On the nature of anomalously high value of yield stress of nanostructured magnetic fluid

Based on magnetic fluids, new effective technical devices have been implemented, such as magnetic fluid bearings, seals, and dampers. The magnetic-viscous effect inherent in magnetic fluids can not only improve the properties of magnetic fluid units, but significantly complicate their operation after a long stop. This refers to the so-called «stop effect», which occurs due to an abnormally high limiting shear stress in a structured liquid. It is shown that, based on the existing ideas about the thixotropic properties of a magnetic fluid, it is not possible to convincingly explain the experimental value of the yield strength. Estimations according to the known formulas obtained for the chain model give a significantly underestimated value of the yield strength of a real magnetic fluid. A hypothesis is proposed according to which the rheological properties of the carrier medium change in the process of structure formation in the magnetic fluid under the action of compressive stresses created by a network of dispersed particles. Experiments have confirmed an increase in the density of the magnetic fluid in the magnetic field under the influence of such stresses. It can be assumed that high values of the yield strength are due to the presence of the intrinsic yield strength of the dispersion medium, which is in a quasi-solid state.

magnetic fluid, yield point, dispersed particles, magnetic interaction, chain model