Project Area B - Soft Matter: Collective dynamics and hydrodynamic interactions in complex fluids.

We study the complex collective dynamics of interacting entities such as colloidal
spheres and rods or molecular machines (e.g., proteins) in a liquid environment.
Due to the size of the dispersed objects ranging from nano- to micrometers, any
inertial effects (both in the liquid and of the suspended objects) are negligible.
Although a liquid in the regime of small Reynolds numbers only allows for simple
laminar flow, interacting objects suspended in it may exhibit complex motional
patterns that we aim to investigate in this project area.
To keep the suspended objects out of equilibrium, they constantly have to be under
the influence of external or internal driving forces to counteract the strong dissipation
in the viscous environment. One advantage of colloidal systems for the following
projects is that they can easily be manipulated by external magnetic, electric, or light
fields including optical tweezers, or by shear forces. In contrast, molecular machines
constantly consume chemical energy and hence operate naturally out of equilibrium.
Light and chemicals are used here to regulate their performance.
The suspended entities are coupled to each other by direct interactions,  e.g., screened
Coulombic, dipolar, and steric forces, or by indirect interactions mediated by the liquid
solvent or capillary forces at water-air interfaces. One prominent example is the hydro-
dynamic interaction due to the flow fields created by the motion of the particles. This
interaction introduces a nonlinear long-range coupling into the equations of motion that
is able to create oscillatory and even transient chaotic motional patterns.

The projects of area B are as follows:

• B1: Structure formation of ferrofluids driven by oscillating magnetic fields. [1]
  
• B2: Collective dynamics in colloidal model systems. [2]
  
• B3: Shear-induced instabilities and structure formation in colloidal nano-rods. [3]
  
• B4: Active microfluidics based on self-propelling molecular machines. [4]