Nonlinear viscoelasticity and two-step yielding in magnetorheology: A colloidal gel approach to understand the effect of particle concentration

Abstract

The yielding behavior of conventional magnetorheological (MR) fluids is revisited for a wide range of magnetic fields and particle concentrations under a colloidal gel perspective. A two-step yielding behavior is found at intermediate magnetic fields ($10 kA/m) that can be explained as a transition from a strong-link to a weak-link (or transition) regime upon increasing the particle concentration in the MR fluid. This two-step yielding behavior is reminiscent of the classical concepts of static (frictional) and dynamic (Bingham) yield stress. By relating macroscopic elastic properties to a scaling fractal model, we could identify the prevalent gelation regime in MR fluids. V

Study of the effect of particle volume fraction on the microstructure of magnetorheological fluids using ultrasound: Transition between the strong-link to the weak-link regimes

“…Due to defects in particles and the effect of close neighbors, perpendicular interactions are expected theoretically. This region seems to be related to the strong-link regime shown by SegoviaGutiérrez et al [23]. If the particle volume fraction is increased up to 0.06, complex fiber structure interconnections start giving way to the second intermediate region.…”

“…Models have been usually applied successfully for very low particle volume fractions [26][27][28], while for higher volume fractions, simulations are compulsory [15,29,30]. The yielding of MR fluids of iron particles suspended in a low viscosity oil was studied as a function of the particle volume fraction by Segovia-Gutiérrez et al [23]. In that work, a two-step behavior was observed when they were subjected to intermediate magnetic fields.…”

“…As the properties of the MR fluids are strongly dependent on their inner structure, a better knowledge of the microstructure as a function of the external magnetic field will permit a better understanding of the response of these fluids and, therefore, an improvement of their industrial applications. To this end, different scientific works have been made to infer the microstructure of MR fluids from their optical, rheological or acoustical properties, both in static and dynamic conditions [16,[19][20][21][22][23][24][25]. Different models have been proposed to explain the structure formation and the yielding process related to the application of a shear stress in MR fluids.…”

“…The chain aggregates are more resilient than the interlinks between different structures so two different breaking mechanisms are found; this is the weak-link regime. The particle volume fraction which gives way from one regime to another is a critical or threshold particle volume fraction which depends on the features of the suspension [23].…”

Magnetorheological behaviour of propylene glycol-based hematite nanofluids

“…Thermal energy randomizes the nanoparticle distribution while the magnetic dipole interaction tries to align the nanoparticles, and when this second energy is larger, a chain-like distribution structure is induced. Segovia-Gutiérrez et al (2012) have determined the shear behaviour of the particle aggregates when a magnetic field is applied to several samples with nanoparticles at increasing concentrations, demonstrating the existence of an apparent yield stress and a large viscoelastic response.…”