Iron oxide nanorods are considered to be very promising platforms for biomedical applications, such as magnetic hyperthermia, magnetic resonance imaging, or immunoassays based on magnetooptical effects. However, their efficient colloidal stabilization is challenging, and colloidal aggregation could lead to the total loss of their performance. This work is focused on the synthesis and colloidal stabilization of iron oxide nanorods of an average length and diameter, L × d = 31 × 6 nm, synthesized by the hydrolysis of iron(III) salt, followed by reduction of the obtained akaganeite to iron oxide in a microwave reactor. Synthesized nanorods exhibited a weak ferrimagnetic behavior with remnant magnetization MR ∼ 3 emu/g and saturation magnetization MS ∼ 13 emu/g. The nanorods were dispersed in water after adsorption on their surface of three different polymers: linear bisphosphonate–poly(ethylene glycol) (PEG) molecules (denoted as OPT), polymethacrylate backbone/PEG side chains comb polymer (denoted as PCP; w...

In this work, we briefly review magnetic separation of ferrofluids composed of large magnetic particles (60nm of the average size) possessing an induced dipole moment. Such ferrofluids exhibit field-induced phase separation at relatively low particle concentrations (∼0.8vol%) and magnetic fields (∼10kA/m). Particle aggregates appearing during the phase separation are extracted from the suspending fluid by magnetic field gradients much easier than individual nanoparticles in the absence of phase separation. Nanoparticle capture by a single magnetized microbead and by multi-collector systems (packed bed of spheres and micro-pillar array) has been studied both experimentally and theoretically. Under flow and magnetic fields, the particle capture efficiency Λ decreases with an increasing Mason number for all considered geometries. This decrease may become stronger for aggregated magnetic particles (Λ∝Ma−1.7) than for individual ones (Λ∝Ma−1) if the shear fields are strong enough to provoke aggregate rupture. These results can be useful for development of new magneto-microfluidic immunoassays based on magnetic nanoparticles offering a much better sensitivity as compared to presently used magnetic microbeads.

The present paper is focused on the theoretical and experimental study of the kinetics of field-induced aggregation of magnetic nanoparticles of a size range of 20-100 nm. Our results demonstrate that (a) in polydisperse suspensions, the largest particles could play a role of the centers of nucleation for smaller particles during the earliest heterogeneous nucleation stage; (b) an intermediate stage of the aggregate growth (due to diffusion and migration of individual nanoparticles towards the aggregates) is weakly influenced by the magnetic field strength, at least at high supersaturation;

Microfluidic separation of magnetic particles is based on their capture by magnetized microcollectors while the suspending fluid flows past the microcollectors inside a microchannel. Separation of nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bioanalysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregation that amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increases nanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficient capture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickel micropillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as 6-10 kA/m, and experiments were carried out at flow rates ranging between 0.3 and 30 μL/min. Nanoparticle capture is shown to be mostly governed by the Mason number Ma, while the dipolar coupling parameter α does not exhibit a clear effect in the studied range, 1.4 < α < 4.5. The capture efficiency Λ shows a strongly decreasing Mason number behavior, Λ∝Ma^{-1.78} within the range 32 ≤ Ma ≤ 3250. We have proposed a simple theoretical model which considers destructible nanoparticle chains and gives the scaling behavior, Λ∝Ma^{-1.7}, close to the experimental findings.

Polymer nanocomposites of polystyrene matrix containing 5 wt % of organoswy were prepared using the solution method with sonication 23 hours. CPBr is used to modify the SWY clay after suturing with surface with Na+. Polystyrene was synthesized through solution polymerization in the presence of potassium persulfate (KPS) as an initiator. The synthesized PS/oswy were characterized by XRD, FTIR, SEM methods. Frequency dependent complex dielectric function, loss tangent spectra of PS and PS/swy nanocomposites up to 5 wt %.The nanocomposite materials with low dielectric constant and loss tang compared to the pure polystyrene were obtained. The dielectric constant increase with the increase of temperatures.

Zinc sulfide ZnS have been synthesized in reserves cores micelles in PS synthesized by emulsion polymerization. The size and morphology of ZnS/PS particles have been characterized via XRD, TEM, IR, SEM and AFM measurement. The dielectric proprieties of ZnS/PS are synthesized membrane, obtaining a water-swelling percentage around 20% and filled with ZnS nanoparticules were studied as a function of particle coating. The complex permittivity was measured with a 7600 Meter dielectric spectroscopy analyzer at applied voltage of 1 V with frequency varying between 10Hz and up to 1 KHz at different temperatures measurements are performed in dry conditions.