Sedimentation stability and rheological properties of ionic liquid–based bidisperse magnetorheological fluids

Abstract

The sedimentation stability and rheological properties of ionic liquid-based magnetorheological fluids comprising a mixture of micron-and nano-sized particles were experimentally studied. Three different fluids with the same total particle concentration of 15 vol% were prepared for testing: one containing only microparticles and two others in which 5 or 10 wt% of the microparticles were replaced by nanoparticles. The nanoparticles were surface stabilized against oxidation. For comparison purposes, silicon oil-based magnetorheological fluids with similar solid fractions were also prepared and tested. The results indicate that, with ionic liquid as a carrier fluid, the addition of nanoparticles at 10 wt% reduces the sedimentation rate almost by an order of magnitude from that without nanoparticles, while the reduction in the dynamic yield stress is only marginal. The ionic liquid-based fluids also had a better dispersion of particles.

A comparative work on the magnetic field-dependent properties of plate-like and spherical iron particle-based magnetorheological grease

“…The value of the yield stress can be determined either by extrapolating the shear stress at zero shear rate, which is known as static yield stress, or by characterizing the shear stress with respect to the rheological model, which is recognized as dynamic shear stress. In this work, the dynamic yield stress was determined using a Bingham plastic rheological model [ 29 ]. In this model, the shear stress is given by where τ denotes the shear stress, τ y is the yield stress as a function of the magnetic field, η is the apparent viscosity, which represents the slope of the shear stress and shear rate curve at a higher shear rate, and is the shear rate.…”

“…It was evident that the G’ was dominantly dependent on the strength of the CI particle chains, which were formed at a higher magnetic flux density. The dipole-dipole attractive interactions between the CI particles gradually increased with an increase in the magnetic flux density, which led to the enhancement of the stiffness [ 10 , 15 , 28 , 29 ]. In comparing the two types of MR grease, the MRG-P, which was incorporated with 30 and 50 wt% of plate-like CI particles, had a higher G’ compared to the MRG-S with the same fractions.…”

Magnetorheology of Bimodal Fluids in the Single–Multidomain Limit

“…On the other hand, the superior/inferior magnetic response of the nanoparticles compared to the microparticles at the particular field investigated also plays a role. 31 While BaFe 12 O 19 nanoparticles have magnetic properties inferior to those of CIP microparticles, Fe nanoparticles have magnetic properties superior to those of CIP microparticles. This explains their different behavior.…”

“…Anyway, a generalized observation is that the settling problem becomes strongly mitigated presumably because of the thermal convection of nanoparticles that delays the sedimentation of the bigger ones. 27,29,31 However, after a slight initial increase (presumably due to the smaller particles filling the voids between microparticles which locally enhance the magnetic field, 29,34 the on-state yield stress is substantially reduced, (ϕ S /ϕ T ≈ 5 wt % when the total particle loading is 45 wt %, 26 ϕ S /ϕ T ≈ 7.5 wt % when the total particle loading is 60 wt % 28 ), maybe because of chain-growth inhibition, 18 despite the fact that the nanoparticles were observed to fill in the interparticle spaces between the larger particles in the chain-like structures locally rising the magnetic permeability and resulting in a higher magnetic flux density 29 or because of the inferior magnetic properties of the nanoparticles if compared to the microparticles. 31,35 2.3.…”

Improved Magnetorheological Properties by Using Ionic Liquid as Carrier Liquid of Magnetorheological Fluids

“…The traditional method of using surfactants to change the interface will complicate the composition of the rheological fluid, and cannot distinguish its influencing factors and effects well. Although ionic liquids have been used as carrier fluids for MRF (Guerrero-Sanchez et al, 2007;Gómez-Ramírez et al, 2011;Jönkkäri et al, 2014;Bombard et al, 2015), few people have noticed that although its viscosity is similar to that of silicone oil, its surface tension is higher than that of silicone oil. This will bring different interface effects.…”