Performance and Stability of Magnetorheological Fluids—A Detailed Review of the State of the Art

Abstract

Magnetorheological fluids (MRFs) are functional materials, prepared by dispersing magnetic particles in a nonmagnetic carrier fluid, that exhibit a change in mechanical properties (e.g., increase in viscosity and yield stress) when subjected to a magnetic field. Change in mechanical properties is demonstrated by a fast (i.e., fraction of milliseconds) and reversible transition from a liquid‐ to a solid‐like state. This transition, due to a structural reorganization of magnetic particles in the carrier fluid, makes MRFs a valuable material for damping, breaking systems, medical and prosthetics, and robotics. Since the discovery of MRFs in 1948, developing MRF preparation methods that result in improved performance and the storage without oxidation and settling is paramount. This article presents a review on recent developments in the preparation process of MRFs with a special emphasis on the state of the art in additives and coatings used in enhancing MRF chemical, colloidal, and thermal stability. Recent advances in MRF materials and formulations that have increased yield stress and magnetic properties are discussed. Finally, this review analyses the present‐day challenges in MRF research and makes suggestions for the field to improve MRF stability and performance drawing on previous MRF work and work outside of the fields.

Study ofn-Alkanethiol Self-Assembly Behavior on Iron Particles: Effect of Alkyl Chain Length and Adsorption Solvent on Resulting Iron-Based Magnetorheological Fluids

“…Additionally, the greater decrease in M s in chloroform can be attributed to the greater amount of hexadecanethiol adsorbed on iron with chloroform, which leads to increased thinning of the magnetic shell. The percentage decrease in M s demonstrated in Figures and is significantly lower than that of other organic molecular coatings. ,, In addition to the greater mass fraction of iron (density = 7.874 g/mL) relative to the adsorbed alkanethiols (density ∼0.84 g/mL), which causes a reduction in surface spin disorder, , the significantly lower decrease in M s due to the alkanethiol adsorption on iron as compared to other coatings can be explained by the hybridization of iron atomic orbitals and the electron injection barrier. , …”

“…77 Despite the number of applications, the use of these smart liquids has been restricted due to settling, aggregation, and oxidation or corrosion of iron particles. 73,78 Studies have demonstrated that alkanethiol SAMs can act as effective organic surface inhibitors against the corrosion and oxidation of iron 79−84 although without a fundamental understanding of the alkanethiol adsorption. A thorough understanding of alkanethiol SAMs on iron is thus critically important to further improve iron oxidation and corrosion stability and the resulting reliability of iron for MRF applications.…”

Characterization of Magnetorheological Fluid: A Study on Sedimentation and Redispersion

“…[4] To reduce particle sedimentation, different approaches have been attempted: 1) adding thixotropic agents (e.g., carbon fibers, fumed silica, [4] grease [11] ); 2) adding surfactant (e.g., oleic acid, [3] stearic acid [12] ); and 3) adding magnetic nanoparticles. [13,14] The most popular stabilizers are grease [11] and fumed silica. [4,15] The addition of these materials alters the rheological and other properties of the carrier fluid results in sedimentation reduction, albeit it is impossible to eliminate particle settling.…”

Temperature rise of magnetorheological fluid sealing film in a spiral grooved mechanical

“…Magnetorheological fluid (MRF) is a kind of suspension composed of micron-sized magnetic particles uniformly dispersed in the carrier fluid on the surface (Thiagarajan and Koh, 2021). In the absence of an external magnetic field (Li et al , 2016), the fluid behaves as Newton fluid, while in the external magnetic field, the viscosity of the fluid increases with the increase of the magnetic field strength, thus changes from a free-flowing fluid to semisolid (Katiyar et al , 2012).…”