8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.152Wed 711:10-14:00Non-equilibrium forces between dragged ultrasoftcolloidsSunil P. Singh, 1 Roland G. Winkler, 2 and Gerhard Gompper 11 Institute of Complex Systems 2, Forchungszentrum, Juelich 52425, 52425, Juelich,Germany2 Institute for Advanced Simulations, Forschungszentrum, Juelich, GermanyStar polymers exhibit polymer-like as well as colloid-like features. Their properties are stronglyaffected by their functionality, i. e. , the number of polymer arms connected to a commnoncenter. At high functionality, a star polymer behaves like an ultrasoft colloid and its shape isalmost spherical. Under non-equilibrium conditions, these colloids may strongly interact witheach other, and show large conformational changes and dynamical frictional forces. For a detailedunderstanding of the flow behavior of colloidal suspensions, insight into the dynamical interactionis important. We numerically investigate the deformation of ultrasoft colloids as well as thedynamic frictional forces, when one colloid is dragged past another at constant velocity. Toincorporate proper hydrodynamic interactions in simulations, we use the multiparticle collision(MPC) dynamics technique, a particle-based mesoscopic simulation method [1, 2]. We computethe dynamic frictional forces as function of the drag velocity. The effect of the drag velocityon the interaction between the stars is weak when the stars approach each other; however, theequilibrium repulsion changes qualtitatively into an effective attraction during separation. Thiseffect decreases with decreasing drag velocity, and the quasi-static limit is reached for smalldrag velocities. The close encounter of ultrasoft colloids leads to a strong deformation andan asymmetric shape. This deformation is investigated as function of drag velocity, minimumdistance between star centers, and polymer arm length.[1] R. Kapral, Adv. Chem. Phys. , 140, 89 (2008).[2] G. Gompper, T. Ihle, D. M. Kroll, and R. G. Winkler, Adv. Poly. Sci. 221, 1 (2009).152