Regions of crystallinity

Fibers and stretched elastomers are translucent because of the presence of ordered crystallites or regions of crystallinity. 

It is probable that suitable thermal treatment of the tensioned fibres promotes molecular chain displacements, thus permitting the formation of regular bonding between adjacent chains leading to highly oriented regions of crystalline order. 

Fig. 4. A model for the possible relationship between crystalline and disordered regions within a collagen fibril. The cross-sectional model of a 50-nm diameter fibril shows regions of crystallinity interfaced by grain boundaries. The individual crystalline unit cells are shown and the gap region is represented by a darker color. The axial projection of a single microfibrillar unit is also shown. Based on die structures developed by Hulmes et al. (1995) and adapted with permission from Hulmes et al (2002).

If we freeze a pure liquid very slowly, giving the atoms or molecules time to find their places in the lattice, a crystal grows. On the other hand, if we freeze the liquid quickly, the chaos of the liquid may be frozen in. The extreme case where there is no order at all is called a glass, often thought of as a supercooled liquid. Other solids may have regions of crystalline order, but lack long-range order. 

Lattice imaging studies by TEM on a "young" fraction showed extensive regions of crystallinity with minimal evidence of crystallite fracturing. By contrast, similar investigations of an "old" fraction, combined with in situ compositional analysis, revealed small "islands" of crystallinity within a "sea" of disordered material that was once crystalline. Fracture lines at crystallite boundaries are absent. Instead, the small USY crystallites within the "old" fraction are in intimate mixture with the collapsed zeolite. 

Thus far, we have defined nomenclature for amorphous OD nanostructures. Analogous to bulk materials, any nanomaterial that is crystalline should be referred to as a nanocrystal. This term should be reserved for those materials that are singlecrystalline if a particle exhibits only regions of crystallinity, it is better termed a nanoparticle or nanocluster depending on its dimensions. Transmission electron microscopy, especially in tandem with electron diffraction is most useful in determining the crystallinity of any nanostructure (Figure 6.8). 

Figure 8.24 Diagrammatic representation of a solid polymer showing regions of crystallinity and regions which are amorphous the total volume fraction of crystalline regions,

Semicrystalline Plastic - A plastic (polymeric) material characterized by localized regions of crystallinity. See also Amorphous Polymer. 

Waxes are another familiar type of solid-solid solution. Most waxes are amorphous solids that may contain small regions of crystalline regularity. A natural wax is a solid of biological origin that is insoluble in water but dissolves in nonpolar solvents. 

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