Magnetic fluids were historically the first active nano-dispersion material. Despite over half a century of research, interest in these nano-objects continues to grow every year. This is due to the impressive development of nanotechnology, the synthesis of nanoscale structures, and surface-active systems. The unique combination of fluidity and magnetic response allows magnetic fluids to be used in engineering devices and biomedical applications. In this review, experimental results and fundamental theoretical approaches are systematized to predict the micro- and macroscopic behavior of magnetic fluid systems under different external influences. The article serves as working material for both experienced scientists in the field of magnetic fluids and novice specialists who are just beginning to investigate this topic.

This work proposes a new technique for creating active bubbles and droplets with a non-magnetic core and a coating formed by a magnetic fluid. The procedure consists of the injection of a non-magnetic phase into a magnetic one that is supported by the presence of an inhomogeneous magnetic field from the source, which combines an annular magnet and an electromagnet. We explored various modes leading to different active bubbles and drops as well as the influence of the magnetic field on the size, velocity, and acceleration of the formed active droplets. It is shown that active bubbles change their trajectory under the action of a constant magnetic field and also disintegrate under the action of a pulsed one. This provides a new mechanism for controlling the absorption of droplets and bubbles using a magnetic field. Therefore, these results can be applied to create droplet-based microfluidics systems, in which an inhomogeneous magnetic field can be used for focusing droplet and bubble flows in a magnetic fluid.

This article presents the results of a study on the dynamics of a volume of magnetic fluid levitating in a uniform magnetic field of an electromagnet experiencing an oscillatory shift. Samples with different physical parameters were considered, and the dependence of the magnetoviscous effect was studied. It showed that the greatest influence on the dynamics of a magnetic fluid that experiences vibrational-shear and magnetic-viscosity effects is exerted by the sample microstructure and the presence of large magnetic particles. The results of this work can be used in the development of a technique for magnetic fluid samples express testing, as well as in the development of acceleration and vibration sensors based on magnetic fluids

The viscosity of magnetic fluids was studied using a capillary viscometer of our own design and the method of oscillating volume of magnetic fluid in a magnetic field. Samples were tested on various carrier liquids—kerosene and polyethylsiloxane—with a volume concentration φ of the solid phase from 19 to 2.5%. The developed setup based on a capillary viscometer allows viscosity measurements in the magnetic field strength range from 20 to 350 kA/m. Measurements based on oscillations of the system occur in the range from 150 to 900 kA/m. It was experimentally established that the results obtained using these methods agree with each other, which allows us to conclude that both methods provide an identical estimate of the viscosity of a magnetic fluid in a magnetic field.