Sharpening the surface of magnetic paranematic droplets

Abstract

In a non-uniform magnetic field, the droplets of colloids of nickel nanorods and nanobeads aggregate to form a cusp at the droplet surface not deforming the entire droplet shape. When the field is removed, nanorods diffuse away and the cusp disappears. Spherical particles can form cusps in a similar way, but they stay aggregated after the release of the field; finally, the aggregates settle down to the bottom of the drop. The X-ray phase contrast imaging reveals that nanorods in the cusps stay parallel to each other without visible spatial order of their centers of mass. The formation of cusps can be explained with a model that includes magnetostatic and surface tension forces. The discovered possibility of controlled assembly and quenching of nanorod orientation under the cusped liquid surface offers vast opportunities for alignment of carbon nanotubes, nanowires and nanoscrolls, prior to spinning them into superstrong and multifunctional fibers. Magnetostatic and electrostatic analogies suggest that a similar ideal alignment can be achieved with the rod-like dipoles subject to a strong electric field.

Nanostructured Soft Matter with Magnetic Nanoparticles

“…Magnetic nanorods in nonuniform magnetic field experience forces that are proportional to the magnetic field gradient, magnetic properties of the material, and size of the nanorods. X‐ray contrast imaging experiments were conducted to reveal the behavior of nickel nanorods under the influence of a magnetic field gradient ( Figure ) . A droplet of nickel nanorod dispersion was placed on a Teflon surface and the magnet was moved towards the droplet using a computer controlled linear stage.…”

“…g) Vertical component of magnetic field along three dashed lines in Figure a. Reproduced with permission . Copyright 2014, Royal Society of Chemistry.…”

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

“…In applications to manufacturing of high density recording films and discs, spin alignment is required to carry the recorded information when spins in magnetic nanorods are prone to align parallel to the nanorod axis . In optical applications, magnetic liquid crystals are attractive candidates for making reconfigurable magnetooptical devices with the fast time response measured in milliseconds …”

Magnetospinning of Nano‐ and Microfibers

“…The susceptibility and magnetization are each known only up to an order of magnitude, with χ ≈ 10 −3 and M ≈ 10 6 A m −1 ; fitting the resulting curve to the data predicts χM 2 /( χ + 3) ≈ 6 × 10 9 A 2 m −2 , which provides a quantitative parametric prediction for the upper bound in the phase plane where nanofiber spinning is prohibited, which agrees well with the experimental results (Figure d). We note that Tokarev et al provided a force diagram and a scaling law for the initial radius of the liquid bridge following a successful transition.…”