Rheology is a branch of physics dealing with the deformation and flow of matter; in particular the results of rheology provide a mathematical description of the viscoelastic behaviour of matter. There are a lot of rheological fluids able to modify their viscoelastic properties under suitable stimuli; the most known ones are the magneto-rheological fluids (MR).
Magneto-rheological fluids are suspensions consisting of ferromagnetic particles of size 0.1-100 micron in a dielectric base fluid. Since the dielectric constant of suspensions particles differs from the dielectric constant of the base fluid, external magnetic field polarizes particles. These polarized particles interact and form chain-like or even lattice-like organized structures. Simultaneously the rheological properties of the suspension change effectively, e.g. the effective viscosity increases dramatically. The viscosity of magnetorheological fluid is sensitive to the magnetic field. The rheological properties of the MR fluids depend on some parameters like the concentration and density of the particles, their size, composition of the carrier fluid and surfactant, the applied magnetic field, temperature and so on. A MR fluid is usually used in one of three main modes of operation: flow mode, shear mode and squeeze-flow mode. These modes involve, respectively, fluid flowing as a result of pressure gradient between two stationary plates; fluid between two plates moving relative to one another; and fluid between two plates moving in the direction perpendicular to their planes.
Thanks to their special behaviour, the MR fluids were applied in the damping of structures in space; while Grado Zero Espace thought to use this technology in the damping of shoes (for further informations see Adjustable Damping Shoe A.D.S. Project), in order to absorb ground roughness and improve the comfort during the walking process. Walking is an important aspect of everyday life and the possibility to adjust the degree of damping, thanks to the presence of a fluid cushion inserted in the sole, is one of the most important result obtained with this patented project.
