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.     

The contribution of hydrogen bonds to the surface tension of water

The surface energy, the surface free energy and the surface entropy of liquid water are calculated from the decrease in the number of hydrogen bonds in the surface layer, estimated on the bash of a simplified aater structure scheme. In the calculations of the free energy density function only the hydrogen-bond interactions between molecules are taken into consideration. The resulting surface free energy of water is ≈43 mN/m at 25°C. The calculated temperature dependence is consistent with that observed.     

Internal pressure and surface tension of bare and hydrogen coated silicon nanoparticles

We present a study of internal pressure and surface tension of bare and hydrogen coated silicon nanoparticles of 2-10 nm diameter as a function of temperature, using molecular dynamics simulations employing a reparametrized Kohen-Tully-Stillinger interatomic potential. The internal pressure was found to increase with decreasing particle size but the density was found to be independent of the particle size. We showed that for covalent bond structures, changes in surface curvature and the associated surface forces were not sufficient to significantly change bond lengths and angles. Thus, the surface tension was also found to be independent of the particle size. Surface tension was found to decrease with increasing particle temperature while the internal pressure did not vary with temperature. The presence of hydrogen on the surface of a particle significantly reduces surface tension (e.g., drops from 0.83 J/m(2) to 0.42 J/m(2) at 1500 K). The computed pressure of bare and coated particles was found to follow the classical Laplace-Young equation.     

MEA-CO2-水溶液表面张力实验和模型

用全自动表面张力仪测定了293．15-323．15K温度范围内,具有不同C02载荷的乙醇胺（Monoethanolamine,MEA）水溶液的表面张力,提出了计算MEA-CO2-水体系表面张力的半经验模型,计算结果与实验值吻合良好．通过实验和计算相结合,阐明了温度、MEA浓度和C02载荷对MEA-CO2-水体系表面张力的影响规律．     

Experiments and model for the surface tension of carbonated monoethanolamine aqueous solutions

The surface tension of carbonated monoethanolamine aqueous solutions from 293.15 to 323.15 K was measured by using an automatic surface tension-meter.A model applicable for the surface tension of MEA-CO2-water mixtures was proposed and the calculated results agreed well with the experiments.The influences of temperature,MEA concentration and CO2 loading were demonstrated on the basis of experiments and calculations.     

The density and surface tension of high-temperature stratifying mixtures of alkali metal bromides and lithium fluoride

The density and interphase tension of molten mixtures of lithium fluoride with potassium, rubidium, and cesium bromides were measured in the region of limited mutual solubility by the hydrostatic weighing and meniscus weight methods. The dependences of properties on the size ratio between the mixed ions were determined. The critical order parameters for systems with the predominantly ionic character of interparticle interactions were estimated.     

On the difference between hydrogen fluoride and hydrogen chloride crystals

The geometrical and energetical parameters of hydrogen fluoride and hydrogen chloride crystals are calculated using the periodic Hartree–Fock method with 6-31G and 6-31G(d,p) basis sets. The comparison of the stabilisation energies reveals that HCl crystals are about 75% less stable than HF crystals. The activation energy for collective proton movements are computed and discussed in view of data of isolated infinite chains. The barriers of 13.1 and 40.0 kcal mol⁻¹ at 6-31G(d,p) level are found for HF and HCl crystals.     

On the acidity of hydrogen fluoride

An explanation is proposed for the rapid increase in acidity in progressing from dilute solutions of HF in H₂O to solutions of greater concentration ($\text{ca.}$ 10M). Anhydrous HF has been shown to be more acidic than generally believed and to require very small adventitious concentrations of F^? to become quite basic. Oxidation of I₂ is used to demonstrate the dependence of the nature of species in HF solution on the acidity or basicity of the medium.     

Estimations of surface tensions at different temperatures by a corresponding-states group-contribution method

Two new equations (CSGC-ST1 and CSGC-ST2) for estimating surface tensions by applying a corresponding-states group-contribution method (CSGC) were proposed. The CSGC-ST1 equation needs only the normal boiling point data of substances to estimate accurately the surface tensions of pure substances at different temperatures. On the other hand, if the surface tension data at 20°C are available, the CSGC-ST2 equation yields estimates with higher accuracies. Group-contribution parameters for 86 groups were obtained by correlating the surface tension experimental data at different temperatures (totally 3699 datum points) of 427 pure substances including various alkanes, alkenes, cyclo-, aromatic and oxygenated hydrocarbons as well as compounds containing sulfur, nitrogen and halogen. Correlated results showed that the new models provided a wide-range of applicability and their estimation accuracies were significantly superior over the conventional corresponding-states methods currently used.     

Polarization model representation of hydrogen fluoride for use in gas- and condensed-phase studies

The polarization model, originally developed to describe deformable and ionizable water molecules, has been extended to hydrogen fluoride. Since electronic polarization is explicitly included, the interaction energy in aggregates of molecules (with or without ions) is nonadditive. The model properly describes the structure of (HF)₂, including off-axis bending of the proton acceptor molecule. Calculations are presented to illustrate elementary gas-phase reactions involving proton transfer between HF and F^?, and H₂F⁺ and F^?.     

Nonconventional hydrogen bonding between clusters of gold and hydrogen fluoride

The bonding patterns between small neutral gold Au(3 < or = n < or = 7) and hydrogen fluoride (HF)(1 < or = m < or = 4) clusters are discussed using a high-level density functional approach. Two types of interactions, anchoring Au-F and F-H...Au, govern the complexation of these clusters. The F-H...Au interaction exhibits all the characteristics of nonconventional hydrogen bonding and plays a leading role in stabilizing the lowest-energy complexes. The anchor bonding mainly activates the conventional F-H...F hydrogen bonds within HF clusters and reinforces the nonconventional F-H...Au one. The strength of the F-H...Au bonding, formed between the terminal conventional proton donor group FH and an unanchored gold atom, depends on the coordination of the involved gold atom: the less it is coordinated, the stronger its nonconventional proton acceptor ability. The strongest F-H...Au bond is formed between a HF dimer and the singly coordinated gold atom of a T-shape Au4 cluster and is accompanied by a very large red shift (1023 cm(-1)) of the nu(F-H) stretch. Estimations of the energies of formation of the F-H...Au bonds for the entire series of the studied complexes are provided.     

Modification of the CO2 surface tension calculation model under low-temperature and high-pressure condition

Surface tension is an important thermodynamic parameter. In researching the removal mechanism of CO₂ in natural gas in supersonic expansion process, the most basic and important task is to calculate the surface tension of CO₂ under low-temperature and high-pressure condition. In this paper, a comparative study on the relevant calculation methods is carried out and the computational method applied to simulate the phase transition of CO₂ supersonic condensation is selected. On this basis, the CO₂ surface tension calculation model is modified and the calculation method, by using the piecewise function, is proposed. The results show that the average deviation of the piecewise function is only 0.95%, which is lower than the deviation of any single correlation. It can achieve an accurate prediction of the surface tension of the liquid CO₂.     

Application of the UNIFAC model for prediction of surface tension and thickness of the surface layer in the binary mixtures

The specific sorption of Eu(III) and Y(III) on γ-alumina was investigated with solid-state (1)H NMR. Solution pH was shown to influence the recorded (1)H NMR spectra of γ-alumina, and thus, metal ion-containing samples were prepared under constant pH conditions, 8.00±0.05. The metal ion concentration in the samples was varied between 6.58×10(-7) M - 3.95×10(-4) M in case of Y(3+) and 6.58×10(-8) M - 1.32×10(-4) M in case of Eu(3+). The mineral concentration was kept constant at 4 g/l. After separation of the liquid phase, the samples were dried under vacuum to remove physisorbed water from the mineral surface. However, even after 48 h of drying at 150°C and 20 mTorr, water was still detected in the proton spectra as two distinct peaks with chemical shifts at 1.3 and 0.9 ppm. The europium addition to the γ-alumina samples induced significant spectral changes in comparison with yttrium-containing samples. These changes were attributed to the paramagnetism of europium rather than to complexation reactions occurring on the mineral surface. Proton spectra obtained for yttrium samples were therefore used to detect the spectral changes induced by the sorption reaction itself. The results revealed a large distribution of protons being removed from the mineral surface upon yttrium complexation. Removed protons were assigned to both bridging surface hydroxyls such as (Al(VI))(2)-OH as well as to terminal hydroxyls, e.g., of type Al(VI)-OH. Acidic protons belonging to (Al(VI))(3)-OH groups were not observed to participate in the surface reaction.     

Pseudopotential studies of the water and hydrogen fluoride molecules

A model pseudopotential is used to calculate valence electron properties for H₂O and HF. The calculated geometries, force constants, and ionization potentials are in excellent agreement with the results of corresponding all-electron calculations.     

Relationship between surface tension and surface coverage

Surfactant action is caused in part by a dramatic reduction in surface tension. Using surface excess measurements from a radioactive surfactant, it was possible to show that (a) the surface tension declines only slightly when the occupancy of the air/water interface increases from 0 to 60% of the maximum and (b) the steep drop in surface tension in region B (Figure 1 ), frequently observed to be linear, begins at about 80% occupancy. Surfactant continues to enter the interface cooperatively up to and past the critical micelle concentration. Linearity in region B is not indicative of surface saturation despite a seemingly constant surface excess throughout the region. The disparity between interfacial areas determined by surface tension and by other methods is discussed in terms of these results.     

A model for simulating the dynamic surface tension behavior of aqueous surfactant dispersions

A dynamic adsorption model for surface-active materials at air/liquid interfaces with the consideration of aggregate dissolution effect was developed to investigate the dynamic surface tension behavior of aqueous surfactant dispersions. Two catanionic surfactants, cetylpyridinium dodecylsulfate (CP-DS) and dodecyltrimethylammonium dodecylsulfate (DTMA-DS), with low critical aggregation concentrations were chosen as model systems. Dynamic surface tensions of aqueous CP-DS and DTMA-DS systems were measured by a drop volume tensiometer. A model with diffusion-controlled or mixed-kinetic dynamic adsorption mechanisms considering the dissolution effect of dispersed aggregates was developed to simulate the dynamic surface tension data. An analysis by comparing the model predictions with experimental data demonstrated that the dynamic surface tension behavior of aqueous CP-DS and DTMA-DS dispersions could be described with a diffusion-controlled dynamic adsorption model taking the aggregate dissolution effect into account.