Dielectric-spectroscopy approach to ferrofluid nanoparticle clustering induced by an external electric field

Abstract

An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field.

Generation of Fe 3O 4 Nanoparticle Aggregates in a Ferrofluid Driven by External Electric Field

“…Similar effects in mineral oil-based FFs induced by an external electric field have been reported just recently [10,11]. For that purpose, the method of dielectric spectroscopy and in situ small angle neutron scattering were applied.…”

“…Before the appearance of the visible EHD flow, one can assume that the effective polarization of MNPs and their interface (surfactant and surrounding counter ions [11]) takes place during this time, leading to the induced electric dipole-dipole interactions supported by Van der Waals and magnetic interactions (as the MNPs possess permanent magnetic moments). This behavior happens on the nanoscale, far from the resolution of the optical microscopy.…”

Temperature Dependence of a Dielectric Relaxation in Weakly Polar Ferrofluids

“…To analyze this spectrum we take into account that the transformer oil shows constant permittivity (ε = 2.1) in the whole frequency range. As the known conductivity and permittivity values of the sample constituents determine the appearance of the MaxwellWagner relaxation at much higher frequencies, we associate the low frequency process with the ion impurity polarization taking place on the SNP surfaces [10,11], following the famous Schwarz polarization model.…”

Influence of Electric Field on AC Magnetic Susceptibility of a Mineral Oil Based Ferrofluid

“…Recently, it was shown that similar assemblies can be induced by electric fields. Especially ferrofluids based on insulating liquids are characterized by a high dielectric contrast between the particles and the base liquid, which results in the effective particle polarization and dielectrophoresis leading to the particle assembling [13,14]. On the other hand, this type of ferrofluids is of increasing interest due to their potential application in high voltage engineering [15].…”