## Colloids in two dimensions: fluids, crystals and quasi-crystals

By: Roland Roth

From: University Erlangen

At: Instituto de Investigação Interdisciplinar, Anfiteatro

[2010-10-06]

The properties of two dimensions systems are of general interest in statistical mechanics and are studied in great detail both in theory and experiment. Colloids in two dimensions are model systems that can be studied experimentally e.g. by video microscopy and theoretically e.g. by classical density functional theory (DFT), a theory that allows one to study thermodynamic properties and the structure of a system in various phases on equal footing. Using a density functional theory approach based on fundamental measure theory I consider two systems. First I present some aspects of the fluid phase of a binary mixture of hard disks. If the ratio of the radii of the small and the big disks is sufficiently asymmetric, the bulk correlation functions of the mixture can display a sudden change in the wavelength of oscillations when the so-called structural crossover line in the phase diagram is crossed. This effect was predicted and first studied within the framework of DFT and recently verified experimentally with dense colloidal suspensions. In the second part I consider a model of charged disks with a density sufficiently high that the system freezes. If the system is subjected to an external field with five-fold symmetry an interesting competition between the symmetry of the free crystal and that of the external field can be observed.