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 language | English (US) |
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Pages (from-to) | 46-53 |
Number of pages | 8 |
Journal | Rheologica Acta |
Volume | 37 |
Issue number | 1 |
DOIs | |
State | Published - 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