Defects in Nematic Main-Chain Liquid Crystalline Polymers

3 Defects in Nematic Main-Chain Liquid Crystalline Polymers 

As a rule, thin lines of strength 1/2 or singular lines of strength 1 are seen in the threaded textures of nematic thermotropic MCPs [25,57,58]. Rare cases of thick lines have been observed. As we have already pointed out, the reason for this is that the elastic anisotropy is large in these systems. The disclinations with 5= l/2 were also reported to be the most abundant in the Schlieren textures of nematic copolyesters [59-65]. 

Integral lines have been observed in the threaded texture [25] of a random copolyester prepared by the Eastman Kodak Company from 40 mol% poly(ethylene tereph-thalate) and 60 mol% jt -acetoxybenzoic acid and commercially known as X-7G  

They show a blurred contrast in linearly polarized light, but remain weakly contrasted in unpolarized light which may be taken as an indication of their singular character. Integral lines have also been observed in the Schlieren textures of a number of copoly- 

For thermotropic MCPs, stable Schlieren texture with high strength defects ( 5 =3/2 and 5 = 2) was first reported by Galli et al. [70] for the poly(/3-thioester)  

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Chapter II Defects and Textures in Nematic Main-Chain Liquid Crystalline Polymers. 93... 

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