Probing of Field-Induced Structures and Tunable Rheological Properties of Surfactant Capped Magnetically Polarizable Nanofluids

Abstract

Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths.

Dynamic and rate-dependent yielding behavior of Co0.9Ni0.1 microcluster based magnetorheological fluids

“…The response of fluid under magnetic field is attributed to anisotropic, three-dimensional chain-like structures formed parallel to the direction of applied magnetic field. Therefore, MR fluid exhibits changes in viscosity by several orders of magnitude in presence of field [3][4]. As carrier liquid is entrapped in between the fibrous columnar aggregates of magnetized particles, the effective solid phase concentration increases, therefore, the on-state viscosity jumps up manifolds.…”

“…Ferrofluidic systems are colloidal dispersions of superparamagnetic ultra-small (~10 nm) nanoparticles with minimum polydispersity and long term stability [3]. However, very low field-induced mechanical stress limits their usage [6].…”

Ferrofluids: Synthetic Strategies, Stabilization, Physicochemical Features, Characterization, and Applications

“…[225] The magnetorheological properties of oil-based surfactantcapped Fe 3 O 4 FFs synthesized by the coprecipitation method was analyzed. [193] The formation of columnar structures that hinder the flow behavior was confirmed by the increase in both static and dynamic yield stresses under the magnetic field. Besides, the magnetorheology of FFs can be described using the Mason number (MN).…”

“…[210] Other researchers have also predicted the increase in chain length with increasing l by using the Monte Carlo method, the mean-field Fokker-Planck equation, and molecular dynamics. [193] The homogeneity in FF concentration also has a significant role in determining the magnetic dipolar attraction between the particles. López-López et al demonstrated that when ferromagnetic microparticles are immersed in a FF, the expected magnetic dipolar attraction between them disappears owing to a new repulsive force induced by a local inhomogeneity in MNP concentration among the microparticles.…”

“…[238] This was owing to the cluster microstructure consisting of rather small Ni cores surrounded by NiO shells indicating extensive oxidation. [193] Unlike in FFs, magnetoviscosity in MRFs is stronger and the formation of chainlike structures is subjected to a high rate of commercial exploitation. [239] Meanwhile, the magnetoviscosity of FFs has not been much exploited.…”