Dynamics and shear orientation behavior of a main-chain thermotropic liquid crystalline polymer

Wei Jun Zhou, Julia A. Kornfield, Victor M. Ugaz, Wesley Roth Burghardt, Darren R. Link, Noel A. Clark

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

The dynamics and shear orientation behavior of a model thermotropic liquid crystalline polymer (DHMS-7,9) were characterized by mechanical rheometry and in situ wide angle X-ray diffraction (WAXD). In the nematic phase (between 120 and 192°C), DHMS-7,9 shows a three-region flow curve accompanied by a strong and relatively constant orientation over the entire shear rate range. A mysterious mesophase occurs between 92 and 120°C that has much higher viscosity than that of the nematic phase and a monotonically shear thinning flow curve. In this phase, a striking flip of the orientation from the flow direction to the vorticity direction occurs below a critical shear rate. This orientational flipping is reversible in response to step changes of temperature and/or shear rate. Examination of the linear viscoelastic behavior suggests certain rheological similarities between the x-phase and layered fluids.

Original languageEnglish (US)
Pages (from-to)5581-5593
Number of pages13
JournalMacromolecules
Volume32
Issue number17
DOIs
StatePublished - Aug 24 1999

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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