Disordered phases, structural disorder

FIGURE 5.10 (a) Scientific representation of the three-phase structure of a dry ionomer, consisting of cation clusters, lamellae, and disordered regions. (From Cowie, J.M.G., Polymer Chemistry and Physics of Modern Materials, Intertext, London, 1973.)... 

N. Hanada, S. Orimo, H. Fujii, Hydriding properties of ordered-/disordered-Mg-based ternary Laves phase structures, J. Alloys Compd. 356-357 (2003) 429-432. 

Zhu L, Chen Y, Zhang AQ et al. (1999) Phase structures and morphologies determined by competitions among self-organization, crystallization, and vitrification in a disordered poly(ethylene oxide)-b-polystyrene diblock copolymer. Phys Rev B Condens Matter 60 10022-10031... 

While in volumes 180 and 181 of this series several basic aspects of morphology, inter-phase structure and disorder were addressed, in the present volume, molecular interactions, modeling, phase transformation and crystallization kinetics are considered (see the subject index including keywords from volumes 180 and 181 at the end of the book). Needless to say, in spite of substantial success over 60 years or more we are still far from having a complete and unambiguous picture of polymer crystallization. We firmly believe that a fruitful approach to such a complex problem requires one to give way to many different and sometimes conflicting viewpoints, as we have attempted to do in these volumes. We do hope that they are not only a time-capsule left for... 

The traditional model used to explain the properties of the (partly) crystalline polymers is the "fringed micelle model" of Hermann et al. (1930). While the coexistence of small crystallites and amorphous regions in this model is assumed to be such that polymer chains are perfectly ordered over distances corresponding to the dimensions of the crystallites, the same polymer chains include also disordered segments belonging to the amorphous regions, which lead to a composite single-phase structure (Fig. 2.10). 

The advancement of aggregate decomposition process depends on the degree of silica phases structural disorder and on the conditions in which the process occurs, primarily of the alkalis concentration in the liqitid phase, temperature, as well as of their diffusion condition to reaction site. 

It is energetically favourable for the SS and HS not to mix. Thus during cooling from above a critical order-disorder temperature, spontaneous segregation of SS and HS into separate soft (SS-rich) and hard (HS-rich) phases occurs by the process of spinodal decomposition. To achieve elastomeric performance, the SS must be the majority constituent by mass, and the phase structure then takes the form of discrete hard domains dispersed within a soft matrix. Such a phase structure impacts on mechanical properties, and a further structural parameter of importance, therefore, is the degree of phase separation. 

In the case of magic angle sample spinning, the average (Oave) of the principal values and the motionally conformation-averaged chemical shift (Oiso) listed in Table 1 are detectable. Examination of these Oave and Oiso values, as well as the relaxation phenomena associated with these chemical shifts provides information on the phase structure of samples in terms of molecular conformation and dynamics. As is known, the phase structure of LPE samples differs widely depending on the mode of crystallization. For example, when crystallized isothermally from dilute solution or from the melt, LPE usually exhibits a lamellar crystalline structure the thicknesses of lamellae are relatively limited, say ca 100-500 A, in comparison with the lateral dimensions of over several microns, and the crystalline methylene chains orients perpendicularly to the wide face of the lamellae with molecular chains inclined to lamellar normals at angles of up to 38°. These lamellar samples, crystallized either from the melt or dilute solution, contain a non-crystalline component. The problem of whether this non-crystalline component is in an isotropically disordered state or in a particular state due to the coexistence of lamellar crystallites has been extensively studied for a few decades. 

The phase separation process can be divided into two categories (1) nucleation and growth and (2) spinodal decompositions. Spinodal decomposition results in a disordered bicontinuous two-phase structure. The path in the phase diagram traverses the critical point. The morphology is discontinuous. Interfacial tension is a salient consideration. Uniform particle size distribution is possible during spinodal decomposition. 

Proteins in solution are typically more mobile than those in a crystal. At equilibrium the protein in solution will fluctuate and its conformation is best represented as an ensemble of structures. This is not so bad The flexibility can leave certain portions of the protein unstructured. The mobile portions of the protein are often functionally important. Therefore, one can appreciate the disorder in the refined solution phase structure as a clue to the function of the protein and its equilibrium structure. When we seek to determine a protein s structure at room temperature we must appreciate that the native state consists of an ensemble of structures. 

When two or more polymers are mixed, the phase structure of the resulting material can be either miscible or inuniscible. Polymer blend can be classified into three basic categories namely miscible polymer blends, compatible polymer blends, and immiscible polymer blends [34]. The majority of polymers are immiseible at molecular level, as given by the laws of thermodynamics [35]. The internal disorder of the polymer system will eventually result in phase separation on a macroscopic scale after some time. The relative miscibility of polymers controls their phase behavior, which determines the final properties. Partially miscible blends show either two phases or single-phase morphology. However, the manifestation of snperior properties depends on the miscibility behavior of homopolymer. 

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