The Amorphous Phase

The fraction of Ge in tetrahedral configurations also depends on the composition of the GST alloys as shown by the DFT results shown in Table 15.2. 

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Solvent Resistance. At temperatures below the melting of the crystallites, the parylenes resist all attempts to dissolve them. Although the solvents permeate the continuous amorphous phase, they are virtually excluded from the crystalline domains. Consequently, when a parylene film is exposed to a solvent a slight swelling is observed as the solvent invades the amorphous phase. In the thin films commonly encountered, equilibrium is reached fairly quickly, within minutes to hours. The change in thickness is conveniently and precisely measured by an interference technique. As indicated in Table 6, the best solvents, specifically those chemically most like the polymer (eg, aromatics such as xylene), cause a swelling of no more than 3%. 

Crystallinity has been studied by x-ray irradiation (85). An initial increase caused by chain scission in the amorphous phase was followed (above 3 kGy or 3 X 10 rad) by a gradual decrease associated with a disordering of the crystallites. The amorphous component showed a maximum of radiation-induced broadening in the nmr at 7 kGy (7 x 10 rad). 

To erase information by the transition amorphous — crystalline, the amorphous phase of the selected area must be crystallized by annealing. This is effected by illumination with a low power laser beam (6—15 mW, compared to 15—50 mW for writing/melting), thus crystallizing the area. This crystallization temperature is above the glass-transition point, but below the melting point of the material concerned (Eig. 15, Erase). 

Density. Density of LLDPE is measured by flotation in density gradient columns according to ASTM D1505-85. The most often used Hquid system is 2-propanol—water, which provides a density range of 0.79—1.00 g/cm. This technique is simple but requires over 50 hours for a precise measurement. The correlation between density (d) and crystallinity (CR) is given hy Ijd = CRj + (1 — Ci ) / d, where the density of the crystalline phase, ify, is 1.00 g/cm and the density of the amorphous phase, is 0.852—0.862 g/cm. Ultrasonic methods (Tecrad Company) and soHd-state nmr methods (Auburn International, Rheometrics) have been developed for crystallinity and density measurements of LLDPE resins both in pelletized and granular forms. 

Density. Although the polymer unit cell dimensions imply a calculated density of 1.33 g/cm at 20°C, and extrapolation of melt density data indicates a density of 1.13 g/cm at 20°C for the amorphous phase, the density actually measured is 1.15—1.26 g/cm, which indicates the presence of numerous voids in the stmcture. 

Some of the most difficult heterophase systems to characterize are those based on hydrocarbon polymers such as mbber-toughened polypropylene or other blends of mbbers and polyolefins. Eecause of its selectivity, RuO staining has been found to be usehil in these cases (221,222,230). Also, OsO staining of the amorphous blend components has been reported after sorption of double-bond-containing molecules such as 1,7-octadiene (231) or styrene (232). In these cases, the solvent is preferentially sorbed into the amorphous phase, and the reaction with OsO renders contrast between the phases. 

A more polar comonomer, eg, an AN comonomer, increases the water-vapor transmission more than VC when other factors are constant. For the same reason, AN copolymers are more resistant to penetrants of low cohesive energy density. AH VDC copolymers, however, are very impermeable to ahphatic hydrocarbons. Comonomers that lower T and increase the free volume in the amorphous phase increase permeability more than the polar comonomers higher acrylates are an example. Plasticizers increase permeabiUty for similar reasons. 

The quantitative proportion of the mesomorphous phase in PET fibers is strongly diversified and depends on the conditions of fiber manufacture. According to Lindner fl7], it is estimated to be in the range 0.21-0.36. For poorly stretched fibers (below 300% of draw ratio), the mesophase constitutes almost exclusively an ordered part of the polymer in the fiber. With an increase in the draw ratio of the fiber, the proportion of the mesophase in the whole fiber mass increases, mainly at the cost of the amorphous phase. It is assumed that the mesophase constitutes about 0.5 of the amorphous phase mass for poorly stretched fibers and about 1.2 of this mass for highly stretched fibers. 

The amorphous phase differs from the mesophase and the crystalline phase by a clearly lower value of density. The amorphous phase density depends on the internal orientation of the fiber. Us value is in the range 1.335-1.357 g/cm. In the case of a very high orientation, it can even reach the value 1.363 g/cm-. ... 

The existence of the amorphous phase of the fiber is confirmed in x-ray examination by the occurrence of a distinct intensity maximum of the radiation scattered diffusively at 2Q = 21.6 . The fraction of the amorphous phase in the fiber depends on manufacturing conditions and a possible further refining treatment. It is estimated to vary from 0.25 to 0.60. With an increase of the draw ratio and following the thermal treatment of the fiber, the proportion of the amorphous phase only reaches the lower values of this interval,... 

The amorphous orientation is considered a very important parameter of the microstructure of the fiber. It has a quantitative and qualitative effect on the fiber de-formability when mechanical forces are involved. It significantly influences the fatigue strength and sorptive properties (water, dyes), as well as transport phenomena inside the fiber (migration of electric charge carriers, diffusion of liquid). The importance of the amorphous phase makes its quantification essential. Indirect and direct methods currently are used for the quantitative assessment of the amorphous phase. 

Overall orientation is understood as the joint arrangement of all the structural elements of the crystalline phase and noncrystalline part of the fiber in relation to the geometrical axis of the fiber. In its essence, the overall orientation of PET fibers, as a result of the crystalline and amorphous orientation, will be characterized by smaller values of the quantitative index of orientation than for the crystalline phase and by greater ones for the amorphous phase. 

Amorphous alloys are in a thermodynamically metastable state, and hence essentially they are chemically more reactive than corresponding thermodynamically stable crystalline alloyIf an amorphous alloy crystallises to a single phase having the same composition as the amorphous phase, crystallisation results in a decrease in the activity of the alloy related to the active dissolution rate of the alloy . 

Addition of both ion-conducting and inert ceramics enhances the conductivity of a polymer electrolyte. This increase is attributed to an increase in volume fraction of the amorphous phase [133-136]. No... 

Since interactions at the molecular level between polymer components in the blends occur only in the amorphous phase, it is reasonable to assume that these effects are due to kinetic factors and, in particular, to the influence of a polymer component on the nucleation or crystallization kinetics of the other one. 

For the case of the crystallization from the amorphous phase, the blending with PPO for lower contents (less than 30wt%) favours the obtainment of the a" ordered modification with respect to the a disordered modification, which is obtained for the unblended polymer. For higher PPO contents the obtainment of the p form is favored [105]. This behavior would be simply due to the increases of the glass transition temperature, and hence of the crystallization temperature on heating, which correspond to increased PPO contents in the blends [105],... 

Interesting are, as an example, the bands at 902 and 911 cm 1 which characterize a and p forms, respectively, both presenting a shoulder at 906 cm-1, due to the presence of the amorphous phase. These spectral differences appear to be essentially independent of the particular modification obtained (a or a", P or P") and of the preparative route [110]. 

Another interesting case is the much higher solvent resistance of the P crystalline form of s-PS, with respect to the other ones. In fact, it has been found that the sorption of solvents (which are suitable to produce transformations from the a or the y form toward clathrate structures) occurs only in the amorphous phase, for the case of P form samples [122-124]. Sorption kinetic curves of liquid methylene chloride in s-PS samples in the a and p form are, for instance, compared in Fig. 21 [124]. 

DSC 31 The signals of the carbons within the crystalline phase have the same chemical shifts as at 303 K. The signals of the carbons of the amorphous phase changed as can be seen most obviously at the CH3 resonances. Figure 17 shows the CP-MAS 13C-NMR spectra of the threodiisotactic poly(l,2-dimethyltetramethylene)... 

Nevertheless the spectra can give worthwhile evidence ofthe occurence and frequency of particular conformations of crystalline and glassy materials. However, the example of polyethylene shows that the MAS NMR technique does not offer this kind of information always and easily for the amorphous phase. Specific characteristics... 

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