Exploring the limits of cooperative phenomena using complex plasmas

With the advancing miniaturization of technological applications, processes on the mesoscale become increasingly important. This is the scale where the individual movement of particles transforms into cooperative behavior-behavior that cannot be explained by investigating the motion of individual particles alone. Complex plasmas are ideally suited to study the limits of cooperative behavior [1]. The time scales of the dynamics of the microparticles embedded in the plasma are such that their movement can be fully resolved, and an investigation on the atomistic (kinetic) level is possible. In addition, complex plasmas can be considered a model system for ordinary fluids: The internal microparticle dynamics is basically undamped and is characterized by the similarity parameters matching those of other fluids. This similarity does not break down even at small scales: For instance, in [2], microparticle droplets comprised of only a few 1000-10000 particles were examined. In these experiments, the Weber number (the ratio of inertia to surface tension forces) matches that of falling water drops. As another example, the onset of a Rayleigh-Taylor instability in a complex plasma can be described by the ordinary dispersion relation, even at scales of only few particle layers. This allows investigating the "nanoscale" of fluid flows, and, hence, the limits of cooperative behavior.