TY - JOUR
T1 - X-ray scattering studies of orientation in channel flows of a lyotropic liquid crystalline polymer
AU - Cinader, David K.
AU - Burghardt, Wesley R.
N1 - Funding Information:
We gratefully acknowledge financial support from the AFOSR in the form of a MURI project on Liquid Crystals. These experiments were initiated under support of a National Science Foundation Young Investigator Award, grant CTS-9457083. We would also like to thank the staff of DND-CAT at the Advanced Photon Source of Argonne National Laboratory for assistance with the X-ray scattering experiments.
PY - 1999/7
Y1 - 1999/7
N2 - A lyotropic solution of hydroxypropylcellulose in m-cresol has been studied in channel flows containing inhomogeneous shearing kinematics (planar Poiseuille), or mixed shearing and extensional kinematics (slit-contractions and expansions). We have used X-ray scattering as a probe of orientation, to test and extend previous birefringence measurements in the same system [Bedford BD, Burghardt WR. J Rheol 1996;40:235]. Orientation changes dramatically in contraction and expansion regions, which cannot be explained by changes in superficial velocity alone. Calculations using Ericksen's Transversely Isotropic Fluid model show that the addition of a modest amount of extension to otherwise shearing kinematics can influence alignment by perturbing tumbling orbits either into or out of the shear plane, in addition to inducing a transition from tumbling to flow aligning behavior. Away from the centerline, orientation is rotated away from the downstream direction, presumably due to streamline bending near the contraction and expansion. However, the degree of rotation is different in contraction and expansion flows.
AB - A lyotropic solution of hydroxypropylcellulose in m-cresol has been studied in channel flows containing inhomogeneous shearing kinematics (planar Poiseuille), or mixed shearing and extensional kinematics (slit-contractions and expansions). We have used X-ray scattering as a probe of orientation, to test and extend previous birefringence measurements in the same system [Bedford BD, Burghardt WR. J Rheol 1996;40:235]. Orientation changes dramatically in contraction and expansion regions, which cannot be explained by changes in superficial velocity alone. Calculations using Ericksen's Transversely Isotropic Fluid model show that the addition of a modest amount of extension to otherwise shearing kinematics can influence alignment by perturbing tumbling orbits either into or out of the shear plane, in addition to inducing a transition from tumbling to flow aligning behavior. Away from the centerline, orientation is rotated away from the downstream direction, presumably due to streamline bending near the contraction and expansion. However, the degree of rotation is different in contraction and expansion flows.
KW - Channel flows
KW - Liquid-crystalline polymer
KW - Molecular orientation
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U2 - 10.1016/S0032-3861(98)00667-3
DO - 10.1016/S0032-3861(98)00667-3
M3 - Article
AN - SCOPUS:0345004940
VL - 40
SP - 4169
EP - 4180
JO - Polymer
JF - Polymer
SN - 0032-3861
IS - 15
ER -