Dependence Of Surface Tension Research Articles

Numerical modeling of the non-isothermal liquid droplet impact on a hot solid substrate

The heat transfer from a solid phase to an impinging non-isothermal liquid droplet is studied numerically. A new approach based on an arbitrary Lagrangian-Eulerian (ALE) finite element method for solving the incompressible Navier Stokes equations in the liquid and the energy equation within the solid and the liquid is presented. The novelty of the method consists in using the ALE-formulation also in the solid phase to guarantee matching grids along the liquid solid interface. Moreover, a new technique is developed to compute the heat flux without differentiating the numerical solution. The free surface and the liquid solid interface of the droplet are represented by a moving mesh which can handle jumps in the material parameter and a temperature dependent surface tension. Further, the application of the Laplace-Beltrami operator technique for the curvature approximation allows a natural inclusion of the contact angle. Numerical simulation for varying Reynold, Weber, Peclet and Biot numbers are performed to demonstrate the capabilities of the new approach. (C) 2014 Elsevier Ltd. All rights reserved.

New thermodynamics for evaluating the surface-phase enrichment in the lower surface tension component.

Regarding the surface phase of liquid mixtures as a thermodynamic phase, ideal surface phases are designed so that at fixed bulk-phase composition, real and ideal surface phases have the same chemical composition and identical limiting slopes for the dependence of surface tension on mole fraction. Standard chemical potentials are introduced for surface phase components, and quasi-exact expressions are worked out to compute ideal surface tensions and surface-phase compositions of real liquid mixtures. Guidelines for choosing molecular models to estimate the molar surface area of pure constituents are given. Ideal and excess surface tensions are calculated by using literature data for aqueous ethanol solutions at 298 K. These results show treatment based on Butler's equations grossly overestimate predicted surface tensions, thus leading to lower ethanol content in the surface phase. These inaccuracies are ascribed to the use of molar surface areas in model equations that are too small.

Composition and Temperature Dependence of Density, Surface Tension, and Viscosity of EMIM DEP/MMIM DMP + Water + 1-Propanol/2-Propanol Ternary Mixtures and Their Mathematical Representation Using the Jouyban–Acree Model

Room temperature ionic liquids (RTILs) have been ascribed as alternative solvents in separation processes or chemical reactions. This research is concerned with the study of density, ρ, viscosity, η, and surface tension, σ, over the mole fractions of (0.1000 to 1.000) mol and temperature from (293.15 to 333.15) K for ternary mixtures of 1-ethyl-3-methylimidazolium diethylphosphate (EMIM DEP)/1,3-dimethylimidazolium dimethylphosphate (MMIM DMP), water, and 1-propanol/2-propanol. As the temperature increased, surface tension and density results for all the multicomponent mixtures show a linear descending trend. Adversely, viscosity results indicate polynomial descending trend. At the whole ranges of temperature, the density, surface tension and viscosity data show a significant gap between mole fractions of ionic liquid. These experimental results have been evaluated and the most prominent polynomial or linear regressions were obtained. The most prominent correlation for density and surface tension for all ...

Temperature dependent surface tension estimation using COSMO-RS sigma moments

In this work, a nonlinear multivariate QSPR model based on the COSMO-RS sigma moments was presented for the estimation of the temperature dependent surface tension of various organic compounds in wide surface tension (0.07–45.08mNm−1) and temperature (283–373K) range. 1500 data points were used to establish, validate and test the model. An artificial neural network was developed, optimized and used as regression model. The prediction power of the new model was validated with an external data set, with a squared correlation coefficient of R2=0.963 and a mean absolute error of MAE=0.81mNm−1. The factor sensitivity and importance analyses show that all of the proposed five COSMO-RS sigma moments and the temperature are significant input variables of the ANN model and the kind of skewness of the σ-profile, the electrostatic interaction energy and the hydrogen bonding acceptor function are the most sensitive and important molecular descriptors used in the new nonlinear multivariate QSPR model.

Studying three phase contact in the system air/DMPC water dispersion/silica

The studying of lipid vesicles is motivated because they are a useful model of biological membranes. The behavior of three phase contact (TPC) formed on different substrates from lipid dispersions is of high practical importance. In the present paper, we study wetting of hydrophilic silica surfaces with DMPC dispersion by measurement of their three-phase contact (TPC) parameters. These properties can provide more detailed information about the hydrophobicity and structure of the adsorbed lipid layer. The calculation of TPC parameters, from the contact angle and surface tension of liquid–vapor interface experimental data starts with Young's equation. An approach of additional relation among the parameters of Young's equation such as an equation-of-state relation is used to calculate the surface tensions solid–liquid and solid–vapor interfaces. Two states are observed distinctly in dependence of the phase interface surface tension on the DMPC dispersion concentration. The calculated values of the adsorption are reasonable. Surface adsorption at the solid–liquid interface is significantly lower than the adsorption of the other two interfaces. The obtained results about the adsorption are in agreement with the expected physical picture.

Mesoscopic simulation model of selective laser melting of stainless steel powder

A 3D mesoscopic model is developed to simulate selective laser melting processes using the ALE3D multi-physics code. We study the laser-induced melting of a random bed of stainless steel 316 particles on a solid substrate (1000μm×300μm×50μm) and its solidification into either a continuous track or a discontinuous track as a result of Plateau–Rayleigh instability. Our approach couples thermal diffusion to hydrodynamics and accounts for temperature dependent material properties and surface tension, as well as the random particle distribution. The simulations give new physical insight that should prove useful for development of continuum models, where the powder is homogenized. We validate our approach against the experiment and find that we match the main laser track characteristics.

Influence of the size dependence of surface tension on the dynamics of a bubble in a liquid

The Gibbs dividing surface method is used to derive the differential equation defining the dependence of the surface tension of a bubble in a nonpolar single-component liquid on its radius. Exact and asymptotic solutions of this equation have been obtained. It follows from the calculations that the bubble surface tension increases with decreasing radius. The Rayleigh-Plesset equation describing the bubble collapse dynamics is solved numerically by taking into account the size dependence of surface tension. The size dependence of surface tension is shown to affect significantly the final bubble collapse stage and, on the whole, accelerates this process.

Numerical analysis of the influence of surface-active substance in the melt on the distribution of modifying particles and crystallization at the treatment of metal surface by a laser pulse

A mathematical model is proposed for the process of modifying the metal surface layer by refractory nano-size particles with the aid of the pulse laser radiation, which accounts for the surface tension dependence on the presence of surface-active substance in the melt. Numerical modeling has been carried out, from the results of which the influence of the surface -active admixture on the character of forming flows, distribution of particles of the modifying substance in the metal, and the melt crystallization process have been estimated.

Substrate dependent in vitro antifungal activity of Bacillus sp strain AR2.

BackgroundBiosurfactants are a structurally diverse group of secondary metabolites with lots of potential to serve mankind. Depending upon the structure and composition they may exhibit properties that make them suitable for a particular application. Structural and compositional diversity of biosurfactant is unambiguously substrate dependent. The present study investigates the qualitative and quantitative effect of different water soluble carbon source on the biosurfactant produced by Bacillus amylofaciens strain AR2.ResultsStrain AR2 produced lipopeptide type biosurfactant while growing on water soluble carbon sources. Maximum biosurfactant production was observed in the sucrose supplemented minimal salt medium (MSM). Strain AR2 exhibited carbon source dependent surface tension reduction in the range of 30-37 mN/m, critical micelle concentration (CMC) in the range 80-110 mg/l and emulsification index (EI24 kerosene) in the range of 32-66%. In dextrose, sucrose and glycerol supplemented MSM, strain AR2 produced lipopeptides as a mixture of surfactin, iturin and fengycin. However, in the presence of maltose, lactose and sorbitol only iturin was produced. This substrate dependent compositional variation in the lipopeptides significantly influenced antifungal activity. Lipopeptides produced by strain AR2 while growing on sucrose and dextrose based MSM was observed to be most efficient as an antifungal agent.ConclusionsThese results suggest that carbon source provided for the growth and biosurfactant production not only influences the yield but also the type of biosurfactant. Sucrose is the most suitable carbon source for production of lipopeptide biosurfactant with antifungal activity.

Spontaneous cavitation in a Lennard-Jones liquid at negative pressures

We report a molecular dynamics (MD) study of homogeneous bubble nucleation in a Lennard-Jones liquid under a negative pressure (cavitation). The rate of bubble nucleation has been determined in the range 2 x 10(-9) < J(*) = Jσ(4)(m/ε)(1/2) < 6 x 10(-6) by the mean lifetime method at temperatures T(*) = kBT/ε = 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.4, 0.5, 0.6, 0.7, 0.8. In molecular dynamics simulation calculations have also been made of the coefficient of bubble size diffusion, the Zeldovich nonequilibrium factor, and the radius of a critical nucleus R*. Different approaches to the determination of the nucleation rate in a stretched liquid have been considered in the framework of classical nucleation theory (CNT). The values of J obtained in MD simulation are by 8-20 orders higher than those predicted by CNT. The work of formation of a critical bubble and the dependence of surface tension γ(R*) at the critical bubble-liquid interface have been determined by data of MD simulation from CNT. The values of γ obtained have been approximated by an extended Tolman formula that takes into account, besides a linear correction, also the quadratic in curvature terms. The Tolman length δ∞ is negative and equals -(0.1-0.2)σ. The coefficient at 1/R*(2) is positive and does not exceed σ(2).

A model for the latent heat of melting in free standing metal nanoparticles.

Nanoparticles of many metals are known to exhibit scale dependent latent heats of melting. Analytical models for this phenomenon have so far failed to completely capture the observed phenomena. Here we present a thermodynamic analysis for the melting of metal nanoparticles in terms of their internal energy and a scale dependent surface tension proposed by Tolman. The resulting model predicts the scale dependence of the latent heat of melting and is confirmed using published data for tin and aluminum.

Recalcitrant bubbles.

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles).

Thermocapillary-Driven Motion of a Sessile Drop: Effect of Non-Monotonic Dependence of Surface Tension on Temperature

We study the thermocapillary-driven spreading of a droplet on a nonuniformly heated substrate for fluids associated with a non-monotonic dependence of the surface tension on temperature. We use lubrication theory to derive an evolution equation for the interface that accounts for capillarity and thermocapillarity. The contact line singularity is relieved by using a slip model and a Cox-Voinov relation; the latter features equilibrium contact angles that vary depending on the substrate wettability, which, in turn, is linked to the local temperature. We simulate the spreading of droplets of fluids whose surface tension-temperature curves exhibit a turning point. For cases wherein these turning points correspond to minima, and when these minima are located within the droplet, then thermocapillary stresses drive rapid spreading away from the minima. This gives rise to a significant acceleration of the spreading whose characteristics resemble those associated with the "superspreading" of droplets on hydrophobic substrates. No such behavior is observed for cases in which the turning point corresponds to a surface tension maximum.

Bending rigidity and higher-order curvature terms for the hard-sphere fluid near a curved wall.

In this work I derive analytic expressions for the curvature-dependent fluid-substrate surface tension of a hard-sphere fluid on a hard curved wall. In the first step, the curvature thermodynamic properties are found as truncated power series in the activity in terms of the exactly known second- and third-order cluster integrals of the hard-sphere fluid near spherical and cylindrical walls. These results are then expressed as packing fraction power series and transformed to different reference regions, which is equivalent to considering different positions of the dividing surface. Based on the truncated series it is shown that the bending rigidity of the system is non-null and that higher-order terms in the curvature also exist. In the second step, approximate analytic expressions for the surface tension, the Tolman length, the bending rigidity, and the Gaussian rigidity as functions of the packing fraction are found by considering the known terms of the series expansion complemented with a simple fitting approach. It is found that the obtained formulas accurately describe the curvature thermodynamic properties of the system; further, they are more accurate than any previously published expressions.

Temperature Dependence of Surface Tension of Sn-Ag Alloys

The surface tension of molten Sn-Ag alloys was measured using a specially developed high-accuracy sessile drop apparatus. In this apparatus, a molten sample is dropped onto a R-Al2O3 substrate in order to prevent any reaction between the sample and substrate during the heating process. The droplet shape was recorded from two perpendicular directions to confirm its symmetry. The oxygen partial pressure (\( {P_{{{\text{O}}_2}}} \)) was controlled by a Mg furnace to a value of about 10−16 to 10−15 Pa. The sample compositions used were Sn-20Ag, Sn-50Ag, and Sn-80Ag (at.%) and were alloyed from pure Sn (99.999%) and Ag (99.99%) in the dropping tube. The accuracy of the experimental results was confirmed by an extremely small scatter. The measured temperature dependence of the surface tension of the molten Sn-50Ag (at.%) alloy indicated a characteristic curve that changed from positive to negative with increasing temperature. Furthermore, the surface tension of the molten Sn-20Ag (at.%) alloy has a temperature dependence that changes from flat to negative, while the Sn-80Ag (at.%) alloy has a negative temperature dependence across the whole temperature range. Based on a theoretical discussion using Butler’s equation, these temperature dependencies can be determined by negative straight lines when assuming the surface composition.

Regular hexagons and stripes on Marangoni and Rayleigh–Taylor unstable volatile thin films

Thin volatile Newtonian liquid films with a free surface on a cooled horizontal substrate are studied theoretically and numerically. We show that if the fluid is initially in equilibrium with its own vapor in the gas phase, regular surface deformation patterns in the form of long-wave hexagons or stripes having a well defined lateral length scale are observed, depending on the instability mechanism. This is different to the case without evaporation where rupture or coarsening to larger and larger spatially disordered patterns is seen in the long time limit. We propose to use such a system to create a regular structuring of the film’s surface. Heat production by latent heat and the influence of a temperature dependent surface tension (Marangoni effect) are included as well. Special emphasis is laid on the so-called anomalous Marangoni effect. In this case a parameter region where stripes should occur already at threshold is found by means of a systematic weakly non-linear analysis.

Freezing of stressed bilayers and vesicles

We show using a minimalistic theoretical framework that phase transition decoupling in lipid bilayers is caused by a nonuniform stress profile due to an asymmetric distribution of lipids between the two leaflets. Applying this framework to vesicles, we demonstrate that their anomalous freezing is also caused by a stress asymmetry, but that this is due to lipid tail extension on freezing. Finally, we predict a previously unknown dependence of surface tension on temperature, find the phenomenon also in coarse grained molecular dynamics simulations, and suggest that it might have relevance in thermosensitive protein gating.

Evaporation of a thin viscous liquid film sheared by gas in a microchannel

In the present paper a 3D non-stationary two-sided mathematical model of joint motion of evaporating liquid film and cocurrent gas flow in a microchannel with local heating has been developed. This model takes into account a deformable gas–liquid interface, convective heat transfer in the liquid and the gas phases as well as temperature dependence of surface tension and liquid viscosity. Assuming the lubrication theory to be valid, the problem has been reduced to five governing equations for the film thickness, temperature fields in the gas and liquid, vapor concentration in the gas phase and gas pressure. Numerically it is shown that for films sheared by gas in microchannels vapor is transported by forced convection and diffusion, and diffusion plays the most considerable role in vapor transport at low gas velocities. Also, it is shown that concentration and thermal boundary layers are formed. The boundary layers have a specific S-shaped form. The width of the vapor track increases along the gas flow direction in front of the heater and decreasesdownstream the heater. The distance over which the width decreases is an order of magnitude higher than the heater length. This fact can be explained by the condensation of the vapor.

Measurement and study of density, surface tension, and viscosity of quaternary ammonium-based ionic liquids ([N222(n)]Tf2N)

In this work five quaternary ammonium-based ionic liquids with bis(trifluoromethylsulfonyl)imide anion were synthesized and their density, viscosity and surface tensions were measured in the temperature range (298 to 373)K. Surface tensions were measured by capillary rise method using a homemade capillary apparatus, in which the liquid/vapor can be brought into equilibrium practically. Measurements of viscosities and surface tensions were performed under water–vapor free atmosphere.The surface tension of quaternary ammonium-based ILs decreases as the alkyl chain length increases. Also surface energy and surface entropy are found as increasing functions of alkyl chain length with a plateau at high lengths in the surface. The viscosities measured by capillary viscometer fit in VFT equation, indication of non-Arrhenius ionic liquids. Viscosities are also fitted quite accurately in the relation we have developed recently as the fluidity equation with the characteristics exponent ϕ. Values of ϕ for ionic liquids are close to one another and tend to the limiting value, almost 0.328, asymptotically as the alkyl chain length increases.The critical temperatures predicted via the temperature dependent surface tensions decrease with increasing alkyl chain length of the cation. The trend of predicted critical temperature of these ionic liquids conforms to those of imidazolium-based ILs.

Spreading and bistability of droplets on differentially heated substrates

AbstractAn axisymmetric drop spreads on a radially heated, partially wetting solid substrate in a rotating geometry. The lubrication approximation is applied to the field equations for this thin viscous drop to yield an evolution equation that captures the dependence of viscosity, surface tension, gravity, centrifugal forces and thermocapillarity. We study the quasi-static spreading regime, whereby droplet motion is controlled by a constitutive law that relates the contact angle to the contact-line speed. Non-uniform heating of the substrate can generate both vertical and radial temperature gradients along the drop interface, which produce distinct thermocapillary forces and equivalently flows that affect the spreading process. For the non-rotating system, competition between surface chemistry (wetting) and thermocapillary flows induced by the thermal gradients gives rise to bistability in certain regions of parameter space in which the droplets converge to an equilibrium shape. The centrifugal forces that develop in a rotating geometry enlarge the bistability regions. Parameter regimes in which the droplet spreads indefinitely are identified and spreading laws are computed to compare with experimental results from the literature.