Regensburg 2000 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 12: Polymere und Membranen

DY 12.5: Vortrag

Montag, 27. März 2000, 12:00–12:15, H2

Dynamics of Strongly Deformed Polymers in Solution — •R. Rzehak und W. Zimmermann — Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich

Bead spring models for polymers in solution are nonlinear when either the finite extensibility of the polymer, excluded volume effects or hydrodynamic interactions between polymer segments are taken into account. For such models we introduce a powerful method for the determination of the relaxation spectrum and modes from simulation data based on the Karhunen–Loéve technique. The method is applied to a simple model problem, namely a single tethered polymer in a uniform flow. Both spectrum and modes differ significantly from the linear Rouse modes and -times. The shape of the modes depends crucially on the inhomogeneity of the various interactions along the chain which is absent when the polymer is pulled at the ends only. The velocity dependence of the longest relaxation time is different from that assumed in de Gennes theory of the coil–stretch transition in elongational flows.

The assumption that the polymer is in a steady state is probably not valid in flows as they occur e.g. in turbulent drag reduction. As a model for such rapidly varying flows we also investigate the nonlinear response of the polymer to a large sudden change in the velocity of the uniform flow. Several regimes governed by different decay laws are identified which have not been described before. This complex relaxation behavior cannot be captured by a simple dumbbell model and it coincides with the relaxation of fluctuations in the steady state only in the linear regime of polymer dynamics where the Rouse–Zimm model is valid.