Dependence Of Surface Tension Research Articles

Laser-induced capillary effect in thin layers of water-alcohol mixtures.

The effect of droplet formation in thin layers of water-alcohol mixtures upon laser heating was studied. The droplet growth in the laser beam is governed by the surface tension gradient, which induces solutocapillary flows from the periphery to the center of the heated area. This gradient arises due to the local increase in surface tension caused by the evaporation of alcohol from the heated area of the layer. The experimental results have shown that the increase in the initial concentration of water in the mixture gives rise to the increase in droplet size. However, the increase in the power of laser irradiation leads to a decrease in the droplet growth rate. A simplified one-dimensional model of droplet growth is developed. The model involves the dependence of surface tension on both the temperature and concentration of components in the mixture, as well as the evaporation and condensation of alcohol. The experimental results are compared with those obtained using numerical simulations. A reasonable agreement between experimental and numerical results was shown.

Evaluation of the Surface Tension of Silicon-Gold Binary Liquid Alloy

The gold-catalyzed vapor-liquid-solid (VLS) method is widely used for silicon nanowire (Si NW) fabrication. As the VLS process is influenced by the physical properties of the catalytic silicon-gold (Si-Au) droplet, quantifying the surface tension of the liquid alloy is important to achieve better control of the wire growth. Because the experimental measurement of the surface tension is difficult, it is necessary to obtain reasonable estimates from computational models. In this work, we conducted molecular dynamics simulations with a modified embedded-atom potential developed for the Si-Au binary system, and evaluated the surface tension γ based on the Virial stress expression. The dependence of surface tension γ on the Si fraction χ and temperature T is predicted. The entropy of the liquid-vapor interface was extracted from the slope of the γ-T curve. The Si concentration and stress distributions near the surface are also predicted. Our surface tension evaluation enables theoretical predictions of droplet and nanowire shape, and provides physical inputs for continuum phase field models of VLS growth.

Simulation of the main physical processes in remote laser penetration with large laser spot size

A 3D model is developed to simulate remote laser penetration of a 1mm Aluminum metal sheet with large laser spot size (∼ 3x3cm2), using the ALE3D multi-physics code. The model deals with the laser-induced melting of the plate and the mechanical interaction between the solid and the melted part through plate elastic-plastic response. The effect of plate oscillations and other forces on plate rupture, the droplet formation mechanism and the influence of gravity and high laser power in further breaking the single melt droplet into many more fragments are analyzed. In the limit of low laser power, the numerical results match the available experiments. The numerical approach couples mechanical and thermal diffusion to hydrodynamics melt flow and accounts for temperature dependent material properties, surface tension, gravity and vapor recoil pressure.

Liquid-gas asymmetry and the wave-vector-dependent surface tension

Attempts to extend the capillary-wave theory of fluid interfacial fluctuations to microscopic wavelengths, by introducing an effective wave-vector (q)-dependent surface tension σeff(q), have encountered difficulties. There is no consensus as to even the shape of σeff(q). By analyzing a simple density functional model of the liquid-gas interface, we identify different schemes for separating microscopic observables into background and interfacial contributions. In order for the backgrounds of the density-density correlation function and local structure factor to have a consistent and physically meaningful interpretation in terms of weighted bulk gas and liquid contributions, the background of the total structure factor must be characterized by a microscopic q-dependent length ζ(q) not identified previously. The necessity of including the q dependence of ζ(q) is illustrated explicitly in our model and has wider implications; i.e., in typical experimental and simulation studies, an indeterminacy in ζ(q) will always be present, reminiscent of the cutoff used in capillary-wave theory. This leads inevitably to a large uncertainty in the q dependence of σeff(q).

Dispersion media based on water-soluble binary compositions of PEG-nonionic surface-active substances for abrasive metalworking

The results of an investigation of the dispersion, rheological, and surface-active properties of aqueous emulsions of nonionic superficially active substance (SAS) and water-soluble binary compositions of polyethylene glycol (PEG)-nonionic SAS are represented. Synergism in the dispersing effect of both components of water binary compositions is revealed during the abrasive working of iron, copper, and aluminum alloys. The occurrence of synergism is explained by the formation of intermolecular complexes of PEG-nonionic SAS, which is indicated by the results of investigations of the concentration dependence of dynamic viscosity and surface tension of compositions. The occurrence magnitude of the synergism of the dispersion properties of components of compositions of PEG-nonionic SAS is determined by the selectivity of the adsorption interaction of intermolecular complexes relative to the freshly formed surface of dispersed alloys.

Principles of Predicting Temperature and Concentration Dependences of Surface Tension for Molten Metallurgical Slags of the CaO–Al2O3–CaF2 System

An original method is developed for predicting the temperature and concentration dependences of surface tension for molten slag of the CaO‐Al 2 O 3 ‐CaF 2 system and its subsystem components. It is based on approximating component activity within the volume and at the surface of a melt within the scope of associated solution theory. Free model parameters are established on the basis of available experimental data for thermodynamic, structure-sensitive physicochemical, including surface tension, molten slag properties. The method developed makes it possible to predict the temperature and concentration dependences of surface tension for metallurgical slags containing apart from oxides, compounds of a different nature with accuracy no worse than experimental, and it may be extended to melts of any complexity and component content. Prospects for its use are demonstrated for selecting a slag regime in various metallurgical processes.

Dust in brown dwarfs and extra-solar planets

Context.Clouds form in atmospheres of brown dwarfs and planets. The cloud particle formation processes, seed formation and growth/evaporation are very similar to the dust formation process studied in circumstellar shells of AGB stars and in supernovae. Cloud formation modelling in substellar objects requires gravitational settling and element replenishment in addition to element depletion. All processes depend on the local conditions, and a simultaneous treatment is required.Aims.We apply new material data in order to assess our cloud formation model results regarding the treatment of the formation of condensation seeds. We look again at the question of the primary nucleation species in view of new (TiO2)N-cluster data and new SiO vapour pressure data.Methods.We applied the density functional theory (B3LYP, 6-311G(d)) using the computational chemistry package Gaussian09 to derive updated thermodynamical data for (TiO2)Nclusters as input for our TiO2seed formation model. We tested different nucleation treatments and their effect on the overall cloud structure by solving a system of dust moment equations and element conservation for a prescribed Drift-Phoenixatmosphere structure.Results.Updated Gibbs free energies for the (TiO2)Nclusters are presented, as well as a slightly temperature dependent surface tension forT= 500...2000 K with an average value ofσ∞= 480.6 erg cm-2. The TiO2seed formation rate changes only slightly with the updated cluster data. A considerably larger effect on the rate of seed formation, and hence on grain size and dust number density, results from a switch to SiO nucleation. The question about the most efficient nucleation species can only be answered if all dust/cloud formation processes and their feedback are taken into account. Despite the higher abundance of SiO over TiO2in the gas phase, TiO2remains considerably more efficient at forming condensation seeds by homogeneous nucleation. The paper discusses the effect on the cloud structure in more detail.

Enhanced wavelength-dependent surface tension of liquid-vapour interfaces

Due to the simultaneous presence of bulk-like and interfacial fluctuations the understanding of the structure of liquid-vapour interfaces poses a long-lasting and ongoing challenge for experiments, theory, and simulations. We provide a new analysis of this topic by combining high-quality simulation data for Lennard-Jones fluids with an unambiguous definition of the wave-number–dependent surface tension based on the two-point correlation function of the fluid. Upon raising the temperature, develops a maximum at short wavelengths. We compare these results with predictions from density functional theory. Our analysis has repercussions for the interpretation of grazing-incidence small-angle X-ray scattering (GISAXS) at liquid interfaces.

Vapour-to-liquid nucleation in cone pores

In this work, we perform a systematic study on the vapour-to-liquid nucleation in a cone pore by using comparatively the classical nucleation theory (CNT) and the constrained lattice density functional theory (constrained LDFT). Three different nucleation scenarios are observed depending on the contact angle θ and apex angle α: the spontaneous phase transition, nucleation with a critical nucleus in Cassie state and nucleation with a critical nucleus in Wenzel state. We also found that both the diagram for nucleation mechanisms and the reduced nucleation barriers with respect to the homogeneous nucleation given by the CNT are at least qualitatively consistent with those from the constrained LDFT. For an increasingly small critical nucleus, the difference between nucleation behaviours from two methods becomes significant due to the macroscopic approximations embedded in CNT, which fails to describe the curvature dependence of surface tension, the line tension effect and the space confinement effect.

105 3角形分割された膜モデルにおける表面張力の膜形態依存性(OS1-(2),OS1オーガナイズドセッション≪計算力学と数値シミュレーション≫)

105 3角形分割された膜モデルにおける表面張力の膜形態依存性(OS1-(2),OS1オーガナイズドセッション≪計算力学と数値シミュレーション≫)

Non-isothermal bubble rise: non-monotonic dependence of surface tension on temperature

AbstractWe study the motion of a bubble driven by buoyancy and thermocapillarity in a tube with a non-uniformly heated walls, containing a so-called ‘self-rewetting fluid’; the surface tension of the latter exhibits a parabolic dependence on temperature, with a well-defined minimum. In the Stokes flow limit, we derive the conditions under which a spherical bubble can come to rest in a self-rewetting fluid whose temperature varies linearly in the vertical direction, and demonstrate that this is possible for both positive and negative temperature gradients. This is in contrast to the case of simple fluids whose surface tension decreases linearly with temperature, for which bubble motion is arrested only for negative temperature gradients. In the case of self-rewetting fluids, we propose an analytical expression for the position of bubble arrestment as a function of other dimensionless numbers. We also perform direct numerical simulation of axisymmetric bubble motion in a fluid whose temperature increases linearly with vertical distance from the bottom of the tube; this is done for a range of Bond and Galileo numbers, as well as for various parameters that govern the functional dependence of surface tension on temperature. We demonstrate that bubble motion can be reversed and then arrested only in self-rewetting fluids, and not in linear fluids, for sufficiently small Bond numbers. We also demonstrate that considerable bubble elongation is possible under significant wall confinement, and for strongly self-rewetting fluids and large Bond numbers. The mechanisms underlying the phenomena observed are elucidated by considering how the surface tension dependence on temperature affects the thermocapillary stresses in the flow.

Influence of the arc plasma parameters on the weld pool profile in TIG welding

Magneto-hydrodynamic simulations of the arc and fluid simulations of the weld pool can be beneficial in the analysis and further development of arc welding processes and welding machines. However, the appropriate coupling of arc and weld pool simulations needs further improvement. The tungsten inert gas (TIG) welding process is investigated by simulations including the weld pool. Experiments with optical diagnostics are used for the validation. A coupled computational model of the arc and the weld pool is developed using the software ANSYS CFX. The weld pool model considers the forces acting on the motion of the melt inside and on the surface of the pool, such as Marangoni, drag, electromagnetic forces and buoyancy. The experimental work includes analysis of cross-sections of the workpieces, highspeed video images and spectroscopic measurements. Experiments and calculations have been performed for various currents, distances between electrode and workpiece and nozzle diameters. The studies show the significant impact of material properties like surface tension dependence on temperature as well as of the arc structure on the weld pool behaviour and finally the weld seam depth. The experimental weld pool profiles and plasma temperatures are in good agreement with computational results.

Group contribution and parachor analysis of experimental data on densities and surface tension for six ionic liquids with the [PF6] anion

Experimental data over the temperature range from 268 to 365K are presented on the 0.1MPa density and surface tension for three 1-Cn-3-methylimidazolium hexafluorophosphates with n=5, 7, and 9. In addition, experimental data on surface tension dependence on temperature are presented for hexafluorophosphates with [C3MIM], [C4MMIM] and [C4MPy] cation. For all of these ionic liquids there exists only sporadic data sets or they have not yet been studied at all in these two respects. The reported density data were obtained using a single-sinker buoyancy method. The expanded combined uncertainty at 0.95 confidence level in the density and surface tension measurements is estimated to be, respectively, from 0.3 to 0.7kgm−3 and from 0.05 to 0.07mNm−1. To determine the buoyancy and surface forces, the Krűss K100MK2 tensiometer was used. A group contribution model is proposed to generate recommended values of density at 0.1MPa for 1-Cn-3-methylimidazolium hexafluorophosphates with n=2–9 at temperatures from 273 to 365K. The worth-case relative error of the recommended density values is estimated to 0.1%. The homologous series of the imidazolium-based hexafluorophosphates shows statistically discernible odd-even effects in the molar volume, and in enthalpy and entropy of surface formation at the level of the order of magnitude of 10−1cm3mol−1, 100mJm−2 and 10−3mJm−2K−1, respectively.

Novel dicationic pyrimidinic surfactant: Self-assembly and DNA complexation

Novel pyrimidinic surfactant with two morpholinium head groups and two decyl tails has been synthesized. As determined by breakpoints on concentration dependences of surface tension and conductivity, the pyrimidinic amphiphile forms aggregates beyond critical micelle concentration of 3.4 mM, which is supported by fluorescence ratiometry, dye solubilization technique and dynamic light scattering data (DLS). The NMR self-diffusion data testify that different types of aggregates are probably formed in the solution above 12 mM. The dual structural behavior is in line with fluorescence anisotropy results and packing parameter calculations. The complexation ability of the pyrimidinic amphiphile toward plasmid DNA pK18 is supported by DLS and zeta potential measurements indicating the occurrence of the compaction and charge neutralization effect. The lipoplex formation is also supported by ethidium bromide exclusion data. The ability of the amphiphile of integrating with lipid bilayer is revealed by measurements of the temperature of main phase transition.

Properties of Poly (ethylene oxide)/ whey Protein Isolate Nanofibers Prepared by Electrospinning

A mixture of solutions of whey protein isolate (WPI) and poly (ethylene oxide) (PEO) were employed to fabricate nanofibers by the electrospinning technique. The PEO/WPI ratio was varied in order to obtain PEO:WPI nanofibers with different concentrations of homopolymers. The dependence of morphology, viscosity, conductivity, surface tension, thermal and vibrational properties was studied as function of the PEO/WPI ratio. The results show that at higher viscosity, we obtained soft and smooth fibers with diameters ranging between 227 ± 36 nm and 264 ± 66 nm; while the solutions with low viscosity ( 527 μScm−1) promote the formation of beads. The nanofibers were thermally stable for temperatures below 200 °C and the initial thermal degradation temperatures is slightly affected by the PEO:WPI ratio. The FTIR results revealed that the crosslinking favors the formation of fibers. Rosmarinus officialis extract was used for explore a possible application of the nanofibers as a delivery system. The dissolution rate of the rosemary extract from the nanofibers was measured in phosphate buffer solutions with pH of 1.2, 7.5 and 9.0. The total rosemary content was dissolved from the nanofibers, in the aqueous medium, on a time with depends on the pH of the buffer solution.

The dependence of surface tension on surface properties of ionic surfactant solution and the effects of counter-ions therein.

In the present paper, we aim to investigate the dependence of surface tension on the surface properties and reveal the counter-ion effects on the adsorption of ionic surfactants on the solution surface. The surface tension, surface excess and surface concentration (defined as the amount of surfactant adsorbed in the surface phase divided by the surface area) of two anionic surfactants, namely dodecyl sulfate sodium and dodecyl sulfate caesium, dissolved in non-aqueous polar solvent formamide have been separately measured at 6 °C through independent experiments. Then, the correlation of surface tension with surface concentration and that of surface tension with surface excess is inspected in detail. It was found that there is a linear relationship between the surface tension and the surface concentration for the pure solutions of each surfactant, but their surface tension and surface excess cannot be correlated linearly. It is striking that the same surface tension-surface concentration linearity holds for two different surfactants, although they have apparently distinct counter-ions. Based on this finding, it is derived that the surface tension is decided by surface concentration of the surface active ions. After analyzing the surface structure, it is concluded that the counter-ions affect the surface tension indirectly through modifying the adsorption amount of the surface active ions in the surface layer.

Disjoining Pressure, Healing Distance, and Film Height Dependent Surface Tension of Thin Wetting Films

In this work, we simulate the adsorption of wetting liquid argon films on a model substrate. We calculate the disjoining pressure isotherm and show that it is completely dominated by the long-range van der Waals interactions. Thick films exhibit the expected Hamaker power law decay, but a quantitative description of thin films requires consideration of the detailed structure of the adsorbed layer. The spectrum of film height fluctuations is calculated and shown to provide reliable estimates of the disjoining pressure for all films studied. However, it is observed that the full spectrum can only be reproduced provided that we account for a film height dependent surface tension proportional to the derivative of the disjoining pressure. A simple theory is worked out that describes well the observed film height dependence. Having at hand both the surface tension and the disjoining pressure, we calculate the healing distance of the liquid films, which differs from the classical expectation by a constant of the same order of magnitude as the bulk correlation length. We show these findings have important implications on the behavior of adsorbed liquids and determine corrections to the augmented Young–Laplace equation at the subnanometer length scale.

Corresponding states correlation for temperature dependent surface tension of normal saturated liquids

A new simple correlation based on the principle of corresponding state is proposed to estimate the temperature-dependent surface tension of normal saturated liquids. The correlation is a linear one and strongly stands for 41 saturated normal liquids. The new correlation requires only the triple point temperature, triple point surface tension and critical point temperature as input and is able to represent the experimental surface tension data for these 41 saturated normal liquids with a mean absolute average percent deviation of 1.26% in the temperature regions considered. For most substances, the temperature covers the range from the triple temperature to the one beyond the boiling temperature.

Pair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid–vapour interface

We study the density-density correlation function G(r, r′) in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z′; q) and local structure factor S(z; q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension σ(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z′; q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that ‘float’ with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the ‘crossing-criterion’ nor the new ‘floating interface’ definition of σ(q) are quantities directly measurable from the total structure factor Stot(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret σ(q).

Two-dimensional percolation at the free water surface and its relation with the surface tension anomaly of water.

The percolation temperature of the lateral hydrogen bonding network of the molecules at the free water surface is determined by means of molecular dynamics computer simulation and identification of the truly interfacial molecules analysis for six different water models, including three, four, and five site ones. The results reveal that the lateral percolation temperature coincides with the point where the temperature derivative of the surface tension has a minimum. Hence, the anomalous temperature dependence of the water surface tension is explained by this percolation transition. It is also found that the hydrogen bonding structure of the water surface is largely model-independent at the percolation threshold; the molecules have, on average, 1.90 ± 0.07 hydrogen bonded surface neighbors. The distribution of the molecules according to the number of their hydrogen bonded neighbors at the percolation threshold also agrees very well for all the water models considered. Hydrogen bonding at the water surface can be well described in terms of the random bond percolation model, namely, by the assumptions that (i) every surface water molecule can form up to 3 hydrogen bonds with its lateral neighbors and (ii) the formation of these hydrogen bonds occurs independently from each other.