Field-induced columnar structures in a quasi-two-dimensional system of dipolar particles

Abstract

We study the formation of columnar structures of uniaxial dipoles in an external magnetic field both experimentally and theoretically. By applying an external magnetic field parallel to a thin layer of a magnetorheological fluid, we manipulate a single initial cluster of suspended colloidal particles. We find that the cluster breaks up into columns that have approximately uniform widths and intercolumnar spacings. Both the average column width and inter column spacing are observed to vary linearly with column length. The observed linear relationships between column width and spacing versus the column length are interpreted theoretically by computing the potential energy of an ensemble of closed-packed columns of spherical dipolar particles.

Suppressing the Rayleigh–Plateau Instability in Field-Directed Colloidal Assembly

“…Suspensions of dispersed, polarizable colloids typically follow a process of aggregation, coarsening, and arrest in an external field. When the induced dipole–dipole interactions between particles are much stronger than their thermal energy, the particles rapidly form chains parallel to the field. − Interactions between the particle chains lead to further coarsening, − but lateral aggregation eventually halts; particles in the structure are highly localized, and the suspension remains trapped in a system-spanning network that resists further relaxation. This percolated microstructure can be advantageous in smart materials that require rapid changes in viscoelastic properties and underlies the field-responsive fluid–solid transition of electro- and magnetorheology…”

Dynamic Self‐Assembly of Magnetic/Polymer Composites in Rotating Frames of Reference

“…However, these columns are ill‐shaped and at the relatively low value of ω used, they are “pinned” to the bottom of the tube (similar to columns observed in a static system described in ref. ). It is only in the intermediate regime of the field strength (when the magnet is ≲5 mm < d ≲ 10 mm away from the tube; image III) that the drag force of the viscous fluid can overcome the “pinning” and the organizing aggregates can start moving with the rotating fluid.…”