度降低. 聚3-氰基喹啉薄膜的介电性能测试结果表明, 低放电功率(10 W)条件下制得的聚3-氰基喹啉薄膜具有比较低的介电常数值, 仅为2.45.     

物理化学与中学化学实验

“物理化学”是高师化学教育专业的一门重要的基础理论课程,它在培养合格的中学化学师资,提高中学化学教育质量,促进中学化学教学改革中起着重要作用。因此,面向中学实际,就成为高师物理化学教学改革的一个重要方面。     

Equilibrium Constant Studies for Complexation between Ammonium Ions and 18-Crown-6 in Aqueous Solutions at 298.15 K

Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing a fixed concentration of 18-crown-6 (0.2 mol⋅kg⁻¹) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to 0.5 mol⋅kg⁻¹. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant (K) for the 18-crown-6:NH₄ ⁺ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting stability to the complexed species. The log₁₀ K values for the 18-crown-6:NH₄ ⁺ complexed species are lower than for the complexes involving alkali metal ions such as K⁺. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions.     

A Film Model of Sound Propagation in Gas–Liquid Foams: 1. The Sound Velocity

A new (film) model is proposed for the propagation of sound vibrations in gas–liquid foams. The model explains the effect of sound retardation in foams and qualitatively agrees with the experimental data on the velocity of sound propagation in foams of various structures.     

Determination of Bulk and Surface Diffusion Coefficients from Experimental Data for Thin Liquid Film Drainage

This note presents a method for the determination of the surface diffusion coefficient and surface diffusion flux. The theoretical considerations are based on the Onsager linear theory for the definition of the surface diffusion flux and on the Einstein theorem for the definition of the surface diffusion parameter. In this interpretation the surface diffusion coefficient differs from the one commonly defined in the literature. It does not depend on the surfactant concentration and it is a function only of the type of surfactant and the liquid/liquid interface. The theoretical calculations indicate that the effect of the surface diffusion on the film drainage is stronger than that predicted by previous theoretical studies. The experimental data for thin liquid film drainage in the case of low surfactant concentration in the continuous phase could be used for the calculation of the bulk and surface diffusion coefficients. In the present study we utilized the experimental data for the drainage of nitrobenzene films stabilized by different concentrations of dodecanol. Copyright 2000 Academic Press.     

恒温恒压下勒夏特列原理的应用

探讨了恒温恒压条件下浓度对化学平衡的影响,归纳出勒夏特列原理的应用规律。     

Mathematical Modeling of PVC Suspension Polymerization: A Unifying Approach and Some new Results

The aim of the present investigation is the development of a unifying framework for modeling free-radical suspension and bulk vinyl chloride polymerizations. A fairly comprehensive but realistic model is described that has the ability to predict the rate of polymerization as well as the molecular properties of polymer as a function of the process conditions. It is shown that no significant differences exist between the predictions of the present model and those obtained by various well-known two-phase PVC models published before. in addition to the prediction of fractional monomer conversion and rate of polymerization, the new model predicts the anomalous structures observed in commercial PVC, namely, the number of short- and long-chain branches as well as the number of unsaturated terminal double bonds per polymer molecule. Simulation results show that the present model provides realistic predictions of the important molecular properties in agreement with experimental observations reported in the literature. Finally, the validity of the quasi-steady-state approximation for growing macroradicals is tested by comparing conversion and molecular weight results obtained with or without its application.     

Amyloid-Like Assembly to Form Film at Interfaces: Structural Transformation and Application

Protein-based biomaterials are attracting broad interest for their remarkable structural and functional properties. Disturbing the native protein's three-dimensional structural stability in vitro and controlling subsequent aggregation is an effective strategy to design and construct protein-based biomaterials. One of the recent developments in regulating protein structural transformation to ordered aggregation is amyloid assembly, which generates fibril-based 1D to 3D nanostructures as functional materials. Especially, the amyloid-like assembly to form films at interfaces has been reported, which is induced by the effective reduction of the intramolecular disulfide bond. The main contribution of this amyloid-like assembly is the large-scale formation of protein films at interfaces and excellent adhesion to target substrates. This review presents the research progress of the amyloid-like assembly to form films and related applications and thereby provides a guide to exploiting protein-based biomaterials.