Beschreibung

vor 18 Jahren
The dynamics of single semiflexible polymers in solution under the
influence of an external field are investigated with Brownian
Dynamics simulations. Hydrodynamic interactions are included on the
Rotne-Prager level and proof to be essential. Model equations are
used to derive scaling laws. The work consists of five projects
that are distinct but closely related to each other: In the first
project, a neutral semiflexible particle is moved by centrifugal or
gravitational forces relative to quiescent fluid. A coupling
between hydrodynamic interactions and flexibility leads - depending
on the elastic parameters - to a rod orientation perpendicular to
the external field. This coupling is also investigated for a
filament that is rotated at one end by some external torque (second
project). Above a critical torque the filament folds itself around
the rotational axis, with important consequences for the propulsion
with a nano-machine. The third project deals with flexible polymers
in an ultracentrifuge where a novel compactification and unfolding
scenario is predicted: The established theories on sedimentation
use the preaveraging approximation of the hydrodynamic interactions
and cannot explain the polymer configurations at high fields
consisting of a dense head and a long tail, which make a new
efficient separation technique possible. In the forth project, the
diffusion of charged semiflexible polymers under different salt
conditions is treated. Ions are included explicitly and not on a
mean-field level. The theory of electrolyte friction for spherical
objects is qualitatively extended to semiflexible polymers. A
heuristic formula for the diffusion constant over the whole range
of persistence lengths is proposed. In the final project, the
hydrodynamic orientation mechanism found in the first project is
suggested as a possible source of anomalous electric birefringence
which is observed for rod-like polymers. It is compared with the
competing parallel induced dipole orientation. The dependence of
the polarizability on rod length, salt and polymer concentration is
clarified.

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