Glassy amorphous

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.). 

Fig. 7-15 Solidification during processing of glassy amorphous and crystalline TPs.

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

The chains that make up a polymer can adopt several distinct physical phases the principal ones are rubbery amorphous, glassy amorphous, and crystalline. Polymers do not crystallize in the classic sense portions of adjacent chains organize to form small crystalline phases surrounded by an amorphous matrix. Thus, in many polymers the crystalline and amorphous phases co-exist in a semicrystalline state. 

In the glassy amorphous state polymers possess insufficient free volume to permit the cooperative motion of chain segments. Thermal motion is limited to classical modes of vibration involving an atom and its nearest neighbors. In this state, the polymer behaves in a glass-like fashion. When we flex or stretch glassy amorphous polymers beyond a few percent strain they crack or break in a britde fashion. 

Glassy amorphous polymers exhibit excellent dimensional stability and are frequently transparent. Everyday examples include atactic polystyrene, polycarbonate, and polymethylmethacrylate (Plexiglas ), which we encounter in such applications as bus shelters, motorcycle windshields, and compact disc cases. 

As polymers solidify from the molten state, their free volume decreases and their organization increases. Solid polymers fall into one of three classes rubbery amorphous, glassy amorphous, and semicrystalline, which we introduced in Chapter 1. 

Solid polymers can adopt a wide variety of structures, all of which are derived from the three basic states rubbery amorphous, glassy amorphous, and crystalline. Either of the amorphous states can exist in a pure form. However, crystallinity only occurs in conjunction with one of the amorphous states, to form a semicrystalline structure. 

Define the terms rubbery amorphous, glassy amorphous, crystalline and semicrystalline. 

Figure 8.4 shows generic load versus elongation curves for rubbery amorphous, glassy amorphous, and semicrystalline polymers. In each case, the effect of extension on a dogbone specimen is shown at various points along the curve. 

In Fig. 8.4 a), the glassy amorphous polymer extends only a few percent before it breaks abruptly. The extension in the sample up to the point of failure is largely reversible, that is, the material behaves elastically. Polystyrene and polycarbonate, which are used to make CD jewel cases, exhibit this type of behavior. 

The elongation at break of a sample is the strain at which at which it breaks. This value varies widely depending on polymer type and processing conditions. Glassy amorphous polymers typically exhibit low elongations at break because their chains cannot slide past one another. In rubbery amorphous polymers the situation is somewhat different. High molecular weight... 

Our principal concern is often the polymer s mechanical properties. For instance, the requirements of the handle of an electrician s screwdriver are very different from those of wire insulation. In the former application, we are free to choose stiff polymers of many types, including glassy amorphous polymers. In contrast, wire insulation must be flexible, which limits our choice to ductile polymers. 

Why do the tensile behaviors of rubbery amorphous, glassy amorphous and semicrystalline polymers differ as they do ... 

Strongly segregated systems, Todt > Tc < Tg with hard confinement. A strictly confined crystallization within MDs has been observed for strongly segregated diblock copolymers with a glassy amorphous block [29-42]. 

Yellow-brown glassy amorphous sohd sublimes on heating decomposes around 500°C insoluble in cold water ( 1.4 mg/L at 0°C) dissolves in alkahes and solutions of alkali metal sulfides, and in nitric acid. 

Apparently all four curves intersect at the same point, namely at the temperature at which A and B have the same E-modulus. Each blend has the same modulus at this temperature. This situation may occur when B is a glassy amorphous polymer and A... 

The stiffest polymers are both crystalline and have a glassy amorphous phase. They are often useful as engineering istructural) plastics. 

Fig. 9.1. Raman spectra of (left) crystalline D-sorbitol and (right) quench cooled glassy (amorphous) D-sorbitol. Reproduced from [19]...

The properties of the polysilanes, like those of the polyphosphazenes, depend greatly on the nature of the substituent groups. Polysilanes cover the entire range of properties from highly crystalline and insoluble, through partially crystalline, flexible solids, to glassy amorphous materials and rubbery elastomers. 

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