Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Focus: Rheology I (joint focus with DRG)

CPP 35.6: Talk

Thursday, March 29, 2012, 16:30–16:45, C 243

Non-equilibrium Forces between Dragged Ultrasoft Colloids — •Sunil P. Singh, Roland G. Winkler, and Gerhard Gompper — Institute of Complex Systems and Institute for Advanced Simulation,Forschungszentrum Juelich, 52425 Juelich, Germany

Ultrasoft colloids, such as, star polymers, in a suspension strongly interacted with each other under non-equilibrium conditions. Contact of two soft colloidal macromolecules may lead to large conformational changes and significant frictional forces, which determine the macroscopic rheological properties of the fluid. To arrive at an understanding of the non-equilibrium dynamical properties of ultrasoft colloids, we numerically investigate the deformation as well as dynamic frictional forces when two star polymers dragged past each other at constant velocity. We apply a hybrid simulation approach combining with multiparticle collision dynamics method for the solvent, with molecular dynamics simulations for the star polymers. We compute the dynamical frictional forces as function of the drag velocity. At vanishing relative velocity, the equilibrium repulsive force-distance curve is obtained. With increasing drag velocity, this behavior changes and we find an apparent attractive force for departing stars along the dragging direction. The close encounter of ultrasoft colloids leads to significant deformations. This behavior can be traced back to the retardation of polymer relaxation and symmetry breaking of the polymer conformations relative to the mid-plane between the polymer centers.