Calculating the surface tension between a flat solid and a liquid: a theoretical and computer simulation study of three topologically different methods

We discuss three topologically different methods for calculating the surface tension between a flat solid and a liquid from theoretical and computer simulation viewpoints. The first method, commonly used in experiments, measures the contact angle at which a static droplet of liquid rests on a solid surface. We present a new analysis algorithm for this method and explore the effects of line tension on the contact angle. The second method, commonly used computer simulations, uses the pressure tensor through the virial in a system where a thick, infinitely extended slab of liquid rests on a solid surface. The third method, which is original to this paper and is closest to the thermodynamic definition of surface tension, applies to a spherical solid in contact with liquid in which the flat solid is recovered by extrapolating the sphere radius to infinity. We find that the second and third methods agree with each other, while the first method systematically underestimates surface tension values.     

Applicability of corresponding-states group-contribution methods for the estimation of surface tension of multicomponent liquid mixtures at 298.15 K

Corresponding-states group-contribution methods (CSGC-ST1 and CSGC-ST2) have been applied to four binary liquid mixtures (propyl acetate + o-xylene, propyl acetate + m-xylene, propyl acetate + p-xylene and propyl acetate + ethyl benzene); two ternary (benzene + cyclohexane + toluene and n-hexane + cyclohexane + benzene) and two quaternary liquid mixtures (pentane + hexane + cyclohexane + benzene and pentane + hexane + benzene + toluene) at 298.15 K. In this work, the CSGC-ST2 method is modified and extended to multicomponent liquid mixtures. The excess magnitudes of surface tension were also calculated and graphs were plotted using Redlich–Kister method.     

Comparison of Dorris-Gray and Schultz methods for the calculation of surface dispersive free energy by inverse gas chromatography

Inverse gas chromatography (IGC) is an important technique for the characterization of surface properties of solid materials. A standard method of surface characterization is that the surface dispersive free energy of the solid stationary phase is firstly determined by using a series of linear alkane liquids as molecular probes, and then the acid-base parameters are calculated from the dispersive parameters. However, for the calculation of surface dispersive free energy, generally, two different methods are used, which are Dorris-Gray method and Schultz method. In this paper, the results calculated from Dorris-Gray method and Schultz method are compared through calculating their ratio with their basic equations and parameters. It can be concluded that the dispersive parameters calculated with Dorris-Gray method will always be larger than the data calculated with Schultz method. When the measuring temperature increases, the ratio increases large. Compared with the parameters in solvents handbook, it seems that the traditional surface free energy parameters of n-alkanes listed in the papers using Schultz method are not enough accurate, which can be proved with a published IGC experimental result.     

Simple,low‐cost fabrication of semi‐circular channel using the surface tension of solder paste and its application to microfluidic valves

This work presents a simple, low‐cost method to fabricate semi‐circular channels using solder paste, which can amalgamate the cooper surface to form a half‐cylinder mold using the surface tension of Sn–Pd alloy (the main component in solder paste). This technique enables semi‐circular channels to be manufactured with different dimensions. These semi‐circular channels will then be integrated with a polymethylmethacrylate frame and machine screws to create miniaturized, portable microfluidic valves for sequential liquid delivery and particle synthesis. This approach avoids complicated fabrication processes and expensive facilities and thus has the potential to be a useful tool for lab‐on‐a‐chip applications.     

Quantum computation of the properties of helium using two-body and three-body intermolecular potentials: a molecular dynamics study

We have performed the molecular dynamics simulation to obtain energy, pressure, and self-diffusion coefficient of helium at different temperatures and densities using Lennard–Jones (LJ), Hartree–Fock dispersion-Individual damping (HFD-ID) potential, and the HFD-like potential which has been obtained with an inversion of viscosity data at zero pressure supplemented by quantum corrections following the Feynman–Hibbs approach. The contribution of three-body interactions using an accurate simple relationship reported by Wang and Sadus between two-body and three-body interactions has been also involved for non-effective potentials (HFD-ID and HFD-like) in simulation. Our results show a good agreement with corresponding experimental data. A comparison of our simulated results with other molecular simulations using different potentials is also included.     

Relationships between the internal pressure,the cohesive energy,and the surface tension of liquids

The relationship between the internal pressure P_int on the one hand and the cohesive energy density ced on the other and the ratio of the surface tension to the cube root of the molar volume σ/V^1/3 (also called the Gordon parameter) was examined for a large number of liquids. These consisted of four classes: molecular liquids, liquid metals, room temperature ionic liquids (RTILs), and molten salts. Linear dependences, rather than proportionalities suggested by theory, were obtained in all cases, their slopes being independent of the type of the liquid (the exceptions being noted), but differ for P_int and ced.     

Surface crystallization and phase transitions of the adsorbed film of F(CF<Subscript>2</Subscript>)<Subscript>12</Subscript>(CH<Subscript>2</Subscript>)<Subscript>16</Subscript>H at the surface of liquid tetradecane

The interaction between a long chain alkane, tetradecane (abbreviated H₁₄), molecule and a semi-fluorinated alkane, 1-perfluorododecyl-hexadecane F(CF₂)₁₂(CH₂)₁₆H (abbreviated F₁₂H₁₆), molecule at the air/ H₁₄ solution interface was studied by measuring the surface tension of the H₁₄ solutions of F₁₂H₁₆ as a function of temperature and bulk concentration under atmospheric pressure. Pure liquid H₁₄ freezes without forming a condensed film at its surface. Nevertheless, a very small amount of F₁₂H₁₆ initiates the surface freezing of H₁₄. In contrast to the F₁₂H₁₆-hexadecane (abbreviated H₁₆) system, the condensed monolayer of H₁₄ has a finite solubility of F₁₂H₁₆ in the F₁₂H₁₆-H₁₄ system. By further increasing the bulk concentration of F₁₂H_16, the F₁₂ chains of the F₁₂H₁₆ molecules form the other closely packed condensed state. Hence, as in the case of the H₁₆ system, the H₁₄ system also exhibits a surface hetero-azeotrope behavior in the lower temperature region. Below the surface hetero-azeotropic point, the condensed H₁₄ monolayer containing a small amount of F₁₂H₁₆ is completely replaced by the condensed monolayer of F₁₂H₁₆. At 2 °C, for example, a surface of H₁₄ solution of F₁₂H₁₆ covered with a gaseous film of F₁₂H₁₆ is replaced by a condensed H₁₄ monolayer containing an almost gaseous state of F₁₂H₁₆, and is then completely replaced by the condensed monolayer of F₁₂H₁₆ with increasing bulk concentration. Above the temperature of the triple point for the F₁₂H₁₆ monolayer, the F₁₂H₁₆-H₁₄ system exhibits a gaseous, expanded, and condensed state.     

液相色谱-质谱在阿尔茨海默病研究中的应用

液相色谱-质谱联用（LC-MS）作为集高效分离与定性定量检测为一体的联用技术,近年来在化学、医学、药学和生物化学等领域获得了长足的发展,特别是由科研领域拓展到临床诊断,开启了疾病诊断技术的新篇章。阿尔茨海默病（Alzheimer’s disease,AD）,又称老年性痴呆症,是现代社会第四大致死疾病。随着我国人口的快速老龄化,重视对AD的防治是实现健康老龄化以及国民经济持续发展的重要保障之一。本文对LC-MS的新进展进行了简介,并详细综述了近3年来其在AD研究中的应用,以期相关方法获得更好的理解与更多的关注。     

Two-Term and multi-term approximation of the nonstationary electron velocity distribution in an electric field in a gas

A very efficient, strict nonstationary multi-term approach has been developed as a generalization of the conventional and the strict nonstationary two-term approximations used for solving the nonstationary , electron Boltzmann equation. As a first application the temporal relaxation of electrons in a model plasma acted upon by a de electric field has been investigated. The results are compared with corresponding ones obtained by the conventional and the strict nonstationary two-term approach as well as with very accurate Monte Carlo simulations. Perfect agreement between nonstationary eight-term Boltzmann and Monte Carlo calculations is found.     

A theory of adsorption kinetics with time delay and its application to overshoot and oscillation in the surface tension of gelatin solution

A theory of adsorption kinetics with time delay [Ohshima et al. (1992) Colloid Polym. Sci. 270:707] is developed and applied to the surface tension of a polymer solution. It is found that the general appearance of the overshoot and oscillation in the time course of the surface tension of aqueous gelatin solution observed by Sato and Ueberreiter [(1979) Makromol. Chem. 180:829, 1107; (1979) Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 20:907) can be explained by the present theory.     

A computational study of surface tension determination of dense fluids as benzene,toluene, methanol,ammonia, ethylene,and carbon monoxide

In this study, the parameters of linear isotherm regularity, which called LIR equation state used to compute the surface tension of some dense fluids as benzene, toluene, methanol, ammonia, ethylene, and carbon monoxide. An expression has derived for radial distribution function (RDF) at constant temperature, g (σ), for a real fluid by the use of LIR. This expression, which is related to intermolecular interaction, can be used to describe the temperature–density dependency of RDF at constant temperature, g (σ, ρ, T). In addition, we derive an expression for surface tension of dense fluids (CO, C₆H₆, C₆H₅CH₃, CH₃OH, NH₃, and C₂H₄) using the LIR and g (σ, ρ, T). Unlike previous models, it has shown that, surface tension can obtain without employing ΔH and ΔS. Only P-V-T experimental data have been used to calculate the surface tension. Comparison of the calculated values of surface tension by LIR with the values obtained experimentally show this method is not precise. This problem has led us to try to obtain the expression for surface tension using the extended parameters A, B (A and B are the temperature-dependent parameters which noticeably are depended on attraction and repulsion). The obtained result shows that the accuracy of this method is very high and quite admissible.     

Interfacial and micellar properties of some anionic/cationic binary surfactant systems. 1. Surface properties and prediction of surface tension

The surface tension equations of binary surfactant mixtures are established by combining the Szyszkowski equation for pure surfactant solutions and extended nonideal theory for mixed adsorption. They are then successfully applied to two relatively long-chain anionic/cationic binary surfactant systems: triethanolammonium dodecylpoly(oxyethylene)sulfate, as an anionic species (containing about 2 ethylene oxide units), mixed with dodecyltrimethylammonium bromide or hexadecyltrimethylammonium bromide. The composition of the mixed monolayer is mixing-ratio dependent and is slightly asymmetric: for overall equimolar mixtures, the larger mole fraction in the mixed monolayer is that of the more surface-active ion. The strong synergetic effects observed in the surface tension reduction efficiency are reflected by large negative β^s parameters, according to regular solution theory. They can be interpreted by the more negative adsorption free energy of each surfactant and the smaller area occupied by surfactant hydrocarbon chains in the mixed monolayer. Received: 20 April 1998 /Accepted in revised form: 27 August 1999     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Disjoining pressure and the film-height-dependent surface tension of thin liquid films: New insight from capillary wave fluctuations

In this paper we review simulation and experimental studies of thermal capillary wave fluctuations as an ideal means for probing the underlying disjoining pressure and surface tensions, and more generally, fine details of the Interfacial Hamiltonian Model. We discuss recent simulation results that reveal a film-height-dependent surface tension not accounted for in the classical Interfacial Hamiltonian Model. We show how this observation may be explained bottom-up from sound principles of statistical thermodynamics and discuss some of its implications.     

吡啶基离子液体[C_6py][DCA]热力学性质及利用新E?tv?s方程预测其表面张力

制备了吡啶类离子液体N-己基吡啶二氰胺盐[C_6py][DCA],并用核磁共振氢谱(~1H NMR)、核磁共振碳谱(~(13)C NMR)、差热扫描量热(DSC)、傅里叶变换红外(FT-IR)光谱对其进行表征。在288.15–338.15 K温度范围内,采用标准加入法,测定其密度(ρ)、表面张力(γ)和折光率(n_D)。在测得的实验数据的基础上,得到了离子液体[C_6py][DCA]的分子体积(V_m)、表面能(E_a)、摩尔极化度(R_m)和极化率(α_p)。结果显示E_a、R_m和α_p几乎不随温度的变化而发生改变。本文还提出了摩尔表面Gibbs自由能(g_s)的概念,并改进了E?tv?s方程。同时还计算了gs、临界温度(T_c)和E?tv?s方程经验参数(kE),并预测了离子液体[C_6py][DCA]的表面张力,预测值与实验值具有较好的一致性。     

Heterogeneity of the surface energy on unused C18-chromolith adsorbents in reversed-phase liquid chromatography

Single-component adsorption isotherm data were acquired by frontal analysis (FA) for phenol and caffeine on a new C18-Chromolith column (Merck, Darmstadt, Germany), using a water-rich mobile phase (methanol/water, 15/85, v/v). These data were modeled for best agreement between the experimental data points and the adsorption isotherm model. The adsorption-energy distributions, based on the expectation-maximization (EM) procedure, were also derived and used for the selection of the best isotherm model. The adsorption energy distributions (AEDs) for phenol and caffeine converged toward a trimodal and a quadrimodal distribution, respectively. Energy distributions with more than two modes had not been reported before for the adsorption of these compounds on packed columns. The third high energy mode observed for both phenol and caffeine seems to be specific of the surface of the monolithic column while the first and second low energy modes have the same physical origin as the two modes detected on packed columns. These results suggest significant differences between the structures of the porous silica in these different materials.     

Study of the carbon fiber–poly(ether–ether–ketone) (PEEK) interfaces, 1: surface characterization of fibers and matrices,and interfacial adhesion energy

The aim of this general study is to determine the physicochemical characteristics and mechanical properties of carbon fiber–PEEK interfaces. In the first part, the dispersive component of the surface energy and the electron acceptor–donor (acid–base) characteristics of PEEK polymer and different types of untreated and surface-treated carbon fibers are determined by means of inverse gas–solid chromatography at infinite dilution. It appears, in particular, that the acid–base surface properties of PEEK and, consequently, the orientation of macromolecules near the surface, depend on the processing of this polymer. Moreover, according to previous work, an estimation of the adhesion energy, corresponding to physical interactions (London and acid–base interactions) at carbon fiber–PEEK interfaces is proposed. Whatever the surface characteristics of PEEK, the highest level of carbon fiber–PEEK adhesion is achieved in systems involving oxidized or sized carbon fibers.     

Simultaneous oscillations of surface energy, superficial mass and electrode potential in the course of galvanostatic oxidation of formic acid

Simultaneous oscillations of electrode potential, surface mass and specific surface energy have been detected in the course of galvanostatic oxidation of formic acid on platinum by using a Koesters laser interferometer combined with an electrochemical quartz crystal microbalance. Changes of surface energy data measured with the electrochemical Koesters laser interferometer and with the electrochemical bending beam technique are shown to be equivalent. Problems related to the interpretation of the measured data are discussed.Dedicated to Professor György Horányi on the occasion of his 70th birthday     

The effect of counterions on the surface adsorption and micelle formation in mixed surfactant systems of dodecyl sulfates

 The surface tension of the aqueous solutions of sodium dodecyl sulfate (SDS) and tetramethylammonium dodecyl sulfate (TMADS) was measured as a function of total molality of the surfactants at fixed composition of TMADS at 298.15 K under atmospheric pressure. The phase diagrams of adsorption and of micelle formation, the activity coefficients, and the excess Gibbs energy were calculated to estimate the deviation from the ideal mixing quantitatively. The preferential adsorption and the micelle formation for TMA⁺ to Na⁺ is attributable to some extent to the hydrophobicity of the methyl groups of TMA⁺. The composition of TMA⁺ in the micelle is larger than that in the adsorbed film at equilibrium. That is, a larger hydrated counterion is more likely to exist in the micelle than in the adsorbed film owing to geometrical benefit. The negative values of the excess Gibbs energy of the adsorbed film and of the micelle arise from the positive ones of the excess entropy greater than that of excess enthalpy. The counterions of very similar size are mixed ideally in the micelle and the size effect appears sensitively in the adsorbed film. Received: 23 May 2001 Accepted: 16 July 2001