Crystalline materials, dependence

Even within a particular class of polymers made by step-growth polymerization, monomer composition can be varied to produce a wide range of polymer properties. For example, polyesters and polyamides can be low-Tg, amorphous materials or high-Tg, liquid crystalline materials depending on the monomer composition. 

The polyalkene species obtained by ring opening polymerization of cyclic olefins range from amorphous elastomers to crystalline materials, depending on the structure of the repeat units and the configuration about the C=Cbond. 

As seen in Fig. 1.3, crystal density correlates very strictly with molecular self-density, so that a high density in a crystalline material depends primarily on the heavy elements contained in the molecule, and only to a minor extent on efficient space occupation. 

Many molecules are obtained and used in a crystalline form, the nature of which can have e significant impact on their properties and behaviour. Moreover, it is sometimes possible foi a given material to exist in more than one crystalline form, depending upon the conditions under which it was prepared. This is the phenomenon of polymorphism. This can be important because the various polymorphs may themselves have different properties. It is Iberefore of interest to be able to predict the three-dimensional atomic structure(s) that a gi en molecule may adopt, for those cases where it is difficult to obtain experimental data and also where one might wish to prioritise molecules not yet synthesised. 

GVD Coatings. As in PVD, the stmcture of the deposited material depends on the temperature and supersaturation, roughly as pictured in Figure 8 (12). In the case of CVD, however, the effective supersaturation, ie, the local effective concentration in the gas phase of the materials to be deposited, relative to its equiUbrium concentration, depends not only on concentration, but on temperature. The reaction is thermally activated. Because the effective supersaturation for thermally activated reactions increases with temperature, the opposing tendencies can lead in some cases to a reversal of the sequence of crystalline forms Hsted in Figure 8, as temperature is increased (12). 

Guanine (Pearl Essence). Guanine (Cl Natural White 1, Cl No. 75170), is the crystalline material obtained from fish scales and consists principally of the two putines, guanine [73-40-5] (42) and hypoxanthine [68-94-0] (43). The guanine content of the colorant varies from 75% to 97%, whereas the hypoxanthine content ranges from 3% to 25%, depending on the particular fish and tissue from which the crystals ate derived. 

Rake-speed requirements depend on the type of solids entering the thickener. Peripheral speed ranges used are, for slow-setthng sohds, 3 to 8 m/min (10 to 25 rt/min) for fast-setthng solids, 8 to 12 iTi/min (25 to 40 ft/min) and for coarse sohds or crystalline materials, 12 to 30 iTi/min (40 to 100 ft/min). 

The axial elastic modulus of PET fibers E) depends, as with other kinds of fibers, on the value of the elastic modulus of crystalline material ) and amorphous fiber... 

Quartz is a natural crystalline material which exhibits this form of behavior, although its relevant properties are highly temperature dependent and synthetic materials have been developed which, although fundamentally less accurate, are more stable under varying temperature conditions. 

It was found that the dissolution rate of the material depends both on its surface area and on its crystalline size, but the importance of the crystalline size seems to be greater. The empiric equation describing the above dependence of the leaching rate on these two parameters is as follows (130) ... 

As a function of the surface potential the electron work function for a given material depends on the state of the surface of that material (adsorption, the presence of surface compounds, etc.). For crystalline substances (see Table 3.1), various crystal faces have various electron work function values, which can be measured for single crystals. For poly crystalline substances, the final value of the electron work function depends on the contribution of the individual crystal faces to the entire area of the phase and the corresponding electron work functions the final value of the work function, however, is strongly dependent on the experimental method used for the measurement. 

Films of CoB have been prepared by electroless deposition. Chang et al. [25] deposited magnetically soft amorphous films, which could be annealed to give materials with an Hc of 250 Oe. Depending on the annealing temperature, the films crystallized as the hep or fee modifications of Co. Matsui and co-workers [22] obtained crystalline materials in the as-deposited state, the crystalline characteristics being determined by processing conditions. A maximum HQ of 300 Oe was observed for films with 10.0 preferred orientation. 

Table 9. Dependency of Minimum Sintering Temperature on the Electronic Structure of Crystalline Material...

These microporous crystalline materials possess a framework consisting of AIO4 and SiC>4 tetrahedra linked to each other by the oxygen atoms at the comer points of each tetrahedron. The tetrahedral connections lead to the formation of a three-dimensional structure having pores, channels, and cavities of uniform size and dimensions that are similar to those of small molecules. Depending on the arrangement of the tetrahedral connections, which is influenced by the method used for their preparation, several predictable structures may be obtained. The most commonly used zeolites for synthetic transformations include large-pore zeolites, such as zeolites X, Y, Beta, or mordenite, medium-pore zeolites, such as ZSM-5, and small-pore zeolites such as zeolite A (Table I). The latter, whose pore diameters are between 0.3... 

Compound SP-A was prepared according to the method of Zajtseva, et al., (11). The final product obtained from the synthesis was purified on a silicic acid column and recrystallized from 1 10 hexane. Positive identification was made through IR and NMR analysis. The colorless crystalline material had a melting point which was heating rate dependent and had a maximum value of 105°C. 

Laboratory grade agents are typically colorless liquids or solids. Depending on the specific agent, liquids may be mobile, viscous, or even waxy in nature. Many solids are salts of the free-base liquid that are colorless to white to beige crystalline materials. In either state, these materials typically have little or no odor when pure. 

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