Magnetoviscosity in dilute ferrofluids from rotational Brownian dynamics simulations

Abstract

Ferrofluids are suspensions of magnetic nanoparticles which respond to imposed magnetic fields by changing their viscosity without losing their fluidity. Prior work on modeling the behavior of ferrofluids has focused on using phenomenological suspension-scale continuum equations. A disadvantage of this approach is the controversy surrounding the equation describing the rate of change of the ferrofluid magnetization, the so-called magnetization relaxation equation. In this contribution the viscosity of dilute suspensions of spherical magnetic nanoparticles suspended in a Newtonian fluid and under applied shear and constant magnetic fields is studied through rotational brownian dynamics simulations. Simulation results are compared with the predictions of suspension-scale models based on three magnetization relaxation equations. Excellent agreement is observed between simulation results and the predictions of an equation due to Martsenyuk, Raikher, and Shliomis. Good qualitative agreement is observed with predictions of other equations, although these models fail to accurately predict the magnitude and shear rate dependence of the magnetic-field-dependent effective viscosity. Finally, simulation results over a wide range of conditions are collapsed into master curves using a Mason number defined based on the balance of hydrodynamic and magnetic torques.

Ferrohydrodynamic modeling of magnetic nanoparticle harmonic spectra for magnetic particle imaging

“…However, this equation has been shown to be inaccurate in predicting the magnetoviscous response of ferrofluids at moderate field magnitude and frequency. 19,20 For fields comparable to those employed in the MPS, another magnetization equation (the MRSh equation) was derived microscopically from the Fokker-Planck equation by Martsenyuk et al 12 They employed an effective-field method, which resulted in closure of the first moment of magnetization, resulting in…”

A Simulation Study on the Specific Loss Power in Magnetic Hyperthermia in the Presence of a Static Magnetic Field

“…In this case, Equation (1) is reduced to Equation (2), which can be easily solved using convolution integral as shown in Equation (8). Although Equation (2) appears to be valid in considering the magnetic hyperthermia with small MNPs in the superparamagnetic state and we believe that this study will provide the basis for establishing the effectiveness of such magnetic hyperthermia, it will be necessary to solve Equation (1) without any assumptions or another magnetization equation derived microscopically from the Fokker-Planck equation [12] for more detailed analysis. These studies are currently in progress.…”

“…In this study, we derived Equation (12) by solving the magnetization relaxation equation of Shliomis [14] (Equation (1)) with an assumption that there is no bulk flow and the magnetization of MNPs and magnetic field are collinear. In this case, Equation (1) is reduced to Equation (2), which can be easily solved using convolution integral as shown in Equation (8).…”

“…Rosensweig's model [6] has often been used for the estimation of SLP. His model, however, is based on the so-called linear magnetization assumption [12], and thus it is said that his model is strictly valid only in the limit of small amplitude and frequency of AMF. Recently, we have presented three methods for estimating SLP and compared the SLP values estimated by the three methods under various conditions of MNPs and AMF [13].…”

Microcapillary flow behavior of magnetic nanofluids in the presence of plate shaped bentonite particles

“…The flow behavior of such magnetic nanofluid is complex; the complexity depends on induced dipolar interactions between the particles, and anisotropy of the particles. Under the effect of magnetic field, this fluid produces magnetoviscous effects [1][2][3][4][5][6][7][8][9][10][11]. Dispersion of micron size magnetic particles/ non-magnetic particles in magnetic nanofluids produces magnetorheological (MR) fluids [12][13][14][15][16][17][18].…”