Solid solution semi-crystalline

A general presentation and discussion of the origin of structure of crystalline solids and of the structural stability of compounds and solid solutions was given by Villars (1995) and Pettifor (1995). For an introduction to the electronic structure of extended systems, see Hoffmann (1987, 1988). In this chapter a brief sampling of some useful semi-empirical correlations and, respectively, of methods of classifying (predicting) phase and structure formation will be summarized. 

The non-equilibrium condition of most groundwater systems with respect to many primary minerals, or similarly the metastability which exists with respect to many semi-crystalline or amorphous phases are common problems, especially for silicates. Some clear identification is needed for system reaction time, or the rate at which equilibrium is approached, and similarly identification is needed for metastable plateaus of pseudo-equilibrium, especially for compounds such as amorphous silica, cristobalite, quartz, clay minerals, etc. The likely magnitude of saturation indices which could apply to a given mineral could be specified for a variety of conditions. In this volume, Glynn, and elsewhere others, have recently shown that some error occurs in the calculated saturation values for trace elements when pure end member minerals are assumed to be present, when actually the phases are solid solutions. The consensus among modelers appears to be that error is present and significant the challenge is to develop procedures that quantify the error, so models become tools that provide realistic and interpretable results. 

The amorphous polymers can easily be dissolved in non-polar solvents. The situation is different if the polymers are semi-crystalline, and in this case, to dissolve the polymer in the solvent, it is necessary to raise their temperature to a high level (for instance, 110°C for polyethylene in xylene). Therefore, if a polymer is amorphous in its solid state, it is easier to study its solutions. 

Polydiacetylenes allow a unique opportunity to study the relationship between structure and mechanical properties in polymer crystals. The technique of solid state polymerization 11] enables highly-perfect poiydiacetylene single crystals to be produced with macroscopic dimensions. For example single crystal fibres can be grown with lengths in excess of 50 mm 12.3]. Crystalline polymers produced by crystallization from both dilute solution and the molten state are invariably only semi-crystalline 14]. Melt-crystallized... 

When the PEO electrolytes were first investigated, they were frequently considered relatives of crystalline solid electrolytes. In fact, they more-closely resemble classical solutions of salts in non-aqueous electrolytes with very high viscosities. They are semi-solid solutions whose properties and applications lie between those of true liquids and crystalline solids. 

Liquid/solid Equilibria. The solubility of crystalline polymers is normally considerably lower than that of amorphous polymers because they require an additional energy, namely, the heat of fusion, in order for the bulk polymer to mix with solvent. Fig. 6 shows as an example the behavior of semi crystalline polyethylene in two different solvents(20). The solvent xylene is favorable in the temperature range of interest (no liquid/liquid demixing) up to the melting temperature T. o of the pure polymer a saturated solution coexists with the crystalline polyethylene and the components are completely miscible once T has surpassed Tm,o- Nitrobenzene on the other hand, is thermod5mamically less favorable and exhibits liquid/liquid demixing in addition to the solid/liquid phase separation. In this case one observes the coexistence of three phases at a characteristic temperature (broken line in Fig. 6) and concentration. 

The width of the lines in an n.m.r. spectrum is sensitive to molecular motion within the sample. The highest resolution is normally obtained with narrow-line spectra obtained from polymer molecules in solution where molecular motion is relatively easy. The lines are normally broader in solid samples and the line width can be used to study internal molecular motion or determine the degree of crystallinity in a semi-crystalline sample. 

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