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      Concentration dependence of the longest relaxation times of dilute and semi-dilute polymer solutions

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      Journal of Rheology
      Society of Rheology

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          Single polymer dynamics in an elongational flow.

          The stretching of individual polymers in a spatially homogeneous velocity gradient was observed through use of fluorescently labeled DNA molecules. The probability distribution of molecular extension was determined as a function of time and strain rate. Although some molecules reached steady state, the average extension did not, even after a approximately 300-fold distortion of the underlying fluid element. At the highest strain rates, distinct conformational shapes with differing dynamics were observed. There was considerable variation in the onset of stretching, and chains with a dumbbell shape stretched more rapidly than folded ones. As the strain rate was increased, chains did not deform with the fluid element. The steady-state extension can be described by a model consisting of two beads connected by a spring representing the entropic elasticity of a worm-like chain, but the average dynamics cannot.
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            Dynamics of Entangled Polymer Solutions. II. Inclusion of Hydrodynamic Interactions

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              Direct observation of tube-like motion of a single polymer chain.

              Tube-like motion of a single, fluorescently labeled molecule of DNA in an entangled solution of unlabeled lambda-phage DNA molecules was observed by fluorescence microscopy. One end of a 16- to 100-micrometer-long DNA was attached to a 1-micrometer bead and moved with optical tweezers. The molecule was stretched into various conformations having bends, kinks, and loops. As the polymer relaxed, it closely followed a path defined by its initial contour. The relaxation time of the disturbance caused by the bead was roughly 1 second, whereas tube-like motion in small loops persisted for longer than 2 minutes. Tube deformation, constraint release, and excess chain segment diffusion were also observed. These observations provide direct evidence for several key assumptions in the reptation model developed by de Gennes, Edwards, and Doi.
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                Author and article information

                Journal
                Journal of Rheology
                Journal of Rheology
                Society of Rheology
                0148-6055
                1520-8516
                September 2009
                September 2009
                : 53
                : 5
                : 1069-1085
                Article
                10.1122/1.3160734
                5077432e-89b1-4e67-b8df-afa93d1227a8
                © 2009
                History

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