(40b) Directed Assembly of Paramagnetic Colloids in Time-Varying Magnetic Fields

Micron-sized superparamagnetic colloids placed in time-varying magnetic fields can provide us with rich dynamic behavior depending on the magnetic field applied and the particle concentration. In symmetric magnetic fields, a long-range attractive potential is induced resulting in the formation of colloidal clusters, which assemble into circular shapes that exhibit fluid-like behavior at relatively low fields, while becoming crystallized and highly ordered at higher field strengths. The self-assembly of these “colloidal atoms” has led to new insights regarding the dynamics phase transitions in two-dimensions. In particular, we have examined how tuning the “softness” of the interaction potential leads to interesting interfacial dynamics, as shown by coalescing clusters.These systems exhibit interesting coarsening and spinodal decomposition structural transitions for larger particle systems.

By utilizing a time-varying fields, interesting far-from-equilibrium behavior is observed. The questions addressed here involve identifying the effects of complex time-varying field conditions on the assembly structure and dynamics.