Research Interests

Interaction of colloidal particles with a wall

In order to understand the phenomena described in the sections below on a microscopic level, it is necessary to obtain a quantitative picture of the interaction potential of the colloidal particles with the interface. Using, Total Internal Reflection Microscopy (TIRM) it is possible to measure electrostatic interaction potentials, van der Waals potentials and depletion forces as well as attraction potentials between receptor-ligand pairs of proteins. We used TIRM to measure the depletion potentials for a variety of systems. Currently we are investigating possibilities to tune depletion interactions by flow fields, and we attempt to study the non-specific interaction between proteins.

Dynamics at interfaces

The dynamics of colloids in solution is affected by the presence of a solid interface by the mutual hydrodynamic interaction between the particles and the wall. It was theoretically known for a long time that the translational diffusion coefficient of spheres parallel to a nearby interface is different from that in the direction perpendicular to the interface. However, only recently we were able to provide a qualitative experimental verification of these predictions. Similarly, we confirmed that the rotational diffusion of colloids is slowed down and anisotropic, if they come close to an interface. Currently we are investigating the influence particle concentration, long range interactions and shear fields on the wall hydrodynamic effect.

Self – assembly of colloids driven by interfaces

Interfaces represent regions in which the symmetry of the interparticular force field is severely perturbed. This can be exploited to drive the phase behaviour of complex fluids. A wide spread application of this effect can be found in liquid crystal displays. Among others, we have shown experimentally that also the phase behaviour of colloidal suspensions in the ultimate vicinity of an interface is different from the bulk. Currently we are investigating the possibility to induce desired structural transitions of nano-colloidal suspensions by a wall or a liquid/liquid interface. Further the effect flow and shear to promote or suppress such transitions is investigated.

Education / Work experience

since Oct. 2000	Staff Member at the Forschungszentrum Jülich GmbH, Institute of Complex Systems
since 2017	Project manager of the European Soft Mater Infrastructure (EUSMI)
2012 – 2016	Scientific coordinator of the Marie Curie Initial Training Network Soft Matter at Aqueous Interfaces (SOMATAI).
2011 – 2016	Project manager of the European Soft Mater Infrastructure (ESMI)
2005	Private lectureship at the Heinrich-Heine-Universität in Düsseldorf, Germany
1992 – 2000	Scientific staff at the Physical chemistry department of the Technische Universität Berlin, where he accomplished his Habilitation in 1999.
1999	Habilitation in Physical Chemistry at the Technische Universität Berlin, Germany
1991 – 1992	Post-doc at the Kyoto Institute of Technology in Kyoto, Japan
1989 – 1992	PhD student at the Albert-Ludwigs-University in Freiburg, Germany
1987 – 1989	PhD student at the University of Rome “La Sapienza”
1981 – 1987	Study of Chemistry at the Albert-Ludwigs-Universität in Freiburg, Germany