Self-Assembling Chains, Rings and Droplets in Dipolar Granular Fluids

Daniel Blair, Arshad Kudrolli

We visualize the distinct phases of magnetized steel particles in a container vibrated along with non-magnetized
particles that act as thermal carriers. Transition from a gas-like to a liquid-like phase is observed as the vibration
amplitude is decreased. Clusters of magnetized particles are found to spontaneously self-assemble and grow as the
surrounding free particles are exponentially depleted to a saturation value determined by the temperature and volume
fraction. These clusters are initially extended chains that eventually coarsen into compact droplets with fractal
dimension d = 1.5\pm 0.1. These experiments clarify the nature of clusters formed in the context of the dipolar hard
sphere model. We also investigate the connection between clustering of dipolar hard spheres and the behavior of systems
undergoing first order phase transitions.