Small mesophase morphologies

Figure 20 presents mesophase rods produced by extrusion alone and by a light draw after extrusion. As Jenkins and Jenkins observed (34), the strong preferred orientation induced by extrusion was easily disturbed by pyrolysis bubbles or even by small flow irregularities. However, modest draws (e.g., draw ratio = 2) after extrusion produced fibrous morphologies with good uniformity. At these draw levels, the nodes and crosses characteristic of wedge disclinations could be resolved on transverse sections. 

Small isotropic droplets, c, 1 im or smaller in size, are not easily resolved by microscopy. A minor isotropic component is often found to trail at the lower temperature range within the biphase and its presence can be overlooked [25]. Yet a finely dispersed I phase can be expected to influence rheological behavior, order and orientation dynamics in the mesophase, as well as the mechanical properties of the resulting solid phase. In contrast to microscopy or DSC which detect macroscopic behavior, NMR provides a molecular or segment level view of morphology and cannot distinguish between phase and microphase separation. Thus accurate biphase delineation may be delicate to accomplish. We should further note that the customary dynamic scans do not provide the equilibrium value of biphase width but rather an apparent value as determined by thermal history (section 6.5). 

If (1), (2) or (3) prevail, the morphology is metastable and will evolve upon isothermal mesophase aging. Case (1) and case (2) will be mentioned in subsequent sections. Case (3) represents the well known texture defects within PLC mesophases. The N phase in PLCs tends to be formed by coalescence of a large number of very small droplets and is initially characterized by a high density of disclination defects (around which the director orientation varies). These are progressively annihilated upon isothermal annealing [53] and visualized in the coarsening of the N texture observed by microscopy or SALS. 

LC elastomers based on the side-chain and main-chain LC polymers containing rather small concentrations of the chiral mesogens can form SmC mesophase-possessing domains with permanent electric dipole moment, which exhibit piezoelectric properties. The application of an uniaxial mechanical field (shear) produces a centrosymmetric morphology, where the piezoelectric effeas are observed. The piezoelectric coefficient reaches its maximum at a certain shear angle that corresponds to the completion of polydomain to monodomain transformation. The piezoelectric module of different types of such LC elastomers can be higher than those... 

Practically, the experimental results from many studies [1-9] show that the melting of polymers is an irreversible process due to the partial crystalline metastable phase (so-called semicrystalline phase),small crystal size, and crystal defects such as amorphous, mesophases. Generally, the melting process is a function of the thermal history of the crystallization process, the nature of the crystal, and its crystalline state in terms of structure, morphology, and polymer chain macroconformation... 

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