Doina Bica

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.

Agglomerate formation in moderately concentrated ferrofluids from static magneto-optical measurements

In this paper the stability of ferrofluids based on several organic solvents with magnetite particles having different stabilization layers from static linear dichroism and birefringence has been studied. Based on the theory of formation it has been found that the mean number of particles per chain for most samples is very low; the mean ellipticity of chains computed from the formation theory turns out to be that of individual particles. A good agreement with the results of image processing of an electron micrography was found.

The antitumor effect of locoregional magnetic cobalt ferrite in dog mammary adenocarcinoma

The endocytosis of nanosized magnetic particles by tumor cells led to numerous tests to establish the use of this phenomenon in antitumor therapy. The direct antitumor effect of a biocompatible cobalt-ferrite-based magnetic fluid directly inoculated in bitch mammary tumors was studied. A direct correlation between tumor cell lysis and cobalt ferrite was established in tumors. Massive endocytosis of magnetic particles was observed 1 h after the contact of magnetic fluid with tumor cells.

Magnetite Nanoparticles Stabilized Under Physiological Conditions for Biomedical Application

The biomedical application of water based magnetic fluids (MFs) is of great practical importance. Their colloidal stability under physiological conditions (blood pH ∼ 7.2–7.4 and salt concentration ∼0.15 M) and more in high magnetic field gradient is crucial. Magnetite or maghemite nanoparticles are used in general. In the present work, magnetite nanoparticles were stabilized with different compounds (citric acid (CA) and phosphate) and sodium oleate (NaO) as the most used surfactant in the stabilization of MFs. The adsorption and overcharging effect were quantified, and the enhancement in salt tolerance of stabilized systems was studied. Adsorption, electrophoretic mobility and dynamic light scattering (DLS) measurements were performed. The electrolyte tolerance was tested in coagulation kinetic measurements. Above the adsorption saturation, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The aim was to research these two important effects and demonstrate that none of them alone is enough. The phosphate was not able to stabilize the ferrofluid in spite of our expectation, but the other two additives proved to be effective stabilizing agents. The magnetite was well stabilized by the surface complexation of CA above pH ∼ 5, however, the salt tolerance of citrate stabilized MFs remained much below the concentration of physiological salt solution, and more the dissolution of magnetite nanocrystals was enhanced due to Fe-CA complexation in aqueous medium, which may cause problems in vivo. The oleate double layers were able to stabilize magnetite nanoparticles perfectly at pH ∼ 6 preventing particle aggregation effectively even in physiological salt solution.

Magnetic Nanofluids: Synthesis and Structure

Recent results are reviewed concerning the synthesis of magnetic nanoparticles (MNP) and various types of magnetic nanofluids (MNF) or ferrofluids, their structural properties and behavior in an external magnetic field, specially tailored to meet the requirements of some specific engineering and biomedical applications. There are described the chemical co-precipitation procedure and the liquid- and gas-phase thermal decomposition methods to obtain magnetic nanoparticles (Fe3O4, γ-Fe2O3, CoFe2O4, Co, Fe and Fe-C) of adequate size distribution to prepare magnetic nanofluids. Sterical stabilization of MNPs in organic and water carrier liquids is discussed in details, related to the diagrams of magnetic nanofluid synthesis procedures. The macroscopic behavior, especially the magnetic and flow properties of magnetic fluids and their compatibility with various media and exploitation conditions in magnetofluidic devices are described related to composition and structural characteristics, such as nature and size of magnetic nanoparticles, nature and chain length of surfactants used for ultrastable dispersion of magnetic nanoparticles in various non-polar and polar carrier liquids, hydrodynamic size of particles, as well as the formation and characteristics of agglomerates induced by an applied magnetic field.

Concentration and composition dependence of rheological and magnetorheological properties of some magnetic fluids

Rheological and magnetorheological behaviour of magnetic fluids with nonpolar and polar carrier liquids were investigated, using capillary and rotary viscometers, the measuring cells being completed with specially designed electromagnets. In the absence of a magnetic field the relative viscosity—hydrodynamicparticle volume fraction dependence is well fitted especially by the formulas of Vand, KriegerDougherty and Chow. The fitted values of the Chow interaction coefficient are close to the theoretical value, except at low temperatures and close packing of magnetic nanoparticles. The effective viscosity of various types of magnetic fluids in an applied magnetic field is strongly dependent on microstructural characteristics. A relatively large, almost 1 order of magnitude, increase in the relative viscosity was measured for medium-concentration water-based magnetic fluids, with large secondary agglomerates. The magnetoviscous effect was found to be rather small, below 10%, for highly stable magnetic fluid samples on decahydronaphathalene and pentanol carriers.

Concentration dependence of magnetisation and magneto-optical effects in a ferrofluid with double layer stabilized particles

Abstract A wide experimental work concerning the concentration dependence of magnetisation and magneto-optical effects (linear and circular) is presented. This has been performed on a high-quality ferrofluid over a 0.04–16.8% volume fraction range. Data processing was used for granulometric analysis and estimation of Shliomis diameter, magnetic anisotropy constant, components of dielectric permittivity of particles and particle ellipticity.

Experimental investigation of magneticinduced phase-separation kinetics in aqueous ferrofluids

In this article we report microscopy and light scattering investigation of phase-separation phenomenon in ferrofluids. The influence of the temperature and an external magnetic field on the kinetics and on the quantitative extent of the phase separation was investigated.

Leakage-free Rotating Seal Systems with Magnetic Nanofluids and Magnetic Composite Fluids Designed for Various Applications

Recent results are presented concerning the development of magnetofluidic leakage-free rotating seals for vacuum and high pressure gases, evidencing significant advantages compared to mechanical seals. The micro-pilot scale production of various types of magnetizable sealing fluids is shortly reviewed, in particular the main steps of the chemical synthesis of magnetic nanofluids and magnetic composite fluids with light hydrocarbon, mineral oil and synthetic oil carrier liquids. Design concepts and some constructive details of the magnetofluidic seals are discussed in order to obtain high sealing capacity. Different types of magnetofluidic sealing systems and applications are reviewed. Testing procedures and equipment are presented, as well as the sealing capabilities of different types of magnetizable fluids.

Application of Magnetizable Complex Systems in Biomedicine

Magnetic fluids or ferrofluids as they are often called mainly consist of nano sized iron oxide particles (Fe3O4 or γ-Fe2O3) that are suspended in carrier liquid. In recent years, substantial progress has been made in developing technologies in the field of magnetic microspheres, magnetic nanospheres and ferrofluids. Techniques based on using of these biocompatible magnetizable complex systems have found application in numerous biological fields viz. diagnostics, drug targeting, molecular biology, cell isolation and purification, radio immuno assay, hyperthermia causing agents for cancer therapy, nucleic acid purification etc. Biocompatible ferrofluids normally use water as a carrier medium. In order to prevent agglomeration the magnetic nanoparticles have to be stabilized by ionic interaction, a bilayer of an appropriate agent (e.g. fatty acid), aspartic and glutamic acid or peptides. Alternatively, the coprecipitation of ferrous/ferric ions is performed in the presence of appropriate biopolymer such as dextran, polyethylen glycol or polyvinyl alcohol. It has been shown that proteins and enzymes can be bound covalently to freshly prepared magnetite in the presence of carbodiimide. Several clinically important enzymes and proteins that include bovine serum albumin, streptokinase, chymotrypsin, dispase, glucose oxidase (GOD) etc., have been immobilized based on this method. The immobilized enzymes showed about 50-80 of the original added enzyme activity. This contribution will summarize the information about the ways to synthesize biocompatible magnetic nanoparticles and complexes containing them and the application of magnetic complex systems in biomedicine at magnetic drug targeting and hyperthermia.