Lateral crystallite dimensions

The crystallite size values for PPV depend on the drawn ratio, and different results were obtained for the lateral crystallite dimensions [75,102,131]. 

A. Crystal Growth As mentioned above, crystal growth is a process in which the dimensions of stable nuclei, and later the dimensions of polymeric crystallites, increase. The most important physical quantity used to characterize crystal growth is the linear growth rate, which is constant in time, but changes with temperature. This is the rate of crystal size increase in one dimension, and can be determined from polarization optical microscopy experiments. 

The dimensions of crystallites vary widely some measure only a few nanometers in any direction, while others, known as lamellae , are platelets with lateral dimensions of several tens of nanometers and thicknesses of a few nanometers. The chain axes in lamellae typically span the thickness of the crystallite. With reference to the unit cell illustrated in Fig. 7.2 a), the c direction corresponds to the thickness of the crystallite. 

Class Approximate density (g/cm3) Approximate degree of crystallinity <%) Approximate crystallite size (nm) Thickness Lateral dimensions Semicrystalline organization... 

Aiming at explaining the phenomenon, Nijs and Jacobs did lots of work, and many interesting results were obtained [3,12]. They postulated that the simple chain growth scheme occurs,but that the chains are terminated at certain carbon length that is proportional to the size of metal crystallite in the catalysts.Later in 1992,Y.Yang et al [13], based on the restriction of the dimension of the metal crystallites to the carbon chain growth, established a new Fischer-Tropsch product distribution formulation, which extended ASF model This new model has two... 

The XRD pattern of the coprecipitated catalyst (PdZr-c, trace 5) show palladium reflections indicating the presence of palladium crystallites, while the reflections due to zirconia phases are greatly broadened, which suggests amorphous phases. XRD line broadening and electron microscopy indicated that the catalysts prepared by oxidation of the glassy alloy were made up of small poorly crystalline palladium domains of about 5-7 nm lateral dimension. These domains were flilly integrated in predominantly amorphous zirconia. Although the coprecipitated catalyst contained palladium particles of about similar size (8 nm). 

Finally, the spectrum of the Cladophora cellulose which survived the strong acid hydrolysis closely resembled the cotton hydrocellulose spectrum except that the resolution was much better in the former spectrum. A contrast in resolution is consistent with a difference in the average lateral dimensions for the crystallites this difference is corroborated by electron microscopy. The close similarity of multiplet relative intensities in these two samples, in spite of their different crystallite surface-to-volume ratios verifies that surface resoncinces cire not determining the apparent multiplet intensities, particularly, for the 88-92 ppm region of the C l resonance. 

We wish to express our profound thanks to Dr. J.-F. Revol of the Pulp and Paper Research Institute of Canada for his interest, discussions, and his willingness to characterize the lateral dimensions of crystallites in certain of the algal cellulose preparations. 

These materials tend to be very brittle because, although they are highly crystalline, there are few inter-crystalline linking molecules. Figure 5.9 shows an electron micrograph of a replica of a fracture surface of extended-chain crystalline material of polychlorotrifluoroethylene. The lamellae are about 1-2 pm thick and there appears to be no limit on the lateral dimensions of the crystallites except space and availability of material. 

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