Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Focus: Stress Relaxation in Polymers - From single molecules to biological cells (joint focus with BP)

CPP 32.6: Vortrag

Donnerstag, 29. März 2012, 11:15–11:30, C 243

Non-Equilibrium Relaxation in Polymer Solutions — •Chien-Cheng Huang, Gerhard Gompper, and Roland G. Winkler — Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich

Individual DNA molecules in shear flow exhibit large conformational changes due to tumbling motion. A polymer continuously undergoes stretching and compression cycles with a characteristic frequency, which depends on the shear rate. To characterize the tumbling behavior, we perform large-scale non-equilibrium mesoscale hydrodynamic simulations of semidilute polymer solutions, which combine molecular dynamics simulations and the multiparticle collision dynamics approach. The non-equilibrium polymer end-to-end vector relaxation times in the stationary state exhibit the shear rate dependence γ^−2/3. In the dilute limit, the relaxation times for the various spatial directions are identical. For semidilute solutions, screening of hydrodynamic interactions leads to a slower and faster relaxation in the vorticity and gradient directions, respectively. The relaxation times are equal to the tumbling times extracted from cross-correlation functions of fluctuations of radius-of-gyration components. Furthermore, we find a memory effect in the tumbling dynamics, which causes an oscillatory relaxation along the flow and gradient directions. This memory effect decreases with increasing polymer length and is believed to be less pronounced or even absent for long polymers.