Crystalline state, determine product properties

Figure 1.5 Sugar, table salt, and chocolate as examples of everyday life products, where the properties of the crystalline state determine product properties and where the crystallization is tailored to meet this demand.

The phase transition from disordered states of polymer melt or solutions to ordered crystals is called crystallization-, while the opposite process is called melting. Nowadays, more than two thirds of the global product volumes of synthetic polymer materials are crystallizable, mainly constituted by those large species, such as high density polyethylene (HOPE), isotactic polypropylene (iPP), linear low density polyethylene (LLDPE), PET and Nylon. Natural polymers such as cellulose, starch, silks and chitins are also semi-crystalUne materials. The crystalline state of polymers provides the necessary mechanical strength to the materials, and thus in nature it not only props up the towering trees, but also protects fragile lives. Therefore, polymer crystallization is a physical process of phase transition with important practical relevance. It controls the assembly of ordered crystalline structures from polymer chains, which determines the basic physical properties of crystalline polymer materials. 

Many crystalline solids can undergo chemical transformations induced, for example, by incident radiation or by heat. An important aspect of such solid-state reactions is to understand the structural properties of the product phase obtained directly from the reaction, and in particular to rationalize the relationships between the structural properties of the product and reactant phases. In many cases, however, the product phase is amorphous, but for cases in which the product phase is crystalline, it is usually obtained as a microcrystalline powder that does not contain single crystals of suitable size and quality to allow structure determination by single-crystal XRD. In such cases, there is a clear opportunity to apply structure determination from powder XRD data in order to characterize the structural properties of product phases. 

The magnitude of the errors in determining the flat-band potential by capacitance-voltage techniques can be sizable because (a) trace amounts of corrosion products may be adsorbed on the surface, (b) ideal polarizability may not be achieved with regard to electrolyte decomposition processes, (c) surface states arising from chemical interactions between the electrolyte and semiconductor can distort the C-V data, and (d) crystalline inhomogeneity, defects, or bulk substrate effects may be manifested at the solid electrode causing frequency dispersion effects. In the next section, it will be shown that the equivalent parallel conductance technique enables more discriminatory and precise analyses of the interphasial electrical properties. 

The calculated detonation parameters as well as the equations of state for the detonation products (EOS DP) of the explosive materials TKX-50 and MAD-X1 (and also for several of their derivatives) were obtained using the computer program EXPL05 V.6.01. These values were also calculated for standard explosive materials which are commonly used such as TNT, PETN, RDX, HMX, as well as for the more powerful explosive material CL-20 for comparison. The determination of the detonation parameters and EOS DP was conducted both for explosive materials having the maximum crystalline density, and for porous materials of up to 50 % in volume. The influence of the content of the plastic binder which was used (polyisobutylene up to 20 % in volume) on all of the investigated properties was also examined. 

Solid state property differences derived from the existence of alternate crystal forms can lead to extensive differences of pharmaceutical importance, e.g., solubility, dissolution rate, and stability. It is claimed that most drug substances show polymorphism (Borka, 1991). As discussed previously, it is essential to determine which of the various forms should be used in a drug product to assure stable and reproducible formulation. A marked difference between the photostability of various crystal modifications of drug substances has been reported. This can be ascribed to differences in inter- and intramolecular binding, differences in diffusability (crystalline vs. amorphous structure), and differences in water content (crystal water, adsorbed water) (Hiittenrauch et al., 1986). 

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