title: Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating.
abstract: 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).
authors.affiliation: Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Józefczak
authors.affiliation: Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland.
authors.forename: T
authors.initials: T
authors.lastname: Hornowski
authors.affiliation: Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia.
authors.forename: V
authors.initials: V
authors.lastname: Závišová
authors.affiliation: Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Skumiel
authors.affiliation: Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia.
authors.forename: M
authors.initials: M
authors.lastname: Kubovčíková
authors.affiliation: Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia.
authors.forename: M
authors.initials: M
authors.lastname: Timko
keywords: Hydrodynamic size; Magnetic fluid; Nanoparticles; Velocity and absorption of ultrasound