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ORAL PRESENTATION
Session: 3 Non-equilibrium thermodynamics and Molecular Dynamics
(scheduled: Monday, 15:15 )
Flow and Motion of Polymer Droplets on Polymer Brushes
M. Müller1, C. Pastorino2, K. Binder2
1 Institut für Theoretische Physik, Georg-August Universität, D37077 Göttingen, Germany
2 Institut für Physik, WA331, Johannes Gutenberg Universität, D55099 Mainz, Germany
Polymer brushes are soft, elastically deformable substrates giving rise to a rich wetting behavior and additional molecular dissipation mechanisms for the motion of droplets. We study thin polymer films and droplets on flat brush-covered substrates by non-equilibrium molecular dynamics simulation of a coarse-grained bead-spring model. The brush consists of identical polymers as the droplets. Upon increasing the grafting density the free polymers are expelled from the brush and a brush-melt interface gradually builds up. Molecular conformations and the overlap between brush and melt are studied in equilibrium and under shear. The velocity profile across a thin polymer film is investigated. The slip length adopts large positive values (perfect slip) for low grafting densities, but decreases and becomes negative for densely grafted, autophobic brushes. At high grafting density the polymer melt dewets from the brush and forms droplets. Nanoscopic polymer droplets driven by volume forces are investigated in their steady state. © IWNET 2006
ORAL PRESENTATION
Session: 4 Complex fluid deformation and rheology: Theories and thermodynamic relationships
(scheduled: Tuesday, 10:20 )
Polymer rheology and nonlinear transient elasticity
O. Müller1, M. Liu1, H. Pleiner2, H.R. Brand3
1 Theoretical Physics, University of Tübingen, Germany
2 Max Planck Institute for Polymer Research, Mainz, Germany
3 Theoretical Physics III, University of Bayreuth, Germany
We simplify our previously derived general macroscopic equations incorporating transient elasticity by assuming incompressibility as well as linear response for the dissipation. We take into account terms up to quartic order in the elasticity (3 independent coefficients) and have in addition only two dissipative constants: the shear viscosity and the relaxation time of transient elasticity. This simple model can account for many experimentally observed rheological effects qualitatively and sometimes even quantitatively. Flow phenomena discussed include the Weissenberg effect, overshoot, relaxation spectra and elongational flows. © IWNET 2006
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and Kleanthi for IWNET 2006