(471c) Precise Magnetic Manipulation of Anisotropic Microcylinders

Micro/nano-sized magnetic Janus particles (MJPs) are potentially useful in areas of display, sensor, tunable viscosity liquid, drug delivery, and separation. The prerequisites of those applications include the precise preparation and controllability of desired MJPs, of which shape and size, as well as compartmentalization can affect magnetic response and self-assembly. The availability of a variety of anisotropic MJPs enables detailed experimental studies of cooperative organization in magnetic fields.

To obtain micron-sized anisotropic particles with highly defined magnetic compartments, we employed electrohydrodynamic (EHD) co-jetting, a method recently reported for the preparation of multicompartmental microcylinders [Angew. Chem. Int. Ed. 2009, 48, 4589?4593; JACS, 131, 19, 6650?6651]. Here we expand this initial work to prepare magnetic anisotropic microcylinders/disks with different magnetic compartmentalization. Moreover, this technological approach enabled preparation of multicompartmental particles with a range of different aspect ratios. First, to confine a specific magnetic compartmentalization in this study, a magnetite (Fe₃O₄, 30nm in diameter) suspension in a polymer solution (poly(lactide-co-glycolide), PLGA) was introduced into correspondingly configured jetting fluids in the process of EHD co-jetting. Following cryo-sectioning of the microfibers with diameters between 20 - 25 µm, anisotropic microcylinders/disks with different magnetic compartments were readily available.

Associated for controlling MJPs' directionality, a single external magnet is used to rule various conventional rotational motions of magnetic Janus microcylinders/disks, which is very simple to be useful for a practical application. A flipping motion of magnetic Janus microcylinder against the dipole axis is also achieved by applying a second magnetic field. Dissimilarity in rotational and translational behaviors between MJPs with two different aspect ratios were observed under the same magnetic field directions; probably due to shape and size differences. Difference in shape anisotropy between magnetic Janus microcylinders and microdisks caused self-assembly into staggered chain forms in a different way. Finally, by utilizing the fact that shape and size anisotropy of MJPs results in different magnetic rotational locomotion, a simple separation process between magnetic Janus microcylinders and microdisks was demonstrated.