Experimental and Theoretical Study of an Autowave Process in a Magnetic Fluid

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.

Mathematical Modeling of Single and Phase Autowaves in a Ferrocolloid

“…One of the electrodes was transparent with respect to the falling beam. A detailed description of the experimental device and experimental technique can be found in [8,9].…”

“…It was found that stable localized structures-layers in which the concentration of magnetic particles is much higher than in the rest of the solution-were formed at the boundary with the electrode [7]. This phenomenon is a distinctive feature of ferrocolloids, and near-electrode layers represent a new type of liquid membrane [8].…”

“…The first basic mathematical model of autowaves, which was built on a fundamental understanding of the physical and electrochemical processes in a ferrocolloid, is described in [8,10]. As a result of solving the 2D model [10], it was found that the concentration of positively and negatively charged particles changes periodically, as in experiments.…”

Influence of Space Charge Breakdown on the Performance of Electromembrane Systems

“…To assess the effect of the breakdown of the spatial charge on the transport of salt ions using formula (17) and Leveque's formula, the voltage characteristic [8][9][10][11][12][13][14][15] for the boundary value problem (1-16) is constructed and analyzed. It is shown that in the extreme current regime, the appearance of spatial charge breakdowns in the desalination channel worsens the mass transfer of salt ions: in region II (1.4-2.7 V) by 31%, in region III (2.7-3 V) by 42% (Fig.…”

Experimental and Theoretical Study of Forced Synchronization of Self-Oscillations in Liquid Ferrocolloid Membranes

“…A unique feature of ferrocolloids is the formation of dense layers of magnetite particles with a protective shell near the electrodes in a constant electric field. The layer does not mix with the main volume of the liquid and behaves as a liquid ferrocolloid membrane [7][8][9][10]. The membrane is formed as a result of electrophoresis of particles of the dispersed phase.…”