Structural transformations in magnetorheological slurries induced by perturbations

• Published in: The European physical journal. B, Condensed matter physics Vol. 86; no. 4
• Main Authors: de la Calleja Mora, E.M., Carrillo, J. L., Mendoza, M. E., Donado, F.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.04.2013; EDP Sciences; Springer
• Subjects: Analysis; Complex Systems; Condensed Matter Physics; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electro- and magnetorheological fluids; Exact sciences and technology; Fluid- and Aerodynamics; Magnetic fields; Material types; Physics; Physics and Astronomy; Regular Article; Rheology; Solid State Physics; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; Statistical and Nonlinear Physics; Supercooled liquids; Annealing; Fractal dimension; Phase transformations; Magnetic field effects; Thermodynamic properties; Configuration entropy; Relaxation time; Magnetorheological fluid
• ISSN: 1434-6028; 1434-6036
• DOI: 10.1140/epjb/e2013-31014-8

The pattern formation produced by the aggregation of the particles in magnetorheological dispersions when they are in the presence of a static magnetic field, and the process of reconstruction of these structures induced by the application of magnetic perturbations, are investigated experimentally and theoretically. Under the influence of a static magnetic field the aggregation of the dispersed particles generates a multifractal structure, whose corresponding hierarchical structure has been characterized by means of its mass fractal dimensions and other correlations. When this system is perturbed by an oscillatory magnetic field, in addition to the static one, the dispersion rearranges becoming, for certain values of the amplitude and frequency of the perturbation, a more compact and relatively more ordered structure. Here, the analysis of these phenomena is approached as if the pattern formation were a kind of glassy transformation in a supercooled liquid, and the effect of the perturbation were an annealing process. The role of the temperature is taken here by the ratio of the intensities of the applied fields. From high resolution photographs taken at different stages of the structure evolution, it is possible to calculate some complexity measures such as the singularity spectrum, the lacunarity index, enthalpy and the configurational entropy. On this basis it is possible to describe quantitatively these glassy-like transformations. The relaxation time that distinguishes between a cooling process that leads the structure to a glassy or a crystalline one, is experimentally obtained.