Aqueous Magnetic Fluids Research Articles

Size distribution of nanoparticle aggregates in an aqueous magnetic fluid based on atomic-force microscopy data

Atomic-force microscopy (AFM) has been applied in a fluid environment to determine the size distribution function of nanoparticle aggregates in an aqueous magnetic fluid with magnetite particles coated by polyacrylic acid for stabilization. It is proposed to use an external magnetic field to anchor aggregates on the substrate. The data are compared with the AFM data for dried precipitates of the system under consideration, formed during evaporation of the liquid carrier under different conditions, as well as with the particle size distribution in the initial system obtained from small-angle X-ray scattering data.

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.

NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.

Experimental investigation on blood magnetic contamination in the presence of drug molecules

The purpose of the present project was to study the interference of magnetic nanoparticles with drug molecules – rifampicin, used in lung infectious disease and respectively, sodium diclofenac, an antiinflammatory steroid. The controlled magnetic contamination was accomplished using colloidal nanoparticles supplied from diluted magnetic fluids. Various concentrations of diluted aqueous magnetic fluids, based on magnetite cores coated with citric acid and respectively sodium oleate, were tested. The experiment was focused on the capacity of the magnetic nanoparticles to form reversible complexes with the drug molecules, as well as on the monitoring of the nanoparticle-drug complex dynamics, under the action of external magnetic field. The level of released rifampicin ranged between 4 mg/100 ml and 7 mg/100 ml for the magnetic exposure of 20 mT, while the sodium diclofenac decomplexation level was not higher than 2.5 mg/100 ml under magnetic exposure of 60 mT. The experimental arrangement was proved to be an adequate model for the dynamical study of magnetite reversible complexation with drug molecules, evidencing certain specific values of drug concentration and magnetic field induction that favour such interactions.

Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles

The formation of small and large molecular polyanionic coating on the surface of magnetite (Fe 3O 4) nanoparticles and their role in the stability enhancement of aqueous magnetic fluids are compared. Magnetite was synthesized and stabilized with citric (CA) and humic (HA) acids. The macromolecular HA, a notable fraction of the natural organic matter (NOM), contains mainly carboxylic groups similarly to the CA, and both acids are able to form surface complexes on the ≡Fe–OH sites of iron oxides. The pH-dependent charge state of particles and their aggregation were quantified, and the enhanced salt tolerance of stabilized systems was studied. The dynamic light scattering (DLS) method was used to characterize colloidal stability under different conditions. The average particle size and electrophoretic mobility were measured, and the electrolyte tolerance was tested in coagulation kinetic measurements. The colloidal stability of magnetite dispersions depends sensitively on the pH and the concentration of organic acids present. The trace amount of HA neutralizes the positive charges on magnetite surface under acidic condition only in part, and so it promotes the aggregation between the particles having both positive sites and negative humate patches on the surface. Above the adsorption saturation, the surface becomes completely covered causing the reversal of charge sign and overcharging of nanoparticles. The magnetite nanoparticles become stabilized in a way of combined steric and electrostatic effects. The thicker layer of macromolecular HA provides better electrosteric stability than that of CA coating. However, in the presence of either CA or HA, the dissolution of magnetite is enhanced due to the complexation of iron ions in the aqueous medium.

Experimental investigation on heat transfer characteristics of magnetic fluid flow around a fine wire under the influence of an external magnetic field

Experimental investigation is conducted to get insight into convective heat transfer features of the aqueous magnetic fluid flow over a fine wire under the influence of an external magnetic field. The convective heat transfer coefficient of the aqueous magnetic fluid flow around the heated wire is measured in both the uniform magnetic field and the magnetic field gradient. The effects of the external magnetic field strength and its orientation on the thermal behaviors of the magnetic fluids are analyzed. The experimental results show that the external magnetic field is a vital factor that affects the convective heat transfer performances of the magnetic fluids and the control of heat transfer processes of a magnetic fluid flow can be possible by applying an external magnetic field.

A facile method to synthesize carboxyl-functionalized magnetic polystyrene nanospheres

Magnetic polystyrene nanospheres with high magnetite content and abundant surface carboxyl groups were prepared by emulsifier-free emulsion polymerization in the presence of aqueous magnetic fluid coated with oleic acid and 10-undecenoic acid as primary and secondary surfactants respectively. The effects of initiator concentration, initiator type (water-soluble or oil-soluble), monomer concentration and ferrofluid content on the particle characteristics such as the size, morphology, magnetic properties and the number of carboxyl groups were investigated. When water-soluble potassium peroxodisulfate (KPS) was used as the initiator, magnetite nanoparticles were uniformly encapsulated in polystyrene particles, while in the oil soluble benzoyl peroxide (BPO) system, magnetite particles were located on one side of magnetic polystyrene nanospheres. The results showed that two mechanisms for the nucleation and growth of nanospheres were involved according to the kind of initiator used in the polymerization. The magnetic nanospheres were superparamagnetic with the highest saturation magnetization of 29.78 emu/g and the corresponding magnetite content of 41.67%. The maximum amount of surface carboxyls was 0.5594 mmol/g. BSA (bovine serum albumin) was used to test the immobilization capacity of proteins onto the magnetic spheres. The immobilization capacity was about 196.2 mg BSA/g. These carboxylated magnetic polystyrene nanospheres have extensive potential biomedical applications.

CO2 absorption into amine solutions: a novel strategy for intensification based on the addition of ferrofluids

AbstractBACKGROUND: In this paper a novel approach for increasing the mass transfer coefficient in gas/liquid mass transfer is reported and applied to the industrially important system of CO2 absorption. The approach makes use of a ferrofluid additive to the liquid phase. To demonstrate this strategy, a wetted wall column has been built and experiments have been conducted on the CO2/methyl diethanolamine (MDEA) system. This reaction system allows the absorption to be carried out in the transition regime between slow and fast regimes, so that the mass transfer coefficient (kL) and interfacial area (ai) can be measured independently, in the presence and absence of ferrofluids. A surfactant‐coated aqueous magnetic fluid was prepared and shown to be stable in MDEA solutions.RESULTS: The experimental results, with this fluid, show that there is an enhancement in mass transfer in the presence of ferrofluids, the extent of which depends on the amount of ferrofluid added. The enhancement in mass transfer coefficient was 92.8% for a volume fraction of the fluid of about 50% (solid magnetite volume fraction of about 0.39%). Experiments were also carried out to further enhance the mass transfer rates by employing a periodic oscillating magnetic field. Under the conditions employed, there was no further impact of magnetic field on mass transfer rates.CONCLUSIONS: Magnetic nanoparticles are able to significantly enhance gas/liquid mass transfer rates when added to the liquid phase. The reasons for this striking effect are under investigation. It is possible for significantly higher enhancements to be produced by the action of an external field, but this requires special fluids to be formulated which are not affected by the chemical solvent used. These results have significance for the absorption of CO2 in industrial absorbers using amine solutions. Copyright © 2008 Society of Chemical Industry

Microstructural and magnetic properties of magnetic fluid based on magnetite coated with tartaric acid

An aqueous magnetic fluid based on iron oxide particles as solid nano-magnetic phase was prepared by applying the chemical precipitation method. Tartaric acid (C4H6O6) was used to functionalize magnetic cores. Physical tests have been performed in order to reveal the microstructural and magnetic features, their optimization being needed for biomedical utilization. The particles’ size was investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM) and magnetization measurements. Fourier transform infrared absorption spectra (FT-IR) have been recorded aiming to get some information on the solid phase structure. 1. Introduction. Recently, the synthesis of magnetic materials on the nano-scale has become a field of increased interest due to the mesoscopic properties shown by nanoparticles of quantum dimensions located in the transition region between atoms and bulk solids. Magnetic fluids (ferrofluids) are two-phase systems, consisting of small ferri- and ferromagnetic nanoparticles dispersed in a liquid [1]. Because the size of the magnetic particles lies in the nanometer range (often around 10 nm in diameter), those suspensions are referred to as magnetic nano-colloids. The colloidal nanoparticles are subject to random displacement due to their bombardment by impulsive forces from the solvent molecules, in which they are dispersed. Colloidal stability is assured by coating the nanoparticles with shells of a nonmagnetic molecular surfactant, which prevents close approach of the magnetic cores, thereby, reduces the possibility of aggregation via Van der Waals or dipolar attractions. When the dipolar interactions are much stronger than the thermal energies, particle chains start growing and forming more complex structures, depending on the particle volume fraction, size distribution, temperature or a magnetic field applied [2]. The colloidal stability of magnetic fluids is a complex issue related to the synthesis procedure followed, including the nature of surfactant(s) and carrier liquids used [3]. The magnetic fluid stability is the main characteristic that determines the possibility to exploit magnetic fluids in different industrial and biomedical applications. Magnetic fluids are said to be superparamagnetic, meaning that they are attracted by a magnetic field but retain no residual magnetism after the field is removed [1]. When the magnetic nanoparticles are dispersed in an ionic solution, the dissociation of ionogenic groups is followed by the differential adsorption on the particle surface generating a particle surface potential. Biophysicists pay more and more attention to the magnetic nanoparticles functionalized with a biocompatible nonmagnetic molecular surfac

Novel aqueous magnetic fluids stabilized by albumin for biological application

This paper demonstrates bovine serum albumin (A1) and ovalbumin (A2) can be used as stabilizer to prepare aqueous magnetic fluids for gene therapy. The content of magnetite depends on the reaction temperature and time. The reaction is performed at 70 °C for 30 min, which is appropriate to obtain stable aqueous magnetic fluids. The super paramagnetic magnetic fluids composed of Fe 3O 4 cores, which have average diameter about 8 nm. A high positive ζ-potential of +46.0 mV and suitable hydrodynamic diameters were realized.

Dimensional analysis of aqueous magnetic fluids

A comparison of the synthesis and characterization of three aqueous magnetic fluids intended for biomedical applications is presented. Stable colloidal suspensions of iron oxide nanoparticles were prepared by a co-precipitation method with the magnetite cores being coated with β-cyclodextrin, tetramethylammonium hydroxide and citric acid. Rheological properties of the fluids were investigated, i.e. viscosity (capillary method) and surface tension (stalagmometric method) in correlation with their density (picnometric method). The dimensional distributions of the ferrophase particles physical diameter of these three magnetic fluids – revealed on the basis of transmission electron microscopy (TEM) data – as well as the diameter distributions of some other magnetic fluids presented in the literature, were comparatively analyzed using the box-plot statistical method. In order to extract complementary data on the magnetic diameter of an iron oxide core, magnetization measurements as well as X-ray diffraction pattern analysis were carried out. Interpretation of all the measurement data was accomplished by assessing the suitability of the three magnetic fluid samples from the viewpoint of their stability and biocompatibility.

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.

Magnetic nanocomposites for sorbents and glue layers

Magnetic properties were added to original materials via impregnation with magnetic fluids, layer-by-layer (LbL) assembly of magnetite nanoparticles with polyelectrolytes or admixing to adhesive solutions. Thin multilayers with controllable thickness were formed on glass surfaces and lignocellulose fibers by the LbL method. Magnetic sorbents were created by impregnation of activated charcoal with a magnetite magnetic fluid stabilized with triethanolamine oleate. A mechanism of sorbent interaction with the nanoparticles is proposed. Possible application of these aqueous magnetic fluids for the formation of glutinous magnetic layers on metallized foil is demonstrated.

Preparation and characterization of manganese ferrite-based magnetic liposomes for hyperthermia treatment of cancer

Comparative evaluation of two different methods of magnetic liposomes preparation, namely thin film hydration (TFH) and double emulsion (DE) with different molar ratios of egg-phosphatidyl choline (egg-PC) and cholesterol using lauric acid coated manganese ferrite-based aqueous magnetic fluid, is reported. TFH was found to be a better method of encapsulation and TFH 2:1 (egg-PC: cholesterol) magnetic liposomes showed the highest encapsulation efficiency and comparable heating ability to that of magnetic fluids. Stealth TFH 2:1 magnetic liposomes containing DSPE-PEG 2000 were three-fold more cytocompatible as compared to the magnetic fluid. Stealth TFH 2:1 manganese ferrite-based magnetic liposomes might be useful for hyperthermia treatment of cancer.

Measurement of the Viscosity of Dilute Magnetic Fluids

The capillary tube viscometer is used to measure the viscosity of aqueous magnetic fluids under the influence of parallel and perpendicular magnetic fields. The effects of the volume fraction of the suspended magnetic particles, the concentration of surfactants, and the external magnetic field strength, as well as the orientation, on the viscosity of the magnetic fluid are analyzed. The experimental results show that the viscosity of the sample magnetic fluids increases with increases in the concentrations of suspended magnetic particles and surfactants. The external magnetic field is also an important factor that affects the viscosity of the magnetic fluid. The viscosity first increases with the magnetic field and finally approaches a constant as the magnetization attains a saturation state. For the same magnetic fluid, the viscosity in a perpendicular magnetic field is larger than that in a parallel magnetic field for the same magnetic field.

Experimental investigations on transport properties of magnetic fluids

Experimental investigations are carried out to measure the viscosity and the thermal conductivity of the aqueous magnetic fluids in either the absence or the presence of the external magnetic field. The effects of the volume fraction of the suspended magnetic particles, concentration of surfactants and the external magnetic field strength as well as its orientation on the transport properties of the magnetic fluid are analyzed. The experimental results show that the viscosity of the sample magnetic fluids increases with the percentages of the suspended magnetic particles and the surfactants. The viscosity first increases with the magnetic field and finally approaches a constant as the magnetization of the magnetic fluid arrives at a saturation state. For the same magnetic fluid, the viscosity in the magnetic field being perpendicular to the flow direction is bigger than that in the parallel field under the same magnetic field. The thermal conductivity of the sample magnetic fluids is larger than that of pure fluids in both the absence and presence of the external magnetic field. Almost no change in the thermal conductivity of the sample magnetic fluid is found in the magnetic field perpendicular to the temperature gradient. The thermal conductivity of the magnetic fluid increases with the strength of the applied magnetic field being parallel to the temperature gradient.

Molecular composition of iron oxide nanoparticles, precursors for magnetic drug targeting, as characterized by confocal Raman microspectroscopy

The chemical and structural properties of ferrite-based nanoparticles, precursors for magnetic drug targeting, have been studied by Raman confocal multispectral imaging. The nanoparticles were synthesised as aqueous magnetic fluids by co-precipitation of ferrous and ferric salts. Dehydrated particles corresponding to co-precipitation (CP) and oxidation (OX) steps of the magnetic fluid preparation have been compared in order to establish oxidation-related Raman features. These are discussed in correlation with the spectra of bulk iron oxides (magnetite, maghemite and hematite) recorded under the same experimental conditions. Considering a risk of laser-induced conversion of magnetite into hematite, this reaction was studied as a function of laser power and exposure to oxygen. Under hematite-free conditions, the Raman data indicated that nanoparticles consisted of magnetite and maghemite, and no oxyhydroxide species were detected. The relative maghemite/magnetite spectral contributions were quantified via fitting of their characteristic bands with Lorentzian profiles. Another quality parameter, contamination of the samples with carbon-related species, was assessed via a broad Raman band at 1580 cm(-1). The optimised Raman parameters permitted assessment of the homogeneity and stability of the solid phase of prepared magnetic fluids using chemical imaging by Raman multispectral mapping. These data were statistically averaged over each image and over six independently prepared lots of each of the CP and OX nanoparticles. The reproducibility of oxidation rates of the particles was satisfactory: the maghemite spectral fraction varied from 27.8 +/- 3.6% for the CP to 43.5 +/- 5.6% for the OX samples. These values were used to speculate about the layered structure of isolated particles. Our data were in agreement with a model with maghemite core and magnetite nucleus. The overall oxidation state of the particles remained nearly unchanged for at least one month.

Fe3O4 Nanoparticles coated with homopolymers of glycerol mono(meth)acrylate and their block copolymers

Highly stable aqueous magnetic fluids were prepared by coating Fe3O4 nanoparticles with poly(glycerol monoacrylate), poly(glycerol monomethacrylate), or diblock copolymers, poly(acrylic acid)-b-poly(glycerol monoacrylate), poly[(N,N-dimethylamino)ethyl methacrylate]-b-poly(glycerol monomethacrylate) or poly(ethylene glycol) monomethyl ether-b-poly(glycerol monoacrylate). These homopolymers and block copolymers were synthesized by atom transfer radical polymerization. These dispersions were stable in 10% NaCl, 10% CaCl2, or in wide pH ranges. In these magnetic fluids, poly(glycerol monoacrylate) or poly(glycerol monomethacrylate) were chemisorbed onto the Fe3O4 nanoparticle surface through their 1,2-diol groups by forming five-membered chelate rings with the Fe atoms, while the other blocks in the cases of the block copolymers as the stabilizers extended into the water matrix. Thus the nanoparticles prepared with these three block copolymers mentioned above respectively contain negatively charged, positively charged or uncharged and biocompatible surfaces under physiological conditions. This procedure provided a good choice for preparing stable magnetic fluids with tailored surfaces and/or tailored functional groups on the surfaces of the magnetic nanoparticles.

Forced Rayleigh scattering experiments in concentrated magnetic fluids: effect of interparticle interactions on the diffusion coefficient

The structure and dynamics of concentrated aqueous magnetic fluids with tunable interparticle interaction are investigated by small angle neutron scattering and forced Rayleigh scattering. The structure factor and the collective diffusion coefficient are determined. An effect of the interparticle interaction on the diffusion coefficient is observed and related to thermodynamic data with a good agreement.

Preparation and swelling of hydrophilic magnetic microgels

Hydrophilic magnetic microgels were synthesized by a free-radical polymerization in inverse emulsion. Two sizes of magnetic microgels were obtained depending on the initial droplet size of the emulsion. As the polymer matrix is a hydrogel, the novelty of this paper is that the magnetic particles are incorporated from an aqueous magnetic fluid instead of an organic one. In this paper, we underline the physicochemical aspects necessary to control the proper dispersion of the magnetic particles in the polymer matrix. The size, the magnetic content and the swelling degree of micron-sized and sub-micron sized magnetic microgels are characterized.