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Katarzyna Niedzwiedz, Oliver Arnolds, Norbert Willenbacher, Rudiger Brummer
Capillary Breakup Extensional Rheometry of Yield Stress Fluids
Appl. Rheol. 19:4 (2009) 41969 (10 pages)
►
Filament breakup of high viscosity fluids with apparent yield stress has been investigated and strategies for an appropriate
characterization of their behavior in CaBER experiments are discussed. Filament profiles of such fluids exhibit significant concave
curvature. Accurate determination of filament shape is mandatory for understanding deformation behavior. Therefore,
we have set up an optical train including high-speed camera, telecentric objective and telecentric back-light illumination
with a blue light emitting diode (LED) providing high contrast filament shape imaging. Image analysis allows for diameter
determination with an accuracy of 3.55 μm/pixel. In addition to the transient filament diameter at the neck we have extracted
the curvature at this point as a function of time and the region of deformation, in order to characterize the extensional
flow behavior.We have investigated the time evolution of filament shape as a function of various experimental parameters
like stretching time, velocity profile during stretching, stretching ratio and initial sample volume at constant stretching ratio.
Filament thinning is independent of stretching time, tsub>s
and stretching velocity profile. But when the same stretching ratio is
applied at different initial volume fraction, filament curvature increases strongly with decreasing sample volume leading to
an increase of filament life time according to the negative contribution of its curvature to the Laplace pressure inside the
fluid.
► Cite this publication as follows:
Niedzwiedz K, Arnolds O, Willenbacher N, Brummer R: Capillary Breakup Extensional Rheometry of Yield Stress Fluids, Appl. Rheol. 19 (2009) 41969.
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