Volatile surfactants: Characterization and areas of application

Amphiphilic aroma molecules, representatives of fragrance molecules, are introduced as dynamic volatile surfactants. Surface tension of their aqueous solutions proves to be a sensitive and revealing quantity, used for assessment of the adsorption-evaporation behavior both under equilibrium conditions and in regimes of no instantaneous equilibrium. Such volatile amphiphiles are characterized by fast adsorption from bulk solution at an air-water interface, on a timescale of tens of microseconds, and exhibit synergetic effect in mixtures with conventional micellar-forming surfactants. Their ability to evaporate from the interface on a time scale of minutes suggests their applications as “temporal” dynamic cosurfactants in technologies involving fast formation of new surfaces. Current challenges concern evaluation of specific material parameters of volatile aroma surfactants in order to enable their selection for targeted applications.     

最大泡压法测表面张力等温线的数据处理方法比较*

对乙酸、丙酸、正丁酸、2-甲基丁酸、3-甲基丁酸、正戊酸、正己酸、乙醇、丙醇、异丙醇、正丁醇、异丁醇、1,2-丙二醇等13种常用试剂在25 ℃下的表面张力数据拟合方法进行了比较,分析了图解法处理数据及多项式、一阶指数函数、幂函数、Shishkovsky经验公式拟合数据的优缺点。指出Shishkovsky经验公式拟合结果准确,受数据样本量影响小,是理想的表面张力数据拟合方法。     

An investigation on surface tensions of Pb-free solder materials

Surface tensions of some Pb-free solder systems such as Ag–Bi–Sn with cross-sections Ag/Bi = 1/1, Ag/Bi = 1/2, Ag/Bi = 2/1, In–Sn–Zn with cross-sections Sn/In = 1/1, Sn/In = 1/3 and (Ag₇Cu₃)_100?x Sn_x with cross-section Ag/Cu = 7/3 are calculated from the sub-binary surface tension data using the models, such as the Muggianu, Kohler, Toop models, Butler’s equation and Chou’s General Solution Model (GSM) at 873, 923 and 1073 K, respectively. The surface tension of In–Sn–Zn increases wavily with increasing amount of Zn and it is found that the best models are the GSM for both cross-sections in question while GSM becomes the best model for (Ag₇Cu₃)_100?x Sn_x alloy in the whole experimental range. Moreover, the surface tension of (Ag₇Cu₃)_100?x Sn_x decreases slightly with increasing amount of Sn. The Muggianu, Butler and Butler models are determined as the best models for the cross-sections in the order given above for entire measurement range, respectively, and the surface tension of Ag–Bi–Sn decreases slightly with an increasing amount of Bi and Ag but increases with increasing Sn in liquid alloys.     

十二烷基伯胺盐酸盐与十二烷基聚氧乙烯硫酸钠复配体系中的表面性质

研究了十二烷基胺盐酸盐(DAC)和十二烷基聚氧乙烯硫酸钠(AES)复配体系的表面性质与胶束化行为.发现该体系在广泛的复配比例区间和温度区间内保持了极为优异的表面活性,测定了该体系的临界胶束浓度(cmc)与其对应的表面张力(γcmc)的具体值,并研究了温度、pH值和离子强度等环境因素对相关体系的影响.     

Surface Tension Effect on Harmonics of Rayleigh-Taylor Instability

Using the method of the parameter expansion up to the third order, explicitly investigates surface tension effect on harmonics at weakly nonlinear stage in Rayleigh-Taylor instability (RTI) for arbitrary Atwood numbers and compares the results with those of classical RTI within the framework of the third-order weakly nonlinear theory. It is found that surface tension strongly reduces the linear growth rate of time, resulting in mild growth of the amplitude of the fundamental mode, and changes amplitudes of the second and third harmonics, as is expressed as a tension factor coupling in amplitudes of the harmonics. On the one hand, surface tension can either decrease or increase the space amplitude; on the other hand, surface tension can also change their phases for some conditions which are explicitly determined.     

Liquid–liquid equilibrium and interfacial tension of the ternary system heptane + thiophene + 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

The liquid–liquid equilibrium (LLE) of the ternary system comprising heptane, thiophene and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₂mim][NTf₂]) was determined at 25 °C and atmospheric pressure, for preliminary evaluation of the potential of this ionic liquid as solvent for the desulfurisation of transportation fuels. Classical parameters such as solute distribution ratio and selectivity were calculated from the LLE data and subsequently analysed. The LLE data were also correlated by means of the ‘Non-Random Two-Liquid’ (NRTL) equation. Besides the LLE, another critical property for the design of extraction processes, namely the interfacial tension, was determined in parallel, throughout the immiscibility domain of the ternary system. For the first time, the LLE and the interfacial tension of a ternary system involving an ionic liquid are jointly reported.     

Transient two‐layer thin‐film flow

The transient two‐layer thin‐film planar flow is investigated theoretically in this study. The interplay among inertia, viscous and surface/interfacial tension is emphasized. It is found that the film and interface profiles, as well as the flow field, are strongly influenced by the viscosity ratio, velocity and film thickness ratios at inception, and the surface‐to‐interfacial tension ratio. The nonlinear stability of the steady state reveals the formation of a solitary wave after flow inception, which propagates in the form of a convective instability, with the steady state recovered only in the tail (upstream) region of the wave. In the presence of surface/interfacial tension, surface modulation appears, which grows in wavelength and amplitude with position. The flow is found to be particularly stable for higher viscosity of the lower film layer. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface tension-driven shape-recovery of micro/nanometer-scale surface features in a Pt57.5Ni5.3Cu14.7P22.5 metallic glass in the supercooled liquid region: A numerical modeling capability

Recent experiments in the literature show that micro/nano-scale features imprinted in a Pt-based metallic glass, Pt_57.5Ni_5.3Cu_14.7P_22.5, using thermoplastic forming at a temperature above its glass transition temperature, may be erased by subsequent annealing at a slightly higher temperature in the supercooled liquid region (Kumar and Schroers, 2008). The mechanism of shape-recovery is believed to be surface tension-driven viscous flow of the metallic glass. We have developed an elastic-viscoplastic constitutive theory for metallic glasses in the supercooled liquid temperature range at low strain rates, and we have used existing experimental data in the literature for Pt_57.5Ni_5.3Cu_14.7P_22.5 (Harmon et al., 2007) to estimate the material parameters appearing in our constitutive equations. We have implemented our constitutive model for the bulk response of the glass in a finite element program, and we have also developed a numerical scheme for calculating surface curvatures and incorporating surface tension effects in finite element simulations. By carrying out full three-dimensional finite-element simulations of the shape-recovery experiments of Kumar and Schroers (2008), and using the independently determined material parameters for the bulk glass, we estimate the surface tension of Pt_57.5Ni_5.3Cu_14.7P_22.5 at the temperature at which the shape-recovery experiments were conducted. Finally, with the material parameters for the underlying elastic-viscoplastic bulk response as well as a value for the surface tension of the Pt-based metallic glass fixed, we validate our simulation capability by comparing predictions from our numerical simulations of shape-recovery experiments of Berkovich nanoindents, against corresponding recent experimental results of Packard et al. (2009) who reported shape-recovery data of nanoindents on the same Pt-based metallic glass.     

A New Equation between Surface Tensions and Solubility Parameters without Molar Volume Parameters Simultaneously Fitting Polymers and Solvents

Both surface tension and solubility parameter are decided by molecular interactions. There are several empirical equations describing their connection. However, at least two limitations exist for them: polymers cannot be treated and only apolar or weakly polar solvents can be fitted. We found when only the dispersive properties were considered, for 37 solvents and 22 polymers, a linear relationship exists between γ ^d and γ/δ^2/3 _d , fitted by a new equation. Compared with the previous equations, the value of the new equation is that most solvents and common polymers could be treated simultaneously. This equation will be of value for estimating the accuracy of reported surface tension data or solubility parameters of polymers.     

Free (open) boundary condition: some experiences with viscous flow simulations

The free (or open) boundary condition (FBC, OBC) was proposed by Papanastasiou et al. (A new outflow boundary condition, International Journal for Numerical Methods in Fluids, 1992; 14:587–608) to handle truncated domains with synthetic boundaries where the outflow conditions are unknown. In the present work, implementation of the FBC has been tested in several benchmark problems of viscous flow in fluid mechanics. The FEM is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal or non‐isothermal, steady‐state conditions, for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure dependence of the viscosity, slip at the wall, and surface tension are all considered individually in the extrudate‐swell benchmark problem for a wide range of the relevant parameters. The present results extend previous ones regarding the applicability of the FBC and show cases where the FBC is inappropriate, namely in the extrudate‐swell problem with gravity or surface‐tension effects. Particular emphasis has been given to the pressure at the outflow, which is the most sensitive quantity of the computations. In all cases where FBC is appropriate, excellent agreement has been found in comparisons with results from very long domains. The formulation for Picard‐type iterations is given in some detail, and the differences with the Newton–Raphson formulation are highlighted regarding some computational aspects. Copyright © 2011 John Wiley & Sons, Ltd.