Alignment by shear or extensional flow

Ide and Ophir [33] and Viola et al. [34] reported that extensional flow was more efficient than shear flow to orient nematic longitudinal PLCs. Cold drawing of longitudinal PLCs leads to a slippage of domains past each other without any significant increase in the overall degree of orientation [35]. 

Graziano and Mackley [36] reported a very extensive study on oscillatory sheared, nematic, longitudinal PLCs based on a series of random 50/50 copolyesters of chlorophenylene terephthalate and bis-phenoxyethane carboxylate. They observed a variety of textures in the polarized microscope and also noticed a pronounced difference between low and high molar mass samples. 

Injection molded bars of longitudinal PLC (poly(p-hydroxybenzoic acid-co-ethylene terephthalate) X7G ) showed a layered morphology [53]. Thinner specimens, of the order of 3 mm thick, showed three different layers symmetrically around the central plane of the specimen an oriented skin (s 0.5 Young s modulus at 23 C 15 GPa), an oriented layer beneath the skin (5 0.5-0.6 Young s modulus at 

23 C 15 GPa) and an isotropic core (s = 0 Young s modulus at 23 C = 2.8 GPa. Thicker specimens (6 mm) showed a more complex morphology with five different layers. The relative thickness of the isotropic core increased with increasing thickness of the specimen, which resulted in a thickness-dependent Young s modulus of the specimen. 

Blends based on longitudinal PLCs and flexible chain polymers have been the subject of many reports. A comprehensive list is not given here, but emphasis is placed on a few of the early papers [56-63]. The components of the blends should phase separate and the PLC are oriented during the processing and form a reinforcing, often fibrous component. The low viscosity of the nematic PLC components makes the blends readily processable. 

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