V. L. Aksenov

Comparative structure analysis of non-polar organic ferrofluids stabilized by saturated mono-carboxylic acids

The structure of ferrofluids (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 in case of saturated acid surfactants, 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.

Analysis of the structure of aqueous ferrofluids by the small-angle neutron scattering method

The structures of several aqueous magnetic fluids stabilized by different combinations of surfactants have been compared using small-angle neutron scattering. The size distribution functions of colloidal particles in water have been determined. The degree of clustering of magnetic nanoparticles has been obtained from comparison with electron microscopy data. The combinations of surfactants that lead to a minimum clustering have been revealed.

Neutron interference at grazing incidence reflection. Neutron standing waves in multilayered structures: Applications, status, perspectives

Possibilities of creating a field of neutron standing waves (NFSW) in a layered nanostructure for the purposes of formation and analysis of the neutron beam and investigation of the properties of the structure itself are discussed. The status of investigations of such neutron wave fields is formulated and directions of their possible application are indicated. The results of investigations in the regimes of neutron standing waves and enhanced neutron standing waves with a specified neutron spin state carried out at the pulsed reactor IBR-2 using different registration channels are presented. The high sensitivity of NFSW for structural investigations is noted.

Spin-flip spatial neutron beam splitting in magnetic media

Possible uses of the effect of beam splitting for investigations of magnetic media, formation of neutron beams and measurements of their characteristics are discussed. The results of experimental investigations of magnetic layers and layered structures are presented. The application of the effect for the determination of the parameters of uniformly magnetized magnetics and magnetics with a domain structure is noted as perspective.

Solvatochromism and Fullerene Cluster Formation in C60/N-methyl-2-pyrrolidone

UV-Vis spectroscopy and small-angle neutron scattering experiments are performed on the cluster solution of fullerene C60 in N-methyl-2-pyrrolidone before and after dilution of the system with pure solvent. Some changes in the UV-Vis spectra showing solvatochromism at dilution are observed, while the neutron scattering signal does not change. The effect is discussed with respect to the relation between solvatochromism and cluster formation for fullerene solutions in nitrogen-containing solvents.

Magnetic fluids with excesses of a surfactant according to the data of small-angle neutron scattering

Magnetic fluids (magnetite/oleic acid/benzene) with excesses of a surfactant (oleic acid) are studied using small-angle neutron scattering. Solutions of oleic acid in benzene are also studied to reveal whether an aggregation of acid molecules can occur. It is shown that oleic acid does not form micelles in benzene in the range of concentrations under study (up to volume fractions of 35%). It follows from our results that the excess of a surfactant (less than a volume fraction of 25%) in a magnetic fluid does not lead to a noticeable aggregation of its particles. At the same time, an increase in the attraction between free surfactant molecules in the magnetic fluid (compared to pure solutions of oleic acid in benzene) is observed. If the excess of a surfactant is greater than 25%, then the stability of the magnetic fluid is sharply violated, which leads to the aggregation of magnetic particles.

Aggregation in non-ionic water-based ferrofluids by small-angle neutron scattering

Small-angle neutron scattering was applied for detecting structural changes in non-ionic water-based ferrofluids when they were put in a magnetic field and then, after some period, returned to normal conditions. The observed changes in the scattering reflect the formation of elongated chain-like complexes stimulated by the magnetic field. The growth of these complexes takes place long after the magnetic field is turned off.

On the determination of the helical structure parameters of amyloid protofilaments by small-angle neutron scattering and atomic force microscopy

The helical structure of amyloid protofilaments of hen egg white lysozyme was analyzed by small-angle neutron scattering (SANS) and atomic force microscopy (AFM). The structure of these formations in bulk solutions was adequately described by SANS in terms of a simplified model of a helix with spherical structural units. The found main helix parameters (pitch and effective diameter) are consistent with the results of AFM analysis for amyloid fibrils adsorbed on a mica surface. Both methods reveal a strong isotope effect on the structure of amyloid fibrils with respect to the substitution of heavy for light water in the solvent. Specific details responsible for the structural differences when comparing SANS and AFM data are discussed from the viewpoint of methodological aspects, the influence of different (native and adsorbed) amyloid states and sample preparation.

Effect of Surfactant Excess in Non-Polar Ferrofluids Probed by Small-Angle Neutron Scattering

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.

SANS study of clusters in aqueous magnetic fluids

Small-angle neutron scattering studies of the structure of clusters formed in aqueous magnetic fluids are reviewed. The possibilities of contrast variation using hydrogen-deuterium isotopic substitution in these complex systems are shown. Examples of the use of the method in study of the kinetics of cluster organization of aqueous magnetic fluids upon different external conditions (temperature and magnetic field) are presented. Urgent problems related to aqueous magnetic fluids, in which the method seems to be most promising, are outlined.