Project B1: Structure formation of ferrofluids driven by oscillating magnetic fields.

In this project we plan to investigate the nonlinear dynamics of ferrofluids
under the influence of time-dependent magnetic fields. The dipole-field
coupling drives the particles constantly away from equilibrium. Nonlinearity
occurs through the 1/r³ dependence of the dipolar interactions and through
the hydrodynamic interactions. We will mainly employ computer simulation
techniques such as Molecular Dynamics, Brownian Dynamics, and simulations
with additional hydrodynamic interactions. As a long-term goal we further aim
to develop an effective description using concepts of dynamic density functional
theory. In a first step we will focus on the microstructure in an oscillating field.
The effect of such fields on the stability of the self-assembled chain-like
assemblies has so far been studied only experimentally. A particularly important
quantity is the time-dependent structure factor, which can be measured via
suitable SANS techniques. A further focus will be to understand the impact of
rotating fields. The latter have been shown, both experimentally and theoretically,
to induce novel pattern formation effects such as layering and formation of labyrinth
structures in the related system of magnetorheological fluids. Comparing simulations
with and without hydrodynamic interactions we will explore the effect of the solvent on
the dynamics of the magnetic particles. Further issues concern the magnetic response
and the possibility of field-induced crystallization (or other phase transitions).

Project leaders: Prof.Dr.  S. Klapp [1],   Prof.Dr.  H. Stark [2]