Odd-even effect of flexible spacer length on flow-induced isotropic-to-nematic transition in segmented thermotropic polymers

Patrick T. Mather, Hong G. Jeon, Chang Dae Han, Sukky Chang

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

The dependence of the flow-induced isotropic-to-nematic (I-N) phase transition phenomenon on the spacer length is investigated using the well-behaved thermotropic polymers, PSHQn, with n representing the number of methylene groups as flexible spacer in the main chain. Using optical microrheology methods and mechanical rheological methods, the critical shear rate (γ̇cr) required for the onset of nematic-phase formation is measured at temperatures above the quiescent I-N transition temperature (TINo). In particular, flow-induced birefringence is measured for the PSHQn polymers of varying spacer lengths as functions of both temperature and shear rate. As shear rate increases for a fixed temperature higher than the TINo, a clear transition from low-level birefringence (0.0-0.005) to nematic-level birefringence (>0.01) is observed for most PSHQn polymers. Interestingly, the γ̇cr for nematic-phase formation is significantly larger for even-numbered PSHQn compared to odd-numbered PSHQn. This odd-even effect is explained by a significant difference in steady shear viscosity (and terminal relaxation time) at fixed temperature above TINo. A critical dimensionless group, critical Deborah number Decr=γ̇crτ with τ being the terminal relaxation time of polymer, is introduced to explain the experimental observations.

Original languageEnglish (US)
Pages (from-to)1326-1335
Number of pages10
JournalMacromolecules
Volume35
Issue number4
DOIs
StatePublished - Feb 12 2002

ASJC Scopus subject areas

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

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