Microcrystallite structure

Recently, Lee and Pyun17 have intensively investigated the effect of microcrystallite structures on electrochemical characteristics of the mesoporous carbon electrodes for EDLC. They effectively controlled the microcrystallite sizes of the carbon specimens in a- and c-axis direction, i.e., Za (parallel to the basal... 

In the present paper we extend the range of scattering angles as far as five degrees and combine SAXS measurement with wide-angle x-ray diffraction measurements. Me report what we believe to be the first complete SAXS curves for cotton and Valonia cellulose. We also demonstrate how the fractal concept can be applied to explain the microcrystallite structure in cellulose. 

Wood and Hill consider that the role of fluoride in these glasses is uncertain. Phase-separation studies suggest that the structure of the glass might relate to the crystalline species formed, in which case a microcrystallite glass model is appropriate. But other evidence cited above on the structure-breaking role of fluoride is compatible with a random network model. 

Where Jo and S are the current density of the primary beam and the area of the irradiated sample, Z is the wave length, Ohki the structure factor amplitude, Q the volume cell, Z a factor that takes the microstructure of sample into account (Zm - for a mosaic single crystalline film, Zt - for a texture film), t is the sample thickness, dhu the interplanar spacing, a represents the mean angular distribution of the microcrystallites in the film, p is a multiplicity factor (accounts for the number of reflections of coincidence), R is a horizontal coordinate of a particular reflection in DP from textures and (p is the tilt angle of the sample. In the case of polycrystalline films, a local intensity is usually measured and the corresponding relation is ... 

The most important question for the calculation of the structure amplitudes from the intensities is that for the validity of the kinematical approximation. Due to the strong interaction of fast electrons with matter the effects of dynamical scattering become more pronounced with increasing size of the microcrystallites in the film. In order to justify application of the kinematical equations it is necessary that the diffracted intensity is much less... 

However, subtle differences are apparent between the fine structures of conventional and Tyrann-M/E membranes. In subjective terms the former consists of a structure reminiscent of jumbled jacks whereas the latter resembles a mat of spaghetti. Although there is no proof that in this instance differences in microcrystalline habit are responsible for observable differences in SEM fine structure, it is tempting to speculate that the "jacks" indicate the presence of lamellar microcrystallites and the "spaghetti" structure, a more extended chain type of microcrystallite. Although purely tentative at present, this interpretation is consistent with the greater elasticity, and hence flexibility, of Tyrann-M/E. 

Pi0 and P32 have parallel isotherms, as expected for samples of identical structure. The isotherms of Po and P5 have the same slope as those of P10 and P32 which are rather well crystalline. However, this observation is a necessary but not a sufficient condition to affirm that these materials, amorphous to X-rays, already contain microcrystallites having a Faujasite structure. 

II. and III. The intermediate and final stages are both associated with crystallization the former with microcrystaUite formation, the latter with microcrystallite enlargement and its concentration (nncleation and growth of crystalline structures). 

These different casein monomers combine with calcium phosphate to form discrete particles on the nano-size scale. The phosphoserines of the caseins are seemingly clustered for the purpose of linking within the micelle to putative calcium phosphate microcrystallites, also known as nanoclusters (Holt, 1992 Home, 1998, 2002, 2003, 2006 Holt et al., 2003 Home et al., 2007). Structural evidence for the existence of such nanoclusters has come from neutron and X-ray scattering (de Kruif and Holt, 2003 Holt et al., 2003 Pignon et al., 2004 Marchin et al., 2007). The presence of nanoclusters allows native casein micelles to be effective natural suppliers of essential calcium salts in the human diet in a readily assimilated functional form. Protein-nanocluster interactions are the central concept of the cross-linking mechanism in Holt s model of casein micellar assembly (Holt et al., 2003 de Kruif and Holt, 2003). Any analogy with conventional soap-like micelles is considered to be... 

An important conclusion emerging from these studies is that polyvinyl chloride has a three-dimensional network structure where microcrystallites are believed to... 

Above the melting point, disappearance of microcrystallites destroys the network structure of PVC consequently it behaves like a typical high molecular weight linear amorphous polymer. 

In conclusion, we may state that viscoelastic data presented in this paper further reaffirm the contention that polyvinyl chloride has a network structure with microcrystallites acting as cross-links. Incorporation of plasticizer affected PVC in a way similar to amorphous polymers mainly by lowering Tg of the amo-rophous regions. Microcrystallites appear to be stable even in the presence of... 

M(lI)AlSn-LDHs with M(II) being Mg, Ni or Co were synthesized by a coprecipitation method. The influence of Sn on the thermal transformations and redox properties were investigated in detail using XRD, TG/DTA, SEM, TPR, 1 l9Sn-MAS NMR and UV-visible diffuse-reflectance (DR) spectroscopy methods. Some of these samples calcined at 450 °C were tested as catalysts in the partial oxidation of methanol (POM) reaction. In this paper we discuss briefly the effect of Sn-incorporation on the structural features and reducibility of CoAI-LDH. The catalytic performance of Co-spinel microcrystallites derived from CoAl-, and CoAlSn-LDHs was also evaluated. 

Extremely thin, self-supporting film electrodes have been successfully produced. For example, polypyrrole films of 120 nm thickness have been used successfully to grow microcrystallites, followed by removal of the film plus crystallites from the substrate for characterization of the crystallographic structure and orientation of the microcrystallites by transmission electron microscopy with selected area electron diffraction [23]. Thin-film electrodes have been applied to allow transmission of high-energy beams, including x-rays, for in situ... 

Once dehydrated, the microfibrils are practically without functionality in ordinary food processing and preparation operations, because the inert microcrystallites are difficult for water to penetrate. The polymorphs, cellulose I and II (Blackwell, 1982 Coffey el al., 1995), are differentiated by their molecular orientation, hydrogen-bonding patterns, and unit-cell structure. Cellulose I is the natural orientation cellulose II results from NaOH treatment under tension of cellulose I with 18-45% alkali (mercerization). The I—II transition is irreversible. Mercerization strengthens the fibers and improves their lustre and affinity for dyes (Sisson, 1943). Sewing thread was relatively pure mercerized cotton until the advent of synthetic polymer fibers. 

The first and most studied Mossbauer nucleus, iron-57, displays specific catalytic behavior. Mossbauer investigations of supported microcrystallites of iron and its oxide have demonstrated the importance of the techniques in the investigation of surface structure and chemistry. The application to other nuclei that have important catalytic qualities indicates the potential importance of the study of supported microcrystallites by Mossbauer spectroscopy in future investigations of catalysts. Developments in experimental techniques enabling in situ investigations are enhancing the scope of the technique. 

We now turn our attention from chemical to physical gels. As mentioned in the Introduction to this chapter, the junctions in physical gels can consist of locally helical structures, microcrystallites, or nodular domains. 

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