Magnetorheology of fiber suspensions. I. Experimental

Abstract

International audienceThis work reports a detailed study on the shear magnetorheology of suspensions of magnetic microfibers. The steady-state regime was investigated using a controlled-stress rheometer for different concentrations of particles and under the presence of a broad range of applied magnetic fields up to 512 kA m−1. The results were compared with those obtained for conventional magnetorheological fluids suspensions of magnetic microspheres. It was found that the suspensions of magnetic fibers show an enhanced magnetorheological effect. We proposed the existence of field-dependent solid friction between fibers as the main physical reason for this enhancement. In order to ascertain the relevance of the interfiber solid friction, the microscopic structure of fiber suspensions was investigated using an optical microscope. In the absence of applied field, fibers form an entangled network with approximately isotropic orientation. Upon magnetic field application, the fiber network becomes deformed and approximately aligned with the field direction. Nonetheless, interfiber solid friction hinders a complete alignment of the fibers with the field, and the fiber network remains entangled

Outstanding magnetorheological effect based on discontinuous shear thickening in the presence of a superplastifier molecule

“…Although not explained at this time the authors recently prove that it was due to a jamming effect induced by the magnetic field in the presence of a higher total volume fraction of particles 10 . The solid friction between particles, which can be induced by the attractive magnetic forces is also one of the cause of the enhancement of the MR effect in suspensions of magnetic fibers 11 or of faceted particles 12 compared with spheres at the same volume fraction. In our experiments we have used commercial carbonyl iron particles (CIP grade HQ from BASF 13 ) suspended in water and a commercial superplasticizer molecule (Optima 100 from Chryso) which has a head made of two phosphonate groups (PO 3 H -) and an hydrophilic tail made of a polyoxyethylene chain.…”

Impact of Nanowires on the Properties of Magnetorheological Fluids and Elastomer Composites

“…Unlike the ferromagnetic oxide particles used in previous studies (Chin et al, 2001) and those formed from spherical particles adjoined in the presence of a magnetic field (López-López et al, 2009), nanowires have well defined structure and controllable length distributions. This facilitates systematic experimental and theoretical studies and will lead to increased understanding and design control.…”

“…Studies on MR fluids with up to 7 vol. % 60 !m long, 4.8 !m diameter cobalt microfibers displayed substantial mitigation of sedimentation and an increase in yield stress as compared to suspensions containing 1.34 !m diameter cobalt spheres (López-López et al, 2009). It was suggested that the enhancement of the yield stress was due to inter-fiber solid friction.…”

“…The use of MR fluids in more diverse applications have been limited, due to the settling of the particles in the absence of continual mixing (Chen & Chen, 2003) and particle wear (Carlson, 2003) that tends to reduce the efficacy of the fluid over time and eventually lead to device failure. Both the yield stress and settling properties of magnetorheological fluids have been shown to depend on particle morphology; however, few studies have explored the particle shapedependence in either MR fluids (Chin et al, 2001;Nishiyama et al, 2005;Kuzhir et al, 2009;López-López et al, 2009) or electrorheological (ER) fluids (Kanu & Shaw, 1998;Lengálová et al, 2003;Sanchis et al, 2004;Yin & Zhao, 2006). Studies involving electrorheological fluids utilizing elongated titanate (TiO 2 ) whiskers demonstrated greatly reduced sedimentation.…”

Synthesis and magnetorheology of suspensions of submicron-sized cobalt particles with tunable particle size

“…The magnetic field was applied in the vertical direction using a noncommercial electromagnet, specially designed for its use in the above-mentioned rheometer. This electromagnet allows reaching fields up to 580 kA/m in the measuring gap -the radial distribution of the magnetic field in the measuring gap for a given electric current in the coil is shown in López-López et al (2009). Rheological experiments were carried out as follows: (i) in order to ensure reproducible results, suspensions were shaken using a vortex mixer, then immersed in an ultrasonic bath, and finally shaken again.…”