Defect Dynamics in Colloidal Crystals Assembled using Time-Varying Magnetic Fields

Time-varying magnetic fields can be used to assemble colloidal crystals. Specifically, rotating magnetic fields supply a continuous energy input that allows for dynamic changes in the crystal microstructure as a result of grain boundary rearrangements. Interfacial shear acts as a mechanism by which voids within the crystal initially act as a sink to dissipate defects, but can also act as sources of grain boundaries due to local energy and microstructure arrangments. In many cased, local rotation induced by shear at the void produces rapid orientational changes before forming a distinct grain boundary that translates through the bulk of the colloidal crystal. This grain boundary propagation either creates grain boundaries that persist or generates a temporary grain boundary that ultimately merges with an existing one, thereby removing a grain and its grain boundary in the process. In both cases,

the grain boundary propagation results from grain growth that occurs as the crystalline portion near the void rotates. This mechanism is similar to the phenomenon in hard-condensed matter where stress-induced grain rotation induces grain growth.