T. Hornowski

The influence of the concentration of ferroparticles in a ferrofluid on its magnetic and acoustic properties

This paper reports results of a study of magnetic and acoustic properties of a ferrofluid, EMG-605. The measurements were performed for three samples of the same ferrofluid differing in concentration. The magnetic susceptibility was measured as a function of an external magnetic field for each sample, which allowed us to determine the magnetization curves and saturation magnetization. The results provide information on the mean magnetic moment and the mean radius of the magnetite grain. In the samples subjected to an external magnetic field, the anisotropy of the ultrasonic wave absorption coefficient was determined. The mechanisms of ultrasonic wave energy dissipation through the translational and rotational degrees of freedom were established for some ferrofluid concentrations.

Investigation of magnetic fluids by ultrasonic and magnetic methods

The influence of magnetic field on the acoustic and magnetic properties of magnetic liquids is discussed. By fitting the curve of Taketomis theory to the experimental data of the anisotropy of ultrasonic attenuation, the values of quantities describing the structure of magnetic liquids have been determined. Moreover, the dependence of magnetic susceptibility on frequency has been measured. It shows that two processes of magnetization, based on the mechanisms proposed by Brown and Neel, contribute to the magnetization of the magnetic liquid.

Ultrasonic determination of the particle size distribution in water-based magnetic liquid.

Magnetic liquids are stable colloidal suspensions of nano-sized magnetic particles in a carrier liquid medium. In the present paper the determination of the particle size distribution function using ultrasonic spectroscopy is described. The ultrasonic spectra of water-based magnetic fluid measured in the 3.5-50 MHz frequency range are analyzed using formulas for the velocity and absorption of sound in dispersion media obtained by Vinogradov. The results of the ultrasonic studies are compared with the particles size distribution function evaluated from the processing of the magnetic susceptibility data.

Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating

The ultrasonic propagation in the water-based magnetic fluid with doubled layered surfactant shell was studied. The measurements were carried out both in the presence as well as in the absence of the external magnetic field. The thickness of the surfactant shell was evaluated by comparing the mean size of magnetic grain extracted from magnetization curve with the mean hydrodynamic diameter obtained from differential centrifugal sedimentation method. The thickness of surfactant shell was used to estimate volume fraction of the particle aggregates consisted of magnetite grain and surfactant layer. From the ultrasonic velocity measurements in the absence of the applied magnetic field, the adiabatic compressibility of the particle aggregates was determined. In the external magnetic field, the magnetic fluid studied in this article becomes acoustically anisotropic, i.e., velocity and attenuation of the ultrasonic wave depend on the angle between the wave vector and the direction of the magnetic field. The results of the ultrasonic measurements in the external magnetic field were compared with the hydrodynamic theory of Ovchinnikov and Sokolov (velocity) and with the internal chain dynamics model of Shliomis, Mond and Morozov (attenuation).

The effect of particle aggregate shape on ultrasonic anisotropy in concentrated magnetic fluids

The effect of aggregate shape on the ultrasonic anisotropy in magnetic fluid was studied. Experimental results were compared with the theory of Ahuja and Hendee. Analysis of experimental results in terms of the theoretical model show the formation of ellipsoidal aggregates composed of several particles. The chain-like aggregates (h = b/a >> 1; a and b being minor and major axis lengths, respectively) are most conspicuous in diluted ferrofluids while dense ferrofluids are characterized by a more homogeneous drop-like (h = b/a > 1) structure. This finding is supported by some theoretical simulations.

Resonance absorption of the ultrasonic waves in magnetic liquids in DC magnetic field

An external magnetic field, applied to a magnetic fluid, gives rise to spherical and chain-like clusters. The present paper is based on an acoustic method permitting the determination of the presence and size of the clusters by having recourse to resonance absorption of an ultrasonic wave in a magnetic fluid acted on by a magnetic field. We report our measurements of the variations Δα of the ultrasonic absorption coefficient for three frequencies of the wave in a selected magnetic fluid versus the external magnetic field strength applying the pulse method.

Magnetic nanoparticles for enhancing the effectiveness of ultrasonic hyperthermia

Ultrasonic hyperthermia is a method of cancer treatment in which tumors are exposed to an elevated cytotoxic temperature using ultrasound (US). In conventional ultrasonic hyperthermia, the ultrasound-induced heating in the tumor is achieved through the absorption of wave energy. However, to obtain appropriate temperature in reasonable time, high US intensities, which can have a negative impact on healthy tissues, are required. The effectiveness of US for medical purposes can be significantly improved by using the so-called sonosensitizers, which can enhance the thermal effect of US on the tissue by increasing US absorption. One possible candidate for such sonosensitizers is magnetic nanoparticles with mean sizes of 10–300 nm, which can be efficiently heated because of additional attenuation and scattering of US. Additionally, magnetic nanoparticles are able to produce heat in the alternating magnetic field (magnetic hyperthermia). The synergetic application of ultrasonic and magnetic hyperthermia can lead...

Investigation of magnetic and hyperthermic effects in ferrofluids with PEG biocompatible surfactant

The aim of this study was to investigate the influence of polyethylene glycol) surface-active coating on the magnetic and thermal properties of biocompatible magnetic liquids. The magnetization of the samples was measured using VSM method. From the magnetization data the distribution function of the size of the magnetite particles was determined. Heating ability of the PEG-stabilized magnetic fluids was determined by the calorimetric measurement of the heating rate at 750 kHz frequency and 0.52 kA/m field to evaluate the possibilities of their successful use in hyperthermia treatment. The experimental data of the heating rate were compared with theoretical expression derived by Rosensweig.

The effect of the rate of magnetic field and temperature changes on the ultrasonic wave absorption coefficient in a magnetic fluid

The rate of external magnetic field changes as well as temperature influences the structure of a magnetic fluid. This work presents experimental results on changes in the ultrasonic wave absorption coefficient of EMG-605 water-based magnetic fluid as a function of the external magnetic field intensity for different rates of magnetic field changes, at different temperatures. On the basis of these studies, radii of spherical clusters formed in the fluid under the influence of an external magnetic field have been determined.

The effect of magnetic field on the anisotropy of the ultrasonic attenuation in magnetic liquids

Experimental results for the DC magnetic field influence on the anisotropy of attenuation of ultrasound in ferrofluids are presented. The measurements were performed for the frequency 1.18 MHz, at the temperatures 10 and , with magnetic field strengths H = 39.8, 79.58 and . Comparison of the experimental results with the Taketomi theory allowed the determination of the cluster radius and the number density of the colloidal particles.