Crystallinity multicomponent systems, thermodynamics

The objective of this review is to characterize the excimer formation and energy migration processes in aryl vinyl polymers sufficiently well that the excimer probe may be used quantitatively to study polymer structure. One such area of application in which some measure of success has already been achieved is in the analysis of the thermodynamics of multicomponent systems and the kinetics of phase separation. In the future, it is likely that the technique will also prove fruitful in the study of structural order in liquid crystalline polymers. 

Pharmaceutical solids can generally be described as either crystalline or amorphous (or glassy). In fact, the actual solid phase composition of a pharmaceutical formulation is usually characterized by an intermediate composition composed of both crystalline and amorphous character. In a multicomponent system such as a solid formulation comprising drug and exci-pient(s), certain components or even a single component may be amorphous. Because the amorphous form of a material is always a less stable, higher-energy form than its crystalline counterpart, the distinction between these forms relates to thermodynamic stability of the solid. 

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Although occasionally papers appear speaking of the inapplicability of Gibbs phase rule [Li, 1994, 13] or beyond the Gibbs phase rule [Mladek et al, 2007], this invariably means no more than that one of the ceteris paribus conditions Gibbs already mentioned is not fulfilled for example, the phase rule doesn t cover systems in which rigid semi-permeable walls allow the development of pressure differences in the system. Gibbs explicitly allows for the possible presence of other thermodynamic fields. An extended phase rule has been proposed for, inter alia, capillary systems (in which the number and curvature of interfaces/phases play a role), multicomponent multiphase systems for which relative phase sizes are relevant [Van Poolen, 1990], colloid systems (for which, even if in equilibrium, it is not always easy to say how many phases are present), unusual crystalline materials, and more. 

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