Solid State Phenomena Vols. 152-153

Abstract: The instability of convection patterns representing a combination of vertical Rayleigh rolls and horizontal rolls resulting from longitudinal horizontal magnetic field is investigated in an inclined layer of magnetic colloid by experiments and numerical simulations. Visualization of convection patterns is provided by a temperature-sensitive liquid crystal film. The rich spectrum of convection structures is observed against different values of inclination angles and uniform magnetic fields. If the horizontal longitudinal magnetic field is strong enough it extinguishes the convection perturbations along the field direction and stabilizes Rayleigh flows. Observed patterns at about two supercriticalities and with small inclination angles show mostly spatially and temporally chaotic structures.

Abstract: Magnetic birefringence in kerosene based magnetic fluid in variable and pulsing field is investigated. It is shown, that the size of aggregates of defining effect is about 70 nanometers. The absence of spontaneous magnetisation at such aggregates is installed. The value of the parameter connecting the permanent and induced magnetic moments of the aggregate of nanoparticles is experimentally defined.

Abstract: A suspension of magnetic particles in a viscous liquid magnetized in an alternating uniform magnetic field is theoretically studied. The suspension is regarded as so dilute that interaction of a single particle with the applied magnetic field can be considered without taking into account the influence of other particles. The complex magnetic susceptibility of the suspension is found as a function of the frequency of the applied magnetic field. The heat generation power density averaged over the period of the oscillations is calculated.

Abstract: The behavior of a magnetic fluid drops in a thin film under the action of a perpendicular magnetic field is investigated. Instability of the form of a drop and formation of star-like patterns in the spot of contact of the deformed drop with layer boundaries is detected. The disintegration of a drop attended fractal pattern formation is investigated. Dependence of character of these processes on a size of drops, concentration and rate of a magnetic field rise is determined.

Abstract: This paper presents computational and experimental studies of two phenomena occurring in magnetic suspensions under strongly non-equilibrium conditions created by high-frequency (in comparison with the inverse characteristic time of the particle mechanical motion) magnetic fields. First is the dynamic magnetic hysteresis in a dilute suspension of highly-coercive particles subjected to linearly polarized fields. Energy absorption by particles is of great interest for cancer treatment, chemical technology, biology and smart materials science. Second is related to polymer composite technologies and represents dissipative self-organization of a system of magnetically soft particles in a drying thin layer of polymer solution set under a rotating magnetic field

Abstract: The structure of magnetic fluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids.

Abstract: Contrast variation method in small-angle neutron scattering (non-polarized neutrons) is applied to magnetic fluids (MFs) with magnetite dispersed in benzene and coated with myristic or oleic acid in zero external magnetic field. The basic functions approach for polydisperse superparamagnetic systems is used to get structure parameters of particles in MFs.

Abstract: In the present paper we report temperature dependent magnetization measurements done on a magneto-active elastomers (MAEs) consisting of a siloxane rubber filled with carbonyl iron particles. The experiments performed in this study are similar to the conventional Zero-Field-Cooled and Field-Cooled magnetic tests. To the best of our knowledge, this approach, successfully used for studies on magnetic fluids, has never ever been applied to MAE. This test allowed us to reveal the effect of change of MAE structure under the action of an external magnetic field.

Abstract: The aim of this work is to elaborate nanocomposite thin films sensitive to a magnetic field by incorporating magnetic nanoparticles in a symmetrical diblock copolymer matrix organized in lamellae on plane substrates. On the one hand, the symmetrical diblock copolymer P(n-BMA)-b-PS is synthesized by ATRP and characterized by several methods. On the other hand, nanoparticles made of maghemite -Fe2O3 are functionalized with PS using the “grafting from” technique in order to make them compatible with polystyrene and to insert them in PS lamellae. Composite films are elaborated by “spin coating” a solution containing both the -Fe2O3@PS core-shell nanoparticles and the copolymer onto a silicon substrate. After annealing, these films are characterized mainly by AFM and neutron reflectivity to investigate the lamellar order.

Abstract: The microstructure of ferrofluids (magnetite/oleic acid/benzene) with an excess of free oleic acid is investigated by small-angle neutron scattering (SANS). For such excess higher than 25 vol. % a sharp break in the stability of ferrofluids occurs followed by coagulation and precipitation. Below this value the influence of the surfactant excess on the stability of ferrofluids is insignificant; neither particle aggregation nor surfactant agglomeration is observed. The interaction of free acid molecules in the ferrofluids is compared with that in pure benzene solutions. A significant increase in the attraction is observed for acid molecules in the ferrofluids, which is related to the loss of magnetic fluids stability at high excess of acid.