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Published September 2009 | Published
Journal Article Open

Real-time depth sectioning: Isolating the effect of stress on structure development in pressure-driven flow

Abstract

Transient structure development at a specific distance from the channel wall in a pressure-driven flow is obtained from a set of real-time measurements that integrate contributions throughout the thickness of a rectangular channel. This "depth sectioning method" retains the advantages of pressure-driven flow while revealing flow-induced structures as a function of stress. The method is illustrated by applying it to isothermal shear-induced crystallization of an isotactic polypropylene using both synchrotron x-ray scattering and optical retardance. Real-time, depth-resolved information about the development of oriented precursors reveals features that cannot be extracted from ex-situ observation of the final morphology and that are obscured in the depth-averaged in-situ measurements. For example, at 137 °C and at the highest shear stress examined (65 kPa), oriented thread-like nuclei formed rapidly, saturated within the first 7 s of flow, developed significant crystalline overgrowth during flow and did not relax after cessation of shear. At lower stresses, threads formed later and increased at a slower rate. The depth sectioning method can be applied to the flow-induced structure development in diverse complex fluids, including block copolymers, colloidal systems, and liquid-crystalline polymers.

Additional Information

©2009 The Society of Rheology. Received 24 February 2009; revised 10 June 2009. Financial support for this work was provided by the National Science Foundation under Grant Nos. DMR-0505393 and DMI-0218112, and by the ARCS Foundation. We are grateful to Dr. Weijun Zhou and Dr. R. L. Sammler of Dow Chemical Co. for kindly providing the materials used in this study. We thank Jan Willem Housmans for microfocus measurements, and Lixia Rong and Igors Sics for help with experimental setup at X27C (NSLS). We acknowledge NSLS and ESRF for providing beamtime and facilities.

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Created:
August 18, 2023
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October 19, 2023