Fully miscible systems

It is readily seen from Fig. 3.6 that for each value of x abovethere are two different values of (f>2 at which the chemical potential of the solvent in the two phases is the same. This means that solutions with concentrations represented by these two values of thermodynamic equilibrium fox x >Xc- It also implies that a solution which has an intermediate value of (p2 wiU spontaneously separate into two stable liquid phases with these two concentrations and a concomitant decrease in the free energy. Thus, if is increased by decreasing the temperature, a fully miscible system at higher temperatures is transformed to one of limited miscibility at the lower temperature. At some critical temperature Tc, during this process, incipient phase separation (as indicated by the onset of an... 

Figure 27.1 shows a schematic phase diagram for binary blends showing the relationship between free energy of mixing AG ) and blend composition cp). For sample A, an immiscible system is obtained (AG j > 0), for sample B a fully miscible system is obtained in which AG < 0, and C represents a partially miscible system that satisfies AG < 0 for all compositions, but d AG Idcpi is lower than 0 at certain compositions, indicating that at these compositions the blend will be immiscible. 

For fully miscible systems, the deviation, STg, defined as = ATg — (wiATgi — H 2ATg2), is, by definition, very small. Table 3.4 shows BT ... 

If the desired yield target cannot be achieved then an antisolvent system can be selected using the same techniques. The antisolvent should be fully miscible with the primary solvent and have a low solubility for the solute. It should be noted that the addition of an antisolvent to reduce solubility and generate supersaturation may introduce scale up issues, caused by the differences in micro-mixing performance between the laboratory and manufacturing plant. 

Other than compounds, the activities of CaO in solid solutions have also been measured using CaFj solid electrolyte. The CaO-CdO system is one such example. Here also CaO and CdO are both having NaCl-type FCC lattice structure and are fully miscible in the entire composition range. Through the measurement of EMF of the following cell, the activities of CaO in the CaO-CdO solid solutions were determined Prasad et al, 1975)... 

First, if, for example, a powder is to be examined, then it should be freely soluble in the solvent chosen for injection into the chromatographic system. Secondly, the solvent should be fully miscible with the mobile phase. For these reasons, methanol is frequently chosen for heroin analysis, although the drug should not be left in this solvent for long periods because of the risk of hydrolysis of some of its components, e.g. monoacetylmorphine and diamorphine. 

Gibbs monolayers are widespread. The simplest system is that of the surface of a fully miscible binary liquid. More complex ones are monolayers of uncharged molecules adsorbed from dilute solutions (example aliphatic alcohols from aqueous solution) electrolytes surfactants (non-ionic or ionic) polymers and polyelectrolytes and yet more. On the other hand, the methods for characterizing... 

Acetone Does not form an azeotrope with water but requires a large reflux when distilled. Pervaporation is ideal for final dehydration or for de-bottlenecking existing distillation systems. Acetonitrile Forms an azeotrope with water fully miscible with water. Can easily be dehydrated to low water concentrations. Avoids messing with contaminated salt solution andre-distilla-tion of salt-contaminated organic phase. 

The determined two-phase envelopes of the DiPA-H20-NaCl and the DMiPA-H20-NaCl systems (saturated with sodium chloride) are also displayed in Figure 5. The LCST s of the DiPA-H20-NaClsat and the DMiPA-H20-NaClsat systems were estimated to be -11.7 °C and 6.6 °C. The LCST of the DiPA-H20-NaCl system deviates from the one presented by Weingartner et al. who estimated the LCST at -7.5 °C. The LCST s of the amine-water systems as well as the mutual solubilities of the water and the amines in the two liquid phase area decreased substantially as a result of the presence of sodium chloride. The dissolved sodium chloride decreases the miscibility of the amine-water mixtures, due to the fact that it prefers to be surrounded by water molecules and not by amine molecules. At lower temperatures however, the amines are sufficiently hydrophilic to be fully miscible with water saturated with sodium chloride. 

The action taking place in this section requires that 7ie/ Y2e should be high. Since there will be effectively no component 2 at the top of Section B, this is the place where the entrainer may not be fully miscible with the solvent system to be separated. 

While it is fully miscible with water in all proportions, the partition coefficient in ternary mixtures of n-propanol with water and a possible entrainer such as cyclohexane or benzene is favourable to the hydrocarbon phase (Table 16.3). The lower values of partition coefficient are for those systems in which it is more likely to be economically advantageous to recycle part of the potential reflux to a phase separation with the feed. 

Another option is extractive crystallisation. Here, the tendency of particular aqueous-solvent mixtures such as water-propanol, water-amines, water-micelles, water-polar polymers to split into two liquid phases upon small variations in temperature is used to dehydrate solutions of crystallisable solutes. At low temperatures, these systems form homogeneous mixtures, whereas at high temperatures, a solvent rich phase is created. The aqueous solute becomes concentrated in a smaller volume and consequently crystallises, whereas the pure solvent is recycled. Also, alternative schemes may be used depending on the exact phase behaviour of the component. For instance, a solute such as amino acids and peptides may crystallise from an aqueous solution upon introducing a fully miscible component, such as in water-ethanol mixtures. In a second stage, after the separation of the crystals, the conditions may be altered to induce an L - L phase split that allows easy recovery of the auxiliary component. Maurer and co-workers [25] described the use of high pressure CO2 in water-alkanol systems. At low pres-... 

Figure 21.16. Phase diagram of the Ci2EOs/water system Lj and L2, surfactant solutions L2, liquid surfactant containing dissolved water, not fully miscible with water L3, sponge phase, not fully miscible with water or surfactant other phases, etc. as for Figure 21.13 (reproduced from ref. (113) by permission of The Royal Society of Chemistry)...

For pure, fully annealed polymers, the glass transition is approximately symmetrical [5]. For partially miscible systems in which there are interfaces, the transition will be asymmetric and become broadened [5]. This asymmetry and broadening may provide a wealth of information of both practical and theoretical value that has not yet been fully extracted. 

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