Showing papers on "Surface tension published in 1991"
TL;DR: It is demonstrated in this work that the surface tension, water‐organic solvent, transfer‐free energies and the thermodynamics of melting of linear alkanes provide fundamental insights into the nonpolar driving forces for protein folding and protein binding reactions.
Abstract: We demonstrate in this work that the surface tension, water-organic solvent, transfer-free energies and the thermodynamics of melting of linear alkanes provide fundamental insights into the nonpolar driving forces for protein folding and protein binding reactions. We first develop a model for the curvature dependence of the hydrophobic effect and find that the macroscopic concept of interfacial free energy is applicable at the molecular level. Application of a well-known relationship involving surface tension and adhesion energies reveals that dispersion forces play little or no net role in hydrophobic interactions; rather, the standard model of disruption of water structure (entropically driven at 25 degrees C) is correct. The hydrophobic interaction is found, in agreement with the classical picture, to provide a major driving force for protein folding. Analysis of the melting behavior of hydrocarbons reveals that close packing of the protein interior makes only a small free energy contribution to folding because the enthalpic gain resulting from increased dispersion interactions (relative to the liquid) is countered by the freezing of side chain motion. The identical effect should occur in association reactions, which may provide an enormous simplification in the evaluation of binding energies. Protein binding reactions, even between nearly planar or concave/convex interfaces, are found to have effective hydrophobicities considerably smaller than the prediction based on macroscopic surface tension. This is due to the formation of a concave collar region that usually accompanies complex formation. This effect may preclude the formation of complexes between convex surfaces.
5,295 citations
TL;DR: In this paper, the collision dynamics of a liquid droplet on a solid metallic surface were studied using a flash photographic method, which provided clear images of the droplet structure during the deformation process.
Abstract: The collision dynamics of a liquid droplet on a solid metallic surface were studied using a flash photographic method. The intent was to provide clear images of the droplet structure during the deformation process. The ambient pressure (0.101 MPa), surface material (polished stainless steel), initial droplet diameter (about 1.5 mm), liquid (n-heptane) and impact Weber number (43) were fixed. The primary parameter was the surface temperature, which ranged from 24 degrees C to above the Leidenfrost temperature of the liquid. Experiments were also performed on a droplet impacting a surface on which there existed a liquid film created by deposition of a prior droplet. The evolution of wetted area and spreading rate, both of a droplet on a stainless steel surface and of a droplet spreading over a thin liquid film, were found to be independent of surface temperature during the early period of impact. This result was attributed to negligible surface tension and viscous effects, and in consequence the measurements made during the early period of the impact process were in good agreement with previously published analyses which neglected these effects. A single bubble was observed to form within the droplet during impact at low temperatures. As surface temperature was increased the population of bubbles within the droplet also increased because of progressive activation of nucleation sites on the stainless steel surface. At surface temperatures near to the boiling point of heptane, a spoke-like cellular structure in the liquid was created during the spreading process by coalescence of a ring of bubbles that had formed within the droplet. At higher temperatures, but below the Leidenfrost point, numerous bubbles appeared within the droplet, yet the overall droplet shape, particularly in the early stages of impact (< 0.8 ms), was unaffected by the presence of these bubbles. The maximum value of the diameter of liquid which spreads on the surface is shown to agree with predictions from a simplified model.
1,032 citations
TL;DR: Alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol-1 A-2, which predicts a macroscopic alkane-water surface tension that is close to the macroscopy value.
Abstract: The magnitude of the hydrophobic effect, as measured from the surface area dependence of the solubilities of hydrocarbons in water, is generally thought to be about 25 calories per mole per square angstrom (cal mol-1 A-2) However, the surface tension at a hydrocarbon-water interface, which is a "macroscopic" measure of the hydrophobic effect, is approximately 72 cal mol-1 A-2 In an attempt to reconcile these values, alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol-1 A-2 This value, when used in a simple geometric model for the curvature dependence of the hydrophobic effect, predicts a macroscopic alkane-water surface tension that is close to the macroscopic value
502 citations
TL;DR: In this paper, a cell volume fraction field is obtained by integrating the advected area underneath the interface line-segment and a criterion is developed for identifying the line segment orientation by inspecting the cell volume fractions.
285 citations
TL;DR: In this paper, the authors investigated how the vibrations of a non-rotating liquid droplet are affected by the asphericity and additional restoring forces that the levitating field introduces and showed that the expected single frequency of the fundamental mode is split into either three, when there is an axis of rotational symmetry, or five unequally spaced bands.
Abstract: In experiments to measure the surface energy of a magnetically levitated molten metal droplet by observation of its oscillation frequencies, Rayleigh's equation is usually used. This assumes that the equilibrium shape is a sphere, and the surface restoring force is due only to surface tension. This work investigates how the vibrations of a non-rotating liquid droplet are affected by the asphericity and additional restoring forces that the levitating field introduces. The calculations show that the expected single frequency of the fundamental mode is split into either three, when there is an axis of rotational symmetry, or five unequally spaced bands. Frequencies, on average, are higher than those of an unconstrained droplet; the surface tension appears to be increased over its normal value. This requires a small correction to be made in all analyses of surface energy. A frequency sum rule is derived from a simplified model of the magnetic field which allows the corresponding Rayleigh frequency to be evaluated from the observed frequencies of the fundamental and translational modes. A more detailed analysis shows a similar correction but one that is also sensitive to the position of the droplet in the field.
281 citations
TL;DR: In this article, a theory of homogeneous nucleation from the vapor phase is presented, which is based on an extension of Fisher's semiphenomenological droplet model for the Gibbs free energy of formation of a cluster.
Abstract: A theory of homogeneous nucleation from the vapor phase is presented, which is based on an extension of Fisher’s semiphenomenological droplet model for the Gibbs free energy of formation of a cluster. This droplet model allows translational, rotational, vibrational, and configurational degrees of freedom of the cluster as well as the variation of surface tension with cluster size. By suitable choice of the three free model parameters, known nucleation theories such as the classical Becker–Doring–Zeldovich theory and others are obtained as special cases. Since, however, an ansatz for the Gibbs free energy of formation allows the construction of an equation of state for real gases below the critical point, a new method of determining the model parameters is suggested, which is based on the idea of forcing the identity of the constructed equation of state with an experimentally verified one. Thus, all free model parameters can be determined purely from well‐known handbook properties. It is shown that the new theory gives a better prediction of observed nucleation rates than the classical one.
263 citations
TL;DR: In this article, the authors derived an evolution equation for two-dimensional disturbances of a uniform viscous liquid in a uniformly heated inclined plate and derived a linear theory to describe the competition among the instabilities, and derived the finite-amplitude behaviour that determines the propensity for dryout.
Abstract: A layer of volatile viscous liquid drains down a uniformly heated inclined plate. Long-wave instabilities of the uniform film are studied by deriving an evolution equation for two-dimensional disturbances. This equation incorporates viscosity, gravity, surface tension, thermocapillarity, and evaporation eifects. The linear theory derived from this describes the competition among the instabilities. Numerical solution of the evolution equation describes the finite-amplitude behaviour that determines the propensity for dryout of the film. Among the phenomena that appear are the tendency to wave breaking, the creation of secondary structures, and the preemption of dryout by mean flow.
258 citations
01 Jan 1991
TL;DR: In this paper, an improved method has been developed for the determination of surface and interfacial tensions from primary drop shape data, in which wetting angles of sessile drops may be determined.
Abstract: An improved method has been developed for the determination of surface and interfacial tensions from primary drop shape data. In addition, wetting angles of sessile drops may be determined. The method has been built around a commercial pendant drop instrument and an IBM-compatible PC with a frame grabber card. In order to differentiate the drop profile, a filter routine using a local threshold and interpolation technique has been developed that is combined with an edge-tracing algorithm. The program for calculation of surface tension is divided into two parts. The first part is based on the traditional optical method and uses inflection of the drop profile. By means of several polynomial interpolations and curve fitting of theoretical profiles, the form factor β and surface tension γ are determined. The second part of the calculation utilizes the above values as a first estimate and then performs a further optimalization of γ by comparison between experimental and theoretical Young—Laplace profiles. With a PC AT with a 80287 mathematical coprocessor the measurements take about 5 s and the reproducibility is typically 0.01–0.03 mN/m for a wide range of known liquids.
246 citations
TL;DR: The RIPPLE model as mentioned in this paper obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology, which represents surface tension as a localized volume force.
Abstract: A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the continuum surface force model which represents surface tension as a (strongly) localized volume force. Other features include a higher-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE's unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods.
192 citations
01 Jan 1991
TL;DR: In this article, the effect of surfactant molecular structure and environment on the parameters, γm, t∗, and n in the equation describing the surface tension of an aqueous solution at constant surface concentration, C, is explored.
Abstract: The effect of surfactant molecular structure and environment on the parameters, γm, t∗ , and n in the equation, γt = γm + (γ0 − γm/[1 + ( t t∗ )n], describing the surface tension, γt at time t, of an aqueous solution at constant surfactant concentration, C, is explored. From the equation, t∗ is the time at which the rate of change of γt with log t reaches a maximum, equal to 0.576ν(γ0 − γm), where γ0 and γm are the surface tension of the solvent and the solution at mesoequilibrium, respectively. A variety of anionic surfactants in swamping amounts of electrolyte and nonionic surfactants were studied. At a given value of C, t∗ decreases with a decrease in the equilibrium surface excess concentration, Γeq, of the surfactant; at a given Δeq/C value, it generally increases with an increase in the hydrophobic character of the surfactant. The value of n also increases with an increase in the hydrophobic character of the surfactant. The value of γm is affected by the same factors that determine the value of γeq, the equilibrium surface tension. The maximum rate of surface tension reduction with log time, which depends upon the values of n and γm, consequently increases with an increase in the hydrophobic character of the surfactant. For low γt values, γm must be low and t∗ less than t.
169 citations
TL;DR: In this article, the authors attributed the origin of surface tension relaxation to intermolecular cohesive forces among the adsorbed surfactant molecules which developed as the surface coverage increases.
Abstract: The relaxation in surface tension due to the adsorption of bulk-soluble, unbranched, long chain surfactants with small polar groups at the air-water interface is often characterized by an initial induction period in which the surface tension relaxes very slowly. In this study, the origin of this induction in the surface tension relaxation is attributed to intermolecular cohesive forces among the adsorbed surfactant molecules which develop as the surface coverage increases.
TL;DR: In this article, the authors used matched asymptotic expansions to solve for the free surface of a thin liquid drop draining down a vertical wall under gravity, based on the smallness of the surface tension term in the lubrication equation.
Abstract: The method of matched asymptotic expansions is used to solve for the free surface of a thin liquid drop draining down a vertical wall under gravity. The analysis is based on the smallness of the surface tension term in the lubrication equation. In a region local to the front of the drop, where the surface curvature is large, surface tension forces are significant. Everywhere else, the surface curvature is small, and surface tension plays a negligible role. A numerical time‐marching scheme, which makes no small surface tension assumptions, is developed to provide a datum from which to gauge the accuracy of the small surface tension theory. Agreement between the numerical scheme and the small surface tension theory is good for small values of surface tension. Extension to the propagation of drops by spinning and by blowing with a jet of air is also discussed. It is shown that there are inherent similarities between all three spreading mechanisms.
TL;DR: In this article, it is argued theoretically and demonstrated experimentally that fluid movement on the surface of a drop or bubble can remain unhindered in the presence of a single adsorbed surfactant if desorption is fast, and the bulk concentration is high enough so that diffusion away from the particle is fast.
Abstract: Surfactant molecules adsorb onto the interfaces of moving fluid particles and are convected to regions in which the surface flow converges. Accumulation of surfactant in these regions creates interfacial tension gradients that retard the surface flow. In this study it is argued theoretically and demonstrated experimentally that fluid movement on the surface of a drop or bubble can remain unhindered in the presence of a single adsorbed surfactant if, relative to the convective rate of transport of adsorbed surfactant along the surface, desorption is fast, and the bulk concentration is high enough so that diffusion away from the particle is fast. For this circumstance, a uniform surface concentration of surfactant is maintained, and no gradients in surface tension arise to retard the surface velocity. The fluid particle flow behaves as it would in the absence of surfactant save that it has a reduced, uniform surface tension. The remobilization of surfactant‐laden interfaces of fluid particles is demonstrated experimentally in a three‐phase periodic slug flow in a capillary tube in which a train of alternating air and aqueous slugs ride on an annular wetting film of fluorocarbon oil. Surfactant, dissolved in the aqueous slug phase, adsorbs onto and retards the aqueous–oil interface. The hydrodynamics of this flow is such that small changes in the mobility of this interface create large shear rates in the oil layer. This significantly increases the pressure drop required to drive the slug train at constant velocity. Three surface adsorbers are used to demonstrate surface remobilization: The polyethoxy, nonionic surfactants Triton X‐100 and Brij‐35, which have fast desorption kinetics and do not retard the surface flow at high concentrations and, as a counter example, the desorption hindered protein bovine serum albumin, which is shown to be unable to remobilize an interface even at high concentration.
TL;DR: In this paper, a thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles, and the predicted morphologies showed good agreement with the observed particle morphology of the composite latexes.
Abstract: A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K2S2O8) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight–volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.
TL;DR: In this paper, the existence of solitary water waves of elevation, as exact solutions of the equations of steady inviscid flow, taking into account the effect of surface tension on the free surface, was proved.
Abstract: We prove the existence of solitary water waves of elevation, as exact solutions of the equations of steady inviscid flow, taking into account the effect of surface tension on the free surface. In contrast to the case without surface tension, a resonance occurs with periodic waves of the same speed. The wave form consists of a single crest on the elongated scale with a much smaller oscillation at infinity on the physical scale. We have not proved that the amplitude of the oscillation is actually nonzero; a formal calculation suggests that it is exponentially small.
TL;DR: In this paper, the morphological and chemical characteristics of the metal-ceramic interface were determined by scanning electron microscopy and microprobe analysis, and three distinct effects of the Ti solute on wetting can be identified and evaluated semi-quantitatively: (a) a reduction in the solid-liquid interfacial tension by adsorption into the liquid side of the interface.
Abstract: The wetting (kinetics of spreading and stationary contact angles) of CuTi alloys on monocrystalline alumina under high vacuum, at a temperature of 1373 K, by the sessile drop technique was investigated. The morphological and chemical characteristics of the metal-ceramic interface were determined by scanning electron microscopy and microprobe analysis. When the results are analysed, three distinct effects of the Ti solute on wetting can be identified and evaluated semi-quantitatively: (a) a reduction in the solid-liquid interfacial tension by adsorption into the liquid side of the interface; (b) a reduction in this tension by formation of a TiO metallic-like oxide layer in the solid side of the interface; (c) a contribution to the wetting driving force due to the free energy released at the interface by the reaction between Ti and Al2O3.
TL;DR: It is shown that previously measured isotherms can be reproduced by corrugated surfaces with a single characteristic length scale, and do not necessarily imply that the surfaces studied were self-similar.
Abstract: We study the conformation of thin liquid films on rough or heterogeneous solid substrates. The liquid-substrate interaction dominates for sufficiently thin films, and heterogeneity roughens the liquid interface. As the film thickens, surface tension becomes increasingly important, and the liquid interface flattens. A general equation for the equilibrium interface shape is derived. Analytic results are obtained in the limit of weak disorder for rough or self-affine surfaces as well as chemically heterogeneous solids. The effect of disorder depends strongly on the wave vector. Fluctuations at scales smaller than the film thickness or a ``healing length'' \ensuremath{\xi} produce little roughness. At larger wavelengths, the film conforms to the local fluctuations. Exact numerical solutions of the general equation are presented for surfaces with square grooves. These confirm the qualitative predictions of the analytic theory, and are in quantitative agreement when the depth of the grooves is small. The variation of roughness with film thickness, as well as the calculated adsorption isotherms, are compared to recent experimental results. We show that previously measured isotherms can be reproduced by corrugated surfaces with a single characteristic length scale, and do not necessarily imply that the surfaces studied were self-similar.
TL;DR: In this article, a computer assisted tomography (CAT) was used to visualize liquid distribution in a quiescent gaseous phase with a column of uniform, nonporous glass spheres, distilled water, or a mixture of water and ethanol.
Abstract: Liquid distribution in trickle beds with a quiescent gaseous phase was visualized by using computer-assisted tomography. The model system was made up of a column packed with uniform, nonporous glass spheres, distilled water, or a mixture of water and ethanol for a lower surface tension. Flow patterns at the bed scale were recorded as a function of various parameters (liquid flow rate, particle size, type of liquid inlet distributor used, and surface tension)
01 Aug 1991-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: The test shows that it is possible to compute the net production of organic matter in the photic zone, using the formula for oxygen exchange presented here, and salinity, temperature, and oxygen data from the surface layer, and indicates that the formula is reliable.
Abstract: The transfer F,, of oxygen between the ocean and the atmosphere is computed from the formula Fo, = UO, (1 + x)O,s] where V is the transfer velocity, 0, the actual oxygen concentration of the surface water, 0,s the saturation concentration, and x a factor that takes into account the effect of gas transfer due to bubbles. Monthly mean oxygen fluxes were calculated from the formula with historical hydrographical data. By adjusting the value of X, the formula was tuned to obtain a vanishing net annual oxygen flux through the sea surface in the Baltic proper. This occurs when x equals 0.025. Bubble-driven gas transfer thus tends to supersaturate surface water. The gas transfer formula is tested by a comparison between published estimates of the net production of organic matter in the photic layer and estimates obtained with computed oxygen fluxes through the sea surface. The test indicates that the formula is reliable. The test further shows that it is possible to compute the net production of organic matter in the photic zone, using the formula for oxygen exchange presented here, and salinity, temperature, and oxygen data from the surface layer. The flux through the sea surface of a chemically unreactive gas is thought to be governed by a transfer velocity and the difference between the partial pressures of the gas in the surface layer of the sea and in the atmosphere. The transfer or piston velocity is controlled by the molecular diffusion of the gas in a thin viscous water layer or film at the sea surface. It is not clear whether the film is stagnant or is renewed on a short time scale. On natural water bodies the film thickness, if the film is stagnant, or the film renewal time, if the film is perpetually renewed, are thought to be functions of the windspeed and of the molecular viscosity of water. Both the molecular viscosity and the molecular diffusivity vary with temperature. Oxygen concentration in the surface layer of the sea changes as a result of biological production and consumption and gas exchange through the sea surface. Also, entrainment of water underlying the mixed surface layer, having a different oxygen conAcknowledgments This work was supported by the Swedish Natural Science Research Council (NFR). Comments on the manuscript by Ragnar Elmgren, Lena Lundberg, and Fredrik Wulff are hereby acknowledged. I owe a debt of gratitude to all those who have contributed to the ICES data bank. centration, may change the oxygen concentration of the surface layer. The oxygen saturation concentration is a function of salinity and temperature. Changes of the latter two properties may therefore give rise to oxygen exchange with the atmosphere. Changes of atmospheric pressure give rise to proportional changes of the saturation concentration of oxygen in surface water. It has often been suggested that air bubbles in the surface layer, created by breaking surface waves, might be important for gas transfer. Air bubbles increase the area of the air-water interface. This effect should result in an increased gas transfer per unit of horizontal area of the sea surface. The pressure in air bubbles in the surface layer is greater than atmospheric pressure. This disparity is due to the hydrostatic pressure of the overlying water column and, in particular for small bubbles, excess pressure caused by surface tension. Excess gas pressure in the bubbles tends to supersaturate surface water. Broecker and Peng (1982) showed that the surface water in the open ocean typically is supersaturated with respect to oxygen by 3%. They argued that this effect could not be explained by heating of the water (without accompanying gas exchange). Plant production was estimated to account for supersaturation of -0.5%. They therefore
TL;DR: In this article, the effect of the distribution equilibrium coefficient K of a surfactant in a liquid/liquid system on the interfacial tension response after area changes is discussed, and the application of non-periodic relaxation studies is demonstrated by experimental data obtained at the solution air interface with n-dodecyl dimethyl phosphine oxide solutions.
TL;DR: In this article, results of Monte Carlo and molecular-dynamics simulations of Lennard-Jones systems are presented in order to compare various methods of computing interfacial properties of liquid-vapour systems.
Abstract: Results of Monte Carlo and molecular-dynamics simulations of Lennard-Jones systems are presented in order to compare various methods of computing interfacial properties of liquid-vapour systems. For the computation of the surface tension gamma a new method is developed, which makes use of the Bennett procedure for calculating free-energy differences. The method is compared with the conventional route to the surface tension via the virial expression. For the temperature derivative of the surface tension, gamma /dT, both a fluctuation equation and the Gibbs adsorption equation are employed. It is found that d gamma /dT is determined more accurately by the absorption equation (through the surface entropy). Results of simulations of binary Lennard-Jones mixtures are also presented. For the argon-krypton system, values of the adsorption of argon at the interface are determined from density profiles, and are compared with values predicted by the adsorption equation. Positive adsorption of argon manifests itself in krypton-rich mixtures as a significant 'bump' in the argon density profile near the interface.
TL;DR: In this article, the authors studied the interfacial properties of a model dipolar fluid using a generalization of the density functional mean-field approximation, which leads to a bulk phase diagram which depends explicitly on the strength of the multipole moments, in contrast with the results of the simpler version of the theory.
Abstract: The authors have studied the interfacial properties of a model dipolar fluid using a generalization of the density functional mean-field approximation. The generalization consists in weighting configurations in the mean-field average of the perturbative part of the energy by the low-density approximation of the radial distribution function. This leads to a bulk phase diagram which depends explicitly on the strength of the multipole moments, in contrast with the results of the simpler version of the theory. The calculated surface tension and density-orientational profile are in fair agreement with computer simulation (molecular dynamics) results: the addition of a dipole moment causes the surface tension to increase and there is interfacial ordering induced by purely multipolar forces. An extension of the theory to binary fluid mixtures is also briefly discussed.
TL;DR: In this article, the surface tension of LiBr solution with surfactant decreases with increasing LiBr concentration and the Marangoni convection in this system is not essentially induced by the presence of surfactants islands on the surface of the solution as proposed by the previous workers.
Abstract: The Marangoni convection during steam absorption into aqueous LiBr solution with a small amount of surfactant was observed by Schlieren photography, and the surface tension of the absorbing solution was measured to investigate the mechanism of the convection. Also, a numerical simulation of the Marangoni convection was carried out.It is found experimentally that the surface tension of LiBr solution with surfactant decreases with increasing LiBr concentration and that the Marangoni convection in this system is not essentially induced by the presence of surfactant islands on the surface of the solution as proposed by the previous workers, but is in accordance with the general criterion of Marangoni instability. The calculated results could simulate qualitatively the initiation and growth of convection in this system.
TL;DR: In this paper, a technique called film flotation is used for assessing the wetting characteristics of particulates, where particles placed onto the surface of a liquid are imbibed into the liquid only when their critical wetting surface tension is equal to or higher than the surface tension of the liquid.
TL;DR: In this paper, a simple method for measuring the surface dilational modulus of a liquid is described, which makes use of a completely wetted cylindrical ring placed vertically in the liquid surface.
TL;DR: In this article, the micellization and adsorption at the liquid/air interface of these surfactants are governed, primarily, by the entropy gain rather than the energy effect.
TL;DR: In this article, the stability of wet foams of fatty acid solutions (n-pentanoic to n-decanoic acid) in 0.005 N HCl was studied.
TL;DR: In this article, the authors used two different methods to estimate surface tension of binary liquid-vapor mixtures of CO2 and a hydrocarbon near a critical point, based on the gradient theory and the concept of two-scale-factor universality.
Abstract: We use two different methods to estimate surface tension of binary liquid–vapor mixtures of CO2 and a hydrocarbon near a critical point. The first method is based on the gradient theory, which is essentially a mean‐field approximation to the problem that reduces the determination of the interface’s structure and the surface tension to a boundary value problem. The theory’s input is an equation of state of homogeneous fluid and the influence parameters of inhomogeneous fluid. The Peng–Robinson equation and a modification of it are used as the equation of state of homogeneous fluid. The second method is based on the concept of two‐scale‐factor universality which can predict the surface tension from the singularity in the thermodynamic properties of the bulk fluid. The inputs of the method are an equation of state and certain universal amplitude ratios near the critical point. As the equation of state, we use a modification of a model first proposed by Leung and Griffiths, and further developed by Moldover, Rainwater, and co‐workers. We use the two models to examine in detail CO2+n ‐butane and CO2+n ‐decane mixtures. While both models provide accurate estimates of surface tension of CO2+n ‐butane mixtures, only the gradient theory can predict accurately surface tension of CO2+n ‐decane mixtures. Moreover, while the gradient theory and the Peng–Robinson equation of state use very few adjustable parameters (at most three parameters), calculation of surface tension based on two‐scale‐factor universality and the corresponding equation of state requires many adjustable parameters whose number has to be increased dramatically as the fluid mixture becomes more complex. We then use the gradient theory to predict surface tension of binary liquid–vapor mixtures of CO2 and benzene, cyclohexane, and n‐hexadecane. In all cases, the predictions of the gradient theory are in good agreement with the available experimental data.