(401e) Aggregation of Two-Dimensional Microparticle Structures in Ferrofluids

Under the influence of an external magnetic field, magnetic microparticles can be directed to assemble into linear chains. We have shown that once these linear chains are formed, these chains can be cross-linked to form permanent structures that can then be manipulated through external magnetic fields. Conversely, chains of nonmagnetic particles can be formed when they are placed in a ferrofluid medium and subjected to a magnetic field. In a magnetized ferrofluid, these nonmagnetic particles form ?magnetic holes? that aggregate similarly to magnetic particles in nonmagnetic mediums.

In ferrofluids, the magnetic dipole of any particle is proportional to the difference of the susceptibility of the particle and the susceptibility of the fluid. Thus, particles with susceptibilities smaller than that of the medium acquire dipoles of direction opposite that of the field while particles with susceptibilities larger than that of the fluid have dipoles in the same direction as the field. Two particles with parallel dipoles align in a head-to-tail fashion along the direction of the field and particles with dipoles that are antiparallel will align in the direction perpendicular to the magnetic field.

By creating systems with particles of different susceptibilities we are able to form structures in two-dimensions, which offers a step forward in creating complex systems. In this talk, we will describe the mechanisms by which these structures are created and the different structures that are formed by mixing magnetic and nonmagnetic particles together in a ferrofluid.