Dependence Of Surface Tension Research Articles

Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory.

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO2). The molecular model of CO2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Thermophysical properties of the liquid Ga–Sn–Zn eutectic alloy

Higher demand and increased working temperatures in the energy production sector have prompted work on the development of new, more efficient and higher performance cooling for liquid metals. However, a lack of understanding of the thermophysical properties of the materials involved has limited the potential applications of such materials. This study presents the results of the temperature dependency of density, surface tension, viscosity, electrical conductivity, thermoelectric power and thermal conductivity for eutectic GaSnZn. The conducted measurements show higher melting temperature and surface tension, and lower thermal expansion coefficient, density, viscosity, electrical conductivity and thermal conductivity of eutectic GaSnZn compared to eutectic GaInSn.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

Marangoni natural convection in a cubical cavity filled with a nanofluid

Natural convection in a differentially heated cubical cavity filled with a water-based nanofluid under the Marangoni effect from the upper free surface is studied numerically. It is supposed that the Brownian diffusion and thermophoresis are the major slip mechanisms for nanoparticles. Dimensionless governing equations formulated using vector potential functions, vorticity vector and temperature have been solved by the finite difference method of the second-order accuracy. It should be noted that the Marangoni effect is owing to the dependences of surface tension on the temperature and nanoparticles concentration. The effects of the Marangoni number, Lewis number, buoyancy ratio parameter, Brownian diffusion parameter and thermophoresis parameter on nanofluid flow, heat and mass transfer have been analyzed. It has been revealed that a growth of Marangoni number results in the heat transfer rate reduction.

Thermal rupture of a free liquid sheet

We consider a free liquid sheet, taking into account the dependence of surface tension on the temperature or concentration of some pollutant. The sheet dynamics are described within a long-wavelength description. In the presence of viscosity, local thinning of the sheet is driven by a strong temperature gradient across the pinch region, resembling a shock. As a result, for long times the sheet thins exponentially, leading to breakup. We describe the quasi-one-dimensional thickness, velocity and temperature profiles in the pinch region in terms of similarity solutions, which possess a universal structure. Our analytical description agrees quantitatively with numerical simulations.

SYNTESIS of DIMERIC SURFACTANTS based on SYNTHANOL DS-10 AND ADIPINIC ACID

Mono- and di- esters of adipinic acid with long chain ethoxylated aliphatic alcohols (mixture of C10 – C12 and C16 – C18 alkohols) were obtained by the reaction of Synthanol DS-10 and adipinic acid and its dichloroanhydride. If adipinic acid with p-toluenesulfonic acid as catalyst were used as acylating agent and the mole ratio of Synthanol DS-10 to adipinic acid is 1:1 the yield of monoacylated product was 76 %. (temperature 120-125 °C, 3 h). If the mole ratio of Synthanol DS-10 to adipinic acid is 2:1 the yield of diacylated product was 80 % (temperature 120-125 °C, 6 h). Using dichloroanhydride of adipinic acid as acylating agent gives the 90 % (temperature 90-100 °C, 7.5 h) yield of diacylated product. The structure of all compounds was established by IR and NMR spectroscopy. Surface tension dependence on concentration in aqueous and alkaline medium was investigated for the obtained compounds. It was determined that the colloidal properties of the synthesized products differ significantly from the original Synthanol DS-10. The minimal surface tension of synthesized compounds is 25-33 mN/m. The surface activity of monoester in 5 % sodium hydroxide is 5.74 N·m2·mol-1 (for Synthanol DS-10 3.06 N·m2·mol-1). But in water their surface activity is 4.00 and 4.17, respectively. Opacity temperature in different mediums was established for the new compounds. Cloud point at the concentration of 0.25 g/dm3 of diester of adipinic acid in water (>100 °C) is significantly higher than for Synthanol DS-10 (81 °C) and for monoester (46 °C). In 5 % solution of sodium hydroxide the cloud points of all these compounds are the same (difference is 2-3 °C). The new products are stable in water and alkaline medium, but not stable in 0.1N solution of hydrochloric acid. The new synthesized surfactants from Synthanol DS-10 and adipinic acid (by the complex of colloidal and physical-chemical properties) are interesting as the ingredients of technical and household compositions. Forcitation:Lominoga E.A., Burmistrov K.S., Gevod V.S. Syntesis of dimeric surfactants based on synthanol DS-10 and adipinic acid. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N2. P. 91-96

Surfactant Interactions and Organization at the Gas-Water Interface (CTAB with Added Salt).

We have studied adsorbed layers of cetyltrimethylammonium bromide (CTAB) at air-water interfaces in the presence of added electrolyte. Fast bubble compression/expansion measurements were used to obtain the surface equation of state, i.e., the surface tension vs CTAB surface concentration dependence. We show that while a simple model where the surfactant molecules are assumed to be noninteracting is insufficient to describe the measured response of the surfactant layer, a modified Frumkin equation where the local interactions between the molecular components depend on their surface concentration captures the response. The variation of the effective interactions in the surfactant layer in the model shows that the interactions in the surfactant layer change from effectively repulsive to attractive with increasing surface concentration. Molecular dynamics simulations are performed to probe the origins of the change in the interactions. The simulations indicate that already at low surface concentrations the surfactants aggregate as highly dynamic rafts with surfactant orientation parallel to the interface. Increasing the concentration leads to a change in the assembly morphology at the interface: the surfactant layer thickens and the surfactants sample a range of tilted orientations with respect to the interfacial plane. The change from transient raftlike assemblies to dynamical aggregates at the interface involves a clear increase in the degree of counterion binding: we speculate that the flip of the effective interaction parameter in the model used to interpret the experimental results could result from this. The work here presents basic steps toward a proper understanding of the molecular organization and interactions of surfactants at an air-water interface. This is crucially important in understanding macroscopic properties of surfactant-stabilized systems such as foams, emulsions, and colloidal dispersions.

Effect of Channel Geometry and Properties of a Vapor–Gas Mixture on Volume Condensation in a Flow through a Nozzle

A method of direct numerical solution of the kinetic equation for the droplet size distribution function was used for the numerical investigation of volume condensation in a supersonic vapor–gas flow. Distributions of temperature for the gas phase and droplets, degree of supersaturation, pressure, fraction of droplets by weight, the number of droplets per unit mass, and of the nucleation rate along the channel were determined. The influence of nozzle geometry, mixture composition, and temperature dependence of the mixture properties on the investigated process was evaluated. It has been found that the nozzle divergence angle determines the vapor–gas mixture expansion rate: an increase in the divergence angle enhances the temperature decrease rate and the supersaturation degree raise rate. With an increase or decrease in the partial pressure of incondensable gas, the droplet temperature approaches the gas phase temperature or the saturation temperature at the partial gas pressure, respectively. A considerable effect of the temperature dependence of the liquid surface tension and properties on gas phase parameters and the integral characteristics of condensation aerosol was revealed. However, the difference in results obtained with or without considering the temperature dependence of evaporation heat is negligible. The predictions are compared with experimental data of other investigations for two mixtures: a mixture of heavy water vapor with nitrogen (incondensable gas) or n-nonane vapor with nitrogen. The predictions agree quite well qualitatively and quantitatively with the experiment. The comparison of the predictions with numerical results from other publications obtained using the method of moments demonstrates the usefulness of the direct numerical solution method and the method of moments in a wide range of input data.

Molecular Conformational Manifolds between Gas-Liquid Interface and Multiphasic

The analysis of conformational changes of hydrocarbon molecules is imperative in the prediction of their transport properties in different phases, such as evaporation/condensation coefficients (β) in the gas-liquid interface and evaporation rates of fuel droplets (k) in multiphases. In this letter, we analyze the effects of entropic contributions ( T Δ S e v ( T ) ) to Δ G e v ( T ) during the evaporation/condensation of chain conformers at the interface with a modified version of the solvation model SMD/ωB97X-D/cc-pVTZ in which the temperature dependency of surface tension and the interfacial flow density of the conformers is taken into account. The evaporation/condensation coefficient (β) and evaporation rate (k) are respectively calculated using the statistical associating fluid theory (SAFT) and a combined quantum-classical reaction rate theory named quantum transition state theory-classical kinetic gas theory (QTST-CKGT). The detailed analyses show the importance of internal entropic states over the interfacial layer induced by meso-confinement phenomena in the very vicinity of fuel droplets surfaces.

Equilibrium between a Droplet and Surrounding Vapor: A Discussion of Finite Size Effects.

In a theoretical description of homogeneous nucleation one frequently assumes an "equilibrium" coexistence of a liquid droplet with surrounding vapor of a density exceeding that of a saturated vapor at bulk vapor-liquid two-phase coexistence. Thereby one ignores the caveat that in the thermodynamic limit, for which the vapor would be called supersaturated, such states will at best be metastable with finite lifetime, and thus not be well-defined within equilibrium statistical mechanics. In contrast, in a system of finite volume stable equilibrium coexistence of droplet and supersaturated vapor at constant total density is perfectly possible, and numerical analysis of equilibrium free energies of finite systems allows to obtain physically relevant results. In particular, such an analysis can be used to derive the dependence of the droplet surface tension γ( R) on the droplet radius R by computer simulations. Unfortunately, however, the precision of the results produced by this approach turns out to be seriously affected by a hitherto unexplained spurious dependence of γ( R) on the total volume V of the simulation box. These finite size effects are studied here for the standard Ising/lattice gas model in d = 2 dimensions and an Ising model on the face-centered cubic lattice with 3-spin interaction, lacking symmetry between vapor and liquid phases. There also the analogous case of bubbles surrounded by undersaturated liquid is treated. It is argued that (at least a large part of) the finite size effects result from the translation entropy of the droplet or bubble in the system. This effect has been shown earlier to occur also for planar interfaces for simulations in the slab geometry. Consequences for the estimation of the Tolman length are briefly discussed. In particular, we find clear evidence that in d = 2 the leading correction of the curvature-dependent interface tension is a logarithmic term, compatible with theoretical expectations, and we show that then the standard Tolman-style analysis is inapplicable.

Multilayer Adsorption of Heptane Vapor at Water Drop Surfaces

The measured dynamic surface tension of a water drop in air saturated by heptane vapor shows a sharp decrease from about 60 mN m−1 to 40 mN m−1, and less after a certain adsorption time. The observed adsorption kinetics is analyzed by a theoretical model based on multilayer adsorption of alkanes from the vapor phase at the water surface. The model assumes a dependence of the kinetic coefficients of adsorption and desorption on the surface coverage and in equilibrium it reduces to the classical Brunauer–Emmett–Teller adsorption isotherm. The calculated time dependencies of adsorption and surface tension agree well with experimental data and predict a five-layer adsorption of heptane.

Surface effects in droplet nucleation

The classical nucleation theory (CNT) concept of a nucleus as a fragment of the bulk new phase fails for nanosized nuclei. An extension of CNT taking into account the properties of the transition region between coexisting bulk phases is proposed. For this purpose, the finite-thickness layer method which is an alternative to Gibbs’ one is used; the transition region is considered as a separate (surface) phase. The nucleus inhomogeneity (difference in the properties of surface and bulk phases) is shown to result in the dependence of surface tension on radius and temperature. An equation for the work of nucleus formation is derived which is basic for the multivariable theory of nucleation; it takes into account the dependences of surface tension on radius (the curvature effect) and temperature. The Kelvin formula for the equilibrium vapor pressure is extended to small radii. It is shown that the ratio of the isothermal nucleation rate to that of CNT can achieve several orders of magnitude due to the curvature effect. The analysis of different dependences of the Tolman length on radius, δ(R), obeying the condition of limiting (spinodal) vapor supersaturation suggests that the curvature effect in the nucleation region is determined by the value of δ(0) which is positive, rather than by the asymptotic value δ∞. The equilibrium temperature of a noncritical droplet is shown to differ from the vapor temperature due to the dependence of surface tension on temperature. Therefore, the calculated mean steady state overheat of droplets relatively the vapor temperature consists of the kinetic (due to the release of the condensation heat) and thermodynamic parts.

Surface concentration or surface excess, which one dominates the surface tension of multicomponent mixtures?

This work is to answer an important question: which parameter, surface concentration or surface excess, dominates the surface tension of multicomponent mixtures? Two series of solutions have been chosen to inspect the dependence of solution surface tension on surface concentration and surface excess of the solutes. The solutions are separately 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in 3-hydroxypropionitrile and tetrabutylphosphonium bromide (TBPBr) in formamide. The surface tension data of these two series of binary solutions have been respectively correlated to the Gibbs surface excess and the surface concentration of the solutes. Both surface excess and surface concentration are experimentally determined by Neutral Impact Ion Scattering Spectroscopy (NICISS). The surface tension of POPC solutions is linearly dependent on the surface concentrations of POPC; whereas, the surface tension of TBPBr solutions depends piecewise linearly on surface concentration but irregularly upon surface excess of TBPBr. The intrinsic linear relationships between surface tension and surface concentration found in those two series of solutions are consistent to those results found in previous work. This observation evidences that the dominant factor to the surface tension of solutions is the surface concentration of solute to which both the surface fraction and the molecular orientation are subject.

Tolman’s length and limiting supersaturation of vapor

The classical Kelvin formula for the equilibrium vapor pressure over a droplet of radius R is extended to small radii and vapor non-ideality, from where the limiting supersaturation condition is obtained by relating the point R=0 to the value of limiting (spinodal) supersaturation of vapor. The analysis of different dependences of the Tolman length on radius, δ(R), obeying this condition suggests that (i) the value of δ(0) is positive and the function δ(R) decreases with increasing radius; (ii) the curvature effect (the dependence of surface tension on radius) in the nucleation region is determined by the value of δ(0). At the same time, this effect is weakly sensitive to the form of the function δ(R) and insensitive to its asymptotic value δ∞ .

Direct numerical simulation of variable surface tension flows using a Volume-of-Fluid method

We develop a general methodology for the inclusion of a variable surface tension coefficient into a Volume-of-Fluid based Navier–Stokes solver. This new numerical model provides a robust and accurate method for computing the surface gradients directly by finding the tangent directions on the interface using height functions. The implementation is applicable to both temperature and concentration dependent surface tension coefficient, along with the setups involving a large jump in the temperature between the fluid and its surrounding, as well as the situations where the concentration should be strictly confined to the fluid domain, such as the mixing of fluids with different surface tension coefficients. We demonstrate the applicability of our method to the thermocapillary migration of bubbles and the coalescence of drops characterized by a different surface tension coefficient.

Surface tension, density and composition in the methane-pentane system at high pressure

A pressure system is described for measuring the pressure dependence of surface tension using digital image processing techniques on pendant drops in systems where the miscibility changes with both temperature and pressure. Measurements can be performed at pressures up to 40 MPa and temperatures up to 423 K. This high-pressure rig allows, additionally, the simultaneous measurement of both phase density and composition. The system is tested with the methane-pentane system at 313.15 K and pressures up to 15.6 MPa; the results compare well with literature data and with values calculated using the Peng-Robinson equation of state in conjunction with the gradient theory approach to computing surface tension, thus validating the experimental technique. Density profiles of the components through the interfacial layer have also been calculated using gradient theory. The Wegner extended scaling approach has been applied to all of the data sets to estimate the critical pressure for this system, which is found to be 16 MPa at 313.15 K.

Threshold dynamics for anisotropic surface energies

We study extensions of Merriman, Bence, and Osher’s threshold dynamics scheme to weighted mean curvature flow, which arises as gradient descent for anisotropic (normal dependent) surface energies. In particular, we investigate, in both two and three dimensions, those anisotropies for which the convolution kernel in the scheme can be chosen to be positive and/or to possess a positive Fourier transform. We provide a complete, geometric characterization of such anisotropies. This has implications for the unconditional stability and, in the two-phase setting, the monotonicity, of the scheme. We also revisit previous constructions of convolution kernels from a variational perspective, and propose a new one. The variational perspective differentiates between the normal dependent mobility and surface tension factors (both of which contribute to the normal speed) that results from a given convolution kernel. This more granular understanding is particularly useful in the multiphase setting, where junctions are present.

Assessment of Surface Tension and Viscosity of In-Zn melt

A comparative study of the concentration dependence of surface tension and viscosity of molten In-Zn alloys at 700 K has been performed using energetics, obtained from thermodynamic analysis in the framework of self-association model. The surface tension of the alloys has been calculated from the two methods, layered structure approach and self associating mixture method, and viscosity from Moelwyn-Hughes equation and Kaptay equation. The theoretically computed results for the thermodynamic properties of the alloys are found in excellent agreement with the corresponding experimental results showing that the alloy is segregating in nature. Both surface tension and viscosity of the In-Zn alloy are found to increase with the addition of Zn atoms.The Himalayan Physics Vol. 6 & 7, April 2017 (15-19)

Model for the Surface Tension of Dilute and Concentrated Binary Aqueous Mixtures as a Function of Composition and Temperature.

Surface tension dictates fluid behavior, and predicting its magnitude is vital in many applications. Equations have previously been derived to describe how the surface tension of pure liquids changes with temperature, and other models have been derived to describe how the surface tension of mixtures changes with liquid-phase composition. However, the simultaneous dependence of surface tension on temperature and composition for liquid mixtures has been less studied. Past approaches have required extensive experimental data to which models have been fit, yielding a distinct set of fitting parameters at each temperature or composition. Herein, we propose a model that requires only three fitting procedures to predict surface tension as a function of temperature and composition. We achieve this by analyzing and extending the Shereshefsky (J. Colloid Interface Sci. 1967, 24 (3), 317-322), Li et al. (Fluid Phase Equilib. 2000, 175, 185-196), and Connors-Wright (Anal. Chem. 1989, 61 (3), 194-198) models to high temperatures for 15 aqueous systems. The best extensions of the Shereshefsky, Li et al., and Connors-Wright models achieve average relative deviations of 2.11%, 1.20%, and 0.62%, respectively, over all systems. We thus recommend the extended Connors-Wright model for predicting the surface tension of aqueous mixtures at different temperatures with the tabulated coefficients herein. An additional outcome of this study is the previously unreported equivalence of the Li et al. and Connors-Wright models in describing experimental data of surface tension as a function of composition at a single temperature.

Kinetic and thermodynamic properties of liquid zinc: An ab initio molecular dynamics study

In this paper, structure, dynamic and kinetics properties of the liquid zinc were calculated by ab initio molecular dynamics simulations. Temperature dependence of self-diffusion coefficient, shear viscosity and surface tension were investigated in the range from 420 to 550°C. The pair correlation functions calculated in this study are in good agreement with those previous results by other scholars. The calculated results indicate that both of self-diffusion coefficient and shear viscosity have very good compatibility with Arrhenius relationship. Moreover, the formula exhibiting temperature dependence of the surface tension had been established in order to evaluate the surface tension at any given temperature in this paper.