Crystallinity materials properties affected

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

LDPE affect the dynamic mechanical, as well as other material properties of these polymers. The similarity of the temperature dependence of E between our toluene cast HB film and the quenched LDPE (both of 40% crystallinity) in Figure 14A as compared to our quenched HB film (% crystallinity 30%) is another indication of the importance of the level of crystallinity on properties. (This topic has already been discussed in some length in the section on stress-strain behavior). 

A solid solution is a solid mixture of one or more compounds within a solvent of another solid crystalline compound. For the mixture to be considered a solid solution the crystal structure of the solvent must remain essentially unchanged upon the addition of the solute (s) and the whole mixture must remain as a single homogeneous phase. We can distinguish two types of inclusion within the solvent crystal substitutional in which the solute molecule replaces a solvent molecule in the lattice, or interstitial in which the solute molecule fits into a space in between solvent particles. The properties of the solvent material are affected by the formation of solid solutions because the process results in distortions in the crystal lattice and disrupts the overall homogeneity of the host material. 

Figure 1.26 summarizes the property behavior of amorphous, crystalline, and semicrystalline materials using schematic diagrams of material properties plotted as functions of temperature. Again, pressures affect the transition temperatures as schematically depicted in Fig. 1.27 for a semi-crystalline polymer. 

In Figure 4.2, crystallization of sucrose can only occur at conditions of temperature and composition that fall between the solubility and glass transition temperature lines. On either side of this crystallization envelope, there is either no thermodynamic driving force (dilute system) for crystallization or nucleation is constrained by kinetic effects due to limited molecular mobility. Thus, processing conditions must be controlled so that the system falls within the crystallization envelope to ensure crystallization. Furthermore, the point within the crystallization envelope at which crystallization occurs can significandy affect the nature of the crystalline phase in the food, and thus affect the material properties. 

For pharmaceutical materials moisture is known to affect a wide range of properties such as powder flow compactibility and stability (physical chemical and microbiological) (8 46-53). The interaction between moisture and a solid is complex and can occur in a variety of ways. For example water can be stoichiometrically incorporated into a solid s crystal structure in the form of a hydrate (pseudo-hydrate) as discussed previously in this section. In addition moisture can have non-stroichiometrical i.e., nonspecific interactions with a solid by adsorbing on the surface or being absorbed into the material and acting as a plasticizer. These non-specific interactions are more common in amorphous or semi crystalline materials and are the subject of this section. 

The density is essentially a material property. The density of a given specimen, however, can be affected by the nature of the specimen. For example, many polymers can be prepared with different percent crystallinities, and hence with different densities, by changing the preparation method or annealing the specimens after preparation. 

Depending upon the parameters chosen, simulations performed using the Gay-Berne potential show behaviour typical of liquid crystalline materials. Moreover, by modifying the potential one can determine what contributions affect the liquid crystalline properties and so help to suggest what types of molecule should be made in order to attain certain properties. 

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