Strong and Stable Magnetorheological Fluids Based on Flaky Sendust-Co_0.4Fe_0.4Ni_0.2 Nanocomposite Particles

Abstract

The magnetorheological (MR) performance of suspensions based on magnetic (flaky Sendust (FS))–magnetic (Co0.4Fe0.4Ni0.2) nanocomposite particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Flaky Sendust@Co0.4Fe0.4Ni0.2 nanocomposite particles were fabricated through wet chemical synthesis of Co0.4Fe0.4Ni0.2 on the surface of FS. The density of the resultant FS@Co0.4Fe0.4Ni0.2 was less than that of FS due to the pore/void formation in the composite particles. Because of the high saturation magnetization of Co0.4Fe0.4Ni0.2 (165 emu/g), FS@Co0.4Fe0.4Ni0.2 (145 emu/g) exhibited greater magnetization than bare FS (130 emu/g), which resulted in the good performance of FS@Co0.4Fe0.4Ni0.2-based MR fluids: the suspension exhibited a remarkably high yield stress, almost one order greater than that of MR fluids based on hierarchically structured (HS) Fe3O4 particles. In addition, the high drag coefficient of FS@Co0.4Fe0.4Ni0.2 in the liquid medium, in conjunction with its lower density, resulted in a substantially improved long-term stability, better than that of Co0.4Fe0.4Ni0.2- or FS-based suspensions. Although the density of the FS@Co0.4Fe0.4Ni0.2 nanoparticles is higher than that of HS-Fe3O4 particles, their stability is much better than the stability of HS-Fe3O4 particle’s suspension. Manufactured magnetic–magnetic nanocomposite particles provide a feasible MR suspension of high MR performance and long-term stability.

Non‐Settling Super‐Strong Magnetorheological Fluids

“…The frequency sweep results in Figure 5b show that the storage modulus is greater than the loss modulus by more than three orders of magnitude, indicating the dominance of the solidlike properties. [21][22][23][24] This behavior confirms again that the solidlike elastic properties imparted by the chain-like structures overwhelm the liquid-like viscous properties and that the mesostructures are strong enough not to be disturbed by external stresses at all over the entire angular frequency range. The storage modulus decreased with the addition of silicone oil.…”

“…All six curves overlap well with each other, which means the behaviors of the three fluids were the same because they followed the same scaling law (Figure 7a) and therefore the same particle magnetization model. [22][23][24] A negligible difference observed at high shear rates and weaker magnetic fields is ascribable to the relatively weaker magnetic polarization force of the 90% CI particles as a result of the inclusion of the magnetically inactive silicone oil. [4,5] In dilute MR suspensions, the yield stress follows a quadratic dependence on the magnetic field strength but becomes less dependent as the magnetic field strength increases.…”

“…[3,5] When the polarization force is dominant, chain-like structures remain undisturbed, and MR suspensions show solidlike properties. [21][22][23][24][25][26][27][28][29] In contrast, typical MR suspensions exhibit liquid-like properties at high shear stresses due to the destruction of the aggregated structures when hydrodynamic shear stresses dominate. [4,5,[17][18][19] Figure 3a shows the strong dependence of the shear stress on the applied field strength.…”

“…[42,43] Under a fixed particle concentration, the master curve for the specific viscosity (i.e., the ratio of the apparent viscosity and the medium viscosity) and the volume fraction correction versus ̇𝛾/𝜇 2 at different magnetic field strengths can be obtained. [22][23][24] The behaviors of different MR fluids are compared for pure CI, 95% CI, and 90% CI fluids at two different magnetic field strengths, as shown in Figure 6b. All six curves overlap well with each other, which means the behaviors of the three fluids were the same because they followed the same scaling law (Figure 7a) and therefore the same particle magnetization model.…”

Balanced Devil Triangle: A Satisfactory Comprehensive Performance Magnetorheological Fluids with Cross‐Scale Particles

“…Regarding MN-MRFs-10, the shear stress exhibits an instantaneous change as the magnetic field is switched on and off, and also increasing as the magnetic field strength rises. [46] Notably, MN-MRFs-10 can essentially revert to their initial state after multiple on-off cycles. This is also similar to the behavior exhibited by CIPs-MRFs (see Figure S5e, Supporting Information), indicating that Micro-Nano bidisperse system can equivalently achieve excellent reversibility and instantaneous response capabilities to a monodisperse system.…”