Polymeric fibers, liquid crystalline

In the end, one obtains some truly fantastic materials. For instance, the airbags which allow for soft landing of spacecraft on Mars are made of liquid crystalline polymeric fiber called vectran. This must be a truly special material ... 

The liquid crystalline polymeric fibers exhibit high degree of order and orientation (greater than 0.9) compare to commodity polymeric fibers such as polyester, nylon, and polypropylene. The structure of commodity fibers is highly defective and contains chain folds and low amorphous orientation and typically crystallinity 30-65%, while the crystalline orientation is in the range of 0.9-0.98. 

More recently, Raman spectroscopy has been used to investigate the vibrational spectroscopy of polymer Hquid crystals (46) (see Liquid crystalline materials), the kinetics of polymerization (47) (see Kinetic measurements), synthetic polymers and mbbers (48), and stress and strain in fibers and composites (49) (see Composite materials). The relationship between Raman spectra and the stmcture of conjugated and conducting polymers has been reviewed (50,51). In addition, a general review of ft-Raman studies of polymers has been pubUshed (52). 

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. 

The first fibers from a thermotropic liquid crystalline melt whose properties were reported were spun from a copolyester of para-hydroxybenzoic acid (PHB) and PET by workers at Tennessee Eastman Co. The preparation of the copolymer proceeds in two stages. First, / ara-acetoxybenzoic acid is reacted with PET in an acidolysis step to give a copolyester prepolymer, which in the second step is condensed further to a higher degree of polymerization suitable for fiber formation. 

In both cases, pretransltional properties (2), the type of liquid crystalline phase and order parameters (8-9). elastic (Ifl) and rheological properties (11=12) have been the object of numerous studies or review articles. Some applications in very different fields (high modulus fibers, self-reinforced polymeric materials, electronic display devices, non-linear optics, etc.) have already been realized or are being pursued. 

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

When the mesogen moiety is included into the main chain of the polymer, the obtained macromolecule contains inherently rigid units, which usually result in remarkable mechanical properties and thermal stability. Fibers made by these polymers compete with the best ceramic fibers and are far superior to metal fibers [83]. They therefore are ideal candidates as reinforcements for polymer-based composites. However, these materials often have a poor miscibility and adhesion to other polymeric substrates, limiting the range of their applications. This problem basically arises from weak intermolecular interactions either within the liquid-crystalline polymer itself or with the matrix of the composite. Strong ionic... 

You can indeed make a super-strong fiber, even stronger than steel, from a polymer, but the polymer must be converted into a special liquid-crystalline state which is really a variety of the viscous state. If you think of a viscous polymer as of some polymeric liquid , then a liquid-crystalline polymer can be regarded as an anisotropic polymeric liquid . The anisotropy occurs spontaneously, with no help from outside (such as orientating fields, mechanical stresses or whatever). 

The rheology of dimolybdenum and dicopper octanoates was studied in their liquid-crystalline state and was found to be similar to that of conventional viscoelastic polymers such as polyethylene or polypropylene. This strongly supports the observation that these metallomesogens form polymeric chains in their columnar mesophases, and thus can be processed in a way similar to that of conventional polymers to form films and fibers. Note, however, that the chains are believed to be dynamic, constantly being formed and re-formed due to the weak nature of the axial, intermolecular M "0 interactions. 

Very recently, the same group has reported lyotropic LCs of polyacrylonitrile-grafted GOs [119]. Polyacrylonitrile chains were covalently and uniformly grafted onto GO surfaces via a simple free radical polymerization process. These functionalized sheets were well-dispersed in polar organic solvents such as dimeth-ylformamide and dimethyl sulphoxide forming nematic and lamellar LCs upon increasing concentrations. Continuous nacre-mimetic fibers have been assembled from these liquid crystalline phases. 

Since porphyrin and phthalocyanine derivatives possess excellent electronic and photophysical properties, they have been extensively studied as functional components for a wide variety of crystalHne, liquid crystalline, and polymeric materials. Increasing attention has also been paid to well-defined nanostructured assemblies of such organic dyes, and indeed, many examples of fibers, tapes, and vesicles have been reported [20]. However, only two examples are known for the formation of nanotubes and nanocoils. 

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