Abstract
Magnetic fluid (MF) is a colloidal system consisting of ferromagnetic particles (magnetite) with a diameter of ~10 nm suspended in a dispersion medium of a carrier fluid (for example, kerosene). A distinctive feature of magnetic fluid is the fact that when an electric field is applied to it using two electrodes, thin layers consisting of close-packed particles of the dispersed phase are formed in the regions near the surface of both electrodes. These layers significantly affect the macroscopic properties of the colloidal system. In this work, the interpretation of the near-electrode layer is for the first time given as a new type of liquid membrane, in which the particles of the dispersed phase become charged with the opposite sign. On the basis of experimental studies, we propose a physicochemical mechanism of the autowave process in a cell with a magnetic fluid. It is based on the idea of oppositely recharging colloidal particles of magnetite in a liquid membrane. A mathematical model of an autowave process, which is described by a system of coupled partial differential equations of Nernst–Planck–Poisson and Navier–Stokes with appropriate boundary conditions, is proposed for the first time. One-dimensional, two-dimensional, and three-dimensional versions of the model are considered. The dependence of the frequency of concentration fluctuations on the stationary voltage between the electrodes was obtained, and the time of formation of a liquid membrane was estimated. Qualitative agreement between theoretical and experimental results has been established.
Highlights
Magnetic fluids (MF) are ultrafine stable colloids of ferro- or ferrimagnetic singledomain particles dispersed in various liquids: water, organosilicon compounds, or hydrocarbons
According to reviews [12,34], the electrical conductivity in MF is due to several mechanisms, including the presence of impurity ions appearing in the MF during its synthesis
In the synthesis of MF, Fe3O4 magnetite nanoparticles are most often obtained by the method of chemical coprecipitation or by the method of “chemical condensation” as a result of the reaction [37] and references in this work
Summary
Magnetic fluids (MF) are ultrafine stable colloids of ferro- or ferrimagnetic singledomain particles dispersed in various liquids: water, organosilicon compounds, or hydrocarbons. The aggregate stability of magnetic fluids, the high dispersion of the magnetic phase, a unique combination of fluidity, and the ability to interact with magnetic and electric fields allow the use of magnetic fluids in various fields. Due to their physicochemical properties, nanoparticles of the “magnetic core–shell” type demonstrate high adsorption efficiency and a high rate of removal of pollutants, as well as easy and quick separation of the adsorbent from the solution using an external magnetic field, which allows them to be used in
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