Ordered Complex Structures Formed by Paramagnetic Particles via Self-Assembly Under an ac/dc Combined Magnetic Field

Abstract

We apply ac and dc magnetic fields simultaneously in orthogonal directions to each other to a solution, in which paramagnetic microparticles are dispersed, and show that complex secondary structures composed of oscillating chain clusters, that is, long linear clusters interconnected by T-, L-, and criss-cross-junctions, are self-assembled. Disklike clusters are formed at some junctions and the number of disklike clusters increases as the frequency of the ac magnetic field increases. We finally show that the angle between long linear clusters can be altered by changing the ratio of the intensities of the ac and dc magnetic fields.

Activity of Lipase and Chitinase Immobilized on Superparamagnetic Particles in a Rotational Magnetic Field

“…Note that a single superparamagnetic particle does not rotate around its center of inertia in a uniform rotational magnetic field and therefore it does not contribute to any increase in the enzyme activity. The value of the control parameter λ was 7.7 in the present case, which was obviously large enough for those clusters to be formed [17]–[21]. The values of the Mason number, at which the activities reached maximum, were, respectively, 6.1×10 −3 (5 Hz) and 8.6×10 −3 (7 Hz) in the cases of lipase and chitinase.…”

“…The values of the Mason number, at which the activities reached maximum, were, respectively, 6.1×10 −3 (5 Hz) and 8.6×10 −3 (7 Hz) in the cases of lipase and chitinase. The clusters were broken even when the Mason number was as low as 6.1×10 −3 and 8.6×10 −3 since the local volume fraction in the clusters was high [18], [21].…”

“…The control parameter, which represents the ratio of viscous drag to magnetic force acting on a cluster in a rotational magnetic field, is the Mason number, which is defined by , where η , ω and M are, respectively, the dynamic viscosity of a solvent, the angular frequency of a rotational magnetic field and the magnetization of a particle. Chain clusters tend to be broken due to viscous drag as the Mason number increases [18]–[21]. In this article, we immobilize lipase and chitinase; enzymes capable of hydrolyzing lipid and chitin [22], [23], on superparamagnetic particles and investigate the effect of the frequency of a rotational magnetic field on the activities of the enzymes.…”

Copper Nanospheres Self‐Propelled into Continuums of Iron Nanoclusters to Fabricate and Engineer Two‐Dimensional Heterometallic Arrays under an External Magnetic Field

“…According to the above results, the secondary structures formed by such moving spheres or clusters may be more complicated under AC‐mode compared to DC‐mode field . This may be due to the various time scales of geometric and magnetic reordering processes within the clusters in comparison to AC‐mode of MFI.…”

Paradigm shift from self-assembly to commanded assembly of functional materials: recent examples in porphyrin/fullerene supramolecular systems

“…Assemblies within confined media often induce high-level alignment and orientations [134,135] that cannot be obtained in unrestricted media. Application of external forces such as electric fields, magnetic fields, and mechanical flows to self-assembling systems can be used to modify the self-assembly motifs [136][137][138]. Guiding and directing procedures of self-assembly are advanced strategies for controlling assemblies of molecules and materials.…”