Rheology of Perfluorinated Polyether-based MR Fluids with Nanoparticles

• Published in: Journal of intelligent material systems and structures 2010-07, Vol.21 (11), p.1051-1060
• Main Authors: Jonsdottir, F., Gudmundsson, K.H., Dijkman, T.B., Thorsteinsson, F., Gutfleisch, O.
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Cross-disciplinary physics: materials science; rheology; Electro- and magnetorheological fluids; Exact sciences and technology; Fluid dynamics; Fluid flow; Fluids; Fundamental areas of phenomenology (including applications); Inelasticity (thermoplasticity, viscoplasticity...); Magnetorheological fluids; Material types; Multiphase and particle-laden flows; Nanomaterials; Nanoparticles; Nanostructure; Nonhomogeneous flows; Physics; Rheology; Solid mechanics; Structural and continuum mechanics; Viscosity
• ISSN: 1045-389X; 1530-8138
• DOI: 10.1177/1045389X10376844

Motivated by the use of magneto-rheological (MR) technology in prosthetic devices, the goal of this study is to develop a MR fluid composition that is tailored for the requirements of a prosthetic knee actuator. A MR fluid composition is sought with a suitable balance between the field-induced shear stress, the off-state viscosity, and sedimentation stability for the proposed application. Rheological characteristics are investigated for samples with monodisperse micron-sized particles and bidisperse fluids with a mixture of micron- and nanosized particles. Two types of nanosized particles are used. All fluid samples employ a novel perfluorinated polyether oil as carrier liquid which enhances stability. The samples are investigated with respect to both field-induced and off-state characteristics. The results are compared to analytical and empirical models that exist in the literature. The monodisperse fluids are shown to give a favorable trade-off between field-induced strength and off-state viscosity. The addition of a small concentration of nanoparticles is found to moderately increase the field-induced shear-yield stress. However, for a larger concentration of nanoparticles, the yield stress begins to decrease. Nanoparticles exhibit an undesirable effect on the off-state viscosity. The results reveal valuable information for the designers of MR fluids and designers of prosthetic actuators.