Polycrystal Annealing and Solid-Solid Phase Transitions in Colloidal Crystals Under a Flow

We experimentally drive NIPA microgel colloidal crystals under a sinusoidal oscillation and studied their polycrystal annealing, grain-boundary melting and solid-solid transitions. The oscillation anneals grains into larger sizes via step-by-step grain rotations or via grain boundary melting and recrystallization. The grains grow as a power law and become faster at stronger oscillations . The lattice orientations of the resulted grains tend to align along the flow. At higher volume fraction but below the equilibrium melting point, the shear induces melting from grain boundaries. Under appropriate volume fraction and wall confinement thickness, the shear drives the thin-film square lattice into a triangular lattice via a melting and recrystallization process.