Berlin 2008 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 18: Soft matter

DY 18.4: Vortrag

Mittwoch, 27. Februar 2008, 15:00–15:15, MA 001

Dynamical Simulations Of Colloids In Optical Tweezers — •Rudolf Weeber and Jens Harting — Institute For Computational Physics, University Of Stuttgart, Pfaffenwaldring 27, D-70569 Stuttgart

Dynamical Simulations Of Colloids In Optical Tweezers Optical tweezers are important tools in the study of colloidal suspensions outside of equilibrium, because they make it possible to perturb the system in a controlled manner. We present simulations of a colloid dragged through both, a colloidal crystal and a polymer suspension using an optical tweezer modeled as a moving parabolic potential. From the behavior of the dragged particle within the trap and the surrounding crystal, dynamical properties like drag forces and the rearrangement of surrounding particles in the suspension are obtained. The simulations for both systems are compared to experiments. For the polymer suspension, we find a linear velocity-force relation. At high polymer concentrations, we find a significant accumulation of polymers in front of the dragged colloid. This leads to an increased drag force, that cannot be explained by the Stokes-Einstein-Relation. For the colloidal crystal, the drag force is non-linear with respect to velocity. Also, the details of the inter-colloid potential play an important role in the velocity-force relation. We also compare two simulation techniques - namely Brownian Dynamics and Stochastic Rotation Dynamics - to evaluate the impact of complex hydrodynamic interactions on these experiments.