Dynamic rheology of sphere- and rod-based magnetorheological fluids

Abstract

The effect of particle shape in the small amplitude oscillatory shear behavior of magnetorheological (MR) fluids is investigated from zero magnetic field strengths up to 800 kA/m. Two types of MR fluids are studied: the first system is prepared with spherical particles and a second system is prepared with rodlike particles. Both types of particles are fabricated following practically the same precipitation technique and have the same intrinsic magnetic and crystallographic properties. Furthermore, the distribution of sphere diameters is very similar to that of rod thicknesses. Rod-based MR fluids show an enhanced MR performance under oscillatory shear in the viscoelastic linear regime. A lower magnetic field strength is needed for the structuration of the colloid and, once saturation is fully achieved, a larger storage modulus is observed. Existing sphere- and rod-based models usually underestimate experimental results regarding the magnetic field strength and particle volume fraction dependences of both storage modulus and yield stress. A simple model is proposed here to explain the behavior of microrod-based MR fluids at low, medium and saturating magnetic fields in the viscoelastic linear regime in terms of magnetic interaction forces between particles. These results are further completed with rheomicroscopic and dynamic yield stress observations.

Enhanced magnetic response of fluids using self-assembled petal-like iron oxide particles

“…When 10 wt % of the spherical particles were added, there is a moderate increase in the storage modulus under the magnetic field, which is previous studies. 4,15,16 At same solid content and magnetic field, as shown in Fig. 3͑b͒, the storage modulus of SAIO fluids is two times as large as that of the spherical particles.…”

Magnetically tunable viscoelastic response of soft magnetic nanocomposites with wormlike surfactant micellar matrix

“…Dependence of storage G (filled symbols) and loss G (open symbols) moduli on mechanical strain (at 1 rad/s frequency) for SMN containing 0.2 vol % magnetite and 0.6 wt % EHAC without field (black diamonds) and at magnetic field strength of 1 T (red circles) and for SMN containing 3 vol % magnetite and 0.6 wt % EHAC at magnetic field strength of 1 T (blue squares). Solvent: 1.5 wt % KCl in water linear viscoelasticity occur at rather large strains, which are much higher than in MRFs based on Newtonian liquids (0.003 -0.1 % [8,12,23]). Therefore, the SMNs under study show a rather wide range of linear viscoelasticity even at magnetic field strength as high as 1 T. This feature is quite important since the dynamic rheological data obtained within linear viscoelastic region characterize the structure undisturbed by mechanical strain [11], and these data are most suitable for further investigation of the structure transformations induced by magnetic field.…”

“…For this reason, the submicron particles are considered more promising for soft magnetic nanocomposite preparation. Carbonyl iron and iron oxide particles are widely used in MRFs due to their high magnetic response and availability [11,12], but their density is very high -nearly 8 g/cm 3 and 5 g/cm 3 , respectively. This makes it difficult to disperse the submicron-or micron-sized particles in a liquid carrier.…”

Magnetorheological Payne effect in bidisperse MR fluids containing Fe nanorods and Fe3O4 nanospheres: A dynamic rheological study

“…However, non-spherical particles e.g. rod-like microstructures can form stronger field-induced aggregates due to easy magnetization when the long axes are aligned parallel to magnetic field [5]. This gives rise to stronger MR response.…”