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Single-polymer dynamics in steady shear flow.

D E Smith1, H P Babcock, S Chu

  • 1Department of Physics, Varian Building, Stanford University, Stanford, CA 94305, USA.

Science (New York, N.Y.)
|March 12, 1999
PubMed
Summary
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Individual flexible polymers in shear flow show tumbling, not a sharp coil-stretch transition seen in elongational flow. Fluctuation rates increase with Weissenberg number, indicating complex dynamics.

Area of Science:

  • Polymer Physics
  • Rheology
  • Soft Matter Physics

Background:

  • Understanding polymer behavior in flow is crucial for materials science and fluid dynamics.
  • Previous studies often focused on ensemble averages or different flow types, limiting insight into individual polymer dynamics.

Purpose of the Study:

  • To directly observe and quantify the conformational dynamics of individual, flexible polymers under steady shear flow.
  • To investigate the relationship between molecular extension, shear rate, and polymer relaxation times.

Main Methods:

  • Utilized video fluorescence microscopy to directly observe individual polymer chains.
  • Measured molecular extension and analyzed probability distributions as a function of shear rate (gamma;).
  • Investigated polymers with two distinct relaxation times (tau).

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Main Results:

  • Observed large, aperiodic temporal fluctuations, indicative of end-over-end molecular tumbling.
  • Found no sharp coil-stretch transition in shear flow, unlike in elongational flow.
  • The rate of tumbling fluctuations increased with the Weissenberg number (gamma;tau).

Conclusions:

  • Individual flexible polymers exhibit distinct dynamic behaviors in shear flow compared to elongational flow.
  • Molecular tumbling is a significant factor influencing polymer conformation in shear flow.
  • The Weissenberg number effectively characterizes the dynamics of polymer tumbling in this regime.