Local orientation

The vector field u(r) describing the local orientational ordering of amphi-philes is split into two fields s and t... 

Woodward and Hoffmann pointed out that the Diels-Alder reaction involved bonding overlap of the highest-occupied molecular orbital (HOMO) on the diene and the lowest-unoccupied molecular orbital (LUMO) on the dienophile. Display the HOMO for 2-methoxybutadiene. Where is it localized Display the LUMO for acrylonitrile. Where is it localized Orient the two fragments such that the HOMO and LUMO best overlap (A clearer picture is provided by examining-the HOMO map for 2-methoxybutadiene and the LUMO map for acrylonitrile.) Which product should result ... 

Several local labels need to be measured, usually one-by-one in individual samples in the case of 19F-NMR. The combined set of anisotropic NMR parameters then allows one to re-construct the geometry of the entire peptide and to determine its alignment in the membrane, as illustrated in Fig. 1 [35-37, 47, 48]. The only prerequisite is that the 19F-labelled moiety has to be rigidly attached to the peptide backbone, and that the peptide assumes a well-defined secondary structure. Provided that a sufficient number of local orientational constraints can be measured... 

Nordeng, H. (1971). Is the local orientation of anadromous fishes determined by pheromones Nature 233,411-413. 

The vibrational spectrum of a molecule adsorbed on a metal surface contains detailed information about the metal-adsorbate bonds, the local orientation of the molecule, and intermolecular interactions within the adsorbate layer. It is this detailed information about the adsorbate layer that makes vibrational spectroscopy and most prominently IR spectroscopy an important tool in heterogeneous catalysis research. 

As a first approximation we postulate the existence of an equally sized hard core volume located in the center of each cylinder that defines the excluded volume per segment, according to the degree of interpenetration of neighboring cylinders. This simple construction includes complicated local intersegmental configurations, but it imposes a unique local orientation correlation of segments within the domains of a PE melt The shape of those impenetrable correlation cylinders is assumed also to be cylindrical. 

Woemer et al. 373) produced polyacetylene with locally oriented regions and an optical anisotropy of 2 x by polymerization on crystals of biphenyl. Yamashita and co-workers 374,375) have recently reported epitaxial polymerization of acetylene on crystals of anthracene, naphthalene and biphenyl where fibrils of cis- or trans-polymer formed, crystallographically aligned with the substrate. Fincher et al. 376) produced a 3 x extension which gave a 4 x optical anisotropy. 

Local Orientation. The most striking observation of this work is that the selected area diffraction patterns are not in general of a Debye-Scherrer type. Among the various hypotheses which can be drawn to understand such a fact, the most probable one is that the sections are not truly transverse ones indeed, if one supposes the existence of a cylindrical symmetry at the level of each selected area, 0.5 to 1 ym in diameter (the symmetry axis being always parallel to the fiber axis) the "detectable" network main planes have to be parallel to 1he "c" axis of the individual... 

Figure IS. (Left) Case of PETP constant local orientation and variable local rotation axis (right) case of PA 66 variable local orientation and constant local...

There are two different ways to get local diffraction patterns "Debye-Scherrer" type (such patterns are obtained if ( y ) is found within (E). In the first case (figure 15 the orientation of the local symmetry axis ( A ) is very close to that of (I) with the consequence tRat the whole cone ( e ) is located within the cone (C) even if the local orientation is relatively good, i.e., angle 0 is small. In the second case, the local orientation is poorer, i.e., 0 is fairly large. 

Local Crystallinity. The "azimutal correction" previously mentioned should be applied only in the second case discussed above, i.e., when the variation of the local orientation is the main factor in affecting the observed diffraction pattern. In this specific case, the diffracted intensity is spread over the whole interference. As a result, the correction should be made for 66 polyamide and not for PETP. This correction could have a large effect and would result in lowering the crystallinity differences between the two kinds of fibers. This azimutal correction gives a better account of the whole azimutal intensity than the normalization of the half-height width value as proposed in another paper (10). 

Morphological explanations for the improved ductility of the fl nucleated materials have focussed on the lamellar texture. That crazes in a iPP are more localised and better defined than in /3 iPP may reflect both the influence of the cross-hatched structure on lamellar slip described in the previous section, and the strong correlation between deformation in ft iPP and the local orientation of the lamellae with respect to the tensile axis. Indeed, the trend towards more localised deformation in a spherulites may simply reflect the relatively homogeneous lamellar textures of these latter [24]. 

Case Study 4 Local Orientational Dynamics - Two Dimensional Raman Scattering... 

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