Low Magnetic Field Response in Ferronematics

Abstract

In this work the 4-n-hexyl-4 -cyanobiphenyl liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements. Influence of the shape of magnetic particles on magnetic Fréedericksz transition depends on the type of anchoring, which is characterized by the density of the anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. It was observed that in the case of doping with spherical particles, the critical magnetic field is shifted to higher values with increase of volume concentration of the magnetic nanoparticles but decreases with increase of biasing voltage. In the case of doping with rod-like particles, the critical magnetic field is almost independent of the volume concentration of the magnetic nanoparticles.

Orientational self-assembly of nanoparticles in nematic droplets

“… 12,16 A rough estimate has also been deduced from these measurements for the anchoring energy density: ∼10 −2 N m −1 (strong anchoring) for 6CHBT 12 and ∼10 −8 N m −1 (weak anchoring) for 6CB. 16 Therefore, the above-described AFM observations are surprising: having the same orientation of n at the surface of NPs for both 6CHBT and 6CB LCs, the different orientations of NPs in 6CHBT and 6CB colloidal droplets obviously cannot be explained by the anchoring at the LC–NP interface exclusively. Therefore, the orientation of n on the supporting mica substrate has also been analysed.…”

“…In 6CB-based LC colloids, the anchoring of n parallel to the long axis of NPs, 16 together with the homeotropic anchoring of 6CB molecules at the mica surface [ Fig. 5(b) ], results in a robust orientational self-assembly of the long axis of the particles perpendicular to the substrate.…”