Local molecular orientation

Thus, in principle, the full distribution of local molecular orientations may be extracted from the analysis of the lineshape. However, in disordered systems, it is often difficult to... 

The Concept of Local Molecular Orientation (LMO). When observed by the naked eye a piece of semi-coke has a macroporous texture. When broken into fragments the pore walls appear as lamellae. After polishing, the pore walls appear as isochromatic areas when observed by optical microscopy. 

Table I. Size Classification for Regions of Local Molecular Orientation (LMO)...

For materials containing only C, H, and 0, oxygen and hydrogen have opposite effects. Therefore, an important parameter is the atomic ratio 0/H (1,2,6,7). As oxygen content increases, the size of the elemental domains of bulk mesophase (local molecular orientation, LMO) decreases. As hydrogen content increases, LMO... 

By combining all of the possible TEM modes, we are able to explain the behavior of carbonaceous materials primarily in terms of the local molecular orientations established in the final stages of liquid-phase pyrolysis. The models established from these observations are supported by the results of other techniques, such as infrared analyses (33), optical microscopy (27), X-ray diffraction (24), and Raman spectroscopy (22). 

Doi molecular theory adds a probability density function of molecular orientation to model rigid rodlike polymer molecules. This model is capable of describing the local molecular orientation distribution and nonlinear viscoelastic phenomena. Doi theory successfully predicts director tumbling in the linear regime and two sign changes in the first normal stress difference,as will be discussed later. However, because this theory assumes a uniform spatial structure, it is unable to describe textured LCPs. 

The negative Ni is the result of the coupling of molecular tumbling under flow and the local molecular-orientation distribution. At low shear rates, the director tumbles with the flow and Ni will be positive. At intermediate shear rates, nonlinear viscoelastic effects are important. The director tumbling competes with the steady director alignment along... 

Figure 2.7 Sketches ofthe possible arrangement ofbasic structural units (BSU)s. (a and b), true spherical symmetry (a, concentric texture b, radial texture) (c-e), statistical spherical symmetry (c, crumpled sheets ofpaper d, lamellar structure with infinite radius of curvature or infinite local molecular orientation (LMO) e, lamellar structure with a long-range statistical orientation) (f and g), cylindrical symmetry (f, true cylindrical symmetry g, statistical cylindrical symmetry). (Reproduced from Ref. [42] with permission fi-om Taylor and Francis Group.)...

Liquid crystals do not lend themselves to electron microscopy, as a liquid phase cannot be easily handled within a vacuum column unless cumbersome wet stages are employed. However, the fact that polymeric liquid crystals can be quenched to the glassy or partially crystalline states without any apparent disturbance of the local orientation characteristic of the liquid mesophase means that the electron microscope becomes a most useful tool. It is now providing new insights into the local molecular orientation in some liquid crystal polymer systems. 

Examples of Coalification and Carbonization of Various Substances (Main Parameters Given Are Local Molecular Orientation [LMO] Occurrence, Solidification, and Elemental Analysis [C, mo])... 

Local Molecular Orientation Occurrence and Description The local molecular orientations (LMOs) are detectable by TEM as a clustering of the bright dots (Figure 1.30a). These clusters are self-associations of BSUs in almost parallel preferred orientation. They are equivalent to classical liquid crystals described by Brooks and Taylor [96]. LMOs are limited by digitized contours and have a roughly isometrical shape in diameter and thickness, determined by... 

FIGURE 1.30 Shapes of liquid crystals (local molecular orientation [LMO]) with digitized contours model of series II kerogens (sporopollenin) (a) 002 dark-field image. Inset is a sketch of a LMO. (b) The same in 11 dark field. (From M. VUley. Simulation ther-mique de revolution des kerog nes. These d Etat Orleans 1979. With permission.)... 

Softening suspension of aromatic molecules at random As concentration increases —> basic structural units (BSUs) piled up face to face by two to three Local molecular orientation (LMO) occurrence Solidification Maximum spins Polygonization ... 

The capabilities of Oberlin and Bonnamy to see the big picture, and thus synthesize the advancements in seemingly unrelated carbon research fields, both old and new, have been amply demonstrated in previous volumes of this series. Here they bring order to the often confusing issue of disordered carbons, whose relevance has increased tremendously as a consequence of the often frustrated (and certainly incomplete) conversion of a wide variety of carbon precursors to nanotubes, fullerenes, or graphene. As they reviewed all the relevant information, unexpected new concepts emerged related to the carbonization and graphitization processes, and they were able to define more precisely the domain of existence of the various substances such as amorphous carbon and [basic structural units], as well as [local molecular orientations and] turbostratic carbons. .. by using diffraction techniques or their associations. ... 

Fig. 9.4 Local molecular orientation structure of antiferroelectric liquid crystal...

Beermann, J., Bozhevolnyi, S., Bordo, V., and Rubahn, H.-G. (2004). Two-photon mapping of local molecular orientations in hexaphenyl nanofibers. Opt.Commun., 237 423-429. 

---