Structure and dynamics of two-dimensional colloidal systems in circular cavities

Abstract

The properties of 2D colloidal crystals have been widely investigated over the last 20 years. Recently, it has been recognized that colloids are also useful for the investigation of systems comprised of only a few particles. We study the melting behaviour of a finite number (N < 30) of paramagnetic colloidal spheres (b = 4.5 mm) in 2D circular cavities. By applying a magnetic field, B, the interaction strength between the particles is varied. At high B, i.e. strong dipole interaction, the particles are arranged in a highly ordered shell-like structure. With decreasing B we observe a loss of angular order between adjacent shells. Upon further reduction of the external field, however, different scenarios are observed. For cavities with hard-wall confinement potentials. In both cases the system melts completely for small magnetic fields.