Morphology amorphous state

To obtain more detailed information on the ultrastructure of lipid dispersions and the morphology of the particles, electron microscopy is usually performed on replicas of freeze fractured or on frozen hydrated samples. These techniques aim to preserve the liquid-like state of the sample and the organization of the dispersed structures during preparation. By using special devices, the sample is frozen so quickly that all liquid structures, including the dispersion medium, solidify in an amorphous state. 

It is important to understand how these characteristics affect the morphology of the crystals and the textures of their aggregations. These specific characteristics allow crystals formed due to biological activity to exist as amorphous states or in metastable phases, and they bring about different characteristics in the morphology and textures of crystals from those present in uncontrolled inorganic systems. 

Beside defects from mineral genesis, grinding of a mineral can produce roentgen amorphous states or a new crystalline phase. This leads to the formation of surfaces which differ morphologically and energetically from equilibrium surfaces. Relations were also observed between the degree of crystallinity and particle size on one side and surface reactivity with water or a surfactant on the other side. For example, the adsorption of xanthates on a very pure surface of pyrite monocrystals occurs much slower than on fine crystalline samples5. ... 

Morphology Some polymers, like PETP, are spun in a nearly amorphous state or show a low degree of crystallinity. In other polymers, such as nylon, the undrawn material is already semi-crystalline. In the latter case the impact of extension energy must be sufficient to (partly) "melt" the folded chain blocks (lamellae) in all cases non-oriented material has to be converted into oriented crystalline material. In order to obtain high-tenacity yarns, the draw ratio must be high enough to transform a fraction of the chains in more or less extended state. 

In this chapter we study the characteristics that determine the crystallinity of polymers, crystalline morphology, and the factors affecting the crystallization and melting of polymers. We describe the amorphous state, focusing on the glass transition, a fundamental property for defining the mechanical behavior of polymers. The entire description refers exclusively to synthetic polymers. 

Poly(ethylene terephthalate) Poly(ethylene terephthalate) is a widely used semicrystalline polymer. The macroscopic properties of PET such as thermal, mechanical, optical, and permeation properties depend on its specific internal morphologies and microstructure arrangement. It can be quenched into the completely amorphous state, whereas thermal and thermomechanical treatments lead to partially crystallized samples with easily controlled degrees of crystallinity. The crystallization behavior of thermoplastic polymers is strongly affected by processing conditions [91-93]. 

CrystallinitY, Fillers, and Morphology. The solubility of low molecular weight compounds is extremely small in the crystallites of polymers in comparison to that in the amorphous regions of the same polymer (15). Thus, equilibrium sorption in semicrystalline polymers is less than that for corresponding completely amorphous ones. For the same reasons crystalline polymers are more chemical resistant than amorphous ones. As a good approximation for gases, the Henry s law solubility coefficient of a semicrystalline polymer is related to that for the same polymer in the amorphous state, S, by the following ... 

Wegner, however, established that radiation-induced solid-state polymerization of BCMO leads to a polymer morphology, which is incompatible with the so-called topochemical polymerization, i.e., a process in which monomer molecules are transformed into polymer without destruction of the crystal lattice 36). Electron microscopy, X-ray analysis and electron diffraction studies, have shown that polymerization starts at the edges and imperfections of the monomer crystals and that amorphous polymer is formed initially. Further transition from the amorphous state leads to the thermodynamically unstable monoclinic p-form. Density measurements indicate that the polymer is only 45-50% crystalline. The density of the amorphous poly-BCMO is 1.368 g/cm3 the density calculated for the crystalline polymer from crystallographic data of the p-form is 1.456 g/cm3. The density of the product of the radiation-induced solid-state polymerization is 1.41 g/cm3 36). 

Several authors have analyzed the miscibility of iPP and PB-1, by means of different analytical approaches. Piloz et al. (16) found a single, composition-dependent, glass transition behavior for these blends, and concluded that they are compatible in the amorphous state. Sjegmann (17,18) reported that the composition dependence of tensile properties evidences a high degree of compatibility of iPP and PB-1 and observed a marked effect of the composition on the morphology of melt-crystallized samples. Conversely, the analysis of the crystallized blends indicates the presence of separated crystal phases of the two polymers, even if a mutual influence during the crystallization cannot be excluded. 

Meanwhile this study reveals that a much shorter dwell time was needed to form a-alumina from the gel powder than the boehmite powder at 1000 °C. This is possibly due to the difference in the crystallinity and the morphology of the gel powder and the boehmite powder. The gel powder is amorphous, while the boehmite is nanocrystalline with several broad peaks in the XRD pattern. Amorphous state is less stable than the crystalline phase, therefore the activation energy required for the transformation to a-alumina will be lower for the amorphous gel powder. Meanwhile, the flaky morphology of the boehmite makes less available contact points which might help to retard the possible diffusion controlled reaction leading to grain growth followed by phase transformation. ... 

The main physicochemical characteristics of the rice husks and the products of its thermal degradation in different atmosphere used as fillers of polymers are morphology, crystalline, or amorphous state, surface reactivity functional groups, thermal stability, and pore structure. Some of them are presented in Table 13.1, and compared with those of Aerosil A200 (AR), Degussa AG, Germany. 

Ice is considered by earth scientists, especially glaciologists, as a particular geological material (i.e., rock) which, in the form of glaciers and ice shields has important consequences for the morphology of Earth s surface. Therefore, its physical properties are briefly described here. Ice exhibits twelve different polymorphic crystal structures plus two amorphous states. Usually, at atmospheric pressure and low pressures, it exists in two polymorphic forms. Phase Ih denotes ordinary hexagonal ice obtained by direct freezing of pure water, while phase Ic denotes cubic ice obtained by crystallization of water vapor at temperatures below -130°C. 

Syndiotactic polystyrene will strain-induce crystalhze, as well as quiescently crystallize as discussed previously. Furthermore, imder certain conditions, it may also be quenched to the amorphous state. In injection molded parts, these processes may lead to skin/core differences in morphology that can be observed (111,112). With higher temperature molds (>150°C) the parts are generally fully... 

---