Brownian Dynamics Simulations of Magnetic Nanoparticles Captured in Strong Magnetic Field Gradients

Abstract

The behavior of spherical single-domain magnetic nanoparticles in strong inhomogeneous magnetic fields is investigated through Brownian dynamics simulations, taking into account magnetic dipole–dipole interactions, repulsive hard-core Yukawa potential, hydrodynamic particle-wall interactions, and the mechanism of magnetic dipole rotation in the presence of a magnetic field. The magnetic capture process of nanoparticles in prototypical magnetic field gradients generated by a sudden reversal in perpendicular magnetization of a flat substrate (defining a “capture line”) is studied as a function of strength of the magnetic field and volume fraction of the magnetic nanoparticles. Capture curves show a regime where capture follows a power law model and suggest that particles with the Brownian relaxation mechanism are captured at a slightly faster rate than particles with the Néel relaxation mechanism under similar conditions of the field gradient. Additionally, evaluation of the shape of the aggregates of captured particles suggests that greater dipole–dipole interactions result in aggregate structures that are flatter/wider than in the case of negligible dipole–dipole interactions. These results can help guide the design of systems for magnetically directed assembly of nanoparticles into complex shapes at a substrate.

Kinetics of Low Field Gradient Magnetophoresis in the Presence of Magnetically Induced Convection

“…This phenomenon is further supported by computation simulation of the dynamical behavior of MNPs under an externally applied magnetic field. For instance, by performing simulations based on Brownian dynamics, Langevin dynamics and the on-the-fly coarse grain model, MNP aggregates were formed under a magnetic field. In ref , magnetophoretic velocities as large as several centimeters per minute were observed for concentrated dispersions (∼10 g/L) of superparamagnetic colloidal particles (with diameters of 200 and 400 nm) under a magnetic field gradient of 30–60 T/m.…”

Correlation of simulation/finite element analysis to the separation of intrinsically magnetic spores and red blood cells using a microfluidic magnetic deposition system

“…We are further assuming that magnetic susceptibility is an average value of the molecular contributions of Mn atoms within the spores, or the hemoglobin molecules in the RBC’s. This is in contrast to recent models for magnetic separation of nanoparticles which takes into consideration Neil relaxation mechanism or a Brownian mechanism which are proposed to reduce the effective magnetic moment (Zhao et al 2017). With these assumptions, Equations 1 and 2 can combined to give: Fmagtrue⇀=χV∇Btrue⇀2μ0=χVSmtrue⇀…”

“…The arrows in the upper magnetic energy plot indicated the direction a cell, with a magnetic susceptibility greater than the suspending buffer, will experience a magnetic force contributions of Mn atoms within the spores, or the hemoglobin molecules in the RBC's. This is in contrast to recent models for magnetic separation of nanoparticles which takes into consideration Ne'el relaxation mechanism or a Brownian mechanism which are proposed to reduce the effective magnetic moment (Zhao, Torrws-Diaz, Velez, Arnold, & Rinaldi, 2017). With these assumptions, Eqs.…”

Magnetic Response of a Charged Brownian Particle Under the Action of Two AC Drive

“…We consider the dynamic of a charged Brownian particle with charge e in a two dimensional harmonic well in the presence of two ac drives along both x and y direction with a phase difference φ between them and an additional linear velocity dependent force f s(1 − v v0 ), where v 0 is the autonomous velocity [20] in both x and y direction. The motion of such a particle including inertia is described by the Langevin's equation of motion [3,4,18,[21][22][23]…”