Phase diagram major features

Most pairs of homopolymers are mutually immiscible, so that phase diagrams are little used in polymer science... another major difference between polymers on the one hand, and metals and ceramics on the other. Two-phase fields can be at lower or higher temperatures than single-phase fields... another unique feature. 

Most work has dealt with the RPM as a generic model for ionic criticality. MC data suggest that the replacement of the solvent s dielectric continuum by discrete solvent molecules does not change the principal topology of the phase diagram. This ensures that the simple RPM covers the major features of real ionic fluids, at least in cases where Coulombic interactions prevail. 

Herein, we expand on the discussion of our recently observed isothermal amorphous-amorphous-amorphous transition sequence. We achieved to compress LDA in an isothermal, dilatometric experiment at 125 K in a stepwise fashion via HDA to VHDA. However, we can not distinguish if this stepwise process is a kinetically controlled continuous process or if both steps are true phase transitions (of first or higher order). We want to emphasize that the main focus here is to investigate transitions between different amorphous states at elevated pressures rather than the annealing effects observed at 1 bar. The vast majority of computational studies shows qualitatively similar features in the metastable phase diagram of amorphous water (cf. e.g. Fig.l in ref. 39) at elevated pressures the thermodynamic equilibrium line between HDA and LDA can be reversibly crossed, whereas by heating at 1 bar the spinodal is irreversibly crossed. These two fundamentally different mechanisms need to be scrutinized separately. 

Surfactant hquid crystals are normally lyotropic. The characteristics of the system, then, are highly dependent on the nature and amount of solvent present. In a phase diagram of a specific surfactant, the LC phases may span a broad region of compositions and may, in fact, constitute by far the major fraction of all possible compositions (Fig. 15.4). With the continued addition of water or other solvent, the system will eventually pass through the regions of the various mesophases into the more famihar isotropic solution phase. The solution is the most highly random state for mixtures of condensed matter and, as a result, tends to have fewer easily detected structural features. Surfactant solutions, however, are far from devoid of structure it is only the scale of the structure that changes as dilution occurs. 

The major features of phase behavior in ternary systems are determined by the types of phase diagrams of the constituting binary subsystems, since all binary equilibria spread into the three-component region of composition and take part in the generation of ternary phase diagrams. 

Another example of the phase behavior of asymmetric molecules is given in Fig. 3.22 for aqueous solutions of hydroxypropyl cellulose.(97) The phase diagram for this system shows all of the major features expected from the Rory theory for an asymmetric polymer solute. The slight tilting of the narrow biphasic region could possibly be attributed to some molecular flexibility as well as anisotropic interac-tion.(98) The phase diagram for the ternary system, polymer and two solvents, for poly(p-phenylene terephthalamide) also shows the major features expected from theory. (99)... 

The Solid-Liquid Line for Water The phase diagram for water has the same four features but differs from others in one major respect that reveals a key property. Unlike almost any other substance, the solid form is less dense than the liquid that is, water expands upon freezing. Thus, the solid-liquid line has a negative slope (slants to the left with increasing pressure) an increase in pressure converts the solid to the liquid, and the higher the pressure, the lower the temperature at which water freezes (Figure 12.8B). The vertical dashed line at - 1°C crosses the solid-liquid line, which means that ice melts with only an increase in pressure. 

Two requisite features must be displayed by the phase diagrams of alloy systems for precipitation hardening an appreciable maximum solubility of one component in the other, on the order of several percent and a solubility limit that rapidly decreases in concentration of the major component with temperature reduction. Both of these conditions are satisfied by this hypothetical phase diagram (Figiue 11.22). The maximum solubility corresponds to the composition at point M. In addition, the solubility limit boundary between the a and a + /3 phase fields diminishes from this maximum concentration to a very low B content in A at point N. Furthermore, the composition of a precipitation-hardenable alloy must be less than the maximum solubility. These conditions are necessary but not sufficient for precipitation hardening to occur in an alloy system. An additional requirement is discussed in what follows. 

Another important reaction supporting nonlinear behaviour is the so-called FIS system, which involves a modification of the iodate-sulfite (Landolt) system by addition of ferrocyanide ion. The Landolt system alone supports bistability in a CSTR the addition of an extra feedback chaimel leads to an oscillatory system in a flow reactor. (This is a general and powerfiil technique, exploiting a feature known as the cross-shaped diagram , that has led to the design of the majority of known solution-phase oscillatory systems in flow... 

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