Crystalline/amorphous phases

On the other hand, a diffuse interface possesses a significantly wider core that extends over a number of atomic distances. A diffuse crystalline/amorphous phase interface is shown in Fig. B.3. Similar structures exist in crystal/liquid interfaces [5]. 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

The collagen gelatin transformation in solution has been recognized as a reversible first-order phase transition, subject to the same physical laws which govern the crystalline amorphous phase transitions observed in systems of linear polymers. The direct relationship between the transition in solution and the well-known thermal shrinkage phenomenon exhibited by collagen fibers has also been established. 

On crystallization of polyethylene at atmospheric pres sure, the structure typical for a semicrystalline polymer results. It usually consists of nanophase-separated crystalline/amorphous phase structures, as described in Chap. 5, and is represented by phase areas 7 and 8 of Fig. 6.1. A zero-entropy production path on heating, discussed in Sect. 2.4, permits to evaluate the free enthalpy distribution in areas 7 and 8, as shown in Fig. 6.3 [4] (see also schematics of G in Figs. 2.88 and 2.120). 

Liang, X., Guo, Y. Q. (1995), Crystalline-amorphous phase transition of a poly(ethylene glycol)/cellulose blend. Macromolecules, 28,6551-5. 

Edman L (2000) Ion association and ion solvation effects at the crystalline-amorphous phase transition in PEG — LITESI. J Phys Chem B 104 7246-7254... 

Figure 3. High magnification electron micrograph of the crystalline-amorphous phase typical for 500A thick films.

As water or other solvent is added to a crystalline surfactant, the structure of the system will undergo a transition from the most highly ordered crystalline state to one of greater disorder usually referred to as a liquid crystalline or mesophase. In such phases some structure is retained in one molecular region of the system, while a more liquid or amorphous structure is developed in the other. Such crystalline/ amorphous phases, 18-20 of which have been reported for some molecular structures, are characterized by possessing some physical properties of both crystalline and fluid phases. These phases will have at least one highly ordered dimension and, as a result, will exhibit relatively sharp X-ray diffraction patterns and optical... 

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). 

Eig. 15. Time—temperature transformation ia a thin-phase change layer during recording/reading/erasiug (3,105). C = Crystalline phase A = amorphous phase = melting temperature = glass-transition temperature RT = room temperature. 

The reading of data is performed optically, based on the difference in reflectivity between the well-reflecting crystalline and the opaque and lower reflecting amorphous phase. A low power laser beam is used to avoid crystallization (Eig. 15, Read). 

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). 

Research has led to alloys which undergo laser-induced crystallization within about 50 ns. This is possible, for example, with TeGe alloys, which also possess the necessary temperature stability up to 180°C and exhibit sufficient reflection (crystalline phase) and transmission characteristics (amorphous phase), respectively. TeGe alloys have not found a practical use because of the formation of depressions in the memory layer typical for them after repeated... 

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. 

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