Phase diagrams, miscibility studies

HF is miscible with water in all proportions and the phase diagram (Fig. 17.4a) shows the presence of three compounds H2O.HF (mp — 35.5°), H2O.2HF (mp-75.5°) and H2O.4HF (mp — 100.4°, i.e. 17° below the mp of pure HF). Recent X-ray studies have confirmed earlier conjectures that these compounds are best formulated as H-bonded oxonium salts [HsOJF, [H30][HF2], and [H30][H3F4] with three very strong H bonds per oxonium ion and average O - - F distances of 246.7, 250.2... 

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

The system polyethylene glycol (PEG)-dextran-water is still the most used and best-studied aqueous polymer two-phase system. A phase diagram for a typical two-phase system is shown in Fig. 10.12 for the PEG-dextran system. Both polymers are separately miscible with water in all proportions. As the polymer concentration increases, phase separation occurs, with the... 

In a system of significant interest to the present works, Graillard, et al. [62] studied the ternary phase diagrams of the systems polybutadiene-styrene-polystyrene and polybutadiene-block-polystrene-styrene-polystyrene. They showed that the presence of block copolymer increased the miscibility of the two poljrmers, as the styrene component polymerized. Similar effects are probable in the IPN s, as compared with the corresponding blends. 

The Al-Zn system was the first studied extensively in an attempt to verify the theory for spinodal decomposition [24], The equilibrium diagram for this system, shown in Fig. 18.12, shows a monotectoid in the Al-rich portion of the diagram. The top of the miscibility gap at 40 at. % Zn is the critical consolute point of the incoherent phase diagram. 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

Another interesting application of HPTMC is encountered in the study of compressibility effects on the phase behavior of polymer blends. While much theoretical work has been devoted to describe the temperature dependence of miscibility for polymer blends, there are relatively few studies of the effect of pressure on miscibility. To a large extent, this is due to the fact that most theoretical models assume that polymer blends are incompressible. HPTMC can be used to determine the miscibility of blends as a function of pressure. Figure 11 shows the phase diagrams for two above-mentioned asymmetric polymer blends. For both of these systems, we can see that in... 

Ti values of PC and PMMA in PC/PMMA = 50/50 agree well to show its miscibility on a scale of —20 nm. They observed relaxation curves after heat treatment for 30 min at various temperatures. When heated above 150°C, the relaxation curve becomes nonsingle exponential, and they attributed this temperature of 150°C to the phase-separation temperature of PC/PMMA = 50/50. The relaxation curves were fitted to Equation (10.9) to deduce the coexistent compositions at various temperatures to give a LCST phase diagram. They further studied kinetics of phase separation, which will be discussed in the following. 

The system toluene-heptane-dicyanobutane was studied at 25 °C and compared with the system toluene-heptane-sulfolane at 25 °C. The ternary phase diagrams (Figures 1 and 2) resemble each other closely, with complete miscibility of phases occurring at somewhat lower aromatics content for the dicyanobutane than for sulfolane. This higher capacity for hydrocarbons by the dicyanobutane compensates for its slightly lower selectivity as shown in Figure 3. 

The thermal analysis of a number of normal alkanes was studied by Mazee (23). In the case of a binary mixture in which the components are completely miscible both in the liquid and solid states, the curves in Figure 10.12 were obtained. Curve a) is the temperature-composition phase diagram, while... 

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