Mutual miscibility

The quantitative treatment of solubiUty is based on the familiar free energy equation governing mutual miscibility ... 

It is seen that as the concentration of C is increased, the tie-lines become shorter because of the increased mutual miscibility of the two phases at the plait point, P, the tie lines vanish. However, P does not necessarily represent the highest possible loading of C which can exist in the system under two-phase conditions. In Figure 2b the plait point Hes on the diagonal because the compositions of the two phases approach each other at P. 

The response of any given feed to sink-float processing can be accurately established in the laboratory by testing with various heavy hq-uids. The hquids generally used for this purpose are listed in Table 19-12. These halogenated hydrocarbons are mutually miscible, which enables the preparation of almost any pulp density attainable in a commercial plant. Heavy-hquid test work provides the basis for specifying the optimum screen size for the preparation of the feed. 

An interface between two immiscible electrolyte solutions (ITIES) is formed between two liqnid solvents of a low mutual miscibility (typically, <1% by weight), each containing an electrolyte. One of these solvents is usually water and the other one is a polar organic solvent of a moderate or high relative dielectric constant (permittivity). The latter requirement is a condition for at least partial dissociation of dissolved electrolyte(s) into ions, which thus can ensure the electric conductivity of the liquid phase. A list of the solvents commonly used in electrochemical measurements at ITIES is given in Table 32.1. 

The transfer energies and distribution coefficients refer to two mutually saturated, i.e., in a sense, mixed solvents. It should be noted that this is a case where, under conditions of distribution equilibrium, the quantities in question can be experimentally measured this would not be possible with mutually miscible solvents [34],... 

Since in this mixture design problem we have to identify a mixture whose constituents perform different functions, i.e., the solvent needs to have high solubility for the solute while the anti-solvent needs to reduce the solubility, we have to solve two different single compound design problems (involving subproblem 1M, 2m and 3M) to identify the candidate solvents and anti-solvents. The mutually miscible pairs are identified in sub-problem 4M and the final optimisation problem is solved in sub-problem 5M. 

The miscibility of solvent anti-solvent pairs is considered in sub-problem 4M through constraint represented by Eqn.38. Only 6 pairs were found to be mutually miscible with each other. 

The mixture is going to be identified by its ability to not mix with water (total immiscibility), normal boiling point (each compound in the mixture has a Tb above 350 K so the mixture will be a liquid), normal melting point (each compound in the mixture has a Tm below 250 K so the mixture will be a liquid), the Hildebrand solubility parameters of each of the compounds should be between 18-22 MPa172 (so the two compounds are mutually miscible). 

E-EA-GMA (see Table 14.3) and EEA are often used in combination as a toughening system. The optimum blend ratio of reactive elastomers non-reactive elastomers (e.g. Lotader Lotryl) is 30/70. Since the E-EA-GMA terpolymer and EEA copolymer are mutually miscible, when blended together with PET the mixture acts as a single elastomeric phase, which is interfacially grafted to the PET continuous phase. 

Solutions are liquid preparations containing one or more drug substances that are molecularly dispersed in a suitable solvent or a mixture of mutually miscible solvents. 

Solvent extraction is another name for liquid-liquid distribution, that is, the distribution of a solnte between two liquids that must not be completely mutually miscible. Therefore, the liquid state of aggregation of matter and the essential forces that keep certain types of liquids from being completely miscible are proper introductory subjects in a study of solvent extraction. Furthermore, the distribution of a solute depends on its preference for one or the other liquid, which is closely related to its solubility in each one of them. Thus, the general snbject of solnbilities is highly relevant to solvent extraction. 

Godfrey gave an alternate approach for the prediction of mutual miscibility of solvents (Godfrey, 1972). As a measure of lipophilicity (that is, affinity for oil-like substances) the so-called miscibility numbers (M-numbers, with values between 1 and 31) have been developed. These are serial numbers of 31 classes of organic solvents, ordered empirically by means of simple test tube miscibility experiments and critical solution temperature measurements. There is a close correlation between M-numbers and Hildebrand s 5-values. 

One feature of the non-amphiphilic cubic mesophases is that they frequently show mutual miscibility even when constituted from dissimilar molecules. Such miscibility, which contrasts with the immiscibility between dissimilarly constituted solid crystals, is also found between nematic mesophases, between corresponding smectic polymorphs, and, of course, between amorphous liquids. This miscibility is important in its implication that in the cubic mesophases of the amphiphilic series there could well be an equilibrium of related globular micellar forms (Figures 1 and 5) rather than a single clearly defined form. 

For two components of a mixture (i.e., drug molecules and the hydrophobic block of the copolymer) to be mutually miscible, the Gibbs free energy of rnixMpmjx, must be negative. 

The mutual miscibility of solvents that does not involve water has been reported on an empirical basis by assigning to each solvent a miscibility number, on a scale of standard solvents ranging from 1 for the very hydrophilic glycerol to 31 for the very lipophilic petrolatum. If the miscibility numbers of two solvents differ by < 15 they are probably miscible, whereas if they differ by > 17 they are probably immiscible. Those that have a miscibility number of 16 ought to be miscible with all solvents, hence act as universal solvents. The miscibility numbers are shown in Table 4.6, where, in the cases where two numbers are shown, the first pertains to miscibility with solvents of high lipophilicity and the second to miscibility with solvents of high hydrophilicity (Godfrey 1972). 

The case of two liquid reagents is more understandable, occurring in the homogeneous phase if the compounds are mutually miscible or as an emulsion. In both cases, enhancements in reactivity are provided by concentration effects on kinetics due the absence of any dilution induced by the solvent. 

Type I Those pairs whose mutual miscibility increases with increasing temperature. 

Reference Electrodes for Use in Nonpolar Solvents. Solvents such as dichloromethane (not highly polar) present special problems. Their low dielectric constants promote extensive ion association, and cell resistances tend to be large. For this reason they are often used in mixtures with more polar solvents. Because dichloromethane and other nonpolar solvents are not miscible with water, use of an aqueous reference electrode with such solvents is not practical unless a salt bridge with some mutually miscible solvent is used. A better approach is to use a reference electrode of known reliability prepared in a solvent miscible with dichloromethane or to use the reference electrode based on the half-cell in dichloromethane.88... 

The function of a protective colloid is to lower cr01 to a minimum. In practical language, wetting is an attempt by a surfactant to accomplish this by lowering the contact angle, which enables liquids to spread over each other, on its mission to make the phases mutually miscible. Relative to solvent and component, the concentration of a protective colloid is quite low, but it accumulates at the interface, theoretically as a thin film. Micromolecules that wet surfaces dissolve completely in the solvent. One unique property of micellar surfactant electrolytes is their ability to solubilize some otherwise insoluble organic molecules (Adamson, 1990). 

Generally, one may establish that in some cases greatly enhanced concentration fluctuations occur under flow, in others, however, the size of concentration fluctuations is reduced and, obviously, flow promotes mutual miscibility of the polymers. Concentration fluctuations are accompanied by inhomogeneities of transport quantities as shear viscosity and diffusity. In a flow field the molecules are transferred into a non-equilibrium situation of extension. Two polymer molecules in a state of excess extension feel an additional repulsion due to the enhanced normal stress difference. Thus, the rate of dissipation by diffusion is low compared with the shear rate and the concentration fluctuations tend to grow. The opposite is true for a state of lower extension. In that case the dissipation of the concentration fluctuations is enhanced owing to an additional attraction between the chain molecules. 

Interface between two liquid solvents — Two liquid solvents can be miscible (e.g., water and ethanol) partially miscible (e.g., water and propylene carbonate), or immiscible (e.g., water and nitrobenzene). Mutual miscibility of the two solvents is connected with the energy of interaction between the solvent molecules, which also determines the width of the phase boundary where the composition varies (Figure) [i]. Molecular dynamic simulation [ii], neutron reflection [iii], vibrational sum frequency spectroscopy [iv], and synchrotron X-ray reflectivity [v] studies have demonstrated that the width of the boundary between two immiscible solvents comprises a contribution from thermally excited capillary waves and intrinsic interfacial structure. Computer calculations and experimental data support the view that the interface between two solvents of very low miscibility is molecularly sharp but with rough protrusions of one solvent into the other (capillary waves), while increasing solvent miscibility leads to the formation of a mixed solvent layer (Figure). In the presence of an electrolyte in both solvent phases, an electrical potential difference can be established at the interface. In the case of two electrolytes with different but constant composition and dissolved in the same solvent, a liquid junction potential is temporarily formed. Equilibrium partition of ions at the - interface between two immiscible electrolyte solutions gives rise to the ion transfer potential, or to the distribution potential, which can be described by the equivalent two-phase Nernst relationship. See also - ion transfer at liquid-liquid interfaces. 

In the example of Table 4.4, the surface energy of solid W in equilibrium with a saturated vapour of Cu is lower than °sv due to adsorption of Cu atoms on the W surface. This is generally characteristic of metallic A-B pairs having a low mutual miscibility (Eustathopoulos and Joud 1980). For this reason, results of sessile drop experiments for such systems cannot be interpreted by taking for the surface energy of the solid metal the value of equilibrium with its own vapour (see Sections 1.4.2 and 5.2). 

---