Magnetoacoustic Assembly of Colloidal Alloys

Self-assembly of microstructures has become a widely used assembly technique due to its high efficiency and low cost. This methodology depends on the spontaneous formation of lattices, and does not require special instruments. Different approaches have been developed in order to induce the self-assembly interaction of particles. Among them magnetic field induced assembly has advantage in controllability and versatility. Previously we applied a uniform field to magnetic and non-magnetic microspheres dispersed in ferrofluid solution, and changed the ferrofluid concentration as a parameter to realize the assembly of different structures including square, honeycome and kagome lattices. In this work we enhance this approach by adding acoustic field to the system. By combining both magnetic and acoustic fields, large lattices were achieved and new structures such as quasi- 3D, and closed packed super-structured rings were observed. In addition, when we used epoxy to achieve solid boundary, standing waves were generated to assemble particles into regular patterns on the macro-scale while preserving the micro-structures. We also used a pair of piezoelectric transducers and modified their phase difference and frequency to change the assembly position of particles. To our knowledge, this is the first example of multi-scale self-assembly technique by using a combination of acoustic and magnetic fields.