Temperature Dependences of the Magnetic Susceptibility of Water-Based Magnetic Fluids

Abstract

This paper presents the results of a study of the temperature dependences of the magnetic susceptibility of water-based magnetic fluids (magnetic colloids) with magnetite particles stabilized by their electrostatic interaction. The average size of dispersed particles was 8 nm, and the volume concentration of particles in the selected samples under study was 1.4% and 1.6%. The investigations were carried out over a wide temperature range. The temperature dependence of the susceptibility, for the first time, was obtained in the region of the colloidal phase transition under supercooling of the dispersion medium (water). Significant differences were found between the temperature dependences of the magnetic susceptibility of such magnetic fluids, where as similar dependences have been found for the susceptibility of magnetic hydrocarbon-based fluids. The observed behavior of such dependences near the water phase transition temperature is determined by the changes in the water phase state, heat release and structuring of the colloid as a result of water crystallization. Moreover, it is suggested that a certain impact on the dependence behavior in the region of the colloidal solidification temperature can also come from the process of blocking the Brownian degrees of freedom of a small fraction of large dispersed particles. It is concluded that the observed maxima in the investigated susceptibility temperature dependences in the lower temperature region are due to magnetic transformations in the colloidal zones formed at the solidification front of the disperse medium with a dense packing of single-domain colloidal particles.

The Influence of Electric and Magnetic Fields on the Structure of Flat Drops of Magnetic Fluids upon Drying

“…Indeed, the action of a magnetic field leads to a change in the direction of colloidal particles' moments and a change in their magnetic dipole interaction energy according to Equation (5). Moreover, in inhomogeneous magnetic fields, magnetic colloidal particles are affected by the force that can be described by Equation (7):…”

“…This technique is applicable not only for homogenous solutions but also for colloid systems that can be drop cast for the nanostructuring of surfaces. In this regard, major attention is paid to the processes associated with a so-called coffee-ring effect that results in non-uniform deposition patterns of colloidal particles from droplets upon drying and the practical application of this effect [1][2][3][4][5][6][7]. It was demonstrated and discussed that both morphology and properties of the formed structures are determined by several parameters such as kinetic factors, substrate properties, and drops composition including properties of the liquid media as well as colloidal particle parameters and their interactions.…”

The Influence of Magnetic Fields on Electrophoretic Processes in Magnetic Colloids with Different Stabilization Mechanisms

“…Measurements and statistical processing of the measurement results were carried out using ImageScope software created by SMA LLC (Moscow, Russia). A more detailed description of the materials may be found in previously published works [8,[54][55][56][57].…”