Binary Colloidal Structures Assembled Through Magnetic Field

The assembly of binary colloidal particle systems of equal size under static and dynamic field isinvestigated through a combination of theoretical calculations and experiments. Under a staticperpendicular magnetic field, by tuning two control parameters including the relative particlemoment and relative particle concentration, many types of diferent structures, such as tiles,chains, and rings were observed. By calculating the potential energy of each structure, a phasediagram is also constructed which can predict which structure will from as a function of the twocontrol parameters and is well consistent with the experimental results. Large clusters of tilephases in the phase diagram (green, blue and red squares) suggest that it is possible to achievelarge size single domain crystals for applications in making novel materials and devices.Under tilted magnetic field, due to the difculties in investigating a large parameter space,the concentration is on the assembly of the commensurate sized particles with equal magneticdipole moment magnitude. By dynamically tilting the external field continuously, the binaryparticle system can form a type of structure with large magnetostriction efect, where thelargest magnetostriction coefcient can be as high as29%. It is much larger than the well-known magnetostriction material Terfenol-D, which is commonly used in engineering such asmagneto-mechanical sensors, actuators, and acoustic and ultrasonic transducers. Also, a specialdimer structure was observed which suggest the existence of various multimer structures. Theformation of these multimer structures can not be predicted by a equilibrium potential energycalculation, but can only be explained by the non-equilibrium kinetics of the phase transition.The significance of the self-assembly of the colloidal systems lies in two categories. First,the assembled structures can be applied in making artificial materials. Second, the colloidalparticles can serve as an ideal system for investigating the behavior of atomic or molecularsystems such as phase transition, defect dynamics.