Effect of Mesophase Order and Molecular Weight on the Dynamics of Nematic and Smectic Side-Group Liquid-Crystalline Polymers

Susan F. Rubin, Rangaramanujam M. Kannan, Julia A. Kornfield, Christine Boeffel

Research output: Contribution to journalArticle

Abstract

The dynamic moduli of side-group liquid-crystalline polymers (SG-LCPs) having methacrylate backbone, hexamethylene spacer, and phenyl benzoate mesogens are characterized as a function of molecular weight in the isotropic, nematic, and smectic phases. Molar mass was varied from 3 × 105 to 3 × 106 g/mol, corresponding to the range where the onset of entanglement is observed in the isotropic phase (approximately 1–10Me,iso). Nematic order produces a profound change in the dynamics of the entangled SG-LPCs relative to the isotropic phase; however, this effect is absent in the unentangled SG-LCPs. Oscillatory shear with large amplitude (γ0 ≥ 40%) is effective in inducing macroscopic alignment in the nematic phase for all the SG-LCPs studied. Smectic order increases the elastic character of the fluid, but its incremental effect in a system that is entangled is relatively small. Large-amplitude shearing can be used to alter the microstructure in the smectic liquid: shearing the smectic phase produces a decrease in modulus, whereas shearing in the nematic phase followed by cooling into the smectic phase produces an increase in modulus.

Original languageEnglish (US)
Pages (from-to)3521-3530
Number of pages10
JournalMacromolecules
Volume28
Issue number10
DOIs
StatePublished - May 1 1995
Externally publishedYes

ASJC Scopus subject areas

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

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