Colloids: Mesoscopic model systems of matter on a nano scale

Colloidal suspensions consist of small particles in (mostly) aqueous medium, which allow to model phenomena in condensed matter on a mesoscopic scale. Due to the dominant length and time scales such systems are readily accessible by means of video microscopy. In this talk examples for both the structure of colloidal particle ensembles and transport phenomena in colloidal systems will be discussed. In the case of structure formation, e.g., configurations of particles with a mesoscopic "spin" will be presented, realized by colloidal spheres with permanent magnetic caps, which allow one to model the spin configurations of magnetic clusters. The transport investigations focus on phenomena in narrow channels and on "active swimmers", i.e. capped magnetic particles which are propelled through the surrounding liquid by a catalytic reaction and can be steered by an external magnetic field.