Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Magnetorheological fluids: a review

A review on the magnetorheological fluid preparation and stabilization

We investigate the magnetorheological (MR) properties of suspensions containing iron microwires with 260 nm diameter and two distinct length distributions of 54 ± 52 µm and 76 ± 51 µm suspended in silicone oil (045 Pa s) The rheological properties of these fluids were determined using a parallel plate rheometer equipped with a variable strength electromagnet The shear stress was measured as a function of shear rate for increasing applied magnetic fields These results were modeled using the Bingham-plastic constitutive model to determine the apparent yield stress and viscosity as a function of increasing volume fraction and length of microwires At a saturated magnetic flux density, the yield stress using the 54 µm microwires was found to be 065, 223, and 476 kPa for the 2, 4, and 6 vol% suspensions, respectively For the 76 µm wires, the yield stress increases to 82 kPa for the 6 vol% suspension Compared with conventional MR fluids employing spherical particles, the degree of settling is markedly decreased in the microwire-based fluids At 6 vol%, conventional fluids display appreciable settling whereas the microwire-based fluids display no discernable settling Moreover, the rod-shaped microwires are shown to increase the yield stress of the fluids and enhance the MR performance

https://iopscience.iop.org/article/10.1088/0964-1726/17/01/015028/pdf

Magnetorheology of submicron diameter iron microwires dispersed in silicone oil

Magnetorheological (MR) properties were investigated for sphere, plate, and rod-like iron particles in suspension under the presence of magnetic fields to ascertain the effect of particle shape in MR performance. A novel two-step synthesis route for micrometer sized iron particles with different morphologies is described in detail. Small-amplitude dynamic oscillatory and steady shear flow measurements were carried out in the presence of external magnetic fields. Finite element method calculations were performed to explain the effect of particle shape in the magnetic field-induced yield stress. Compared to their sphere and plate counterparts, rod-like particle based MR fluids present a larger storage modulus and yield stress. The effect of particle shape is found to be negligible at large particle content and/or magnetic field strengths.

Effect of particle shape in magnetorheology

Introduction: Transdermal patches and medicated plasters (patch) represent well-established prolonged release dosage forms. Even if satisfactory adhesion to the skin is strictly linked to the efficacy and safety of the therapeutic treatment, nowadays numerous reports of in vivo ‘adhesion lacking’ are still addressed to regulatory agencies. The adhesive properties of a patch should be characterized considering i) the ability to form a bond with the surface of another material on brief contact and under light pressure (tack); ii) the resistance of the adhesive to flow (shear adhesion); and iii) the force required to peel away a patch from a surface (peel adhesion). Areas covered: In this manuscript, the most widely used methods to measure adhesive properties during development studies are described, along with the quality control of patches. The influence of formulative variables on patch adhesive properties, and their possible relationship with the in vivo adhesion performances, is also discussed. Expert o...

Adhesive properties: a critical issue in transdermal patch development.

Conventional magnetorheological (MR) fluids are suspensions of micron-sized particles in a hydraulic or silicone oil carrier fluid. Recently, research has been conducted on the advantages of using bidisperse fluids, which are mixtures of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron- sized particles and nanometer-sized particles. The settling rate of such bidisperse fluids using nanometer-sized particles is reduced because the nanoparticles fill pores created between the larger particles, thereby reducing fluid transport during creeping flow. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manifested by such an MR fluid at its saturation magnetization. There is a measurable and predictable variation in rheological properties as the weight percent (wt%) of the nanometer-sized particles is increased relative to the weight percent (wt%) of micron-sized particles, while maintaining a constant solids loading in the MR fluid samples. All bidisperse fluids tested in this study have a solids loading of 60 wt% of iron (Fe) particles. This study investigates the effect of increasing the wt% of 30 nm (nominal) Fe particles relative to 30mm (nominal) Fe particles on rheological characteristics, such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid that provides the best combination of high yield stress and low settling rate based on empirical measurements. The applicability of the Bingham-plastic rheological model to the measured flow curves of these MR fluids is also presented.

Bidisperse magnetorheological fluids using Fe particles at nanometer and micron scale

Influence of penetration enhancers on the thermomechanical properties and peel strength of a poly(isobutylene) pressure sensitive adhesive

Conventional magnetorheological fluids are suspensions of micron sized particles in a hydraulic or silicone oil medium. Recently, research has been conducted into the advantages of using bidisperse fluids, which is a mixture of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron sized particles and nanometer sized particles. The settling rate of such bidisperse fluids using nanometer sizes particles is reduced because of thermal convection and Van der Waals experienced by the nanometer sized particles compete favorably with gravitational forces. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manisfested by such an MR fluid. There is a measurable and predictable variation in rheological properties as the weight percent of the nanometer sized particles is increased, relative to the weight percent of micron sized particles, while maintaining the solids loading in the MR fluid as a constant. In this context, this study investigates the effect of varying the weight percent of nanometer sized particles on rheological characteristics such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid to obtain best combination of high yield stress and low settling rates based on empirical measurements. The applicability of rheological models, such as the Bingham-plastic and the Hershel Buckley models, to the measured flow curves of these MR fluids is also presented.

Impact of varying concentrations of nanometer-sized particles in a bidisperse magnetorheological fluid

The substitution of poly(methyl methacrylate) (PMMA)-based bone cements with photopolymerized acrylate resins for total hip arthroplasties (THAs) was explored. Using a bis-phenol-A-diglycidylether (bis-GMA)-based resin with a blue photoinitiator, we performed three sets of experiments. Two were parametric studies to evaluate the evolving adhesive strength with both illumination time and inert filler content. The last effort studied typical photocuring exotherms for these resins to compare the risk for thermal necrosis with bone cements. An annular cavity adhesive joint construction was designed between two transparent poly(vinyl chloride) (PVC) cylinders, the annular separation distance being preserved by a plug assembly. This cavity was a model for the cavity between the hollowed out femur and a cemented total hip prosthesis. The cavity was filled with resin and cured using a blue-LED light source rotating within the inner ring. For composite cylinders using cured neat resin, shear strengths were measure...

Adaptation of acrylic photopolymerized resins as model bone cements in total hip arthroplasties

Nanometer and Micron Sized Particles in a Bidisperse Magnetorheological Fluid

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