Miscibility of the components

On the basis of mathematical models attempts are made to precalculate the dynamic behaviour of distilling columns. According to Kohler and Schober [264] column dynamics involves these problems  

In general distillation uses completely miscible liquids since in case of phase formation a separation is carried out at first by decanting. It should be noted, however, that there is no complete insolubility. Since dissolved substances cannot be separated mechanically it is distillation which results in a separation. 

Carrier vapour distillation — chiefly steam distillation — and azeotropic distiUa- 

Hildebrand and Rotariu [14] have considered differences in heat content, entro])v and activity and classified solutions as ideal, regular, athermal, associated and solvated. Despite much fundamental work the theory of binary liquid mixtures is still e.ssentiaUy unsatisfactory as can be seen from the. systematic treatment of binar mi.Ktures by Mauser-Kortiim [15]. The thermodynamics of mixtures is presented most instructively in the books of Mannchen [16] and Schuberth [17]. Bittrich et al. [17a] give an account of model calculations concerning thermophysical properties of juire and mixed fluids. 

Vapouf-liquid equilibrium curves of binary mixtures 

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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. 

If more than one component is present in the droplet, the evaporation rate depends on the miscibility of the components. For totally miscible components, distillation of the more volatile component(s) occurs, and the droplet composition changes as evaporation proceeds. If the components are partially miscible or insoluble, evaporation may be greatly retarded by the formation of a surface layer. In the case of evaporation of a surfactant... 

Curve defining the region of composition and temperature in a phase diagram for a binary mixture across which a transition occurs from miscibility of the components to conditions where single-phase mixtures are metastable or unstable (see Note 4 in Definition 1.2). 

Due to the topochemical restrictions of diacetylene polymerization, diacetylenic lipids are solely polymerizable in the solid—analogous phase. During the polyreaction an area contraction occurs leading to a denser packing of the alkyl chains. In addition to surface pressure/area isotherms the polymerization behavior of diacetylenic lipids containing mixed films give information about the miscibility of the components forming the monolayer ... 

Without doubt the simple mixing of two or more polymers is the easiest, most direct and the cheapest way of producing new materials. However, the properties of such mixtures are very dependent on the miscibility of the components. Of the few polymer pairs which are thermodynamically miscible, some examples are ... 

The miscibilities of the components in polymer blends is often ascertained by the measurement of the material s glass transition temperature (Tg). The mixing of two polymers with no mutual interactions usually results in the mixture having two separate phases each with their own distinct glass transition temperature. However, when the two components do interact to form a single phase mixture, their glass transitions combine and there will be the emergence of only one transition temperature that is linearly dependent on composition [118]. 

It emanates from Eq. (5) that as mentioned before the combinatorial entropy of mixing stabilizes the mixture and that X < 0 favors miscibility of the components, especially, in the case of high-molar-mass polymers (each r large) when the combinatorial entropy of mixing tends to very small values. 

One can see that for the both systems shear field causes an increase in miscibility of the components, it leads to the a decrease of gel formation temperatures. So the aggregates of macromolecules formed upon cooling are not stable and can be destroyed by the mechanical field. 

The partitioning of a substance between two liquid phases (multistage partitioning, partition chromatography) and the extraction of solids require similar properties of a solvent [50-55]. When a substance has to be partitioned, a solvent system with limited miscibility of the components is required in order that the substance dissolves to a different extent in the two phases. The greater the chemical differences between any two solvents, the more limited their miscibility. Other requirements that the solvent system must fulfil are, inter alia, a favorable partition coefficient (the average partition coefficient of the component mixture should be between ca. 0.2 and 5), as high a separation... 

The glass transition temperature of amorphous multicomponent mixtures can be used to determine the miscibility of the components. If the mixture is miscible, then a single glass transition temperature is usually obtained. Various equations can be used to predict the glass transition temperature of miscible mixtures. Examples include the Gordon-Taylor equation [Eq. (11)] or the Fox-Flory equation [Eq. (12)]. 

The dependence of the ttv values on the composition of the vapor and condensed states for DML-CHOL, DOL-CHOL, and DOL-DML mixtures is shown in Figure 6. The upper curve is the surface vapor pressure as a function of the mole fraction of the liquid-expanded film the lower curve is for the dependence of irv on the composition of the gaseous phase. Ideal mixing behavior is given by the linear dotted line which joins the 7ry° points for each of the pure compounds. In all cases there was complete miscibility of the components as represented by the continuous function of 7rv with x. In the cholesterol mixtures positive deviations from Raoult s law are observed for the mixture of lecithins, ideal mixing is observed. These results confirm those obtained with lipid mixtures—i.e., cholesterol mixed with liquid-expanded lipid films forms rion-ideal mixtures with positive deviations for mixtures of lipids which are in the same monolayer state, as in the case of the liquid-expanded DOL-DML mixtures, ideal mixing results (8). 

The principal factor is the shape of the two-phase liquid-vapor region in the phase diagram (usually a temperature-composition diagram). The closer the liquid and vapor lines are to each other, the more theoretical plates needed. See Figure 6.15 of the text, But the presence of an azeotrope could prevent the desired degree of separation from being achieved. Incomplete miscibility of the components at specific concentrations could also affect the number of plates required... 

It is worth mentioning that interphase interactions in blends proceed only within mesophases whose thickness for incompatible polymers is between 2 and 50 nm depending on the thermodynamic interactions of the phases, temperature, regimes of mixing, and some other factors (7,11,29,30). The mesophase thickness depends on the miscibility of the components and in first approximation (7) is where xi2... 

The persistence of the glass transition temperatures of the component polymers in each of the blends, and the lack of a third Tg peak at an intermediate temperature (see, for example. Figure 8), confirms that the blends contain two phases. The temperature shift in each Tg is a consequence of the partial miscibility of the component polymers in the melt. The very slight increase in the Tg of PBT and PET in the PC/PBT and PC/PET blends respectively indicates that the polyester-rich phase contains only a small amount of polycarbonate, whereas the significant decrease in Tg in the PC component of the blends suggests the presence of substantial proportions of PBT or PET respectively in the phase consisting predominantly of polycarbonate. 

For impact-modified PC/PBT and PC/PET blends evidence has been presented for partial miscibility of the component polymers and for a two-phase blend morphology with a polyester-rich dispersed phase in a continuous matrix rich in polycarbonate. Other absorptions are attributed respectively to MWS interfacial polarization, to the presence of the impact modifier and to a phosphite processing stabilizer. 

For still lower mutual miscibility of the components critical p(X) curves without any pressure maximum or minimum may be obtained, as indicated in Figure 26d by a dotted line. Such a phase behaviour is attributed to gas-gas equilibria (GG) (see Figure 18) and may be found in mixtures of COg with alkanes having more than 30 carbon atoms it has already been found for the COg + water system (see Figure 21). 

The crystallization of blends tends to depend on the level of mutual miscibility of the components. In miscible blends, the general result is that suppression or otherwise of crystallization with miscibility is dependent on the relative glass transition temperatures of both phases [33, 34]. For example, in a blend of an amorphous and semicrystalline polymer, if the amorphous material has the higher Tg, the miscible blend will also have a higher Tg than that of the semicrystalline homopolymer and, at a given temperature, the mobility and thus the efficacy of the semicrystalline phase molecules to crystallize is reduced. The converse is often true if the amorphous phase has a lower glass transition. Effects such as chemical interactions and other thermodynamic considerations also play a role and the depression of the melting point in a miscible blend can be used to determine the Flory interaction parameter x [40]. 

P number of phases of the heterogeneous system (one gas phase, one or more liquid phases depending on the miscibility of the components, one — at mixed crystal forming - or several solid phases according the number of crystal types) K number of components the minimum number of components of the system forming the phases which must be independently declared... 

Multistage crystallization in systems with complete miscibility of the components in the liquid and solid states and with systems which form mixed crystals, leads to an almost complete separation. In systems forming an eutectic mixture, simple separation is only possible up to the eutectic composition. 

The effect of polymer-polymer interactions on the miscibility and macroscopic properties of PVC/PMMA, PVC/PS, and PMMA/PS blends were studied and the miscibility of the components was characterized by the Flory-Huggins interaction parameter or by quantities related to it by Fekete et al. (Fekete et al. 2005). The comparison of interaction parameters determined by different methods indicates that PVC and PMMA are nearly miscible, while PS is immiscible either with PMMA or with PVC at all compositions. Hory-Huggins interaction parameters calculated from equihbrium methanol uptake (y jj) are plotted as a function of composition in Fig. 10.24. The negative values obtained for the PVC/PMMA blends hint at complete miscibility, although x,2 depends on composition which indicates limited miscibility. The positive interaction parameters determined for the PVC/PS and PMMA/PS blends suggest immiscibility. 

It is well established that blending may greatly influence the thermal stability of the individual polymers (McNeil 1977 McNeil and Gorman 1991 Goh 1993). Under degradation conditions, considerable interactions may occur between components in the blend and/or their degradation products. The type of interaction will depend on the degree of miscibility of the components, as well as on their ratio in the blend. 

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