How chains and rings affect the dynamic magnetic susceptibility of a highly clustered ferrofluid

Abstract

The dynamic magnetic susceptibility, χ(ω), of a model ferrofluid at very low concentration (volume fraction approximately 0.05%), and with a range of dipolar coupling constants (1 ≤ λ ≤ 8), is examined using Brownian dynamics simulations. With increasing λ, the structural motifs in the system change from unclustered particles, through chains, to rings. This gives rise to a nonmonotonic dependence of the static susceptibility χ(0) on λ, and qualitative changes to the frequency spectrum. The behavior of χ(0) is already understood, and the simulation results are compared to an existing theory. The single-particle rotational dynamics are characterized by the Brownian time, τB, which depends on particle size, carrier-liquid viscosity, and temperature. With λ ≤ 5.5, the imaginary part of the spectrum, χ (ω), shows a single peak near ω ∼ τ −1 B , characteristic of single particles. With λ ≥ 5.75, the spectrum is dominated by the low-frequency response of chains. With λ ≥ 7, new features appear at high frequency, which correspond to intracluster motions of dipoles within chains and rings. The peak frequency corresponding to these intracluster motions can be computed accurately using a simple theory.

Stability of an inhomogeneous ferrofluid in a channel, subject to a normal field

“…Under the quasi-equilibrium approach, the magnetization relaxation time of the particles in the FF is much less than the time scale of the hydrodynamic processes of interest [24], and therefore magnetoviscous effects are consistently ignored in this paper. For further discussion of magnetoviscous effects see for example [2,25,26] and [27].…”

Correlating the Dipolar Interactions Induced Magneto‐Viscoelasticity and Thermal Conductivity Enhancements in Nanomagnetic Fluids

“…Reproduced with permission. [ 206 ] Copyright 2021, American Physical Society publications. Reproduced with permission.…”

“…(ii) From (a-d) theoretical and simulation results following the same behavior in the absence of magnetic field, as the 𝜆 ≥ 1 (coupling constant). Reproduced with permission [206]. Copyright 2021, American Physical Society publications.…”

Magneto-Mechanical Approach in Biomedicine: Benefits, Challenges, and Future Perspectives

“…In the ideal case, the maximum of coincides with at ωτ B = 1 (or ω = τ B −1 ), which is a characteristic of a single MNP; however, if the dipolar coupling of the MNP is large (chain, rings), then ωτ B < 1 [ 38 ]. In this regard, for each type of MNP, a critical frequency ω C is introduced.…”