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

Electric Field-Assisted Agglomeration of Trace Nanoparticle Impurities for Ultrahigh Purity Chemicals

With the advancement of semiconductor manufacturing technology, the effects of trace impurities in industrial chemicals have grown significantly. In industrial processes, conventional purification methods, such as filtration and distillation, have reached their limits for removing nanoparticles from aqueous and acidic solutions. Especially, silicon and silicate are two fundamental byproducts in semiconductor fabrication processes. Assembly and subsequent removal of these materials at the nanoparticle level have been confronted with significant challenges. Therefore, it is imperative to develop technologies to effectively control and remove these impurities for next-generation manufacturing processes. In this study, we explored the use of electric field-assisted assembly to agglomerate silicate and silicon nanoparticles in industry-standard aqueous and acidic solutions. By applying an alternating current electric field, we induced dipole moments in the nanoparticles, which led to their agglomeration. Notably, nanoparticles smaller than 4 nm grew into significantly larger ones, with submicroparticle sizes exceeding 87 nm for silicate and reaching 130 nm for silicon. Through systematic analysis of the size distribution changes, we identified optimal agglomeration times of 10 min for silicate and 20 min for silicon, revealing effective agglomeration within the frequency range of 1-1000 kHz. The agglomerated particles were stable for 5 days. Our electric field-assisted approach to obtain assembled nanoparticles that can be subsequently removed by conventional purification processes holds promise for enhancing future microfabrication processes, such as semiconductor manufacturing, potentially improving the manufacturing yield and uniformity by reducing the number of trace particles that can act as defective sites.

Electric and Dielectric Properties in Low-Frequency Fields of Composites Consisting of Silicone Rubber and Al Particles for Flexible Electronic Devices

Understanding the electrical conduction and dielectric polarization properties of elastomer-based composites is important for the design of flexible and elastic electronic devices and circuits. Five samples were manufactured by mixing silicone rubber (RTV-530) with Al particles in different volume fractions, x equal to 0%, 0.5%, 1%, 2.5% and 5.1%. Using the complex impedance measurements, the electric modulus, M, the electrical conductivity, σ, and the dielectric permittivity, ε, over the frequency range 100 Hz–200 kHz were analyzed. The electrical conductivity spectrum, σ(f), follows the Jonscher universal law and the DC conductivity of the samples, σ_DC, increases from 2.637·10⁻⁸ S/m to 5.725·10⁻⁸ S/m, with increasing x from, 0 to 5.1%. The conduction process was analyzed in terms of Mott’s variable-range-hopping (VRH) model. The hopping distance of the charge carriers, R_h decreases with increasing x, from 7.30 nm (for x = 0) to 5.92 nm (for x = 5.1%). The frequency dependence of permittivity, ε(f) = ε′(f) − iε″(f), reveals a relaxation process with the maximum of ε″(f) shifting from 301 Hz to 385 Hz and values of ε′(f) increasing with the increase of x.

Magnetic Field Effect on Thermal, Dielectric, and Viscous Properties of a Transformer Oil-Based Magnetic Nanofluid

Progress in electrical engineering puts a greater demand on the cooling and insulating properties of liquid media, such as transformer oils. To enhance their performance, researchers develop various nanofluids based on transformer oils. In this study, we focus on novel commercial transformer oil and a magnetic nanofluid containing iron oxide nanoparticles. Three key properties are experimentally investigated in this paper. Thermal conductivity was studied by a transient plane source method dependent on the magnetic volume fraction and external magnetic field. It is shown that the classical effective medium theory, such as the Maxwell model, fails to explain the obtained results. We highlight the importance of the magnetic field distribution and the location of the thermal conductivity sensor in the analysis of the anisotropic thermal conductivity. Dielectric permittivity of the magnetic nanofluid, dependent on electric field frequency and magnetic volume fraction, was measured by an LCR meter. The measurements were carried out in thin sample cells yielding unusual magneto-dielectric anisotropy, which was dependent on the magnetic volume fraction. Finally, the viscosity of the studied magnetic fluid was experimentally studied by means of a rheometer with a magneto-rheological device. The measurements proved the magneto-viscous effect, which intensifies with increasing magnetic volume fraction.

Electrode polarization and unusual magnetodielectric effect in a transformer oil-based magnetic nanofluid thin layer

In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid based on transformer oil and iron oxide nanoparticles stabilized by oleic acid. The complex dielectric permittivity measured in the frequency range from 1 mHz to 200 kHz shows an obvious electrode polarization effect and a Debye-like dielectric relaxation process. Both effects stem from the presence of space charge in the oil due to impurity ions, and in the nanofluid represented predominantly by a residual surfactant and uncompensated particle surface charge. It is shown that the spectra, which were measured in the temperature range from 298 K to 358 K, can be well represented by a fitting function consisted of one Havriliak-Negami term and the Jonscher's power law. In the investigated magnetic nanofluid layer, we found that the onset of the electrode polarization is suppressed to lower frequencies by the application of an external magnetic field (300 mT). This phenomenon is explained by a slowed-down migration of the space charge due to the Lorentz force and by a hindering effect of the formed magnetic nanoparticle aggregates. Surprisingly, a moderate decrease in the whole permittivity spectrum was observed for both parallel and perpendicular orientations of the electric and magnetic fields. This is in contradiction with the usual magnetodielectric anisotropy effect. Based on our qualitative analysis, we discuss potential reasons accountable for the observed effect.