Correlation of Rheological Properties of Ferrofluid-Based Magnetorheological Fluids Using Some Dimensionless Numbers Defined in Magnetorheology

In this paper we investigated from rheological point of view some samples of ferrofluid-based magnetorheological fluids (FF-MRFs) with different volumic fractions of Fe microparticles, but with the same ferrofluid used as carrier liquid. We correlated the dimensionless flow curves, measured at different values of the magnetic field induction, using either Mason number or Casson number. It has been shown that in this approach, data sets measured under different conditions collapse on a single curve. This master curve is useful for controlling the concentration of Fe particles, so that the magnetic and magnetorheological properties of FF-MRF to be adapted to obtain high-performance applications.

Life and death of colloidal bonds control the rate-dependent rheology of gels

Colloidal gels exhibit rich rheological responses under flowing conditions. A clear understanding of the coupling between the kinetics of the formation/rupture of colloidal bonds and the rheological response of attractive gels is lacking. In particular, for gels under different flow regimes, the correlation between the complex rheological response, the bond kinetics, microscopic forces, and an overall micromechanistic view is missing in previous works. Here, we report the bond dynamics in short-range attractive particles, microscopically measured stresses on individual particles and the spatiotemporal evolution of the colloidal structures in different flow regimes. The interplay between interparticle attraction and hydrodynamic stresses is found to be the key to unraveling the physical underpinnings of colloidal gel rheology. Attractive stresses, mostly originating from older bonds dominate the response at low Mason number (the ratio of shearing to attractive forces) while hydrodynamic stresses tend to control the rheology at higher Mason numbers, mostly arising from short-lived bonds. Finally, we present visual mapping of particle bond numbers, their life times and their borne stresses under different flow regimes.

Investigations of microstructured behaviors of magnetorheological suspensions

Microstructured behaviors of magnetorheological suspensions under magnetic fields with different magnitudes are investigated using a large-scale atomic/molecular massive parallel simulator. We investigated four kinds of typical characteristics of microstructured behaviors: (a) phase separation of structures, (b) statistics of chain and cluster sizes, (c) structural anisotropy of aggregates, and (d) fluctuation of suspensions. It is found that the higher the magnitude of external magnetic fields, the lesser the time the phase separation of structures undergoes. Magnetic dipolar particles, moreover, exhibit plane size-dependent structured behavior as they tend to cluster into nematic-like sheets along the shorter dimension of the field-perpendicular plane, even under conditions of uniform initial distribution and steady magnetic fields. In the presence of the shear, meanwhile, we observe that the suspensions move along with the flow field and connect to form long sheets along flow direction toward restraining the transportation of the shear flow. The application of the shear weakens the effect of the magnetic fields on the fluctuation of suspensions. Besides, the macroscale shear stress of magnetorheological suspensions is investigated as a function of the Mason number revealing that the constitutive model of rheological suspensions based on the Bingham law is of applicability.