Molecular orientation, "Region I" shear thinning and the cholesteric phase in aqueous hydroxypropylcellulose under shear

Kwan Hongladarom, Wesly R. Burghardt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Birefringence and flow visualization are used to study molecular orientation, texture, and the cholesteric nature of a 60 wt% aqueous hydroxypropylcellulose solution at low to moderate shear rates. There is a sharp transition in behavior at a shear rate near 0.5 s-1. Below this rate, the sample shows "Region I" shear thinning, takes on a frosted appearance, has low flow-induced orientation, and exhibits faint optical diffraction characteristic of cholesteric liquid crystals. Upon flow cessation from low rates, a highly organized cholesteric phase showing bright optical diffraction is re-formed in around 5 min. Above the critical shear rate, the sample exhibits much higher orientation and a striped texture which is readily apparent with or without polarized light illumination. Upon flow cessation, molecular orientation decays significantly for up to around 400 s; however, the striped textures established during shear persist. It is suggested that persistence of the cholesteric phase under shear is responsible for the occurrence of Region I shear thinning at low shear rates in this solution.

Original languageEnglish (US)
Pages (from-to)46-53
Number of pages8
JournalRheologica Acta
Volume37
Issue number1
DOIs
StatePublished - Feb 1998

Keywords

  • Birefringence
  • Cholesteric phase
  • Flow visualization
  • Hydroxypropylcellulose
  • Liquid crystalline polymer

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials

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