Morphology of anisotropic chains in a magneto-rheological fluid during aggregation and disaggregation processes

Abstract

We study the morphology of the chain-like aggregates formed when a external constant and uniaxial magnetic field is applied to a magneto-rheological (MR) fluid. In order to characterize the conformation of the aggregates, we study the evolution of various fractal dimensions during aggregation and disaggregation processes (i.e., when the applied field is switched on and off), using video-microscopy and image analysis. Experiments have been performed by varying the values of two external parameters: the magnetic field amplitude and particle concentration. We found that the box-counting dimension, related with how the aggregates occupy the surrounding space, depends on the ratio R 1 /R 0 . During the first stage of the disaggregation process, when the particles are moving by Brownian motion inside the aggregate, Family-Vicsek scaling function is verified.

Predicting the Self‐Assembly of Superparamagnetic Colloids under Magnetic Fields

“…As we mentioned before, there are many experimental techniques suitable for the study of the kinetics of self‐assembly in the case . A popular approach is to employ in‐situ optical microscopy and determine the size and number of chains by direct counting from images taken at different times, using the appropriate image processing software. Another possibility is to follow the assembly process by dynamic light scattering (DLS).…”

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

“…The microstructure formed under the effect of the magnetic field depends on many factors: the shape, the nature and concentration of the particles, the properties of the carrier oil, the presence of surfactants and thickening agents, the uniformity and intensity of the magnetic field applied and the size of the cell where the fluid is studied [11][12][13][14][15][16].…”

“…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.…”

Aggregation dynamics and magnetic properties of magnetic micrometer-sized particles dispersed in a fluid under the action of rotating magnetic fields

“…Nevertheless, we have found that the kinetics of formation of such structures has not yet been extensively investigated. The formation of the filamentary structures in the uniaxial configuration has been previously studied by means of microscopic image analysis, in magnetic particles in a fluid [18,19], and non-magnetic particles in a magnetic fluid [20]. Previously, we have published a preliminary work as a conference proceeding, regarding this topic [21].…”