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Published April 12, 1993 | public
Journal Article

Rheology of side-group liquid-crystalline polymers: effect of isotropic-nematic transition and evidence of flow alignment


The dynamics of a nematic sidegroup liquid-crystalline polymer (SG-LCP) melt are investigated using transient stress and birefringence measurements. This SG-LCP shows a pronounced drop in the dynamic moduli at sufficiently low frequency upon passing through the transition from the isotropic to the nematic state. In contrast to previous studies, this suggests that liquid-crystalline order does affect the relaxation dynamics of SG-LCP melts. In the isotropic phase we simultaneously measure dynamic birefringence and stress to determine the stress-optic ratio (SOR). Results in the isotropic state near T_(ni) show the anomalously large SOR characteristic of pretransitional effects in liquid-crystalline systems in general. In the nematic state, we find that prolonged, large-amplitude oscillatory shear dramatically reduces the turbidity and increases the birefringence of the sample, suggesting that shearing induces a preferred alignment in this SG-LCP melt. This is accompanied by a decrease in the effective dynamic moduli of the nematic.

Additional Information

© 1993 American Chemical Society. Received November 16, 1992; Revised Manuscript Received January 7, 1993. We gratefully acknowledge the support of the National Science Foundation Presidential Young Investigator Award (J.A.K.), the Gates Grubstake Fund, and the NATO-Travel Grant Program (CRG 901037). We thank Ute Pawelzik at the Max-Planck-Institut für Polymerforschung for synthesizing the polymers for this research.

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