Determination of the Thermal Resistance of the Polymer–Ceramic Interface of Alumina-Filled Polymer Composites

To model the thermal conductivity of polymer composites that are filled with ceramic powders, the conductivity of each component as well as the interfacial resistance at each ceramic–polymer boundary must be known. An indirect method to determine this interfacial boundary resistance is proposed by preparing large-scale "macromodel" simulations of the polymer–ceramic interface. Macromodels, prepared by spin-coating a polymer layer onto sapphire wafers, were formed in a sapphire–polymer–sapphire sandwich type structure. The interfacial boundary thermal resistance was calculated from thermal resistance measurements made on the macromodels.     

A mass transfer model for the extraction of weak acids/based in emulsion liquid-membrane systems

A mathematical model for analysing the extraction of weak acids and weak bases from aqueous solution by liquid surfactant membrane has been presented. The model assumes that the reactions are reversible and the reaction equilibrium to exist in both the internal phase and the external continuous phase. The scheme for mass transfer analysis is based on an immobilized emulsion globule drop model and the classical film theory, i.e. the overall mass transfer resistance includes that due to the external turbulent boundary layer, the interfacial surfactant layer and the diffusion layer within the emulsion globule. The leakage effect of internal phase due to membrane rupture is also discussed in the mathematical treatment. The proposed model predicts satisfactorily the experimental results of the extraction of weak acids as well as weak bases in a batch separation system as presented in the literature.     

Interfacial Segregation in Perovskites: IV, Internal Boundary Layer Devices

A proposed model for interfacial segregation in perovskites, with induced heterogeneous defect distributions, is extended here to account for the formation of internal boundary layer devices, such as positive temperature coefficient of resistance (PTCR) thermistors and internal boundary layer capacitors (IBLC). Boundary layer effects in doped BaTiO₃ are attributed to factors which contribute to the formation of highly resistive boundary layers by a segregation-induced shift in donor incorporation and/or acceptor segregation, and the inhibiting action of segregated donors on boundary mobility and grain growth. The distribution of space charges, formed by electron transfer from conductive grains to resistive boundary layers, leads to the formation of impedance barriers in the grain-boundary vicinity. Depending on the grain size, and on relative size and spatial distribution of the space charge layer and the resistive layer, a transition from semiconducting properties to insulating properties may take place. This model accounts for the observed PTCR and IBLC phenomena.     

CaZrO_3耐火材料的制备及其与钛合金熔体的界面反应

合成了一种CaO-ZrO_2系复合耐火材料,用模压法成型,分别在1 650℃和1 680℃烧结制成坩埚.使用此坩埚在感应炉中熔化钛合金(TiNi),在真空条件下, 1 500℃保温5min.对在1 680℃烧结成的坩埚进行了抗水化性能测试.用X射线衍射仪对CaZrO_3材料进行物相分析.用扫描电子显微镜观察钛合金与此材料的界面反应层的微观形貌,结合能谱仪进行微区成分分析.结果显示:1 680℃烧成的CaZrO_3材料具有良好的抗水化性;用此坩埚熔化TiNi合金后,液态钛合金和耐火材料的界面反应层厚度约为30μm,界面反应层中,Ca,Zr,Ti,Ni等元素无明显扩散.     

Mechanistic study of cobalt,nickel and copper transfer across a supported liquid membrane

The mechanism of cobalt, copper and nickel transport through supported liquid membranes containing di(2-ethylhexyl)phosphoric acid as a mobile carrier has been studied. An equation describing the permeation rate has been derived, taking into account stagnant layer aqueous diffusion, interfacial resistance due to solvatation reaction and liquid membrane diffusion as simultaneous controlling factors. The validity of this model is evaluated with experimental data of mass transfer coefficient measured employing a permeation cell. For these ions it was found that at low stirring conditions the stagnant layer resistance mainly controlled the processes, but it is controlled by diffusion of the ion complex through the supported liquid membrane when the stagnant layer resistance is negligible.     

A qualitative investigation on the importance of boundary layer in pervaporation separation of an aqueous organic reaction

The importance of boundary layer was investigated for the hydrolysis of ethyl acetate using a dense standard poly(vinyl alcohol) (PVA) membrane. A resistance in a series model approach was used to study the effect of a boundary layer for the permeation of aqueous organic mixtures involved in the study. The initial feed mixture consisted of 10% water (H₂O), 40% ethyl acetate (EA), 50% acetic acid (AA), and 0% ethanol (E) (all weight percentage basis). The experiments were conducted at 65°C. The amount of all species in the feed reservoir was found to decrease with time. Selectivity calculations based on a resistance in the series model approach indicates that the boundary layer contributes to selective permeation of aqueous organic compounds. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2361–2369, 1998     

Effects of kinetic and transport parameters on accelerated migration of reactive additive from plastic sheet

The effects of kinetic parameters Hatta number Ha and ?, and transport parameters Biot number Bi and ψ on the migration of a reactive additive have been modeled. The convective boundary layer can be considered inert to fully reactive for Ha → 0 to 2, respectively. The migration is controlled by diffusion, reaction rate, equilibrium partitioning of the migrant between the plastic film and the solvent, and boundary layer resistance, depending on the time scale and values of the above parameters. For a nonreactive boundary layer, at high Bi, migration is initially diffusion-controlled but becomes reaction-rate controlled at later times. However, under similar conditions, a slight increase in the reactivity of the boundary layer immediately changes the transport process from diffusion-controlled to reaction rate-controlled. With further increase in reactivity, migration spontaneously reaches equilibrium. At low Bi, equilibrium partitioning and reactive depletion of the migrant in the fluid phase change predominantly to boundary layer-controlling mass transport phenomenon. For a given sampling time (τ = 1.0), the migration increases with the increase in Bi only for a reactive boundary layer. At low Bi and (τ = 1.0), migration decreases only up to ? ? 0.3 for nonreactive to partially reactive boundary layer, but for intermediate and high Bi, ? and Ha do not influence migration.     

Effect of surface resistance on gas absorption accompanied by a chemical reaction in a gas—liquid contactor

An analysis of gas absorption accompanied by chemical reaction in the presence of interfacial resistance is presented. The analysis indicates that the effect of interfacial resistance on interphase mass transfer is significantly higher in presence of a reaction compared to the pure absorption case. For fixed values of surface resistance and contact time, the difference between the amount of gas transferred across the interface with and without surface resistance increases as the value of reaction velocity increases. For ranges of contact time and surface resistance of practical relevance, the influence of surface resistance is too high to be neglected while designing gas-liquid contactors.     

水中脱除VOC渗透汽化传质模型的研究

推导并回归了水中脱除VOC的PDMS/PS复合膜渗透汽化申连传质阻力模型。以苯的水溶液为实验物系,实验结果表明,料液浓度与苯的渗透通量之间存在线性关系,由此可确定模型总传质系数。研究雷诺数、活性层厚度和基膜结构对渗透通量的影响,可回归得到模型中边界层传质阻力、活性层传质阻力和基膜传质阻力计算公式。由下游压力与渗透通量的对应关系的实验数据,回归得到亨利常数;模型其它相关参数由温度对通量的影响数据进行回归。模型预测值和实测值吻合良好。     

有氧补偿乳状液中多不饱和脂肪酸氧化模型

研究了恒表面氧压搅拌式有氧补偿条件下乳状液中多不饱和脂肪酸(PUFA)的氧化。通过综合考虑气液边界传质阻力、油水边界乳化剂形成的液膜边界层阻力、PUFA自催化氧化反应动力学,建立了相应的扩散-氧化数学模型。实验验证该模型能较好地拟合搅拌式有氧补偿条件下乳状液中氧的扩散和亚油酸的氧化过程,并在乳化剂浓度变化对乳状液中PUFA氧化的影响方面表现出很好的适用性。研究对揭示乳状液中PUFA的氧化机制最终有效控制PUFA的氧化具有重要的理论研究价值。     

搅拌式有限氧补偿条件下乳状液中多不饱和脂肪酸氧化模型

The oxidation of polyunsaturated fatty acids （PUFA） in emulsion with stirring and limited oxygen compensation was studied. A mathematical model of diffusion-oxidation was developed considering the mass transfer resistance of a gas-liquid boundary, the resistance of the boundary layer from the emulsifier membrane, and the autocatalytic-type autoxidation reaction of PUFA. The dynamic mass transfer coefficient of the emulsifier membrane, k0, was introduced. The model was verified by comparing the predictions of the model with the experi- mental data. The results indicated that the model was in good agreement with the oxygen diffusion and linoleic acid oxidation in the emulsion, and showed good applicability in the prediction of the effect of the emulsifier type on the oxidation of PUFA in the emulsion. It indicated that the oxidation of PUFA in emulsions, with stirring and limited oxygen compensation from the atmosphere, was controlled mostly by mass transfer resistance from the emulsifier membrane.     

Unveiling the Effects of In Situ Layer–Layer Interfacial Reaction in Multilayer Polymer Films via Multilayered Assembly: From Microlayers to Nanolayers

Multilayered polymer films are increasingly used in the daily life, but their macroscopic properties are always limited by the layer–layer interfacial compatibility. In this work, the influence of interface modification through in situ layer–layer interfacial reaction during a multilayered assembly is revealed from micro‐ to nanolayer films, based on maleated poly(vinylidene fluoride) and polyamide‐6. In the presence of interfacial reaction and confinement, layer architecture and microstructure are highly dependent on the number of layers. Specifically, for nanolayer films having smaller layer thicknesses and higher reaction extent, layer integrity is reduced with the occurrence of interfacial instabilities. Depending on the microstructural evolution from multilayer assembly, those films exhibit quantitatively different extensional rheological and dielectric properties from micro‐ to nanolayers. More importantly, dielectric spectroscopy reveals the contribution of copolymer‐rich interphases to the dielectric performance of micro/nanolayered films. Additionally, charge transport dynamics in nanolayered films also differ significantly from their microlayered counterparts. They are attributed to the strong dependence of interfacial reaction extent and resulting microstructure on the number of layers and layer thicknesses. This work clearly illustrates how the control of layer–layer interfacial reaction in micro/nanolayer assembly can tune the interfacial, microstructure, and macroscopic properties of multilayered products.     

亚油酸乳状液体系氧化模型与求解

研究了恒表面氧压静置式无限氧补偿条件下乳状液中亚油酸的氧化,通过综合考虑气液边界传质阻力、水相扩散、油水边界乳化剂膜边界层阻力、多不饱和脂肪酸(PUFA)自催化氧化反应动力学,建立了扩散-氧化数学模型。采用非对称正交配置法处理特殊边界,求解偏微分方程组,计算了氧化过程中乳状液中氧和亚油酸在垂直于液膜方向的浓度分布,计算方法快捷、有效;结合数学模拟试验和实验值,确定了气液界面氧的液膜传质系数和水相中氧的扩散系数。实验验证该模型能较好地拟合静置式无限氧补偿条件下乳状液中氧的扩散和亚油酸的氧化过程。     

An analytic solution to the transient diffusion-reaction problem in particles dispersed in a slurry reactor

In this work, we present the solution of the equations that govern the reactant transport in a well mixed system that contains particles where diffusion and first-order reaction occur. The transport equations are coupled by an interfacial boundary condition that includes mass transfer resistance. The statement of the problem allows arbitrary time depending feed functions. The evaluation of the solution obtained by the Laplace method requires the solution of an eigenvalue problem. We discuss the evaluation of the solution, and typical results for three different feed functions: step, pulse and oscillatory functions are presented. The resulting equations are able to show the effect of internal and external mass transfer limitations on the particle and fluid concentrations and on kinetic experimental results.     

硫酸脲分解磷矿反应机理探讨

以硫酸脲分解磷矿是一种新的N、P复肥生产方法,硫酸脲分解磷矿有其特殊的反应机理。利用在线显微摄像与物化分析相结合,可以很好地表征硫酸脲分解磷矿的反应机理。实验表明:硫酸脲与磷矿在液固接触的界面微区进行反应,反应微区内有离解、反应、结晶、复合等过程,并伴随有晶型转变。反应生成的硫酸钙晶体复盖反应粒子表面,形成包裹层增大传质阻力。反应物质通过CaSO40.5H2O晶膜的传递阻力是影响整个反应过程的重要因素。     

On the local conductivity of individual diamond seeds and their impact on the interfacial resistance of boron-doped diamond films

In many electroanalytical and bio-electrochemical applications conductive diamond films act as contact layers. These films are grown starting from a Si-surface seeded with undoped diamond particles. In this study, the impact of the seeds and their electrical properties on the interfacial resistance through the diamond film − substrate is determined on the nanometer-scale by probing the nucleation side of the conductive diamond films using scanning spreading resistance microscopy. We evidence that, although the diamond film is grown in a B-rich ambient, no significant B incorporation occurs into the particles and they remain non-conductive after growth. We demonstrate that they impact strongly on the interfacial resistance, increasing it by more than one order of magnitude depending on the seed layer coverage. We further establish a model linking the seed size and density to this interfacial resistance, with excellent agreement to our experimental results. Based on this model, we predict that it is necessary to limit the undoped particle density to less than 5 × 1010 cm−2, for 20 nm particle size, in order to eliminate the contribution of the undoped seeds to the interfacial resistance. Our model also indicates that the fundamental solution to this problem lies in the use of B-doped seeds.     

Equilibrium Point Defect and Electronic Carrier Distributions near Interfaces in Acceptor-Doped Strontium Titanate

A mathematical model based on Frenkel's theory for charged defect segregation at interfaces is used to calculate the equilibrium grain boundary depletion layer widths and conductivity profiles in acceptor-doped SrTiO₃ ceramics. The calculations examine the effect of oxygen vacancy equilibration during annealing at moderate temperatures (∼1000 K) on the development of interfacial charge that influences grain boundary electrical properties at lower temperatures. Good agreement is demonstrated between the model predictions and experimental results reported in the literature.     

明胶层中的扩散和反应的动力学研究——(Ⅳ)扩散伴随油珠界面反应的动力学数值模型

设计了一个数值模型来模拟一个反应物在明胶层中边扩散边在油珠界面上与另一个反应物反应的动力学过程。提出了处理油珠界面反应的动力学方程,并应用在模型设计中。采用模型模拟与动力学实验测量相结合的方法不仅可以获得反应物在明胶层中的扩散系数和界面反应的比速率常数等重要动力学参数,而且可以提供反应物和生成物在明胶层中的时空分布,并预测不同条件下的动力学过程。对模型的适用性也作了详细的讨论。     

Gradient-IPN-modified hydrogel beads: Their synthesis by diffusion–polycondensation and function as controlled drug delivery agents

Interpenetrating polymer network (IPN) membranes and gradient–IPN polymers were synthesized by immersing crosslinked, 2-hydroxyethylmethacrylate copolymer beads which were swollen in polyol in solutions of diisocyanates. Diffusion of reactants and polycondensation take place simultaneously, and the polymer beads are modified by a polyurethane–IPN layer whose thickness and compositional gradient are a function of reaction rate and diffusion rate. When the reaction is fast relative to diffusion, the reaction zone is narrow and the IPN boundary layer is sharp, whereas when diffusion dominates, the reaction zone and the IPN-modified region becomes broader and more diffuse. A water-soluble drug imbibed into such gradient-IPN-modified hydrogel beads is released over a prolonged time period due to the less permeable IPN barrier and because of a drug-distribution gradient in the polymer, which follows the polyurethane gradient. Diffusion polycondensation can be considered a special case of interfacial polycondensation, one in which the interface area is expanded into and stabilized by a preformed polymer matrix, which serves as reaction medium.