Showing papers on "Surface tension published in 1982"

Microemulsions and the flexibility of oil/water interfaces

Abstract: The purpose of this review is to understand why a random structure of this type does not collapse into an ordered phase. The interface saturated by surfactant has a nearly vanishing surface tension; one essential parameter is then the elastic constant K describing the curvature elasticity of the interface. The persistence length xi/sub K/ of the interface increases exponentially with K. This should have some important effects. (1) When K is above a certain value K/sub c/ the interfaces tend to stack or, more generally, to build up a periodic, stable, phase. (2) When K is below K/sub c/ the interface can become extremely wrinkled and the resulting gain in entropy is larger than the loss of energy due to the departure from a periodic array. This case K < K/sub c/ would correspond to microemulsions. In this picture one major effect of cosurfactants (additives which favor the mocroemulsion phase) is to increase the flexibility of the layers. 10 figures.

Flow and instability of a viscous current down a slope

Abstract: If viscous fluid is released on a horizontal surface it rapidly takes up a circular plan form as it spreads. This form is observed1,2 to be stable to any small disturbances which are initiated on the front due, for example, to irregularities in the horizontal surface or to chance perturbations. Alternatively, if some fluid is released onto a sloping surface—for example, some liquid detergent on a slanted plate—a quite different plan form occurs. One, two or more extended regions of fluid develop downslope, as shown in Fig. 1a, b. A situation intermediate between these two is now discussed. Consider a broad band of viscous fluid, uniform in depth across a slope, released so as to flow down a constant slope. By following the motion, which is initially independent of the cross-slope coordinate, the speed of advance and the depth of the flow before it breaks up into a series of waves of ever increasing amplitude can be determined. I present an expression for the wavelength of the front, which is determined by surface tension and is independent of the coefficient of viscosity.

Electrical conductivity of carbon-polymer composites as a function of carbon content

Abstract: The electrical conductivity of carbon particle-filled polymers was measured as a function of carbon content to find a break point of the relationships between the carbon content and the conductivity. The conductivity jumps by as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point varies depending on the polymer species and tends to increase with the increase in the surface tension of polymer. In order to explain the dependency of the critical carbon content on the polymer species, a simple equation was derived under some assumptions, the most important of which was that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a “universal value”, Δg *, the carbon particles begin to coagulate so as to avoid any further increase of the energy and to form networks which facilitate electrical conduction. The equation well explains the dependency through surface tension, as long as the difference of the surface tensions between the carbon particles and the polymer is not very small.

Relationship of structure to properties in surfactants. 10. Surface and thermodynamic properties of 2-dodecyloxypoly(ethenoxyethanol)s, C12H25(OC2H4)xOH, in aqueous solution

Abstract: The surface and thermodynamic properties of homogeneous surfactants of structure C/sub 12/H/sub 25/(OC/sub 2/H/sub 4/)XOH, where X = 2-8, purified by passages through a column of octadecylsilanized silica gel, have been investigated. Surface tension, as a function of concentration of the surfactant in an aqueous solution, was measured at 10, 25, and 40C, using the Wilhelmy plate technique. From these measurements, the maximum surface excess concentration and the minimum area per molecule at the aqueous solution/air interface, the critical micelle concentration (CMC), the surface pressure at the CMC, and the standard thermodynamic parameters of adsorption and micellization were calculated. Structural effects on adsorption, micellization, and the effectiveness of surface tension reduction are discussed in terms of these parameters. 21 references.

Monte Carlo calculation of the surface tension for two- and three-dimensional lattice-gas models

Abstract: It is suggested that the interface free energy between bulk phases with a macroscopically flat interface can be estimated from the variation of certain probability distribution functions of finite blocks with block size. For a liquid-gas system the probability distribution of the density would have to be used. The method is particularly suitable for the critical region where other methods are hard to apply. As a test case, the two-dimensional lattice-gas model is treated and it is shown that already, from rather small blocks, one obtains results consistent with the exact soluion of Onsager for the surface tension, by performing appropriate extrapolations. The surface tension of the three-dimensional lattice-gas model is also estimated and found to be reasonably consistent with the expected critical behavior. The universal amplitude of the surface tension of fluids near their critical point is estimated and shown to be in significantly better agreement with experimental data than the results of Fisk and Widom and the first-order 4-d renormalization-group expansion. Also the universal amplitude ratio used in nucleation theory near the critical point is estimated.

Steady thermocapillary flows in two-dimensional slots

Abstract: Liquid in a slot flows owing to a temperature gradient applied along its free surface. The thermal variation of surface tension induces a steady viscous flow directed on the surface from hot to cold, and recirculating below. For small aspect ratios A, giving flow in thin, two-dimensional slots, an asymptotic theory valid for A yields to 0 is used to obtain the fluid and thermal fields as well as the interfacial shapes. Solutions are obtained for both fixed lines and fixed angles at the contact between the interface and the solid side walls.

Thermodynamics of cavity formation in water. A molecular dynamics study

Abstract: Thermodynamic quantities related to the solvation of hydrophobic solutes in water can be approximated by the application of scaled-particle theory. The crucial quantity is the Gibbs free energy of cavity formation. A series of six molecular-dynamics simulations of water including repulsive cavities of various sizes has been carried out. Using perturbation statistical mechanics, the free energy has been derived as a function of cavity radius up to 0.32 nm (0.32 nm approach of water oxygens to the cavity centre). The free energy agrees well with predictions from scaled-particle theory and the experimental surface tension is predicted to within 5%. The radial distribution of water molecules with respect to the cavity has been determined for five cavity sizes; for one size (radius of approach of water oxygens of 0.3 nm) the orientational distribution and the residence-time distribution in the hydration shells has been determined.

Aqueous ink for ink jet printing

Abstract: An aqueous ink for ink-jet printing comprising at least a water-soluble dye, a water-soluble organic solvent, a water-soluble preservative and anti-mold agent, and water, wherein (1) the water-soluble dye is a mixture of dye compounds I and II and/or III, the peak ratio of I/II and/or III of the water-soluble dye measured by liquid chromatography is in the range of 0.9 to 3.0; the total concentration of NaCl and Na2 SO4 contained in the water-soluble dye is 3.0 wt. % or less; and the concentration of Ca contained therein is 120 ppm or less; (2) the water-soluble organic solvent is a mixture consisting essentially of glycerin and at least one glycol selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and polyethylene glycol, with the content ratio of (the glycerin:the glycol) being in the range of (1:1) to (1:5) in terms of parts by weight, and the concentration of the water-soluble organic solvent in the aqueous ink is in the range of 10 wt. % to 30 wt. %; and (3) the surface tension of said aqueous ink is 50 dynes/cm or more.

Wetting of solids by surface-active agents: The effects of unequal adsorption to vapor-liquid and solid-liquid interfaces

Abstract: The role of surfactant adsorption in the wetting of relatively low-energy solids was evaluated from contact angle measurement using various aqueous surfactant solution-solid combinations. Analysis of the resulting data indicates that with many systems, pure liquids of low surface tension and aqueous surfactant solutions having the same surface tension do not produce the same contact angles; pure liquids often are better wetting agents. For hydrocarbon surfactants these effects are more significant for semipolar solids such as polymethyl methacrylate than for nonpolar solids. For a fluorocarbon surfactant, perfluoro-n-octanoic acid, the effects were found to be important for semipolar solids as well as nonpolar solids such as paraffin. These differences can be explained by invoking a lower adsorption of surfactants to the solid-liquid interface in comparison to the vapor liquid interface. Independent evidence from adsorption data justifies this explanation both for hydrocarbon and fluorocarbon surfactants. Using directly determined adsorption data on Graphon for both types of surfactants and surface tension values of the aqueous solutions involved, changes in the contact angle for Graphon were calculated. These simulated wetting curves reproduce many features of the observed wetting data for nonpolar solids for similar surfactants.

Correlation between critical solution phenomena and ultralow interfacial tensions in a surfactant/water/oil system.

Abstract: A three-phase region consisting of surfactant (D), water (W), and oil (O) phases appeared due to the superposition of two critical phenomena of D–W and O–D in a nonionic surfactant/water/oil system. Three interfacial tensions, γO–W, γO–D and γD–W, among the three phases were determined at various temperatures. The generalized Antonoff’s rule (γO–W=γO–D+γD–W) holds approximately in the three-phase region. γO–D and γD–W disappear at the respective critical solution temperatures, and ultralow interfacial tensions are attained in the vicinity of both critical temperatures. The oil–water interfacial tension, γO–W, reaches its minimum in the midst of the temperature range of the three-phase region, and the narrower the temperature range of the three-phase region, the lower the interfacial tension. The correlation between the interfacial tensions and the types of emulsions is also discussed.

Tissue processing apparatus

Abstract: A tissue or like processing method involving application of liquids to carrier-mounted material, e.g. a thin tissue section mounted on a microscope slide (10), is characterized by disposing a channel-defining element (1) adjacent to the carrier (10) to form an assembly providing an enclosure (11) for the material on the carrier. The enclosure (11) has an inlet (13) and an outlet (14) and has capillary dimensions. The assembly is disposed with the inlet (13) above the outlet (14) and liquid introduced into the inlet fills the enclosure and is retained in contact with the material on the carrier by surface tension effect. Further liquid introduced to the inlet (13) displaces the first liquid progressively to the outlet (14). A sequence of liquids can thus be brought successively into contact with the material with minimum wastage, by feeding the liquids successively to the inlet (13) of an assembly. A support for a plurality of assemblies to permit concurrent operations upon a set of material samples is disclosed, and a machine for automated processing, e.g. immunostaining, of a batch of tissue samples is also disclosed.

Convection in arc weld pools

Abstract: A mathematical model was developed to account for convection and temperature distributions in stationary arc weld pools driven by buoyancy, electromagnetic and surface tension forces. It is shown that the electromagnetic and surface tension forces dominate the flow behavior. In some cases, these forces produce double circulation loops, which are indirectly confirmed by experimental measurements of segregation in the weld pool. It is also shown that the surface tension driven flows are very effective in dissipating the incident energy flux on the pool surface which, in turn, reduces the vaporization from the weld pool.

Surface-tension-driven breakup of viscoelastic liquid threads

Abstract: A linearized stability analysis is carried out for the breakup of small-diameter liquid filaments of dilute polymer solutions into droplets. Oldroyd's 8-constant model expressed in a corotational reference frame is used as the rheological equation of state. The crucial idea in this theory is the recognition that the liquid may be subject to an unrelaxed axial tension due to its prior history. If the tension is zero, the present analysis predicts that jets of shear-thinning liquids are less stable than comparable jets of Newtonian liquids; this is in agreement with previous analyses. However, when the axial tension is not zero, and provided the stress relaxation time constant is sufficiently large, the new theory predicts that the axial elastic tension can be a significant stabilizing influence. With reasonable values for the tension and stress relaxation time the theory explains the great stability observed for jets of some shear- thinning, dilute polymer solutions. The theory explains why drops produced from jets of such liquids are larger than drops from corresponding Newtonian liquids. The theory also appears capable of explaining the sudden appearance of irregularly spaced bulges on jets after long distances of t,ravel with little amplification of disturbances.

Roughening transition, surface tension and equilibrium droplet shapes in a two-dimensional Ising system

Abstract: The exact surface tension for all angles and temperatures is given for the two-dimensional square Ising system with anisotropic nearest-neighbour interactions. Using this in the Wulff construction, droplet shapes are computed and illustrated. Letting temperature approach zero allows explicit study of the roughening transition in this model. Results are compared with those of the solid-on-solid approximation.

Synergism in binary mixtures of surfactants: II. Some experimental data

Abstract: The conditions derived previously for three types of synergism in aqueous binary mixtures of surfactants-mixed micelle formation, surface tension reduction efficiency, and surface tension reduction effectiveness-are reviewed and verified by use of experimental data from the chemical literature. They involve the experimentally determined parameters, β and βM, related to the interaction between the two surfactants in the mixed monolayer at the aqueous solution/air interface and in the mixed micelle, respectively. The experimental data needed to determine whether a binary surfactant system is capable of synergism in these respects are: (a) the surface tension/log concentration curves of the individual surfactants in the vicinity of their critical micelle concentrations (cmc); (b) the cmc of at least one mixture of the two surfactants; and (c) the solution phase concentration of at least one mixture of the two surfactants needed to produce a surface tension attainable by both individual surfactants. From the available data, some tentative generalizations regarding the effect of chemical structure and the molecular environment of the values of β and βM have been made.

Total surface energy and equilibrium shapes: Exact results for the d = 2 Ising crystal

Abstract: Explicit relations between the surface tension (interfacial energy density), the equilibrium shape of a crystal, and the total surface energy are given. For the $d=2$ Ising model with anisotropic couplings, the exact equilibrium shape is cast into a closed form of elementary functions. The surface energy is compared with Monte Carlo simulations. A discussion of the solid-on-solid approximation is presented.

Surface Tension and Foaming of Protein Solutions

Abstract: The relationship between surface tension and foamability of protein solutions was examined. Proteins including egg albumin, soybean protein, casein, milk whey protein and gelatin were used. Foamability was expressed as “foaming power” which corresponded to the ratio of gas volume to the liquid volume in the foam. The absolute surface tensions of protein solutions were not correlated to foamability, but the rate constant of surface tension decay of protein solutions was significantly correlated to foamability of protein solution.

Bubble entrainment in breaking wind waves

Abstract: Processes of bubble formation and spreading in breaking wind waves are experimentally investigated in a wind-wave tank. The distribution and movement of bubbles relative to the wave form are measured using photographic techniques. The main mechanism of bubble formation in these waves is intermittent bubble entrainment by an ordered convergent flow on the leading slope near the crest. This conclusion is supported by a simple experiment for modeling the bubble entrainment, where a small jet of water is injected into water whose surface is at rest: bubbles are entrained by the water jet. In the oceans, the mechanism under consideration will be important in understanding the breaking process of smaller scale waves superposed on dominant waves. A model experiment also shows that the existence of a stagnation point on a water surface (convergent flow) is not a sufficient condition for bubble entrainment. The downward force of the convergent flow must be greater than the restoring force of the surface tension at the stagnation point for bubble entrainment to occur. DOI: 10.1111/j.2153-3490.1982.tb01836.x

Conformation and Surface Properties of Deamidated Gluten

Abstract: The surface properties of deamidated gluten were investigated with respect to their conformational changes. The helix content of gluten decreased curvilinearly with its decrease of deamidation. The surface tension decreased in proportion to the degree of deamidation. On the other hand, the surface hydrophobicity of gluten increased remarkably in proportion to the degree of deamidation. The emulsifying properties of gluten were improved greatly by deamidation, correlating linearly with the surface hydrophobicity. From these results, the relationships between the conformational changes and functional properties of deamidated gluten are discussed.

Flow beneath a stagnant film on water: the Reynolds ridge

Abstract: Surface-active material is present in most naturally occurring water samples, and it naturally diffuses steadily to free surfaces, where it both reduces the surface tension and gives the surface elastic properties which enable it to resist compression. When the water flows so that the surface layer is trapped and compressed against a fixed shallow-draught barrier the film material makes the surface incompressible, and flow beneath the barrier forms a viscous boundary layer under the film. The stresses associated with this boundary layer are found to distort the surface in the region of the leading edge of the film, giving rise to a phenomenon which is commonly observed in nature and which has been called the Reynolds ridge. This paper describes experimental work on the measurement of the ridge, and compares the results with a theoretical model due to Harper & Dixon. Good agreement is indicated.

Mass transport in laser surface alloying: iron-nickel system.

Abstract: The role of fluid flow in producing uniformly alloyed beads in laser surface alloying is examined and the experimental finding that the uniformity of alloying increased with a decrease in the beam diameter is analyzed. Fluid flow can dominate the process of solute redistribution in the melt pool by producing a fine dispersion of solute rich pockets. The fineness of the scale is estimated and found to compare favorably with the experimentally measured scale of local fluctuations in composition. It is found that the magnitude of the surface tension gradients is primarily dependent upon the magnitude of the surface temperature gradients. This can be used to estimate the effect of process parameters on the vigor of the fluid flow in the pool, which controls the process of mass transport in laser surface alloying.