Crystalline-amorphous structures

FIGURE 2.14 Schematic two-dimensional representation of a modified micelle model of the crystalline-amorphous structure of polymers. 

Structure of Polymers Kinetics of Polymerization Property-Molecular Weight Relationships Interchain and Intrachain Forces Crystalline-Amorphous Structures Transitions... 

Crystalline-amorphous structures n. The typical form of crystalline polymers. Crystalline polymers contain a large number of crystallites, as well as devoids of crystallinity. Most plastics are amorphous at... 

The optical observations cannot resolve the crystalline-amorphous structure. Observation of single crystallites requires methods which provide an analysis in the 10-nm range. Electron microscopy is particularly suited for this purpose. Figure 4.4 shows as an example the surface of a partially crystalline polyethylene, as it becomes reproduced in the electron microscope when using a carbon film replica technique. The picture of the surface resembles a landscape with many terrasses. These obviously result from cuts through stacks of laterally extended, slighty curved lamellae whiqh have thicknesses in the order of 10 nm. 

Albrecht, T. and Strobl, G. (1995) Temperature-dependent crystalline-amorphous structures in linear... 

Small angle X-ray scattering experiments provide insight into the crystalline-amorphous structure of the fibrils and the changes following from annealing processes. Of importance is also the question of the drawability of semicrystalline polymers. It is controlled by the properties of the entanglement net-... 

We begin by looking at the smallest scale of controllable structural feature - the way in which the atoms in the metals are packed together to give either a crystalline or a glassy (amorphous) structure. Table 2.2 lists the crystal structures of the pure metals at room temperature. In nearly every case the metal atoms pack into the simple crystal structures of face-centred cubic (f.c.c.), body-centred cubic (b.c.c.) or close-packed hexagonal (c.p.h.). 

Polyetherimides show no crystallinity as evidenced from calorimetry measurements. The heteroarylene like phenylquinoxaline [27], oxadiazole [30], and benzoxa-zole [56] activated polyethers show TgS from DSC thermograms, with no evidence of crystallization, indicating amorphous or glassy morphology. Furthermore, wide angle x-ray scattering measurements show no evidence of crystalline or liquid crystalline type morphologies, consistent with an amorphous structure. F polyether... 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

The development of the internal orientation in formation in the fiber of a specific directional system, arranged relative to the fiber axis, of structural elements takes place as a result of fiber stretching in the production process. The orientation system of structural elements being formed is characterized by a rotational symmetry of the spatial location of structural elements in relation to the fiber axis. Depending on the type of structural elements being taken into account, we can speak of crystalline, amorphous, or overall orientation. The first case has to do with the orientation of crystallites, the second—with the orientation of segments of molecules occurring in the noncrystalline material, and the third—with all kinds of structural constitutive elements. 

In addition to the broad categories of TPs and TSs, TPs can be further classified in terms of their structure, as either crystalline, amorphous, or liquid crystalline. Other classes (terms) include elastomers, copolymers, compounds, commodity resins, engineering plastics, or neat plastics. Additives, fillers, and reinforcements are other classifications that relate directly to plastics properties and performance. 

Processing conditions influence the performance of plastics. For example, heating a crystalline material above its melting point, then quenching it can produce a plastic that has a far more amorphous structure. Its properties can be significantly different than if it is cooled properly (slowly) and allowed to recrystallize during processing it becomes amorphous. The effects of time are similar to those of temperature in the sense that any... 

Silicate glasses have amorphous structures produced by addition of salts that disrupt the crystalline structure. They can be attacked by strong base and hydrofluoric acid. 

Amorphous Silicon (a-Si). Amorphous silicon is considered a promising new material.As mentioned above, only a very thin coating is necessary, since the amorphous structure is much better at absorbing sunlight than is the crystalline material. The most common process to produce a-Si is the decomposition of silane by plasma CVD (see Ch. 8). Thicknesses of a few micrometers can be deposited and,... 

The major components of the phase structure of semi-crystalline polymers and the most common techniques of characterization of the crystalline, amorphous... 

Callisto orbits Jupiter at a distance of 1.9 million kilometres its surface probably consists of silicate materials and water ice. There are only a few small craters (diameter less than a kilometre), but large so-called multi-ring basins are also present. In contrast to previous models, new determinations of the moon s magnetic field suggest the presence of an ocean under the moon s surface. It is unclear where the necessary energy comes from neither the sun s radiation nor tidal friction could explain this phenomenon. Ruiz (2001) suggests that the ice layers are much more closely packed and resistant to heat release than has previously been assumed. He considers it possible that the ice viscosities present can minimize heat radiation to outer space. This example shows the complex physical properties of water up to now, twelve different crystallographic structures and two non-crystalline amorphous forms are known Under the extreme conditions present in outer space, frozen water may well exist in modifications with as yet completely unknown properties. 

The structure of a vapor-quenched alloy may be either crystalline, in which the periodicity of the unit cell is repeated within the crystallites, or amorphous, in which there is no translational periodicity even over a distance of several lattice spacings. Mader (64) has given the following criteria for the formation of an amorphous structure the equilibrium diagram must show limited terminal solubilities of the two components, and a size difference of greater than 10% should exist between the component atoms. A ball model simulation experiment has been used to illustrate the effects of size difference and rate of deposition on the structure of quench-cooled alloy films (68). Concentrated alloys of Cu-Ag (35-65%... 

Although there is no consistent explanation of the relationship between organic polymer morphology and electrical properties,51 amorphous structures are generally preferred over a crystalline structure. An experiment was conducted to study the structure of the fdm deposited using an inert carrier gas. The PNT-N... 

Structure as deposited Crystalline Crystalline/ amorphous Crystalline/ amorphous Amorphous Microcrystalline/ amorphous Mcirocrystalline/ amorphous Cross-linked... 

At the macroscopic level, a solid is a substance that has both a definite volume and a definite shape. At the microscopic level, solids may be one of two types amorphous or crystalline. Amorphous solids lack extensive ordering of the particles. There is a lack of regularity of the structure. There may be small regions of order separated by large areas of disordered particles. They resemble liquids more than solids in this characteristic. Amorphous solids have no distinct melting point. They simply become softer and softer as the temperature rises. Glass, rubber, and charcoal are examples of amorphous solids. 

As determined from X-ray diffraction measurements, the unit cell of crystalline PET is triclinic with a repeat distance of 1.075 nm along the major axis [5, 6], This corresponds to >98 % of the theoretical extended length of the monomer repeat unit [6], There is very little molecular extensibility remaining in a PET crystal, resulting not only in a high modulus but also a relatively short extension range over which the crystal can be extended and still recover elastically. The density of the crystalline structure is 1.45 g/ml, or about 9% higher than the amorphous structure [3],... 

At speeds beyond 4000 m/min, inertial and air drag effects become the dominant contributors to fiber stress. Sufficient orientation can be induced so that significant crystallization occurs in the as-spun fiber. The structure begins to partition into either highly oriented crystalline regions, or amorphous regions of relatively low orientation. There is relatively less oriented-amorphous structure. 

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