Quantitative NMR velocity imaging of a main-chain liquid crystalline polymer flowing through an abrupt contraction |
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Authors: | Michael Gentzler Yi Q Song Susan J Muller Jeffrey A Reimer |
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Institution: | (1) Materials Sciences Division Lawrence Berkeley National Laboratory and Department of Chemical Engineering University of California Berkeley CA 94720-1462, USA e-mail: muller2@socrates.berkeley.edu, US |
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Abstract: | The flow of isotropic and liquid crystalline (LC) hydroxypropylcellulose (HPC) aqueous solutions into an abrupt axisymmetric
contraction has been quantitatively measured by pulsed-field-gradient NMR techniques. Steady-state axial velocity profiles,
acquired upstream of the contraction, reveal a large contraction entry length for the LC solution. This entry flow field exists
over an order of magnitude change in flow rate and is attributed to elasticity that is associated with polydomain liquid crystallinity.
Pronounced, off-centerline velocity maxima (in an axisymmetric flow field) were present upstream of the contraction, in the
entry flow region. Apparently, a more viscous and elastic core of fluid was present along the centerline; this fluid resisted
elongational strain more than the fluid closer to the walls. Quantitative velocity profiles were extracted from displacement
distributions and corrected for elongational dispersion. The isotropic solution velocity profiles matched those obtained from
viscoelastic simulations using an approximate Doi-Edwards model, parameterized with independent rheological data.
Received: 29 April 1999/Accepted: 30 August 1999 |
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Keywords: | Contraction flow NMR velocity imaging Liquid crystalline polymer |
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