Rotational diffusion of magnetic nickel nanorods in colloidal dispersions

Abstract

Colloidal dispersions of Ni nanorods were synthesized by pulsed electrodeposition of Ni into nanoporous aluminum oxide layers followed by dissolution of the templates. Geometrical characterization of the nanorods by transmission electron microscopy and scanning electron microscopy allowed us to determine the average length (100-250 nm) and diameter (20-40 nm) of the rods and to estimate the thickness of the polyvinylpyrrolidone surfactant layer. Due to their acicular shape, nanorods of the given size are uniaxial ferromagnetic single domain particles and exhibit a distinct anisotropic polarizability. These two characteristic properties are the physical basis for magnetic field-dependent optical transmission and allow us to investigate the rotational diffusion of the nanorods in liquid dispersion. In the present study, we employed AC magnetization measurements, dynamical light scattering and optical transmission measurements in a rotating magnetic field to determine the rotational diffusion coefficient. The results from all three methods were consistent and agree with theory within a factor of 2.

Directing the orientational alignment of anisotropic magnetic nanoparticles using dynamic magnetic fields

“…The rotational diffusion coefficient determined here is associated with the barrier for rotation around the minor spindle axis in the applied conditions of temperature (RT) and carrier liquid (water) viscosity and relates to a characteristic frequency of n c ¼ D r =p ¼ 29ð1Þ Hz. 25 AC susceptibility measurements are sensitive to a characteristic frequency resulting from a superposition of the barriers for rotation around the minor and major spindle axes. Consequently, the characteristic frequency of n ¼ 160 Hz determined here is signicantly larger than that obtained from depolarized DLS, and comparison of both values indicates a characteristic frequency of rotation around the major spindle axis beyond 200 Hz.…”

Non-chemotoxic induction of cancer cell death using magnetic nanowires

“…Using direct current fields, MNPs can be trapped, concentrated, [11][12][13][14] or used in cell separation. [15][16][17] Under alternating fields, MNPs can be heated 18 or rotated, 19,20 and, in cases of elongated structures, they can transmit forces or torques to whatever they are in contact with.…”

“…Regarding the latter, an issue observed throughout the experiments that could have a strong influence on the results is aggregation of NWs. Currently, protocols are being adapted to coat the NWs with polymers 20 to improve their dispersion. Fundamental studies characterizing the particular type of cell death and its distinctive features as well as analyzing the molecular-biology mechanisms that can be triggered by the treatment, such as Ca 2+ signaling and overexpression of proinflammatory cytokines, would be very useful.…”

Translational and rotational dynamics in suspensions of magnetic nanorods

“…[1][2][3][4][5] An important question related to the properties of the magnetic dispersed phase concerns the effect of the shape of the particles, as colloidal particles are not always spherical and a rod-like shape is quite common. Indeed, magnetic nanorods can nowadays be synthesized from a variety of materials, [6][7][8][9] and experiments of ensembles of such particles already suggest that they display special material properties when compared to those of ferrouids with spherical particles. Examples are enhancements of the magnetoviscous effect, 10 magnetic birefringence 11 and the thermal conductivity.…”