Showing papers on "Surface tension published in 1968"

Surface potentials of aqueous electrolyte solutions

Abstract: : The effect of added electrolytes on the surface potential of water was determined using the radioactive electrode technique. Changes in surface potential were found to vary from +64 mV for Na2SO4 at 1.8m to -180 mV for NaCNS at 7.5m. The Group IA chlorides in water gave surface potential differences that decreased in the order K(+) = NH4(+) Na(+) Li(+), and the surface potentials of the Group IIA cations decreased in the order Ba(++) Sr(++) Mg(++). At a constant anion concentration of 2m the surface potential differences due to the sodium salts were in the order SO4(--) CO3(--) CH3COO(-) Cl(-) NO3(-) Br(-) I(-) CNS(-). In general the anion with the smaller hydration energy gave the greatest decrease in surface potential. The magnitude of each surface potential change, however, does not appear to be a simple function of the hydration energy or of some related property. The surface potential changes must involve the orientation and structure of the water molecules at the water/air interface, which may be only partially dependent upon the ionic properties as determined in bulk solution.

The thermodynamics of volume change and creep

Abstract: 1 With some exceptions, early observers of creep of concrete assumed that time-dependent strain is due to plastic flow or viscous flow. It is now becoming understood that creep, like shrinkage, is a phenomenon depending on adsorption and desorption of water and related phenomena. Understanding shrinking and swelling is prerequisite to understanding creep. An analysis of these phenomena based on thermodynamics is especially instructive and reliable because in general it does not depend on the correctness of the model of structure adopted for the discussion. 2 Spontaneous volume change is due to a change in the balance of forces and counterforces within the specimen. It cannot be due to the removal or addition, per se, of water molecules. 3 The volume of a porous body will vary with the density of the material of which it is made. Material density will vary with hydrostatic pressure, with temperature, or with change in surface tension of the material. 4 Change of surface tension presumably affects both the inner part and the outer tension shell of particulate material, and oppositely. 5 Surface tension, which is the same as surface free energy, varies with the amount of water adsorbed, and that is a function of ambient vapor pressure at constant temperature. The change in solid surface tension can be calculated from the concomitant change in ambient humidity. 6 The volume change of the body corresponding to a given change in surface tension is the resultant of the change of the inner and outer parts, is at present indeterminate, and is in any case a small fraction of the amount of volume change to be accounted for. 7 Data on paste structure show that adsorbed water must produce disjoining pressure in the narrowest places between solid bodies, where adsorption is hindered.

Fluid Motion Induced by Surface‐Tension Variation

Abstract: Fluid motion in a long straight channel induced by longitudinally varying surface tension has been discussed by Levich. This problem is re‐examined and a different solution is given. In addition, the stability of laminar flows involving surface‐tension variation is briefly discussed, and a correction of a previous result [C.‐S. Yih, J. Fluid Mech. 28, 493 (1967)] is made.

Surface tension skrinkage and strength of hardened cement paste

Abstract: The surface tension and the surface energy of a solid is reduced by the presence of an adsorbed water film When the surface tension of a porous material with a large interior surface is reduced, the length increases whereas the strength decreases With the help of Griffith's theory of crack propagation it is possible to calculate the surface energy For hardened cement paste with a water cement ratio of 045 and 06 the surface energy is found to be 1370 erg/cm2 and 657 erg/cm2 respectively The cement paste was allowed to hydrate for 28 days without loss of moisture at a temperature of 20 °C These results are in agreement with the surface energy of porous glass with a similar interior surface

Effect of adsorbed water on the critical surface tension of wetting on metal surfaces

Abstract: Contract angles of a variety of pure nonhydrophilic liquid polar and nonpolar compounds, covering a wide range of surface tensions, were measured on clean smooth surfaces of fourteen metals and one metal oxide. At 0.6% relative humidity (RH) and 95% RH, each of these high-energy, solid surfaces was converted at 20°C to one of much lower critical surface tension of wetting (γc) by the physical adsorption of a thin film of water. The formation of only a fraction of a monolayer at 0.6% RH decreased γc to about 45 dynes/cm for each metal surface; additional water adsorption at 95% RH to form a more condensed film further lower γc to a common value of 38 dynes/cm. Since γc values were nearly identical for each surface at each extreme of the RH, the surface energy of these hydrophilic solids must be independent of the constitution of the underlying solid substrate and dependent only upon the surface concentration of the adsorbed water.

The surface tension of binary liquid mixtures.

Abstract: There are several theories of surface tension of liquid mixtures.'-3 From a quasi-lattice model for the liquid state, Guggenheim' derived the equation which relates the surface tension of a binary mixture to the activities of its components in the bulk liquid and in the surface. However, this equation can be applied only to mixtures whose components are similar in molecular size and shape. Prigogine et al.2' I developed their theory by treating the equilibrium surface tension of a mixture as a perturbation on the \"dynamic surface tension\" using a smoothed potential function. This theory is applicable only to very nearly ideal systems. Hildebrand and Scott's equation4 is an extension of Guggenheim's ideal equation, taking into account the molecular size effect. Recently, Eckert and Prausnitzb obtained an equation for the surface tension of simple nonpolar binary liquid mixtures using the cell theory and the grand partition function of the surface. They expressed the surface tension in terms of the activity coefficients of the components. Formally, the Eckert-Prausnitz equation is an improved Guggenheim equation. All the above mentioned theories, however, are limited in their use. There are several ways'ea for obtaining the surface tension of pure liquids from the significant structure theory of liquids. An extension of the approach to binary liquid mixtures is made in this paper by assuming that the approximation of random mixing is valid and that the surface of the mixture consists of a monomolecular layer which makes the principal contribution to the surface tension. The advantage of our equation is that it can be applied to any system. (1) Formulation of Equation of Surface Tension of Liquid Mixtures.-(a) Partition function: If we accept the approximation of random mixing of components of mixtures and that the chief contribution to the surface tension comes from a monomolecular surface layer, the partition function of a liquid mixture is given by 6bW

Impingement of gas jets on liquid surfaces

Abstract: An investigation of the interaction of a jet of air impinging normally on a liquid surface has been carried out. The regimes of stable, oscillating, and dispersing indentions were established as a function of velocity and surface tension.For the stable region, energy and force balances were formulated. The force balance, when integrated, described the indention profile well and will have further use in predicting the point of onset of instability.A linear relationship between the square of the instability velocity and the surface tension and between the square of the critical dispersion velocity and the surface tension has been determined experimentally.

Statistical‐Mechanical Calculation of Surface Properties of Simple Liquids and Liquid Mixtures. I. Pure Liquids

Abstract: Calculation of density transition curves and surface tension in a series of mixtures of argon and nitrogen at 84°K are presented. The densities of the two components as a function of position in the interface furnish insight in the structure of the transition region and predict certain features in regard to the (excess) surface tension, which are confirmed experimentally. The calculated values of surface tension as a function of liquid mole fraction are in satisfactory agreement with experiment. Certain problems pertaining to the numerical solution of simultaneous nonlinear integral equations are discussed.

Gas bubbles in solids.

Abstract: This note points out that, as a consequence of the distinction in solids between surface tension γ and surface energy [sgrave], a strain field generally exists around gas bubbles even in thermodynamic equilibrium. The existence of this strain field leads to a small attraction between bubbles but in typical practical situations this is only significant for bubble migration when they are close together compared to their radii.

The effect of surface tension on the waves produced by a heaving circular cylinder

Abstract: In this paper the effect of surface tension on water waves is considered. The usual assumptions of the linearized theory are made. A uniqueness theorem is derived for the waves at infinity for a general class of bounded two-dimensional obstacles in a free surface by means of an energy argument. It is shown how the wave amplitude at infinity depends on the prescribed angle at which the free surface meets the normal to the obstacle. The particular case of a heaving half-immersed circular cylinder is considered in detail, and an expression obtained for the velocity potential in terms of a convergent infinite series, the coefficients of which may be computed.

Transport of ions across lipid monolayers. I. The structure of decylammonium monolayers at the polarized mercury-water interface.

Abstract: To study ion transport processes across well-defined monolayers, it has been necessary to determine the structure of n -decylammonium monolayers at the mercury-water interface under a variety of conditions. The differential capacity of the interface was measured as a function of potential for several decylamine and salt concentrations. The capacity data were integrated twice with respect to potential to yield the electrocapillary curves (surface tension as a function of potential). The values of the variation of surface concentration as a function of potential were calculated from surface tension with the bulk concentration of decylamine. The results, which give the area per molecule under a variety of bulk decylamine and salt concentrations as well as polarizations, are in general agreement with previous ideas on electrical repulsive energy in monolayers. The results also raise a question regarding the estimation of cohesive contributions to the surface tension.

The influence of surface tension on the reflection of water waves by a plane vertical barrier

Abstract: In this paper the effect of surface tension is included in a well-known problem in the theory of two-dimensional infinitesimal water waves. The problem is that of the reflection of waves from a fixed vertical barrier immersed to a depth a into deep water. It is shown how the solution for the velocity potential may be determined uniquely when simple assumptions are made concerning the behaviour of the free surface near the barrier. In particular, expressions are derived for the reflection coefficient, defined as the ratio of the amplitude of the reflected wave to that of the incident wave, at infinity, and the transmission coefficient, defined similarly. It is shown how these coefficients, for small values of the surface tension force, tend to the values obtained by Ursell (4) when surface tension is ignored. The related problem of a completely immersed vertical barrier extending to a distance a from the surface may be solved in a similar manner. Expressions for the reflection and transmission coefficients for this case are given.

A Reexamination of Homogeneous Nucleation Theory: Thermodynamic Aspects

Abstract: This paper presents a thermodynamic discussion of homogeneous nucleation. Some serious misconceptions are exposed concerning the proper thermodynamic energy representation that is required for the nucleation problem. The thermodynamic definition of surface tension is found, and the conditions for unstable equilibrium between a liquid drop and its vapor-air environment are developed. A derivation of Kelvin's equation is presented, and the free energy barrier that a cluster of molecules must surmount in order to become a growing drop is discussed. The conventional approach to this problem is compared with our treatment.

Surface disintegration of liquid in longitudinally excited containers.

Abstract: The results of an experimental and analytical study of liquid surface responses in a container excited longitudinally at high frequency are presented. A theory developed to predict surface disintegration, when compared with experimental results, is shown to give conservative estimates. The theory appears valid for arbitrary gravity conditions and a dimensionless plot, valid for Bond numbers less than 100, is presented to aid predictions of disintegration. Results of several experiments performed on spray-excited low-frequency waves are considered conclusive proof of the validity of Yarmovych's hypothesis, and testing to determine the conditions necessary for the existence of these waves was insufficient to allow a general prediction method. Nomenclature an - amplitude of the nth axisymmetric component of <£ as = effective acceleration at liquid surface; surface acceleration

Application of thermodynamics to the athabasca tar sands

Abstract: Significant changes in the interfacial areas often accompany transformations in highly dispersed systems containing oil, water, solid and gas phases. When such changes in area are considered, interfacial tension expressions diametrically opposed to the conventional criteria for oil spreading or de-wetting may result. Further modifications in the energetics criteria are obtained when the electrical contributions to the free energy of the system (resulting from the adsorption of ionic surfactants) are included.

The Shape and Energy of a Revolving Liquid Mass Held Together by Surface Tension

Abstract: The shape of a drop of incompressible fluid held together by the action of surface tension and made to rotate about an axis is determined, the effect of gravity being neglected. Two distinct problems are investigated. In the first an isolated drop of liquid in the form of a surface of revolution is considered. At zero angular speed the drop is spherical and with increasing angular momentum the oblateness increases until a maximum angular speed is reached (where the total mechanical potential is a minimum) beyond which a new linear series of equilibrium forms emerges. A solution in the form of a toroid is also found.

Temperature Dependence of Surface Tension for Liquid Metals

Abstract: The surface‐tension temperature dependence is calculated for liquid metals. In this calculation the ion motion is taken as a harmonic oscillation and it is shown that the difference in oscillation frequencies for surface and inner ions is mainly responsible for the temperature dependence of the surface tension. There is, however, a second influence caused by the change of particle density due to thermal expansion. An expression for the surface tension is derived and comparison is made with experimental values. The change of oscillator frequency, the surface tension at zero temperature, and a characteristic temperature corresponding to the critical temperature are calculated.