流体在固体表面超铺展特性的研究进展

对流体在固体表面超铺展特性的研究进展进行了综述,总结了具有超铺展特性的动态湿润体系、超铺展特性的影响因素、内在机理以及实验关联式建立和数值模拟方法。部分丙硅氧烷类和烷基乙氧基化物类以及少数离子型表面活性剂溶液具有超铺展特性,浓度和固体表面能是超铺展的重要影响因素。气液界面的浓度Marangoni效应被认为是超铺展过程的控制因素,表面活性剂在气液、固液和三相接触线前缘固气界面的输运和吸附对浓度Marangoni效应有重要影响。分析认为,实验方面未来应拓展实验体系,建立超铺展产生的判据;深入研究宏观影响因素以及微观输运和吸附机理,同时考虑外加物理场影响,为超铺展的实际应用奠定基础。理论方面需综合考虑表面活性剂向界面的输运、吸附对界面性质的作用规律以及浓度Marangoni效应的影响,借鉴相对成熟的牛顿流体动态湿润理论,建立描述超铺展特性的全过程理论模型。数值模拟方面应以分子动力学模拟为基础建立表面活性剂输运和界面吸附的微观物理模型,将其引入流体动力学模型,实现对超铺展过程精确定量化的描述。本文还给出了可能的超铺展体系铺展全过程的物理图景。     

多相传质过程中的Marangoni效应

Marangoni效应广泛存在于液液、气液相际传质过程中,通常会对传质速率产生重要影响。对Marangoni效应的实验及理论研究有助于增进对微观传质机理的理解,是强化相间传质过程效率的重要因素。重点介绍了液液体系中单液滴萃取的实验和模拟研究,对液液体系中Marangoni效应不稳定性的判据,对气液体系有效传质面积的影响,以及两种体系中利用表面活性剂进行传质调控的研究等方面的进展进行了综述,还探讨了传质过程中Marangoni效应应用研究的方向。     

硅表面活性剂的超铺展现象及本质（待续）

综述了超铺展(superspreading)领域的基础研究及最新进展。在自然界中,液滴在很多表面上能完全快速铺展,这一特殊现象是在20世纪六十年代发现的。自此便开始对这类现象进行集中研究,但时至今日超铺展的机理仍未了解透彻。本综述详细调研了过去25年里超铺展方面的基础文献,并列出与超铺展剂相关的一部分结果。超铺展方面的文献可分为如下几组:①关于三硅氧烷表面活性剂的研究工作;②关于超铺展机理的研究工作;③分子动力学模拟;④关于三硅氧烷表面活性剂对薄液膜的影响的研究工作。过去十年里有许多综述类文章重点收录前两类工作。对于后两类工作,即分子动力学模拟和三硅氧烷表面活性剂对薄液膜的影响,尽管从科学角度来看很重要,但研究工作仍较少。A. Sankaran等研究了超铺展剂对矩形框内泡沫液膜的影响,确认了超铺展剂在泡沫液膜内导致强烈的Marangoni效应。常规表面活性剂从未观察过如此强烈的Marangoni效应。结合A.Sankaran等人对超铺展剂和非超铺展剂对泡沫薄膜的影响的差别的研究,本综述将对前述4类工作做进一步调研和搜集,这对于润湿(wetting)、反润湿(de-wetting)和超铺展领域的初学者和专家都很有帮助。     

不同反离子双癸基季铵盐对聚四氟乙烯表面的吸附行为

利用座滴法研究了系列反离子双癸基季铵盐和Gemini型季铵盐表面活性剂对超疏水材料聚四氟乙烯(PTFE)表面的吸附行为。考察了表面活性剂的表面活性、类型和浓度对接触角的影响规律,并探讨了铺展系数、黏附张力和黏附功的变化规律。研究表明:双癸基季铵盐表面活性剂在PTFE表面的接触角随着反离子基团的增大呈现先减小后增大的趋势,其中反离子最大的双癸基二甲基戊酸铵(DDAV)在PTFE表面的润湿效果最好;铺展系数(S)随着反离子有机酸基团的增大呈现先减小后增大的趋势;当表面活性剂的质量浓度低于cmc时,粘附力和表面张力之间呈现出良好的线性关系;当质量浓度大于cmc时,反离子基团小的表面活性剂溶液在固-液界面和气-液界面形成了饱和吸附层。反离子基团较大的表面活性剂在气-液界面达到饱和吸附,但在固-液界面上没有达到饱和,随着浓度的增加继续吸附,润湿性能增强。     

三硅氧烷超润湿剂及其在植物叶表面超润湿铺展机理研究进展

超润湿剂能够显著增大药液在植物标靶表面润湿沉积覆盖率,提高农药的利用率,提升农作物产量。具有独特结构的三硅氧烷聚醚型表面活性剂呈现出良好的超润湿铺展性。本文综述了植物叶表面的微观结构和润湿性、超润湿剂的结构与超润湿性关系,及从超润湿剂的浓度、溶液中聚集体形态、润湿基底、Marangoni效应、自亲效应等对超润湿性的影响不同角度地揭示了超润湿铺展机理,并对超润湿机理的深入研究提出了展望,为今后超润湿剂的设计合成和超润湿铺展机理的深入认识和研究提供了理论依据和指导。     

无碱二元复合驱中表面活性剂对驱油效果的影响

表面活性剂在无碱二元驱油体系中可以促使残余油启动,扩大波及体积,提高微观驱油效率。本文研究了无碱二元驱油体系中表面活性剂通过改变界面张力、毛管力和吸附浓度对驱油效果的影响。结合前期室内实验和大庆油田萨中西区一类油层试验区矿场试验数据,配合使用化学驱模拟软件ChemEOR,建立9注16采理想模型进行无碱二元复合驱数值模拟。通过改变表面活性剂浓度改变界面张力、毛管力和表面活性剂吸附浓度,分析含水率、累产油和采出程度,从而得到无碱二元驱油体系中界面张力、毛管力和表面活性剂吸附浓度对驱油效果的影响。研究结果表明,无碱二元复合体系中适宜的表面活性剂界面张力为10-3数量级,表面活性剂作用下改变毛管力对驱油效果影响不明显,表面活性剂吸附浓度为0.25wt%时驱油效果最好。     

分离压/结合压作用下的活性剂液滴演化特征

当含活性剂液膜厚度小于100 nm时,分子间力表现出的分离压或结合压效应将对其演化特征及去润湿特性产生重要影响。针对可溶性活性剂液滴的铺展历程,采用润滑理论建立了液膜厚度、活性剂表面浓度和内部浓度的演化模型,模拟了正负体系中受分离压或结合压影响的液滴演化过程。结果表明,分离压可促进正体系下的液滴稳定铺展,并抑制去润湿现象的发生;而负体系下,分离压则加剧不稳定性,并改变Marangoni负效应对液滴演化的影响。正体系下液滴受结合压作用呈现不稳定特征,在极短时间内发生破断;结合压对负体系下的液滴演化影响与分离压作用相似,具有促进液滴不稳定演化的作用。     

平板浸涂过程中的液膜排液影响因素

针对一端与活性剂溶液池相接的竖直平板浸涂液膜排液过程，基于润滑理论建立了液膜厚度、活性剂浓度及液膜表面速度的演化方程组，通过数值计算分析了Marangoni效应和表面黏度对液膜排液特征的影响。结果表明，Marangoni效应是影响液膜排液过程的重要因素，可导致液膜厚度增加，随Marangoni效应增强可得到更均匀的液膜。液膜表面速度随表面黏度增大而减小，较大的表面黏度将推迟表面速度逆流现象的发生，但其对膜厚均匀度几乎没有影响。     

平板浸涂过程中的液膜排液影响因素

针对一端与活性剂溶液池相接的竖直平板浸涂液膜排液过程,基于润滑理论建立了液膜厚度、活性剂浓度及液膜表面速度的演化方程组,通过数值计算分析了Marangoni效应和表面黏度对液膜排液特征的影响。结果表明,Marangoni效应是影响液膜排液过程的重要因素,可导致液膜厚度增加,随Marangoni效应增强可得到更均匀的液膜。液膜表面速度随表面黏度增大而减小,较大的表面黏度将推迟表面速度逆流现象的发生,但其对膜厚均匀度几乎没有影响。     

Al_2O_3纳米流体液滴蒸发特性的数值模拟研究

纳米流体液滴蒸发现象在电子设备冷却、喷墨打印以及医学检测等领域都有广泛应用。为了研究水基Al_2O_3纳米流体液滴的蒸发特性,建立了纳米流体液滴蒸发的二维瞬态模型,考虑了纳米颗粒输运行为以及液滴内部流动的影响,并采用任意拉格朗日-欧拉法(ALE)捕捉气液运动界面。基于所建立的模型,分析了水基Al_2O_3纳米流体液滴内部Marangoni流、纳米颗粒初始浓度以及基板温度对纳米流体液滴蒸发特性的影响规律。结果表明,液滴内部Marangoni流会影响气液界面温度分布和蒸发速率。由于液滴内部纳米颗粒浓度分布和气液界面温度发生变化,纳米流体液滴的蒸发速率随着纳米颗粒初始浓度和基板温度升高而增加。     

3D multiphase flow simulation of Marangoni convection on reactive absorption of CO2 by monoethanolamine in microchannel

A multiphase flow 3D numerical simulation method employing the coupled volume of fluid (VOF) and level set model is established to study the reactive absorption of CO₂ by the monoethanolamine (MEA) aqueous solution in a falling film microchannel. Based on the flow-reaction-mass transfer model of the MEA-CO₂ system in the falling film microchannel, the enhancement effect of the Marangoni convection in this reactive absorption process is analyzed. The enhancement factor of the Marangoni convection obtained in this work is in good agreement with experimental results in the literature. With consideration of the absorption ratio as well as the enhancement effect of the Marangoni convection, the influence of different MEA concentrations on absorption of CO₂ is investigated. Furthermore, the appropriate MEA concentration for absorption enhanced by the Marangoni convection is acquired.     

Numerical simulation of the Marangoni effect on transient mass transfer from single moving deformable drops

A level set approach was adopted in numerical simulation of interphase mass transfer from a deformable drop moving in a continuous immiscible liquid, and the simulation results on Marangoni effect were presented with respect to three experimental runs in the methyl isobutyl ketone–acetic acid–water system. Experiments showed that when the solute concentration was sufficiently high, the Marangoni effect would occur with the interphase mass transfer enhanced. Numerical results indicated that the mass‐transfer coefficient with Marangoni effect was larger than that without Marangoni effect and stronger Marangoni effect made the drop deform more easily. The predictions were qualitatively in accord with the experimental data. Numerical simulation revealed well the transient flow structure of Marangoni effect. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

两液层体系传质引发的Marangoni效应的数值模拟

The Marangoni effect induced by mass transfer at the interface between two immiscible liquids displays important influence on laboratory and industrial operation of solvent extraction. A systematic numerical study of the two-dimensional Marangoni effect in a two liquid layer system was conducted. The linear relationship of the inter- facial tension versus the solute concentration was incorporated into a mathematical model accounting for liquid flow and mass transfer in both phases. The typical cases analyzed by Sternling ＆ Scriven （AIChE J., 1959） using the linear instability theory were simulated bv the finite difference method and good agreement between the theory and the numerical simulation was observed. The simulation suggests that the Marangoni convection needs certain time to develop sufficiently in strength and scale to enhance the interphase mass transfer, the Marangoni effect is dynamic and transient, and remains at some stabilized level as long as the mass transfer driving force is kept con- stant. When certain level of shear is imposed at the interface as in most cases of practical significance, the Maran- goni effect is suppressed slightly but progressively as the shear is increased gradually. The present two-dimensional simulation of the Marangoni effect provides some insight into the underlying mechanism and also the basis for further theoretical study of the three-dimensional Marangoni effect in the real world and in chemical engineering applications.     

A description of phase inversion behaviour in agitated liquid-liquid dispersions under the influence of the Marangoni effect

The influence of the Marangoni effect on phase inversion behaviour is examined by integrating a microscopic study of the drop coalescence process, in which thin film drainage in the presence of insoluble surfactant occurs, into a macroscopic phase inversion model which has been developed previously using a Monte Carlo technique. This is achieved via an immobility factor, obtained from a comparison of the film drainage times for surfactant-laden systems and surfactant-free systems as a function of the drop approach velocity, surface Péclet number, initial surfactant concentration and the Hamaker constant, which is then used to modify the coalescence probability in the phase inversion model. On the one hand, the results indicate that the Marangoni effect removes any influence that the viscosity ratio has on phase inversion due to immobilisation of the interface, thus shielding the flow in the film from the effects of the flow in the dispersed phase; the point at which phase inversion occurs therefore tends towards equivolume holdups with the addition of surfactant. On the other hand, when comparisons are made with pure systems in which surfactant is absent, the system is seen to be either stabilised or de-stabilised from inversion depending on the viscosity ratio of the system. This is attributed to the influence of surfactant on the dispersion morphologies on either side of the inversion (i.e. water-in-oil dispersions and oil-in-water dispersions) and depends on the dispersed phase holdup; the Marangoni effect is felt stronger when the dispersed phase holdup is low.     

碱、聚合物对表面活性剂吸附影响分析

油藏对表面活性剂的吸附作用,是砂岩表面化学物质与表面活性剂间相互作用的结果。ASP复配体系溶液中,碱对表活剂的吸附影响较大,在表活剂溶液中加入碱后,砂岩对表活剂的吸附量下降,且吸附量下降幅度与碱浓度成正比。实验结果表明,碱可以使粘土矿物对阴离子表面活性剂吸附量降低70%~80%,而油藏砂岩对表活剂吸附量可降低10%~40%。聚合物对表活剂的吸附影响较小,数值模拟结果表明吸附量降低15%~30%。这是由于聚合物在表活剂溶液中水解后,部分分子团带有负电荷,这就抑制了砂岩对表活剂的吸附作用;另外,加入聚合物后,复配体系溶液变稠,使得溶液扩散速率降低,减小波及体积,进而削弱表活剂吸附效果。     

Experimental investigation and numerical simulation of Marangoni effect induced by mass transfer during drop formation

Marangoni effect induced by interphase mass transfer plays an important role in liquid–liquid extraction and reaction processes. The interaction of Marangoni effect and interphase mass transfer during drop formation at different injection rates and different initial solute concentrations was investigated by experimental and numerical simulation. The extraction fraction was measured and the corresponding correlation was proposed. The level‐set method coupled with mass‐transfer equation is for the first time used to simulate the mass‐transfer induced Marangoni effect during drop formation. The simulated drop volume, shape, and extraction fraction are in good accordance with experimental data. Through the numerical simulation, it is found that the mass transfer in the first mass‐transfer period is the most efficient during drop formation when Marangoni convection occurs. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4424–4439, 2013     

固体粉末在聚合物基体中分散混合的数值模拟研究

根据聚合物混合理论以及固体粉末团聚体在聚合物基体中的破碎理论,提出利用累积尺度分布函数直接表征固体粉末团聚体在聚合物中分散效果的表征方法,并建立了相应的数值模型。利用这种方法得到的模拟结果与理论分析一致,说明在数值模拟中利用累积尺度分布函数表征固体粉末团聚体在聚合物中的分散混合效果是正确可行的。     

A model of bubble coalescence in the presence of a nonionic surfactant with a low bubble approach velocity

A bubble coalescence model for a solution with a nonionic surfactant and with a low bubble approach velocity was developed, in which the mechanism of how coalescence is hindered by Marangoni stress was quantitatively analyzed. The bubble coalescence time calculated for ethanol–water and MIBC–water systems were in good agreement with experimental data. At low surfactant concentrations, the Marangoni stress and bubble coalescence time increased with bulk concentration increase. Conversely, in the high concentration range, the Marangoni stress and coalescence time decreased with bulk concentration. Numerical results showed that the nonlinear relationship between coalescence time and surfactant concentration is determined by the mass transport flux between the film and its interface, which tends to diminish the spatial concentration variation of the interface, that is, it acts as a “damper.” This damping effect increases with increased surfactant concentration, therefore decreasing the coalescence time at high concentrations.     

Relationship of structure to properties in surfactants. III. Adsorption at the solid-liquid interface from aqueous solution

Surfactants adsorb onto solid substrates from aqueous solution by a number of different mechanisms: ion exchange, ion pairing, hydrogen bonding, physical adsorption by polarization or dispersion forces. The relationship of the mechanism of adsorption to such factors as the nature of the solid substrate, the molecular structure of the surface active adsorbate, and the pH, electrolyte content, or other additive content of the aqueous phase is discussed. The effect of structural groups in the surfactant molecule on the efficiency, effectiveness, and rate of adsorption onto various types of solid substrates, charged, polar, and nonpolar, is reviewed and explained, and typical adsorption isotherms are presented. Adsorption of surfactant affects the properties of the solid substrate, such as hydrophilic or hydrophobic character, dispersibility, and reactivity towards reagents and dyes. These effects are discussed and explained.     

Effect of initial temperature on the velocity of flame spread over a fuel film on a metal substrate

The influence of ambient temperature in the range of −42 to 25°C on the velocity of flame spread over films of liquid and solid fuels on a metal substrate in a thermally thin system is studied experimentally. It is shown that the previously proposed model for flame spread satisfactorily describes the dependence of the flame velocity on initial temperature. A strong influence of the phase transition of the fuel into the solid phase on the flame velocity was not observed. The limit of steady-state flame spread is due to the inability to provide a sufficient thickness of the evaporating film due to the Marangoni effect.