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ReportsObservation of Polymer Conformation Hysteresis in Extensional Flow
Highly extensible Escherichia coli DNA molecules in planar extensional flow were visualized in dilute solution by fluorescence microscopy. For a narrow range of flow strengths, the molecules were found in either a coiled or highly extended conformation, depending on the deformation history of the polymer. This conformation hysteresis persists for many polymer relaxation times and is due to conformation-dependent hydrodynamic forces. Polymer conformational free-energy landscapes were calculated from computer simulations and show two free-energy minima for flow strengths near the coil-stretch transition. Hysteresis cycles may directly influence bulk-solution stresses and the development of stress-strain relations for dilute polymer flows.
1 Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
2 Departments of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA. 3 Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA. * Present address: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
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To whom correspondence should be addressed. E-mail: Science. ISSN 0036-8075 (print), 1095-9203 (online)
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