(349a) Dynamics of Colloidal Droplets Under Rotating Magnetic Fields

Micron-sized paramagnetic colloids in a AC magnetic field can be used to form 2-D droplets-like structures. By changing the magnetic field strength, we change the interaction energy, leading to the formation of droplets of different phases - such as a fluid or crystal - that grow and coalesce. We characterize these droplets at quasi-equilibrium and quantify their structure to show how the bulk phase differs from the interface, which depends largely on the interaction energy between the particles that make up the cluster. We also determine the stability of these colloidal, clustered, droplets by calculating their energy using a modified dipolar model and measuring the surface excess energy. We look at the fluctuation of the interface and use Fourier analysis to measure interfacial tension and compare the results to the stability found using surface excess energy. We also capture the dynamics of grain boundaries that form as a result of their coalescence with other droplets and compare these dynamics to colloidal droplets of different sizes and phases.