Effect of Neck Formation on the Measurement of Dynamic Interfacial Tension in a Drop Volume Tensiometer

Dynamic interfacial tension values obtained by drop volume tensiometry will be affected under certain experimental conditions by the formation of a neck between the drop and the capillary tip. This phenomenon must be accounted for to obtain accurate values of interfacial tension. In this work, neck formation for a water–mineral oil system is studied under conditions where hydrodynamic effects can be neglected. A model originally developed for the determination of the surface tension of a suspended drop is modified for application to dynamic interfacial tensions of surfactant-containing liquids. The model relates apparent values of interfacial tension calculated from drops possessing necks to actual values. Experiments with Span 80 (sorbitan monooleate) and sodium dodecyl sulfate (SDS) surfactants in a mineral oil–water system are used to test the validity of the developed model. For the small tip diameter used, good agreement is obtained for Span 80 up to the critical micelle concentration, and for low concentrations of SDS, when the surfactant adsorption is diffusion-limited. In both cases, the neck diameter of the growing drop can be considered constant over the range of dynamic interfacial tensions tested.     

最大气泡法测溶液表面张力的改进

用最大气泡法测定不同浓度正丁醇水溶液的表面张力是许多高校开设的物理化学实验之一。该实验要求毛细管底端与待测液面相切 ,操作比较困难 ,而且结果处理比较麻烦 ,且易引入人为误差。本文对该实验进行了改进     

A Growing Drop Technique for Measuring Dynamic Interfacial Tension

A novel, growing drop technique is described for measuring dynamic interfacial tension due to sorption of surface-active solutes. The proposed method relates the instantaneous pressure and size of expanding liquid drops to the interfacial tension and is useful for measuring both liquid/gas and liquid/liquid tensions over a wide range of time scales, currently from 10 ms to several hours. Growing drop measurements on surfactant-free water/ air and water/octanol interfaces yield constant tensions equal to their known literature values. For surfactant-laden, liquid drops, the growing drop technique captures the actual transient tension evolution of a single interface, rather than interval times as with the classic maximum-drop-pressure and drop-volume tension measurements. Dynamic tensions measured for 0.25 mM aqueous 1-decanol solution/air and 0.02 kg/m³ aqueous Triton X-100 solution/dodecane interfaces show nonmonotonic behavior, indicating slow surfactant transport relative to the imposed rates of interfacial dilatation. The dynamic tension of a purified and fresh 6 mM aqueous sodium dodecyl sulfate (SDS) solution/air interface shows only a monotonic decrease, indicating rapid surfactant transport relative to the imposed rates of dilatation. Conversely, an aged SDS solution, naturally containing trace dodecanol impurities, exhibits dynamic tensions which reflect a superposition of the rapidly equilibrating SDS and the slowly adsorbing dodecanol.     

吊片法测试液体表面张力的实验设计

表面张力是液体的重要物性数据,在科学研究、工业生产和日常生活中皆有广泛应用。介绍了采用吊片法测量液体表面张力的实验设计,该实验过程简单,准确度高,实验内容和时间易于调节,对于培养学生认真细致的科研作风有很大帮助。     

Direct Correlation of Surface Tension and Surface Composition of Ionic Liquid Mixtures—A Combined Vacuum Pendant Drop and Angle-Resolved X-ray Photoelectron Spectroscopy Study

We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C₈C₁Im][PF₆] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG₂)₂Im]I in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of [C₈C₁Im][PF₆] and the PEG chains of [(mPEG₂)₂Im]I are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low [C₈C₁Im][PF₆] contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy.     

A Home-made Simple Set-up for Measurement of Electrochemical Surface Tension Spectrum on a Mercury Drop Electrode

A setup for recording surface tension curves at a mercury drop during potential scanning is designed based on photo-sensitive detection system. Surface tension spectrum at Hg drop can be recorded by voltammetric study. A Yb(III)-NO2- catalytic reduction system was used for characterization. The simple, sensitive technique can be expected to provide fresh information on molecular interactions at electrode surfaces.     

最大气泡压力法测表面张力实验数据处理的改进

最大气泡压力法测溶液表面张力的实验是许多高校开设的物理化学经典实验。实验的操作并不复杂,但教材或讲义所用的数据处理方法有些却比较复杂,而且人为引入的误差较大。本文运用MATLAB软件,用两种拟合方法对实验数据的处理方法进行了改进。     

旋转滴方法研究界面扩张流变性质

采用旋转滴方法, 对2-丙基-4,5-二庚烷基苯磺酸钠(DHPBS)在癸烷-水界面上的扩张流变性质进行了研究, 较为详细地介绍了SVT20N视频旋转滴张力仪的装置和实验方法, 考察了油滴注入体积、基础转速及振荡振幅等实验条件对扩张模量的影响. 研究结果表明, 旋转滴方法是一种研究扩张流变性质的新型手段, 在涉及低界面张力现象的领域具有良好的应用前景.     

液滴在不互溶液体表面上的相对界面自由能曲面及Neumann三角形的导出

根据系统的界面Helmholtz自由能自发地趋于最低的热力学原理,以浮在不互溶液体(2)表面上透镜状液滴(3)在气(1)、液₂、液₃三相交界处,气-液₃、液₂-液₃界面各自和气-液₂界面通过液滴内部的夹角θ₁、θ₂为变量(0°≤θ₁≤180°,0°≤θ₂≤180°),证明出3个界面张力γ₁₂、γ₁₃、γ₂₃各种可能组合情况下液体₃稳定时的θ₁、θ₂值与它们之间的关系,导出Neumann三角形;并按照计算数据绘出几种类型相对于气相中圆球形液滴的界面自由能曲面图。     

Surface Tension of the Liquid Hg-In Alloys

Abstract

The measurements of the surface tension of the liquid Hg-In alloys were made by means of a maximum drop pressure method. The surface tension increases monotonously with increasing the In concentration. It is thermodynamically shown that the composition of the Hg atoms adsorbed on the surface is larger than that in the bulk. Experimental results are compared with calculated results due to various model theories; in particular the hard sphere model with a density-dependent cohesive potential is found to be in qualitative agreement with experimental results of both surface tensions and its temperature coefficients.     

由表面活性物质溶液的动界面张力外推求平衡界面张力的研究

表面活性物质溶液的界面张力往往随时间而变,难以测得平衡界面张力J。Kloubek^[1]曾应用经验式:1/(δ_H2O-δ_t)=b/(At^1/2)+1/A,以[1/(δ_H2O-δ_t)]对1/t^1/2作图外推求得溶液的平衡表面张力,但所得结果仅与文献值大致相符。本文从理论上分析该经验式的由来,以及产生偏离的原因,并寻求了解决的办法。     

Surface Tension of Ternary Liquid Mixtures

Abstract

Surface tension has been measured by the differential capillary rise method for three ternary mixtures containing alkanes (hexane + cyclohexane+benzene, pentane + hexane + benzene and cyclohexane + heptane + toluene at 298.15pm 0.1°K). The sign and magnitude of the excess surface tension and excess volume depend ultimately upon the chain length of the component of the mixtures. The results of the surface tension were compared with theoretical values obtained from Flory theory, Sanchez method, Brock-Bird relation and volume fraction statistics. There is reasonable agreement between theory and experiment.     

Determining the Surface Tension of Microliter Amounts of Liquid

We describe a method for determining the surface tension of liquids by measuring the pull-off force between curved surfaces with a bridging droplet. The technique is useful for cases when only very small amounts of liquid are available, as in medical and biological applications. Data on the surface tension of saliva samples are in agreement with literature values. Copyright 2000 Academic Press.     

Transient Surface Tension of an Expanding Liquid Sheet

We address the problem of dynamic surface tension using measurements of sheet diameters that results from the impact of a liquid jet of diameter d(0) on a small disk of diameter d(i) (d(i)/d(0) approximately 4). At low velocities, the sheet diameter D is related to d(0) by the Weber number We, constructed with the liquid density rho, the jet velocity u(0), and the surface tension sigma at the rim: D/d(0)=18 We=18 [rho u(0)(2)/(sigma/d(0))]. This relation expresses the equilibrium between inertial forces and surface tension forces at the sheet rim. When a surfactant has been dissolved in the bulk of the liquid prior to the formation of the initial jet, the rim surface tension, and therefore the sheet diameter, depends on the amount of surfactant adsorbed at the rim. This amount is fixed by a competition between surface formation induced by radial extension and repopulation of the liquid interface in surfactant. The experimental setup proposed here provides a method to measure dynamic surface tension from sheet diameter measurements and symmetrically to monitor the adsorption of a surfactant on a liquid surface. The available adsorption time ranges from 10 to 100 ms. Experimental data obtained with two surfactants are in agreement with a model of a diffusion-controlled adsorption at the interface. Copyright 2000 Academic Press.     

利用标准加入法研究离子液体EMIBF4的密度和表面张力

在278.15～338.15 K温度范围内, 分别用Anton Paar密度计和最大气泡法测定了含有不同微量水的离子液体EMIBF₄ (1-ethyl-3-methylimidazolium tetrafluoroborate)的密度和表面张力, 讨论了微量水对这些性质的影响, 进而用标准加入法确定了无水离子液体EMIBF₄的密度和表面张力. 借助Glasser理论和空隙模型讨论了EMIBF₄的热力学性质. 用空隙模型计算的离子液体热膨胀系数与实验测定值较好一致, 说明空隙模型具有合理性.     

Study on the Mechanism of Asphaltenes Reducing Oil-Water Interfacial Tension

As high polar components of crude oil, asphaltenes play a significant role in reducing oil-water interfacial tension(IFT). In this paper, the effects of asphaltenes on reducing IFT in the presence of surfactant were compared, and the mechanism of asphaltenes reducing the IFT was studied by the dynamic interfacial tension(DIFT) equation. Whether asphaltenes were added to the oil or 2,5-dimethyl-4-(4-dodecyl) benzene sodium sulfonate(p-S14-4) was added to the water phase, either of all results in the IFT reducing and the IFT is related to the coverage and the mass of asphaltenes adsorption at the interface. In the presence of asphaltenes, the adsorption of the active substances to the interface is not entirely dependent on diffusion, and the process can be divided into three regions. Region I: the IFT rapidly reducing, this process is controlled by diffusion of surfactant; Region II: the IFT reducing slowly, resulted from the lower diffusion rate that is limited due to the aggregates formed by the interaction of asphaltene-asphaltene; Region III: the interaction of asphaltene-asphaltene is broken by the interaction of surfactant-asphaltene. The asphaltene aggregates are reduced and adsorbed rapidly at the interface. Furthermore, the results reveal that the asphaltenes concentration affects the coverage rate and adsorption at the interface.     

Measurement of Surface Tension in Aqueous Polymerizing Systems

Surface tension measurements on a polymerizing system can yield information concerning concentration changes of surface-active species present in the system. Such measurements have hitherto been performed under conditions more or less remote from those obtaining during the actual polymerization. The use of a twin-capillary dilatometer permits, in principle, the simultaneous determination of both conversion and surface tension as a function of time. The design of such a dilatometer is described, the precautions associated with its use examined, and its application to the monitoring of the surface tension of various polymerizing systems discussed.     

Experimental and Theoretical Study of the Surface Tension in Liquid Ag–Cu–Sn Alloys

Summary. The surface tension in the ternary Ag–Cu–Sn system in a wide composition and temperature range has been determined experimentally. Besides, the surface tension of the investigated alloys has been modeled using the theoretical approach of Butler. The measured and the calculated absolute values of the surface tension are compared and analyzed.     

液态低沸点气体的表面张力

利用双毛细管法测定了液氮沸点温度下液氮的表面张力。用非线性方程γ=γ0(1-T/TC)n描述了液态N2、O2、Ar、Xe、H2、Ne、He、F2和Kr的表面张力与温度的关系,并采用一元线性回归的方法拟合了上述各流体的参数γ0和n,准确度高于文献值,说明方程能正确表达表面张力与温度的关系。这些数据有利于对上述低沸点气体进行准确的热力学计算。     

Surface Tension of the Vapor–Liquid Interface with Finite Curvature

Based on the division of particles into internal and surface particles, the expression is derived closing the system of equations of classical thermodynamics for curvature-dependent surface tension, equimolar radius, and radius of tension surface. A solution to this system allows one to find the surface tension of new phase nucleus of any size (including minimal) and any sign of surface curvature. The obtained results indicate the weak size dependence of thermodynamic parameters that are the functions of surface tension; it is shown that Tolman's length cannot be determined using experimental determination of these parameters. It is shown that the work of nucleus formation strongly depends on its size and is the function of effective rather than true surface tension. Numerical simulation of clusters by the molecular dynamics method indicates that the pressure inside a fairly small cluster is described by Laplace's formula with the coefficient of surface tension for the plane surface of a liquid that agrees with the proposed theory.