Rheo-optical evidence of a flow-induced isotropie-nematic transition in a thermotropic liquid-crystalline polymer

Patrick T. Mather, Angel Romo-Uribe, Chang Dae Han, Seung Su Kim

Research output: Contribution to journalArticle

67 Scopus citations

Abstract

A direct rheo-optical characterization of the flow-induced isotropic-nematic (I-N) transition in a semiflexible thermotropic liquid-crystalline polymer (TLCP) was investigated, using a specially constructed apparatus enabling in-situ optical microscopic observations at elevated temperatures, along with cone-and-plate rheometry. For the investigation, an aromatic polyester, poly[(phenylenesulfonyl)-p-phenylene 1,10-decamethylenebis(4-oxybenzoate)] (PSHQ10), was synthesized via solution polymerization. Above the equilibrium isotropic-nematic transition temperature for this polymer, T = 170.5 °C, application of steady-state shear flow above a certain critical value of shear rate, γ + ̇c, produces a first-order I-N transition, with γ + ̇c increasing with temperature. This transition is evidenced by the formation of elongated nematic (birefringent) domains in the isotropic matrix, accompanied by a drastic decrease in shear viscosity (η). Remarkably, the nematic domains that form for γ + ̇ > γ + ̇c are optically uniform under cross-polarized optical microscopy; i.e., they are apparently free of disclinations (defects), typical of textured TLCPs. The flow-induced I-N transition in PSHQ10 is found to be reversible; i.e., upon cessation of shear flow, the domains melt to the original isotropic phase and the dynamic moduli rise toward the pretransition values. The observed flow-induced I-N transition may find important applications, such as envisaging new routes for processing TLCPs with better mechanical properties and helping to understand bioprocesses such as silk thread spinning.

Original languageEnglish (US)
Pages (from-to)7977-7989
Number of pages13
JournalMacromolecules
Volume30
Issue number25
DOIs
StatePublished - Dec 15 1997

ASJC Scopus subject areas

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

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