Interfacial tension defined

Flow and mass transfer are influenced in many ways by the energetic conditions at the interface [26]. These conditions are described by the interfacial tension defined by the change of the free enthalpy with interfacial area. In general, interfacial tensions between liquids, and especially between liquid mixtures, cannot be calculated, but must be measured. 

The Spreading process is governed by the spreading coefficient S defined as in equation 4 (30) where c is the surface tension of the foaming medium, C the surface tension of the defoamer, and C. the interfacial tension between them. 

Detergency may be defined as the removal of dirt from solid surfaces by surface chemical means [29], and may be related to several surfactant properties, including wetting and rewelting ability, foam generation, and surface and interfacial tension. It has long been observed... 

Spreading Coefficient. The spreading coefficient is defined as the difference of the surface tension of the foaming medium cry, the surface tension of the defoamer aj, and the interfacial tension of both materials a /. 

This type of difficulty associated with measurements using chemical ly iI I-defined substrates was also observed during sessile drop measurements carried out on Athabasca bitumen in D20 T311. Values in the range of 15-20 mN/m were obtained for measurements with several drops of bitumen, while interfacial tensions for other pure aqueous and oleic systems were accurate to 0.5 mN/m. 

The complex interfacial dilational modulus ( ) is a key fundamental property governing foam and emulsion stability. It is defined as the interfacial tension increment (da) per unit fractional interfacial area change (dA/A) i.e.,... 

Equation (3) represents the reduction in interfacial tension resulting from molecular attraction between liquid and solid. The term ([) is defined by Eq. (4),... 

Unfortunately, little direct information is available on the physicochemical properties of the interface, since real interfacial properties (dielectric constant, viscosity, density, charge distribution) are difficult to measure, and the interpretation of the limited results so far available on systems relevant to solvent extraction are open to discussion. Interfacial tension measurements are, in this respect, an exception and can be easily performed by several standard physicochemical techniques. Specialized treatises on surface chemistry provide an exhaustive description of the interfacial phenomena [10,11]. The interfacial tension, y, is defined as that force per unit length that is required to increase the contact surface of two immiscible liquids by 1 cm. Its units, in the CGS system, are dyne per centimeter (dyne cm" ). Adsorption of extractant molecules at the interface lowers the interfacial tension and makes it easier to disperse one phase into the other. 

At the pore level, flnids are conveniently characterized by three main parameters. The viscosity ratio is given by M = pyp, where p and p are the viscosities of the displacing and resident fluids, respectively, while the capillary number is defined as Ca = gpyy, where q is the specific discharge of the displacing flnid and y is the interfacial tension. The Bond number. Bo = gr Ap/y, where g is the... 

Many authors have worked on drop deformation and breakup, beginning with Taylor. In 1934, he published an experimental work [138] in which a unique drop was submitted to a quasi-static deformation. Taylor provided the first experimental evidence that a drop submitted to a quasi-static flow deforms and bursts under well-defined conditions. The drop bursts if the capillary number Ca, defined as the ratio of the shear stress a over the half Laplace pressure (excess of pressure in a drop of radius R. Pl = where yint is the interfacial tension) ... 

The effect of protein and other monolayers on mass-transfer rates depends quantitatively 50) on the surface compressional modulus, Cr this is defined as the reciprocal of the compressibility of the contaminating surface film, i.e., Cr = —A dU/dA. For films at the oil-water interface Cr is often close to II, the surface pressure, which is equal to the lowering of the interfacial tension by the film. 

The interface between two fluids is in reality a thin layer, typically a few molecular dimensions thick. The thickness is not well defined since physical properties vary continuously from the values of one bulk phase to that of the other. In practice, however, the interface is generally treated as if it were infinitesimally thin, i.e., as if there were a sharp discontinuity between two bulk phases (LI). Of special importance is the surface or interfacial tension, a, which is best viewed as the surface free energy per unit area at constant temperature. Many workers have used other properties, such as surface viscosity (see Chapter 3) to describe the interface. 

During the past few years, the determination of the interfacial properties of binary mixtures of surfactants has been an area in which there has been considerable activity on the part of a number of investigators, both in industry and in academia. The Interest in this area stems from the fact that mixtures of two different types of surfactants often have interfacial properties that are better than those of the individual surfactants by themselves. For example, mixtures of two different surface-active components sometimes reduce the interfacial tension at the hydrocarbon/water interface to values far lower than that obtained with the individual surfactants, and certain mixtures of surfactants are better foaming agents than the individual components. For the purpose of this discussion we define synergism as existing in a system when a given property of the mixture can reach a more desirable value than that attainable by either surface-active component of the mixture by itself. 

Define the following terms used in Section 6.4 (a) surface excess, (b) contact adsorption, (c) interface and interphase, and (d) interfacial tension. (Gamboa-Aldeco)... 

The partial derivative of the Gibbs free energy per unit area at constant temperature and pressure is defined as the interfacial coefficient of the free energy or the interfacial tension (y), a key concept in surface and interface science ... 

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