Magnetically tunable liquid dielectric with giant dielectric permittivity based on core–shell superparamagnetic iron oxide

Abstract

A liquid dielectric based on a core-shell architecture having a superparamagnetic iron oxide core and a shell of silicon dioxide was synthesized. The frequency dependence of dielectric properties was evaluated for different concentrations of iron oxide. The dependence of magnetic field on the dielectric properties was also studied. Aqueous ferrofluid exhibited a giant dielectric constant of 6.4 × 10 at 0.1 MHz at a concentration of 0.2 vol% and the loss tangent was 3. The large rise in dielectric constant at room temperature is modelled and explained using percolation theory and Maxwell-Wagner-Sillars type polarization. The ferrofluid is presumed to consist of nanocapacitor networks which are wired in series along the lateral direction and parallel along longitudinal direction. On the application of an external magnetic field, the chain formation and its alignment results in the variation of dielectric permittivity.

Synthesis of magnetite/silica nanocomposites from natural sand to create a drug delivery vehicle

“…Moreover, the silica surface is chemically stable and biocompatible and can be easily functionalized for bioconjugation [24]. Silica coating of materials has been successfully applied in the fields of optics, erosion resistance, biosensing, biocatalysts, and biomedical devices [25,26,27,28,29]. Silica is not only a stabilizing factor but also provides sites for surface treatment with various ligands that are susceptible to the development of a drug delivery vehicle [26].…”

A stealth emulsion based on natural rubber latex, core-shell ferrofluid/carbon black in the S and X bands

“…The crystallite size estimated using Scherer's formula is found to be ∼15 nm. Figure 4(a) and (b) shows the TEM and HR-TEM images of Fe 3 O 4 @SiO 2 nanoparticles [22]. Core-shell architecture is clearly evident from the micrographs.…”

“…From figures 6(a) and (b), it is clear that the complex permittivity of pristine FF is much larger than the emulsions FFR, 2FFR, HR, FFHR, 2FFHR and dispersion of HAF. Dielectric constant of 110 at microwave frequencies is not normal and the material used for the current investigation (FF) is a giant dielectric permittivity ferrofluid with a conducting core and non-conducting shell [22]. All the emulsion samples exhibited enhanced dielectric permittivity compared to its individual permittivity of solid fillers.…”

“…A ferrofluid based on core-shell nanoparticles used for the loading was synthesised by the controlled co-precipitation and the hydrolysis of tetra ethyl ortho silicate (TEOS), details are cited elsewhere [22]. Stable aqueous dispersions of the individual ingredients were separately prepared and added to NR latex aided by ultra-sonication.…”

“…Recently we developed a ferrofluid that exhibits giant dielectric permittivity at low frequencies [22]. The fluid was based on superparamagnetic iron oxide nanoparticles (SPION).…”