Electrorheological Fluids and Complex Systems

Such fluids are just another remarkable example of complex systems – in the broadest sense a crossbreed of simple fluid and anisotropic solid. The phase transition from weakly anisotropic fluids to string fluids (also known as chain fluids) is controlled by strength of the applied external field. A nice snapshot of such string fluids is shown in the figure on the righthand side. The shear resistance in string fluid phase is significantly increased. Therefore, viscosity and other rheological properties are tunable. This, in turn, means ER/MR systems are also smart materials.

String fluids on the molecular level (Monte Carlo simulation snapshot); colors indicate "string-likeness" of neighboring particles: red, yellow: disordered neighbors → green, blue, purple: fully aligned.

In my current work, I focus on the development of models which describe properties of such anisotropic ER/MR-fluids. It is quite impressive in how many different fields of physics such anisotropic fluids can be found, including electrorheological plasmas (see also PK-3 plus and PK-4).

Phases in magneto- and electrorheological systems

Previously, I worked on the determination of phase diagrams of such ER/MR-systems - with a special focus on solid-solid phase transitions. A quite basic and approximate approach, based on the Bogoliubov-Variation, led to some nice results (which are in good agreement with Monte Carlo and molecular dynamics simulations).

Solid phases of ER/MR Systems provide a wide variety of structural phases: fcc, hcp, bcc, bco and bct. So far, we can find three different interaction regimes – each regime is characterized by its behavior. Notably, the soft regime may be a starting point for future industrial applications.

Contact:

Theory Group & Complex Plasmas
Max-Planck-Institut für extraterrestische Physik (MPE)
Giessenbachstr. 1
D-85748 Garching bei München