| Combined velocity and stress measurements in complex flows of polymer melts are of great importance for a better understanding of the material behavior relevant to polymer processing. For a direct optical determination of the stress distribution in nonhomogeneous flows by flow-birefringence measurements the flow field should be two-dimensional, with no variations of the optical properties along the optical path in the neutral direction. In practice, however, no experimentally realizable flow is two-dimensional: boundary layers and confining windows cause variations along the optical path. We first discuss the problem of end effects when the small-retardation approximation is invalid, and we then argue that the end effects should have been considered more carefully in various previous experiments on polymer melts. Finally, we propose two ideas for avoiding the problem of end effects in flow-birefringence experiments on polymer melts: performing measurements in flow channels of different width, and lubrication of the channel walls forming the boundaries in the neutral direction. By these ideas the optical path length can be reduced considerably, thus reducing some fundamental problems with flow-birefringence experiments for polymer melts (spatial resolution, beam deflections and distortions).
for LaTeX users @article{HC\"Ottinger1999-43,
author = {H. C. \"Ottinger},
title = {End effects in flow-birefringence experiments for polymer melts},
journal = {J. Rheol.},
volume = {43},
pages = {253-259},
year = {1999}
}
\bibitem{HC\"Ottinger1999-43} H.C. \"Ottinger,
End effects in flow-birefringence experiments for polymer melts,
J. Rheol. {\bf 43} (1999) 253-259.HC\"Ottinger1999-43
H.C. \"Ottinger
End effects in flow-birefringence experiments for polymer melts
J. Rheol.,43,1999,253-259 |
mk@mat.ethz.ch
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