Showing papers on "Surface tension published in 1995"

Surface Tension of Alcohol Water + Water from 20 to 50 .degree.C

Abstract: The surface tension of mixtures is a physical property of great importance for mass transfer processes such as distillation, extraction, or absorption. The surface tension of aqueous solutions of methanol, ethanol, 1-propanol, and 2-propanol was measured over the entire concentration range at temperatures of 20--50 C. The experimental values were correlated with temperature and with mole fraction. The maximum deviation was in both cases always less than 3%.

The effects of an elastic solid surface layer on the radial pulsations of gas bubbles

Abstract: Most previous theoretical investigations of gas bubble dynamics have assumed an uncontaminated gas–liquid interface. Recently, however, the potential importance of layers of surface active agents on bubble dynamics has been increasingly recognized. In this work it is assumed that a continuous layer of incompressible, solid elastic material separates the gas from the bulk Newtonian liquid. Elasticity is modeled to include viscous damping. A Rayleigh–Plesset‐like equation describing the dynamics of such surface‐contaminated gas bubbles is derived. The equation predicts that the surface layer supports a strain that counters the Laplace pressure and thereby stabilizes the bubble against dissolution. An analytical solution to this equation which includes both the fundamental and second‐harmonic response is presented. The dispersion relation describing the propagation of linear pressure waves in liquids containing suspensions of these bubbles also is presented. It is found that (1) the resonance frequencies of ...

Molecular dynamics simulation of the orthobaric densities and surface tension of water

Abstract: Molecular dynamics simulations have been performed to study the liquid–vapor equilibrium of water as a function of temperature. The orthobaric densities and the surface tension of water are reported for temperatures from 316 K until 573 K. The extended simple point charge (SPC/E) interaction potential for water molecules is used with full Ewald summation. The normal and tangential components of the pressure tensor were calculated and are presented at 328 K. The nature of the long‐range contribution to the surface tension has been studied in detail. At 328 K the calculated surface tension is 66.0±3.0 mN m−1 in comparison with the experimental value of 67 mN m−1. The simulated surface tensions between 316 K and 573 K are in good agreement with experiment. The orthobaric densities are in better agreement with experimental values than those obtained from the Gibbs ensemble calculation for the SPC model of water.

Wetting effects on the spreading of a liquid droplet colliding with a flat surface: Experiment and modeling

Abstract: In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact‐angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spre...

Computer simulation of liquid/liquid interfaces. I. Theory and application to octane/water

Abstract: Statistical ensembles for simulating liquid interfaces at constant pressure and/or surface tension are examined, and equations of motion for molecular dynamics are obtained by various extensions of the Andersen extended system approach. Valid ensembles include: constant normal pressure and surface area; constant tangential pressure and length normal to the interface; constant volume and surface tension; and constant normal pressure and surface tension. Simulations at 293 K and 1 atm normal pressure show consistent results with each other and with a simulation carried out at constant volume and energy. Calculated surface tensions for octane/water (61.5 dyn/cm), octane/vacuum (20.4 dyn/cm) and water/vacuum (70.2 dyn/cm) are in very good agreement with experiment (51.6, 21.7, and 72.8 dyn/cm, respectively). The practical consequences of simulating with two other approaches commonly used for isotropic systems are demonstrated on octane/water: applying equal normal and tangential pressures leads to an instabil...

Newtonian drop impact with a solid surface

Abstract: The spreading of Newtonian liquid drops after impact with a solid surface is reproted for a range of liquid and surface proeprties, drop diameters, and impact velocities. Results for liquid viscosities up to 300 mPa.s are given. For a given drop diameter and velocity, a range of liquid viscosities result in splashing even for smooth surfaces. The maximum spread radius, made dimensionless with the drop radius, is correlated as Rmax* = 0.61(Re2Oh)0.166, where Re and Oh are the Reynolds and Ohnesorge numbers. respectively. A model is proposed to account for inertial, viscous, and surface tension forces on the maximum spread radius. Good agreement is found between the model and experimental data from several sources.

Young-Dupre Revisited

Abstract: The Young-Dupre equation for the work of adhesion of a liquid drop to a solid surface, where the solid surface is in equilibrium with the vapor of the liquid, is given as W = γ L (1 + cos θ), where γ L is the surface tension of the liquid and θ the contact angle. This work (W) has generally been identified with the free energy of adhesion. It is shown here that it constitutes the total work of adhesion only under the artificial condition that the sessile drop retains its shape after detaching from the solid surface. Under real conditions, W represents only one component of the total free-energy change taking place when a drop is separated from, or attached to, a vapor-equilibrated smooth solid surface. In the present work, a Net Free Energy of Adhesion, ΔF N , is derived which gives the total free energy necessary to separate a sessile drop from a smooth solid surface to form a free sphere (its negative, of course, is the free energy of attachment of the sphere). It is given by ΔF N = πr 2 γ L [(2α/sin θ) 2/3 - α], where r is the radius of the solid-liquid interface and α, called the effective area, is [2/(1 + cos θ)] - cos θ. The Net Free Energy of Adhesion and Young-Dupre work of adhesion are compared as functions of the contact angle. This is done for systems of constant solid-liquid interfacial area and for systems of constant drop volume.

The spreading of volatile liquid droplets on heated surfaces

Abstract: A two‐dimensional volatile liquid droplet on a uniformly heated horizontal surface is considered. Lubrication theory is used to describe the effects of capillarity, thermocapillarity, vapor recoil, viscous spreading, contact‐angle hysteresis, and mass loss on the behavior of the droplet. A new contact‐line condition based on mass balance is formulated and used, which represents a leading‐order superposition of spreading and evaporative effects. Evolution equations for steady and unsteady droplet profiles are found and solved for small and large capillary numbers. In the steady evaporation case, the steady contact angle, which represents a balance between viscous spreading effects and evaporative effects, is larger than the advancing contact angle. This new angle is also observed over much of the droplet lifetime during unsteady evaporation. Further, in the unsteady case, effects which tend to decrease (increase) the contact angle promote (delay) evaporation. In the ‘‘large’’ capillary number limit, matched asymptotics are used to describe the droplet profile; away from the contact line the shape is determined by initial conditions and bulk mass loss, while near the contact‐line surface curvature and slip are important.

Computer Simulation of Hydrophobic Hydration Forces on Stacked Plates at Short Range

Abstract: The potential of mean force between two large parallel hydrophobic oblate ellipsoidal plates in liquid water is determined by molecular dynamics Each ellipsoid displaces approximately 40 water molecules and has major and minor axes of 31 and 93 A, respectively, has a surface area of 650 A*, and interacts repulsively with the solvent water molecules The potential of mean force is calculated from thermodynamic perturbation theory for a series of decreasing plate separations, using constant-pressure molecular dynamics As the plates are moved together, they are first separated by three water layers and then by two, but for shorter distances, a dewetting transition occurs, and one water layer is never observed despite the fact that one can fit As the plates are brought together, there is a corresponding weak oscillation in the potential of mean force corresponding to the removal of each water layer until the dewetting transition takes place, and for closer separations, the surrounding water molecules induce a constant average attractive force of 25 (kJ/mol)/A between the plates This hydrophobic attraction is largely entropic in character, and the potential of mean force is found to be proportional to the area of the water-vacuum surface in this dewetting regime The constant of proportionality is found to be smaller than the gas-liquid surface tension of the water model used There is a very strong short-range driving force toward contact pairing

Adsorption of Globular Proteins at the Air/Water Interface as Measured via Dynamic Surface Tension: Concentration Dependence, Mass-Transfer Considerations, and Adsorption Kinetics

Abstract: The pendant drop technique was used to measure the dynamic surface tension (DST) of eight globular proteins at the air/water interface as a function of protein bulk concentration ( C b ) at C b values of 0.01, 0.1, and 1.0 mg/ml. Initial periods of negligible decrease in the DST ("induction times") were observed for many of the proteins III C b = 0.01 mg/ml, but were less common at higher C b values. DST kinetic parameters varied by up to several orders of magnitude for different proteins, even those with similar bulk diffusion coefficients. All eight proteins achieved initial values of the mesoequilibrium surface tension (MST) within 15 h at C b = 1.0 mg/ml, although only four of the proteins attained steady-state surface tension within this time. The 15-h MST value at C b = 1.0 mg/ml did not vary much among the eight proteins, with an average value of 47 ± 6 mN/m. The DST data were numerically modeled by a 4-parameter Hua-Rosen equation and analyzed with respect to protein surface hydrophobicity, conformational stability, bulk depletion effects, and the apparent vs theoretical diffusion-limited rate of adsorption.

Interfacial tension in high-pressure carbon dioxide mixtures

Abstract: High-pressure interfacial- and surface-tension phenomena govern the migration and recovery of oil and gas from hydrocarbon reservoirs. The phenomena are of particular relevance to phase separation and mass transfer in light hydrocarbon fractionation plants and in propane deasphalting in lubricating oil refining. Interfacial tensions of carbon dioxide-water-alcohol mixtures were measured at temperatures in the range 5--71 C and pressures 0.1--18.6 MPa, using the capillary rise method. The alcohols were methanol (0.136 mf), ethanol (to 0.523 mf), and isopropyl alcohol (to 0.226 mf). Interfacial tension (IFT) decreased linearly with both temperature and pressure din the low-pressure range (gaseous CO{sub 2}) but was largely independent of pressure at high pressure (liquid or supercritical CO{sub 2}). There was a zone in the vicinity of the critical pressure of CO{sub 2}-as much as 20 C below and 10 C above the carbon dioxide critical temperature--where IFT became small. This is attributed to the formation of a second CO{sub 2}-rich phase. The isotherms exhibited a crossover pressure near 3 MPa for all systems examined.

The surface-associated surfactant reservoir in the alveolar lining.

Abstract: A small atmospheric bubble was introduced into a surfactant suspension in a captive bubble surfactometer. After film formation to the equilibrium surface tension at the bubble air-liquid interface, th

Computer simulation of liquid/liquid interfaces. II. Surface tension-area dependence of a bilayer and monolayer

Abstract: A constant normal pressure‐surface tension algorithm for molecular dynamics simulation, developed in the preceding paper, was used to laterally expand and compress the surface area of a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Then, from simulations carried out at constant normal pressure and surface area, values of the surface tension and other thermodynamic variables such as the internal energy and system volume were determined at four different values of the surface area per lipid, 60.0, 65.1, 68.1, and 72.1 A2. The surface tension shows dramatic variations with area, going from 6 to 60 dyn/cm at areas per molecule of 65.1 and 68.1 A2, respectively. An approximate thermodynamic analysis indicates that an area of 68.1 A2/lipid is the closest of the four to the free energy minimum for this system, in agreement with experimental measurements. The effect of surface area changes on the calculated deuterium order parameters, which can be compared with those obtained from nuclear magnetic resonanc...

Tail corrections to the surface tension of a Lennard-Jones liquid-vapour interface

Abstract: The Kirkwood-Buff formula for surface tension is used to derive an expression for the tail correction to the surface tension. This expression reduces to the expression for the tail correction, given by Chapela, G. A., Saville, G., Thompson, G., and Rowlinson, J. S. (1977, J. chem. Soc. Faraday Trans II, 8, 1133), when the interface is sharp but differs from it near the critical point. The difference appears to be the result of a mistake in the algebra by Chapela et al. In an example we show that, for a comparison with the surface tension of real fluids, both the tail correction to the surface tension, and the influence of the cut-off radius on the phase diagram are important.

Surface-Tension and Bubble Coalescence Phenomena of Aqueous-Solutions of Electrolytes

Abstract: The inhibition of bubble coalescence by electrolytes beyond a critical transition concentration has been assessed by the relationship between transition concentration and surface tension gradients of electrolytes (d(Δγ)/dc) and gas solubility. The correlation between transition concentration and [d(Δγ)/dc] -2 was mediocre (0.74), suggesting that the Gibbs-Marangoni effect cannot fully account for inhibition of bubble coalescence. Preliminary bubbling experiments on mixed electrolytes supported this conclusion. A much better correlation was found between the transition concentration and gas solubility (represented by the exponential decay coefficient of O 2 solubility with increasing electrolyte concentration). Hence, the inhibition of bubble coalescence may be linked with the decreased dissolved gas concentration in the electrolyte solution

Surface Tension of Liquid Metals: Results from Measurements on Ground and in Space

Abstract: The surface tensions of liquid gold and of a gold-copper alloy were measured on electromagnetically levitated drops as a function of temperature in ground-based and in microgravity experiments. In terrestrial experiments, strong electromagnetic fields are necessary to compensate the earth's gravity. Their influence on the drop cannot be neglected, and a correction formula is applied to obtain the true surface tension. In microgravity, the positioning forces are negligible. Comparison of the corrected ground-based results with our microgravity data yield excellent agreement.

A lattice Boltzmann model of ternary fluid mixtures

Abstract: A lattice Boltzmann model is introduced which simulates oil-water-surfactant mixtures. The model is based on a Ginzburg-Landau free energy with two scalar order para meters. Diffusive and hydrodynamic transport is included. Results are presented showing how the surfactant diffuses to the oil-water interfaces thus lowering the surface tension and leading to spontaneous emulsification. The rate of emulsification depends on the viscosity of the ternary fluid.

LCD columnar spacers made of a hydrophilic resin and LCD orientation film having a certain surface tension or alignment capability

Abstract: A liquid crystal display using a hydrophobic material as the material of resinous columns to orient the molecules of the liquid crystal parallel to the substrates. A hydrophilic material can also be used as the material of resinous columns to orient the molecules of the liquid crystal vertical to the substrates. The liquid crystal molecules are oriented horizontally by making the surface tension of the orientation film greater than the surface tension of the resinous columns. The liquid crystal molecules are oriented vertically by making the surface tension of the orientation film smaller than the surface tension of the resinous columns. A mixture of a liquid crystal material and an uncured resin is placed in a liquid crystal cell. The uncured resin is precipitated (deposited) out of the mixture. The molecules of the liquid crystal material are oriented. Then, the uncured resin is cured. Thereafter, an aging step for reorienting the molecules of the liquid crystal material is carried out. This prevents disturbance of the orientation around the resinous columns and leads to an improvement in the voltage holding ratio.

Development of an Objective Method for Dough Stickiness

Abstract: An objective method was developed to measure dough stickiness. The texture analyser provided the required compression force and measured the tension. A cell was designed and built that caused the dough to separate from the probe surface under tensile stress. This is critical for the measurement of dough surface stickiness. The procedure was highly reproducible and appeared to correlate well with subjective measurements of dough stickiness. A number of factors that affected dough stickiness were studied by the developed procedure. Although many factors were shown to affect dough stickiness, none appeared to explain the increased stickiness found with certain flours.

Handbook of Organic Solvents

Abstract: * Refractive index * Solubility * Spectral data fields * Density * Vapor pressure at several temperatures * Viscosity at several temperatures * Critical temperature and pressure * Heat capacity * Heats of fusion, formation, combustion, and vaporization * Flash point and other flammability data * Surface tension * Acid-base dissociation constants * Dielectric constant * Dipole moment * Thermal conductivity * Merck and Beilstein reference numbers

Molecular Dynamics Study of the Dependence of Water Solvation Free Energy on Solute Curvature and Surface Area

Abstract: We have investigated changes in water properties when deforming an initially spherical cavity into an oblate ellipsoid of equal volume in liquid water. The purely hydrophobic cavity has an initial thermal radius of 6.45 A and is flattened out to an oblate ellipse with a thickness corresponding to one layer of methane molecules. The water-solute interactions are modeled by a repulsive, single-site Gay-Beme potential that preserves the volume of the solute; water-water interactions are modeled using a pairwise additive potential. The Gibbs free energy change, AG, of the aqueous solution was calculated using thermodynamic perturbation theory. Comparison with the process of radially expanding a sphere shows that the free energy change cannot consistently be interpreted as being solely proportional to an exposed solute area but contains terms involving the curvature of the solute. As the meanings of exposed surface area and molecular curvature are not welldefined concepts on the microscopic length scale, these terms have to be defined to yield a consistent interpretation of the free energy data. The microscopic origin of the curvature dependence of the free energy is traced back to changes in water-water interactions in the region immediately surrounding the solute. The process of deforming the liquid around the hydrophobic pocket was found to be dominated by entropic contributions. The free energy values do not contain any contributions arising from the deformation of the hydrophobic solute itself nor any attractive solute-solvent term and thus cannot be compared directly with hydrocarbon-water surface tension data.

Surface Tension of Structured Colloidal Suspensions of Polystyrene and Silica Spheres at the Air-Water Interface

Abstract: Surface tensions, γ, of 19 kinds of colloidal spheres of monodispersed polystyrene and silica (6-460 nm in diameter) in crystal-like, liquid-like, and gas-like suspensions are studied systematically at the air-water interface by the Wilhelmy method. γ-values of the aqueous suspensions of colloidal silica spheres are close to that of pure water, though very weak surface activity [maximum in Δγ (surface tension of suspension minus that of water) is ca. -2 mN/m only] is detected for silica spheres of diameters ranging from 100 to 200 nm. The surface activity of polystyrene spheres, on the other hand, is high especially for spheres of diameters between 100 and 200 nm. The maximum in - Δγ is ca. 20 mN/m. The large difference in the surface activity between the two kinds of spheres is due to the difference in surface characters, i.e., highly polar and strongly hydrophobic for silica and polystyrene spheres, respectively. Furthermore, surface tension lowering of the crystal-like suspensions is substantial when compared with that of the liquid-like or gas-like suspensions. It is highly plausible that the intersphere distance in the two-dimensional colloidal crystals at the interface is shorter compared with that in the bulk phase by the shortened electrical double layers at the interface.

Dimensional limitations of silicon nanolines resulting from pattern distortion due to surface tension of rinse water

Abstract: In a nanometer‐scale regime, high‐aspect‐ratio Si lines running in parallel bend plastically toward each other during the drying process after being rinsed in water. Pattern distortion occurs when the line distance is smaller than the product of the squared aspect ratio and a constant k dependent on the condition of the Si surface, i.e., (distance)

A phase field model of capillarity

Abstract: The phenomenological derivation of a phase field model of capillarity that accounts for the structure of an interfacial layer formed by two immiscible incompressible liquids is addressed. A rheological expression for the reversible component of capillary stresses is obtained in terms of the free energy of a binary fluid, which depends on the absolute temperature, composition, and gradient of composition. This model can be applied to those flows that involve change of topology of a capillary interface, such as coalescence and breakup of drops. As an illustration, an equilibrium of a binary fluid with either a flat or spherical interfacial layer is analyzed, and a thermocapillary flow in an infinite gap is considered.