Surface tension liquid mixtures

Finally Papkov [52] observed that the surface tension of the solvent is a further factor influencing the solubility of cellulose esters. This worker established that the best solvents from a series of liquids resembling each other chemically, e.g. in a homologous range, were characterized by a moderate, optimum surface tension. Liquids having higher or lower surface tensions than this optimum value are worse solvents. The rule is also valid for mixtures. Thus a 50 50 acetone-water solution with a surface tension a = 30.4 dyne/cm caused only a weak swelling of... 

Measurements of the surface tensions of mixtures and solutions have been made in great numbers Musculus (1864) indicated that solutions may be classified into two groups according as the solute has little influence on the surface tension of the solvent (when Traube called it capillary inactive), or when it produces a marked lowering of surface tension (when Traube called it capillary active). A consideration of the second group is closely connected with adsorption phenomena, which are not dealt with here, the present discussion being mainly confined to solutions of the first group, especially electrolytes, and to mixtures of liquids. 

LIQUIDS AND SOLUTIONS AT INTERFACES 445 A simple equation for the surface tension of mixtures is... 

We have considered the surface tension behavior of several types of systems, and now it is desirable to discuss in slightly more detail the very important case of aqueous mixtures. If the surface tensions of the separate pure liquids differ appreciably, as in the case of alcohol-water mixtures, then the addition of small amounts of the second component generally results in a marked decrease in surface tension from that of the pure water. The case of ethanol and water is shown in Fig. III-9c. As seen in Section III-5, this effect may be accounted for in terms of selective adsorption of the alcohol at the interface. Dilute aqueous solutions of organic substances can be treated with a semiempirical equation attributed to von Szyszkowski [89,90]... 

It was noted in connection with Eq. III-56 that molecular dynamics calculations can be made for a liquid mixture of rare gas-like atoms to obtain surface tension versus composition. The same calculation also gives the variation of density for each species across the interface [88], as illustrated in Fig. Ill-13b. The density profiles allow a calculation, of course, of the surface excess quantities. 

Surface tension is usually predicted using group additivity methods for neat liquids. It is much more difficult to predict the surface tension of a mixture, especially when surfactants are involved. Very large molecular dynamics or Monte Carlo simulations can also be used. Often, it is easier to measure surface tension in the laboratory than to compute it. 

Liquid surface tension is calculated using the Sugden Parachor method [242]. Neglecting vapor density, surface tension for the liquid mixture is ... 

X = mole fraction in the liquid y = mole fraction in the vapor i, = liquid viscosity, Ib/hr-ft p = density, Ib/ft o = surface tension, dynes/cm i[) = mixture parameter... 

Separation of phases is sometimes a problem, especially in the case of mixtures of alkaline aqueous solutions and organic liquids. Addition of materials that decrease the surface tension, filtration of the emulsion to remove interfacial contamination, and the use of sedimentation centrifuges should be considered if the separation time is too long. 

The situation is, however, different in the alveolar region of the lung where the respiratory gas exchange takes place. Its thin squamous epithelium is covered by the so-called alveolar surface liquid (ASL). Its outermost surface is covered by a mixture of phospholipids and proteins with a low surface tension, also often referred to as lung surfactant. For this surfactant layer only, Scarpelli et al. [74] reported a thickness between 7 and 70 nm in the human lung. For the thickness of an additional water layer in between the apical surface of alveolar epithelial cells and the surfactant film no conclusive data are available. Hence, the total thickness of the complete ASL layer is actually unknown, but is certainly thinner than 1 gm. 

Experiments [43] with very high flash point fuels (JP, kerosene, Diesel, etc.) revealed that the flame propagation occurred in an unusual manner and a much slower rate. In this situation, at ambient conditions, any possible amount of fuel vapor above the liquid surface creates a gaseous mixture well outside the fuel s flammability limits. What was discovered [44, 45] was that for these fuels the flame will propagate due to the fact that the liquid surface under the ignition source is raised to a local temperature that is higher than the cool ambient temperature ahead of the initiated flame. Experimental observations revealed [45] that this surface temperature variation from behind the flame front to the cool region ahead caused a variation in the surface tension... 

Enhanced-fluidity liquids (EELs) are mixtures that contain high proportions of liquefied gases, such as carbon dioxide [5]. Eluidity,/, is defined as the inverse of viscosity. EEL mixtures combine the positive attributes of commonly-used liquids, such as high solvent strength, with the positive attributes of supercritical fluids, such as low viscosity or high fluidity, low surface tension, high diffusivity. These attributes allow EELC to contribute to the quest for increased separation power. 

Emulsion and emulsifiers. An. .emulsion is a mixture of two liquids that do not mix very well—they are immiscible—but are held in stable suspension by the addition of a substance called an emulsifier. Emulsifiers are composed of molecules that attract the two liquids, one each at either end of the molecule, reducing the surface tension between the two liquids. 

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