Maria Balasoiu

Modelling of magnetodipolar striction in soft magnetic elastomers

The origin of the so called magnetostriction effect, i.e., the deformation of a soft magnetic elastomer (SME) in response to a uniform magnetic field is discussed. We note that up to now there exists a number of cases, where the theory is unable to explain the facts well established for real SMEs. In our view, the essential issue, formerly not adequately accounted for, is the type of structural short-range order in the magnetic microparticle assembly. Two-dimensional model problems are formulated and solved, which demonstrate the validity of the hypothesis.

Magnetic properties of biomineral particles produced by bacteria Klebsiella oxytoca

Ferrihydrite nanoparticles (2–5 nm in size) produced by bacteria Klebsiella oxytoca in the course of biomineralization of iron salt solutions from a natural medium exhibit unique magnetic properties: they are characterized by both the antiferromagnetic order inherent in a bulk ferrihydrite and the spontaneous magnetic moment due to the decompensation of spins in sublattices of a nanoparticle. The magnetic susceptibility enhanced by the superantiferromagnetism effect and the magnetic moment independent of the magnetic field provide the possibility of magnetically controlling these natural objects. This has opened up the possibilities for their use in nanomedicine and bioengineering. The results obtained from measurements of the magnetic properties of the ferrihydrite produced by Klebsiella oxytoca in its two main crystalline modifications are reported, and the data obtained are analyzed theoretically. This has made it possible to determine numerical values of the magnetic parameters of real biomineral nanoparticles.

Microstructure of stomaflex based magnetic elastomers

Stomaflex elastomers filled with two types of magnetic particles (nano- and micro-sized) were investigated. It was observed that doping with Fe3O4 nanoparticles and applying a magnetic field during the polymerisation process led to a significant change in the local structure of the elastomer. Decreases in the quasi-crystalline phase concentration, in the average size of the crystalline blocks, and in the ordering distance were observed after doping the elastomer with magnetite nanoparticles. After filling the polymer with Fe3O4 nanoparticles, yet the elastomer fractal dimension changes. For the elastomer filled with a large amount of Fe microparticles (75% particle concentration) a texture effect is observed, and this effect is larger for the samples polymerised in a magnetic field. At all microparticle concentrations, these elastomers exhibit surface fractal structure.

Scattering from generalized Cantor fractals

A fractal with a variable fractal dimension, which is a generalization of the well known triadic Cantor set, is considered. In contrast with the usual Cantor set, the fractal dimension is controlled using a scaling factor, and can vary from zero to one in one dimension and from zero to three in three dimensions. The intensity profile of small-angle scattering from the generalized Cantor fractal in three dimensions is calculated. The system is generated by a set of iterative rules, each iteration corresponding to a certain fractal generation. Small-angle scattering is considered from monodispersive sets, which are randomly oriented and placed. The scattering intensities represent minima and maxima superimposed on a power law decay, with the exponent equal to the fractal dimension of the scatterer, but the minima and maxima are damped with increasing polydispersity of the fractal sets. It is shown that, for a finite generation of the fractal, the exponent changes at sufficiently large wave vectors from the fractal dimension to four, the value given by the usual Porod law. It is shown that the number of particles of which the fractal is composed can be estimated from the value of the boundary between the fractal and Porod regions. The radius of gyration of the fractal is calculated analytically.

New opportunities provided by modernized small-angle neutron scattering two-detector system instrument (YuMO)

Main features of the modernized small-angle neutron scattering spectrometer (YuMO) at IBR-2M pulsed reactor are described. New installations for sample environment of the spectrometer are highlighted. The modernized SANS instrument (YuMO) is equipped with a new type of position sensitive detector as well as two detector system which provide a unique dynamic range (Qmax/Qmin ratio is about 90). Sample environment is extended with a magnetic system (magnetic field about 2.5 Tesla), automated high pressure setup which allows simultaneous SANS and volumetric high pressure studies and light illumination system. In particular, these developments led to considerable improvements of resolution of the instrument (about 1%) and opened the possibility to study anisotropic materials and perform efficient high pressure studies.

Anisotropic Silicone Rubber Based Magnetorheological Elastomer with Oil Silicone and Iron Microparticles

Results on anisotropic magnetorheological elastomers magnetoelasticity are presented and discussed. In the dipole approximation, and considering the MRE as a continuous linear body, the effects of magnetic field on its main elastic properties (linear deformations and Young module) are investigated. Experimental evidences that the compression of the cylindrical bar is influenced by the intensity of the longitudinal magnetic field and the Young module of the MRE sample increases with the intensity H of the longitudinal magnetic field are obtained and the results discussed.

Structure organization and magnetic properties of microscale ferrogels: The effect of particle magnetic anisotropy

The equilibrium structure and magnetic properties of a ferrogel object of small size (microferrogel(MFG)) are investigated by coarse-grained molecular dynamics. As a generic model of a microferrogel (MFG), a sample with a lattice-like mesh is taken. The solid phase of the MFG consists of magnetic (e.g., ferrite) nanoparticles which are mechanically linked to the mesh making some part of its nodes. Unlike previous models, the finite uniaxial magnetic anisotropy of the particles, as it is the case for real ferrogels, is taken into account. For comparison, two types of MFGs are considered: MFG-1, which dwells in virtually non-aggregated state independently of the presence of an external magnetic field, and MFG-2, which displays aggregation yet under zero field. The structure states of the samples are analyzed with the aid of angle-resolved radial distribution functions and cluster counts. The results reveal the crucial role of the matrix elasticity on the structure organization as well as on magnetization of both MFGs. The particle anisotropy, which plays insignificant role in MFG-1 (moderate interparticle magnetodipole interaction), becomes an important factor in MFG-2 (strong interaction). There, the restrictions imposed on the particle angular freedom by the elastic matrix result in notable diminution of the particle chain lengths as well as the magnetization of the sample. The approach proposed enables one to investigate a large variety of MFGs, including those of capsule type and to purposefully choose the combination of their magnetoelastic parameters.

Magnetic field and particle concentration competitive effects on ferrofluid based silicone elastomer microstructure

Structural peculiarities of ferroelastomers composed of polydimetylsiloxane with embedded magnetite particles during polymerization have been studied by small-angle neutron scattering. The effects of ferroparticles’ concentration in the range of C = 0–6 wt %, and external magnetic fields of induction B = 0−1 kG applied during the polymerization on the structure of polymeric matrix and particles distribution in polymer were analyzed.

Characterization of bio-synthesized nanoparticles produced by Klebsiella oxytoca

Structural and morphological properties of biogenic ferrihydrite nanoparticles produced by bacteria Klebsiella oxytoca are investigated. The stability of water dispersions of biomineral particles produced by Klebsiella oxytoca was monitored by UV-Vis spectroscopy. Their chemical composition was determined by FT-IR spectroscopy. The vibrational spectra of biogenic ferrihydrite nanoparticles revealed typical absorption peaks of exopolysaccharides. Morphological analysis based on Raman spectroscopy indicated the presence of exopolysaccharides on the surface as well as inside the pores of the ferrihydrite nanoparticles. Structural investigations of ultrasonic assisted samples of different concentration of water dispersed particles were performed using small angle X-ray scattering analysis. Model calculations and fitting procedures revealed scattering objects of an elongated shape with 6.73±0.16 nm radius of gyration.

Iron oxide-silica nanocomposites yielded by chemical route and sol–gel method

Magnetic nanoparticles yielded by chemical route were surface modified with stabilizing agents being further coated by sol–gel method with silica shell to be used for various applications. Iron oxide magnetic cores were dispersed in water by single citrate layer and, respectively, by double oleate hydrophilic coating. Sol–gel reaction with tetraethylorthosilicate provided further coating with silica that confers increased reactivity for ligand coupling. Microstructural and magnetic properties were investigated by standard methods evidencing nanometric size, good crystallinity, and superparamagnetic behavior. Comparative analysis evidenced similar crystallite size for both citrate- and oleate-coated magnetic nanoparticles, while granularity was changed after silica adding. Saturation magnetization diminished less for oleate-stabilized nanoparticles than for citrate-stabilized ones after silica coating and moderate thermal treatment. Such prepared magnetic nanocomposites could have possible utilization as magnetic vectors for targeted biomolecules.Graphical Abstract