Crystallites lamellar

Vermeylen, R., Derycke, V., Delcour, J. A., Goderis, B., Reynaers, H., and Koch, M. H. J. (2006). Gelatinization of starch in excess water Beyond the melting of lamellar crystallites. A combined wide- and small-angle X-ray scattering study. Biomucromolecules 7, 2624-2630. 

In view of the use of a similar repeating unit, tetramethylenecarboxyl, Seebach s approach should be included here. He incorporated oligomers and polymers of 3-hydroxybutanoic acid (3-HB) into planar bilayers and observed single-channel currents. It is known that poly(3-HB) forms lamellar crystallites with thickness in the range of 40 to 60 A when crystallized from dilute solutions. Therefore it is assumed that poly(3-HB) forms lamellar crystallites with a thickness of ca. 50 A. 

Figure 1.61 Schematic illustration of chain folding leading to lamellar crystallites (inset) and lamellar stacking to form spherulites.

The model proposed above accounts for orientation produced at low extension. To account for the c-axis orientation observed at high extension, either c-axis slip, or breakup of the large lamellar crystallites accompanied by rigid rotation and formation of microfibrils must occur. Both mechanisms can occur as elongation progresses, and an example of the latter is shown in Figure... 

One curious observation is that high activities for direct sulfur extraction from thiophene derivatives are only exhibited by metal sulfides that form stacked lamellar crystallites, similar to graphite structures (1-3). MoS2 is classic in this regard and has found applications as a high-temperature lubricant with properties very similar to those of graphite. The other widely used metal sulfide in HDS is WS2, which also forms lamellar crystal struc-... 

Within this molecular weight range, f/x varies from 1/4 to 1/7 6S). As the molecular weight increases, the number of molecular chains that penetrate many lamellar crystallites or participate repeatedly in a crystallite will increase, accompanying a pronounced decrease in the degree of crystallinity. This will result in a loss in the restriction on mobility of noncrystalline molecular chains caused by crystalline regions. As... 

The spectrum for samples with a very low molecular weight, ie., lower than about 1000, is fairly independent of the mode of crystallization, whether from the melt or from dilute solution. The spectrum is characterized by a very large broad component (wb 0.95) and a medium component with a large second moment, but no narrow component. In such samples the extended molecular chain length will be comparable to or slightly larger than the lamella thickness. The conformation of molecular chains to form the lamellar crystallites will be similar to that depicted schematically in Fig. 10 (B), independent of the crystallization mode. 

Our broad-line XH NMR analysis showed that this type of sample generally consists of the phase structure of lamellar crystallites and noncrystalline overlayer with a negligible amount of the noncrystalline amorphous phase [16,62]. In broad-line H NMR spectra of solution-grown linear polyethylene samples, a narrow component that suggests the existence of a liquid-like amorphous phase is hardly recognized. In Table 2, the three-component analysis of the broad-line XH NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

The major feature of polymers that have been bulk crystallized under quiescent conditions are polycrystalline structures called sphemlites. These are roughly spherical supercrystalline structures which exhibit Maltese cross-extinction patterns when examined under polarized light in an optical microscope. Spheruliies are characteristic of semicrystalline polymers and are also observed in low-molecular-weight materials that have been crystallized from viscous media. Sphemlites are aggregates of lamellar crystallites. They are not single crystals and include some... 

Drawn fibrillar morphology (developed when a spherulitic polymer is stretched below its melting point and the original lamellar crystallites are fragmented and rearranged into an oriented fibrous structure) (29)... 

Shortly afterwards (in 1957) Fischer showed by electron microscopy that the crystallites in melt-grown spherulites of polyethylene and nylon were most likely to be lamellar rather than fibrillar, as would be expected from the fringed-micelle model. It is now accepted that chain-folded lamellar crystallites play an important part in the structure of most ordinary... 

Strobl G (2000) From the melt via mesomorphic and granular crystalline layers to lamellar crystallites A major route followed in polymer crystsallization Eur Phys JE 3 165-183... 

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