Ternary Immiscibility Diagrams

Figrue 4.9 Immiscibility contour diagram for the lithium sodium silicate system 

The spinodal boundary is rarely shown on ternary immiscibility diagrams. Since this boundary is also represented by a dome, similar contour lines could be drawn. However, since the spinodal boundary is rarely known for these systems, it is usually neglected in the presentation of ternary immiscibility regions. 

Determination of tie-lines in these systems is more difficult, since they do not necessarily follow as simple a pattern as those, for example, in the lithium-sodium silicate system. Tie-lines can also rotate with temperature, so that the lines at 1000 °C are not necessarily co-linear 

Figrue 4.11 Immiscibility contour diagram for an arbitrary alkali borosilicate system 

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Case I. At sufficiently low pressures, the solubility curve does not intersect the coexistence curve. In this case, the gas solubility is too low for liquid-liquid immiscibility, since the coexistence curve describes only liquid-phase behavior. Stated in another way, the points on the coexistence curve are not allowed because the fugacity f2L on this curve exceeds the prescribed vapor-phase value f2v. The ternary phase diagram therefore consists of only the solubility curve, as shown in Fig. 28a where V stands for vapor phase. 

Consider one-dimensional, steady-state, ternary diffusion along a capillary tube as shown in part (a) of the accompanying figure. Two immiscible liquids occupy the two halves of the tube with the position of the interface between them taken as the origin of the coordinate system (z = 0). Compositions A and D at the ends of the tube are known. Compositions B and C at the interface are not known initially. But if local equilibrium is assumed at the interface, B and C must be at the ends of a tie-line on the (known) ternary phase diagram as shown in part (b) of the figure. The question is which tie-line Once the tieline is determined, the concentration profiles are known and the question of whether spontaneous emulsification occurs can be settled. 

Mixtures of partially immiscible liquids separate into two liquid phases for some compositions. For example, hexane and methylcyclopentane (mcp) are miscible for all compositions. Also, aniline and mcp are miscible for all compositions. However, aniline and hexane are immiscible. The ternary phase diagram for mcp-hexane-aniline at 45 "C and 1 atm is sketched below. 

As indicated by the alcohol-water-TEOS ternary-phase diagram shown in Fig. 7, large values of r cause liquid-liquid immiscibility however both alcohol produced as the by-product of the hydrolysis reaction and partial hydrolysis of the TEOS precursor lead to homogenization. Finally, because water is the by-product of the condensation reaction (Eq. 10), large values of r promote siloxane bond hydrolysis (the reverse of Eq. 10). The effects of reverse reactions are discussed extensively in Sections 2.3.6 and 2.4.5. 

While the majority of microemulsions use oil and water as immiscible liquid pairs, if a cosurfactant is used it may sometimes be represented at a fixed ratio to the surfactant as a single component and treated as a single pseudo-component , so that the relative amounts of these three components can then be represented in a pseudo-ternary phase diagram. These diagrams can be used to depict the phase behavior of the system as a function of the volume fractions of different components. 

Ternary-phase equilibrium data can be tabulated as in Table 15-1 and then worked into an electronic spreadsheet as in Table 15-2 to be presented as a right-triangular diagram as shown in Fig. 15-7. The weight-fraction solute is on the horizontal axis and the weight-fraciion extraciion-solvent is on the veriical axis. The tie-lines connect the points that are in equilibrium. For low-solute concentrations the horizontal scale can be expanded. The water-acetic acid-methylisobutylketone ternary is a Type I system where only one of the binary pairs, water-MIBK, is immiscible. In a Type II system two of the binary pairs are immiscible, i.e. the solute is not totally miscible in one of the liquids. 

Figure 7.11 shows a ternary diagram for a system with components 1-3 and 2-3 immiscible in all proportions at solid state. However, here components 1 and 2 form an intermediate compound with fixed stoichiometry (ratio 30 70). 

Figure 7.17 Ternary A/B/C phase diagram (at 25°C, 1 atm) for A = acetic acid, B = vinyl acetate, C = water, showing nonhorizontal tie-lines in the immiscible two-phase region (organic liquid + aqueous liquid), culminating at a plait point (x). Concentration grid values (dotted lines) are in wt% at 10% intervals.

SIDEBAR 7.17 TERNARY DIAGRAM PROBLEMS FOR IMMISCIBLE LIQUIDS... 

A promising way to create LLC systems with sufficient stability is the use of immiscible ternary mixtures to create what is called a dynamic (or solvent-generated ) LLC system. The principle of such a phase system is illustrated in figure 3.9. This figure shows an example of a thermodynamic phase diagram of a mixture of three components (A, B and C). Both the binary mixtures A + B and A + C are miscible in all proportions. 

Fig. 29.4. Phase diagram at constant T and p for ternary system with two immiscibility triangles.

A schematic representation of type-I ternary phase behavior is shown in figure 3.29. The three diagrams in this figure represent mixtures at a fixed temperature slightly higher than the critical temperature of the SCF but at three different pressures. The distinguishing feature of type-I ternary phase behavior is the absence of LLV immiscibility regions within the ternary... 

Ternary blends that comprise two immiscible polymers and a copolymer are of a particular interest. They not only represent an ideal model for studying compatibilization of polymer blends, but also they have found direct commercial applications. Phase diagram information can be found in reviews by Ajji and Utracki [1996, 1997] and in Chapter 2 in this Handbook. 

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