Eutectic phase behavior

Industrially, milk fat is commonly added to cocoa butter to produce milk chocolate. However, there is a thermodynamic incompatibihty between the miUc fat and cocoa butter solids which results in eutectic phase behavior. This eutectic formation leads to a chocolate with a decreased hardness (Timms 1980 Bama et al. 1992 Bystrom and Hartel 1994 Reddy et al. 1996). Extensive work has been carried out on the addition of milk fat to cocoa butter because of its abihty to reduce the incidence of bloom formation in chocolate (Hartel 1996 Kleinert 1961 Dimick et al. 1993). Chocolate bloom is evident as a white-gray layer on top of the chocolate surface and eventually the chocolate will acquire a crumbly texture. 

Mabrey S, Sturtevant JM. Investigation of phase-transitions of lipids and lipid mixtures by high sensitivity differential scanning calorimetry. Proc. Natl. Acad. Sci. U.S.A. 1976 73 3862-3866. Lin HN, Huang CH. Eutectic Phase-behavior of l-stearoyl-2-cap-rylphosphatidylcholine and dimyristoylphosphatidylcholine mixtures. Biochim. Biophys. Acta 1988 946 178-184. 

Most water-soluble solids, like salts and sugars, show eutectic phase behavior, which means that they have phase diagrams of the type depicted for fructose. Some eutectic points are as in the table. 

In a purity experiment you measure two successive steps of 0.100 K each, close to the melting peak of 495 K, to yield partial molar heats of fusion of 3.754 and 9.863 kJ. What is the impurity (Assume ideal eutectic phase behavior). 

Figure 4.14 Solid solution of polyethylene fractions in comparison with the experimental phase diagram of (a) two polyethylene fractions [76] and (b) PCL/trioxane blends [77], showing the liquidus-solidus loop and eutectic phase behavior, respectively.

Nonideal Separations. In numerous iastances, the ideal equations 2 and 4 have been verified experimentally. However, ia other experiments different results were obtained, reflecting failure of one ore more of the assumptions made ia deriving equations 2 and 4. Likewise, much theoretical work is concerned with modified assumptions, iucluding varyiag distribution coefficient k (19), eutectic-forming phase behavior (4,20—21), varyiag mass of 2one (22), and soHd-state diffusion (23). 

There are many types of phase diagrams in addition to the two cases presented here these are summarized in detail by Zief and Wilcox (op. cit., p. 21). Solid-liquid phase equilibria must be determined experimentally for most binaiy and multicomponent systems. Predictive methods are based mostly on ideal phase behavior and have limited accuracy near eutectics. A predic tive technique based on extracting liquid-phase activity coefficients from vapor-liquid equilib-... 

A brief discussion of sohd-liquid phase equihbrium is presented prior to discussing specific crystalhzation methods. Figures 20-1 and 20-2 illustrate the phase diagrams for binary sohd-solution and eutectic systems, respectively. In the case of binary solid-solution systems, illustrated in Fig. 20-1, the liquid and solid phases contain equilibrium quantities of both components in a manner similar to vapor-hquid phase behavior. This type of behavior causes separation difficulties since multiple stages are required. In principle, however, high purity... 

The SEE diagram for a longer alkyl chain IL (2-hydroxy-ethyl)dimethyl undecyloxymethylammonium dicyanamide, [CnOCiEtOH(Ci)2N][dca] (1) in 1-octanol presents a typical SLE/LLE phase diagram—a simple eutectic system with immiscibility in the liquid phase with the UCST. The influence of the [dca] anion in spite of the long alkyl chain makes this salt liquid at room temperature = 283.5 K). Therefore, the choice of the anion can have a huge effect on the phase behavior of ammonium and imidazolium ILs. 

A significant number of studies have characterized the physical properties of eutectic-based ionic liquids but these have tended to focus on bulk properties such as viscosity, conductivity, density and phase behavior. These are all covered in Chapter 2.3. Some data are now emerging on speciation but little information is available on local properties such as double layer structure or adsorption. Deposition mechanisms are also relatively rare as are studies on diffusion. Hence the differences between metal deposition in aqueous and ionic liquids are difficult to analyse because of our lack of understanding about processes occurring close to the electrode/liquid interface. 

Phase behavior of solution systems depends on the nature of the interactions between the two components. Although numerous types of phase diagrams can be found in nature (and foods), many systems of importance in foods exhibit eutectic... 

Figure 4. Phase behavior in binary systems (a) monotectic, continuous soiid soiution (b) eutectic (c) monotectic, partiai soiution and (d) peritectic (18).

The phase behavior of the binary TAG mixtures is classified into three cases solid-solution, eutectic, and molecular compound formation, as introduced in Section 1. Peculiarities in the mixtures of the TAGs may be explained by the following ... 

The polymorphic nature of the multicomponent TAG systems is related to phase behavior that is affected by molecular interactions among the component TAGs. The fat crystals in a miscible phase may exhibit simple polymorphic properties. By contrast, the immiscile eutectic phase may show complicated polymorphic properties as a superposition of the polymorphic forms of the component TAGs. Furthermore, if the molecular compound is formed by specific TAG components, the polymorphic behavior becomes complicated, as shown for the case of POP-OPO (see Section 5.2). Therefore, knowing the phase behavior of the principal TAG components is a prerequisite for precise understanding of the polymorphism of natural fats. 

The phase behavior of the mixed TAG system is influenced by polymorphism. For example, a miscible phase is formed in a and p polymorphs, but it transforms into a eutectic phase in p, as revealed in the SSS-PPP mixture. Then, the polymorphic occurrence is largely affected by cooling rate and temperature fluctuation, and it is therefore necessary to observe the polymorphic properties of the natural fats by varying the rate of coohng or by fluctuating the temperature (so-called tempering). 

The determination of purity by means of DSC is based on the assumption that impurities depress the melting point of a pure material according to the eutectic phase diagram behavior. 

Many SCWO applications involve mixtures of different salts. In such cases eutectic-type phenomena can occur, with broader regions of liquid phase behavior than with water-single salt systems. Further discussion of supercritical water systems containing mixed salts may be found in Hodes et al. ... 

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