| non-equilibrium systems |
non-equilibrium systems  In many systems that are dealing with soft matter the particles of interest are immersed in fluids. Therefore, a thorough understanding of the interplay between the mechanical properties of the molecules, like bending or twisting, and the hydrodynamics are important. In the past we have predicted several novel effects that are caused by a coupling of flexibility and hydrodynamic interactions, where we concentrated on semiflexible filaments. For example, these filaments show orientation effects in the sedimentation processes. In the low Reynolds number regime propulsion mechanisms, for example swimming bacteria, are very different from our daily experience. We investigated a propulsion mechanisms consisting of a rotating filament which leads to a repulsion. Also problems like the pumping of liquids with grafted polymer chains with possible applications in the field of microfluidics are addressed. In a recent research project we investigated the unfolding of a collapsed protein in the shear flow of a blood vessel, in close collaboration with an experimental group at the University of Augsburg. related publications: |
|
|
|
|
polymer-surface interaction In recent AFM experiments, it has been shown that the lateral mobility of a polymer on a solid surface crucially depends on the experimental conditions such as ionic strength, pH, etc. (C. Friedsam, private communication; F. Kühner et al., Langmuir, accepted 2006). Thus, in certain regimes polymers virtually stick laterally on the surface while in others they are able to rearrange on microsecond time scales. Using a simplistic rod model, we propose a series of experiments how to measure the friction of a single polymer on a solid substrate using common AFM technology. We are currently also investigating the mechanism and the microscopic origin of polymer friction, see also water section. related publications: |
|
|
|
|
microhydrodynamics  Hydrodynamics at low Reynolds number as relevant for most sub-micron scale objects show distinct features that are not present at the intermediate and high Reynolds number situations we are used to in normal life. In the regime of low Reynolds numbers, inertia is negligible and viscous forces are dominating (suggested reading: E. M. Purcell, A. J. Phys. 45, 3 (1977)). As moving objects in a viscous medium will drag the fluid along with them, this will lead to hydrodynamic interactions between different particles since the objects will move along with the fluid field. To account for these HI, the correct fluid field has to be calculated. In our approach, this is done by using the proper Greensfunction which satisfies the boundary condition of the respective problem. The effect of stochastic processes at finite temperatures are taken into account in a coarse grained fashion using the langevin approach. With these methods we are able to model non-equilibrium situations like polymers which are subject to external fields. |
|