Nematic liquid crystalline

A relatively new class of high-performance carbon fibers is melt-spun from mesophase pitch, a discotic nematic liquid crystalline material. This variety of carbon fibers is unique in that it can develop extended graphitic crystallinity during carbonization, in contrast to current carbon fibers produced from PAN. 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Ordered dialkoxy PPV derivative has been prepared by Yoshino et al. [491. oly(2 -nonoyloxy-1,4-phenylene vinylene) 27a forms a nematic liquid-crystalline phase upon melting. The material retains its order upon cooling to room temperature, and its band gap (2.08 eV) is measurably smaller than in an unoricnted sample. Oriented electroluminescence may be achieved by rubbing a thin fdin of the material to induce molecular orientation [50],... 

The types of liquid-crystalline phases of interest can be defined by the direction describing the preferred orientation (see Chapter 8). The limits are the usual completely ordered (crystalline) and completely disordered (isotropic) phases, with a nematic liquid-crystalline phase ("mesophase") between them. 

Abe, A., Furuya, H., Zhou, Z., Hiejima, T. and Kobayashi, Y. Stepwise Phase Transitions of Chain Molecules Crystallization/Melting via a Nematic Liquid-Crystalline Phase. Vol. 181, pp. 121-152. 

H Shi, BM Conger, D Katsis, and SH Chen, Circularly polarized fluorescence from chiral nematic liquid crystalline films theory and experiment, Liq. Cryst., 24 163-172, 1998. 

NS Sariciftci, U Lemmer, D Vacar, AJ Heeger, and RAJ Janssen, Polarized photoluminescence of oligothiophenes in nematic liquid crystalline matrices, Adv. Mater., 8 651-653, 1996. 

Kim reported on liquid crystalline properties observed for hyperbranched aromatic amides obtained from 3,5-diaminobenzoic acid and derivatives thereof. The resulting polymers exhibited nematic liquid crystalline phases [89]. 

Alternating dark and bright bands observed, following shear, in a wide range of main-chain nematic and chiral nematic liquid-crystalline polymers. 

Interconnecting nematic liquid crystalline materials, (V), prepared by Alfred et al. (2) were effective as liquid crystalline emitter and as charge-transport... 

Comparison of Properties of Smectic and Nematic Liquid-Crystalline... 

Photochemical modulation of the helical screw sense and pitch of a cholesteric phase was achieved with the combination of a nematic liquid crystalline host and an optically active photoresponsive guest as illustrated in Scheme 25.[92] Doping of 4 -(pentyloxy)-4-biphenylcarbonitrile 41 with P-trans-17b (1 wt%) converts the nematic phase into a cholesteric phase. 

Liquid crystals can be in the smectic, nematic, or isotropic states. In the smectic liquid crystalline state there is a long-range order in the direction of the long axis of the molecules. These molecules may be in single- or bilayer conformation, have molecular axis normal or tilted to the plane of the layer, and frozen or melted chains. In the nematic liquid crystalline state the molecules are aligned side by side but not in specific layers. The isotropic liquid crystalline state is more or less a liquid state, but where clusters with short-range order persist (Small, 1986, pp. 49-51). 

Synthesis and characterization of a thermotropic nematic liquid crystalline dendrime-ric polymer. [V. Percec, M. Kawasumi, Macromolecules 1992, 25(15), 3843-3850] [ 466]. 

Figure I Schematic representation of an example of hierarchical self-assembly at microscopic, mesoscopic, and macroscopic levels. At the microscopic level, molecules assemble into supramolecular polymer-like assemblies. This involves conformational changes to the monomer units that themselves are complex molecules. The polymers assemble into bundles at mesoscopic levels that under appropriate conditions spontaneously align macroscopically along some preferred direction to form a uniaxial nematic liquid-crystalline phase (after Aggeli et al., 2001).

Stepwise Phase Transitions of Chain Molecules Crystallization/Melting via a Nematic Liquid-Crystalline Phase... 

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