Immiscibility complete

Condensed phases of systems of category 1 may exhibit essentially ideal solution behavior, very nonideal behavior, or nearly complete immiscibility. An illustration of some of the complexities of behavior is given in Fig. IV-20, as described in the legend. 

If an ideal solution is formed, then the actual molecular A is just Aav (and Aex = 0). The same result obtains if the components are completely immiscible as illustrated in Fig. IV-21 for a mixture of arachidic acid and a merocyanine dye [116]. These systems are usually distinguished through the mosaic structure seen in microscopic evaluation. 

Steam Distillation. Distillation of a Pair of Immiscible Liquids. Steam distillation is a method for the isolation and purification of substances. It is applicable to liquids which are usually regarded as completely immiscible or to liquids which are miscible to only a very limited extent. In the following discussion it will be assumed that the liquids are completely immiscible. The saturated vapours of such completely immiscible liquids follow Dalton s law of partial pressures (1801), which may be stated when two or more gases or vapoms which do not react chemically with one another are mixed at constant temperature each gas exerts the same pressure as if it alone were present and that... 

Some liquids are practically immiscible e.g., water and mercury), whilst others e.g., water and ethyl alcohol or acetone) mix with one another in all proportions. Many examples are known, however, in which the liquids are partially miscible with one another. If, for example, water be added to ether or if ether be added to water and the mixture shaken, solution will take place up to a certain point beyond this point further addition of water on the one hand, or of ether on the other, will result in the formation of two liquid layers, one consisting of a saturated solution of water in ether and the other a saturated solution of ether in water. Two such mutually saturated solutions in equilibrium at a particular temperature are called conjugate solutions. It must be mentioned that there is no essential theoretical difference between liquids of partial and complete miscibility for, as wdll be shown below, the one may pass into the other with change of experimental conditions, such as temperature and, less frequently, of pressure. 

Most solvents, which are immiscible with water, may be dried by simple distillation until the distillate is clear (compare Section 11,39) the residue is anhydrous. It is usually necessary to remove about 10 per cent, by dis tillation before the residue is completely anhydrous. 

Methylene chloride CHjCl, b.p. 41°, is obtained as a by product in the com mercial preparation of chloroform by the reduction of carbon tetrachloride with moist iron and also as one of the products in the chlorination of methane it is a useful extraction solvent completely immiscible with water. 

Eutectics melting at about —30, —47, and —40° C are formed in the binary systems, cesium—sodium at about 9% sodium, cesium—potassium at about 25% potassium, and cesium—mbidium at about 14% mbidium (34). A ternary eutectic with a melting point of about —72°C has the composition 73% cesium, 24% potassium, and 3% sodium. Cesium and lithium are essentially completely immiscible in all proportions. 

Liquid-liquid fractionation, or fractional extraction (Fig. 15-6), is a sophisticated scheme for nearly complete separation of one solute from a second solute by liquid-liquid extraclion. Two immiscible liquids travel countercurrently through a contaclor, with the solutes being fed near the center of the contactor. The ratio of immiscible-liquid flow rates is operated so that one of the phases preferentially moves the first solute to one end of the contactor and the other phase moves the second solute to the opposite end of the contactor. Another way to describe the operation is that a primaiy solvent S preferentially extracts, or strips, the first solute from the feed F and a wash solvent... 

The efficiencies which may be obtained can consequently be calculated by simple stoichiometry from the equilibrium data. In the ease of countercurrent-packed columns, the solute can theoretically be completely extracted, but equilibrium is not always reached because of the poorer contact between the phases. The rate of solute transfer between phases governs the operation, and the analytical treatment of the performance of such equipment follows closely the methods employed for gas absorption. In the ease of two immiscible liquids, the equilibrium concentrations of a third component in each of the two phases are ordinarily related as follows ... 

Beaded acrylamide resins (28) are generally produced by w/o inverse-suspension polymerization. This involves the dispersion of an aqueous solution of the monomer and an initiator (e.g., ammonium peroxodisulfates) with a droplet stabilizer such as carboxymethylcellulose or cellulose acetate butyrate in an immiscible liquid (the oil phase), such as 1,2-dichloroethane, toluene, or a liquid paraffin. A polymerization catalyst, usually tetramethylethylenediamine, may also be added to the monomer mixture. The polymerization of beaded acrylamide resin is carried out at relatively low temperatures (20-50°C), and the polymerization is complete within a relatively short period (1-5 hr). The polymerization of most acrylamides proceeds at a substantially faster rate than that of styrene in o/w suspension polymerization. The problem with droplet coagulation during the synthesis of beaded polyacrylamide by w/o suspension polymerization is usually less critical than that with a styrene-based resin. 

Since Ag is a function of pressure, it follows that, under certain conditions, a change in pressure may produce immiscibility in a completely miscible system, or, conversely, such a change may produce complete miscibility in a partially immiscible system. The effect of pressure on miscibility in binary liquid mixtures is closely connected with the volume change on mixing, as indicated by the exact relation... 

Equation (91) tells us that if AJRT < 2 (complete miscibility at I atm) and if B > 0, then there is a certain pressure P (larger than 1 atm) at which immiscibility is induced. On the other hand, if A/RT > 2 (incomplete immisd-bility at 1 atm) and if B < 0, then there is a certain pressure P (larger than 1 atm) at which complete miscibility is attained. 

In the previous sections, we indicated how, under certain conditions, pressure may be used to induce immiscibility in liquid and gaseous binary mixtures which at normal pressures are completely miscible. We now want to consider how the introduction of a third component can bring about immiscibility in a binary liquid that is completely miscible in the absence of the third component. Specifically, we are concerned with the case where the added component is a gas in this case, elevated pressures are required in order to dissolve an appreciable amount of the added component in the binary liquid solvent. For the situation to be discussed, it should be clear that phase instability is not a consequence of the effect of pressure on the chemical potentials, as was the case in the previous sections, but results instead from the presence of an additional component which affects the chemical potentials of the components to be separated. High pressure enters into our discussion only indirectly, because we want to use a highly volatile substance for the additional component. 

If two immiscible liquids A and B (i.e., possessing very different 8 values) form two layers when brought together, and an elastomer of similar 6 to A is completely immersed in the (denser) B layer (schematically in Eigure 23.5), nevertheless, the elastomer will evenmaUy swell as if immersed completely in A. This arises because each liquid of an immiscible mixture stiU dissolves a minute amount of the other. At equilibrium, the chemical potential p of A will be the same, whether as pure liquid, dissolved in B, or dissolved in the elastomer. At the same temperature, the same p would apply for the elastomer immersed directly in A. However, the kinetics of absorption will be different, being much slower than... 

We plan to make studies on palladium-copper, iridium-copper, and platinum-copper catalysts to extend our investigation of the effect of varying miscibility of the components on the structural features of the bimetallic clusters present. With these additional systems, the whole range from complete immiscibility to total miscibility of copper with the Group VIII metal will be encompassed. 

A special case of interfaces between electrolytes are those involving membranes. A membrane is a thin, ion-conducting interlayer (most often solid but sometimes also a solution in an immiscible electrolyte) separating two similar liquid phases and exhibiting selectivity (Fig. 5.1). Nonselective interlayers, interlayers uniformly permeable for all components, are called diaphragms. Completely selective membranes (i.e., membranes that are permeable for some and impermeable for other substances) are called permselective membranes. 

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