Synthesis and rheological properties of an iron oxide ferrofluid

A ferrofluid (FF) was synthesized in air using a co-precipitation method. Some rheological properties and magnetoviscous effects of this sample were studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for characterization of the solid particles, and the rheological properties were investigated with a special rheometer with variable magnetic field. Magnetic particles with mean particle size of 10.6 nm were obtained. Rheological results show that the shear thinning behavior in the absence and presence of magnetic field is different from that based fluid behavior. Moreover, contrary to expectation, the magnetoviscous effect showed an initial increase at low shear rates (near 15 s⁻¹) and decrease at higher shear rates. The rheological properties of FF depend on the rearrangement of nanoparticles. In addition, time is an effective factor in the formation and destruction of magnetically induced structures.     

离子型钴铁氧体磁流体的稀土改性与机理研究

采用化学共沉淀法以柠檬酸三钠为表面改性剂制备了离子型稀土复合钴铁氧体磁流体.利用X衍射仪和透射电镜对磁粒子的组成、结构及粒径进行了分析.利用古埃磁天平和分光光度计研究了稀土离子改性对磁流体饱和磁化强度和磁感应的影响,实验结果表明:合成过程中添加稀土离子能明显降低磁性纳米粒子的粒径,制得的磁粒子均呈球形,钴铁氧体磁粒子的粒径为12～15nm,稀土钴铁氧体磁粒子的粒径为6～8nm.利用稀土改性的微观模型解释了粒径的降低.添加Dy3+能提高饱和磁化强度和磁感应,添加Y3+则能提高磁感应,却降低了饱和磁化强度.并从理论上对其改性机理进行了详细的分析.     

Mechanism of chain formation in nanofluid based MR fluids

Mechanism of structure formation in bidispersed colloids is important for its physical and optical properties. It is microscopically observed that the mechanism of chain formation in magnetic nanofluid based magnetorheological (MR) fluid is quite different from that in the conventional MR fluid. Under the application of magnetic field the magnetic nanoparticles are filled inside the structural microcavities formed due to the association of large magnetic particles, and some of the magnetic nanoparticles are attached at the end of the chains formed by the large particles. The dipolar energy of the large particles in a magnetic nanofluid matrix becomes effective magnetic permeability (μ_eff) times smaller than that of the neutral medium. Inclusion of magnetic nanoparticles (∼10 nm) with large magnetic particles (∼3-5 μm) restricts the aggregation of large particles, which causes the field induced phase separation in MR fluids. Hence, nanofluid based MR fluids are more stable than conventional MR fluids, which subsequently increase their application potentiality.     

纳米Fe3O4磁性液体稳定性的研究

从理论上解析了磁性颗粒之间的相互作用对纳米磁性液体稳定性的影响 ,指出磁粒半径和浓度 ,表面活性剂的包覆是影响磁液稳定性的重要因素 .采用湿化学共沉淀法制备了纳米Fe3O4 磁性液体 ,经过TEM等手段的表征 ,证明平均粒径为 10nm ,稳定性良好 .实验研究了加料方式、搅拌速度、分散作用、表面活性剂包覆时机、包覆时间和加入量以及pH值诸多工艺因素对磁液稳定性的影响 ,并分析了这些因素的影响机制     

The roles of hydrochloric acid and polyethylene glycol in magnetic fluids

Increasing interest has been drawn to the studies of magnetic fluids due to their multiple applications from industry to medicine. However, further exploration is still required for the techniques of preparing satisfying, convenient and stable magnetic fluids. We explored characteristics of magnetic liquids prepared by employing co-precipitation techniques of hydrochloric acid (HCl) and polyethylene glycol (PEG), and the functions of HCl and PEG in the magnetic liquid. According to the improved technique, after preparing Fe₃O₄ by a co-precipitation method, hydrochloric acid and PEG2000 react with magnetic particles at a certain temperature to generate the anticipated magnetic nanoparticles. The process could be under an air atmosphere rather than a N₂ atmosphere. Compared with traditional techniques, the magnetic nanoparticles prepared by this method have smaller size, better dispersion and stability, with the average hydrodynamic diameter adjustable between 8 and 50 nm. This study revealed that reduction of nanoparticles size is not mainly due to a [Cl⁻] coating over the magnetic nanoparticles, but that HCl reacts with Fe₃O₄ particles after being heated. Meanwhile, PEG can stabilize or coat Fe₃O₄ nanoparticles as a dispersing and stabilizing agent.     

Site-directed research of magnetic nanoparticles in magnetic drug targeting

The targeting of ferrofluids composed of 20 nm magnetic particles was studied through simulation and animal experiment. The results showed that some magnetic particles were concentrated in the target area depending on the applied magnetic field. Through theoretical analysis, the retention of the magnetic nanoparticles in a target area is due to large magnetic liquid beads formed by the magnetic field.     

Ionic magnetic fluid based on cobalt ferrite nanoparticles: Influence of hydrothermal treatment on the nanoparticle size

Magnetic fluid based on cobalt ferrite nanoparticles was obtained using a hydrothermal treatment added to the Massart procedure. This treatment increases the average size of the nanoparticles from 11.9 to 18.7 nm and also improves the dispersity and crystallinity of the cobalt ferrite particles. The nanoparticles obtained after the hydrothermal treatment were dispersed in aqueous solvent by the classical procedure for ionic magnetic fluids. The ferrofluid thus obtained is stable at pH 7 and may be useful for hyperthermia applications.     

An experimental study of the dynamic properties of nanoparticle colloids with identical magnetization but different particle size

Measurements of the frequency dependent complex magnetic susceptibility, χ(ω)=χ′(ω)−iχ″(ω), have been used to determine the dynamic properties of three specially prepared 400 G (0.04 T) magnetic fluids. The samples, denoted by sample 1, sample 2 and sample 3, consisted of magnetite particles of mean diameter 6.4 nm, 7.5 nm and 9 nm respectively and were identical in terms of carrier liquid, surfactant and particle material.     

Core-shell structure and magnetic properties of magnetite magnetic fluids stabilized with dextran

The adsorption process of different dextran molecules onto the surface of in water dispersed magnetite nanoparticles has been investigated to optimize the preparation of magnetite magnetic fluids (MMFs). An average magnetite core size of 7.1 nm was found by X-ray diffraction and that of 8 nm was found by transmission electron microscopy for the samples prepared at 90 °C. An average hydrodynamic diameter of 25 nm was observed by scanning electron microscopy and that of 25-300 nm was obtained by photon correlation spectroscopy. The dextran was adsorbed by physical adsorption, a molecular weight of 20 kDa gave the best stability of these MMFs. The shell layer of the particles was weakly negatively charged in buffer solutions of pH values between 5.5 and 9.5. The particles seem to be mainly stabilized by sterical repulsion. The maximum available saturation magnetization of the MMFs was 3.5 kA/m.     

Magnetic fluid in ionizing electric field

This article describes influence of strong (ionizing) electric field on sprayability of magnetic fluid containing colloid particles with size in the range from 10 to 20 nm of magnetite Fe₃O₄. Magnetic fluids can be based for example on both transformer oil and physiological solution for application in medical using (in human medical science research), that supports a fluid colloidal system. Further component of magnetic fluid is surfactant. It is acting as surface-active substance that prevents from nanometric dimension particle settlement. Magnetic fluid gets off nozzle with diameter in range 0.3–1.0 mm from container in surroundings of ionizing (i.e. strong) electric field (E > 10⁷ V m^?1). As a consequence of action of electric field it gives out suppression surface tension in fluid what leads onwards to decomposition of magnetic fluid ligament at the end of nozzle. The diameter of nozzle oneself respects basic theoretical calculations in regards of fluid concentration and thereinbefore its selected size. Magnetic fluid in dependency on its used liquid base has weak-polar till polar orientation polarization character. It gives out sprayability in non-homogeneous electric field E in combination with magnetic field of intensity H. Orientation of vectors Ê and ?, resp. induction of magnetic field B is defined by parallel or vertical direction. Results are confronted with measurements realized explicitly only at action of electric field (variable B = 0). In the case of magnetic field applications with permanent magnet together with electric non-homogeneous field it gives out unconventional dynamics of electrical charging particles of macroscopic dimension. Orientation particle track is influenced by orientation of field vector combinations. This phenomenon develops magneto-dielectric anisotropy, which oneself manifests behaviour of electrophysical quantities characterizing examination system. In consideration of technology utilization of this method it is very important to respect applied magnetic fluid concentration. Electrical characteristics were examined for volume concentration of magnetite particles in the range from 0.125% to 18%. Nevertheless efficiency optimization of given media suggests to boundary concentration of magnetic fluid of 4.0%, when it is in the regions of weak polar till polar material. Electrophysical research refers to exploitation of applied magnetic layer technology on dielectric insulating substances with inorganic origin as well as thin layer technology coating plastic foils created from macromolecular organic substance.     

Fe3O4@SiO2@An磁性纳米荧光粒子的制备及对锌离子的识别

通过微乳法一步合成了SiO2包覆Fe3O4的磁性纳米颗粒(MNP)并通过硅烷偶联剂将表面氨基化,进一步通过化学成键将荧光分子蒽修饰到氨基化的纳米粒子表面,制得Fe3O4@SiO2@An磁性纳米荧光粒子.采用XRD、TEM、FTIR等实验方法对该粒子进行一系列的表征,其直径约为9nm,常温时具有超顺磁性,通过外加磁场,能够使粒子从溶液中简单有效地分离.该粒子在溶剂中具有较好的分散性,荧光实验表明,对锌离子具有较好的选择性,在锌离子存在下基于光诱导电子转移( PET,PhotoinducedElectron Transfer)机理,粒子荧光强度显著增强,检出限为2.8571×10-5mol/L.     

Characterization of different magnetite–cobalt nanoparticles in hydrocarbon-based magnetic fluids by means of static and dynamic magnetization measurements

Magnetic nanoparticles with different compositions (Co_xFe_3−xO₄, 0?x?0.1) were synthesized from metal salts using a coprecipitation technique to produce magnetic fluids following a peptization technique. The liquid carrier was the hydrocarbon Isopar M and the surfactant was oleic acid. The colloidal-sized ferrimagnetic nanoparticles produced were found to be superparamagnetic. Measurements of the complex magnetic susceptibility were carried out to evaluate the resonant frequency f_res, the anisotropy constant K, and anisotropy field H_A. f_res was found to be a linear function of the cobalt content of the magnetic nanoparticles over the range of cobalt content studied.     

Preparation of ultrafine TiO2 nanocrystals via pulsed-laser ablation of titanium metal in surfactant solution

This work reports the attempts to perform pulsed-laser ablation in a liquid medium for synthesizing oxide semiconductor nanocrystalline particles. Ultrafine TiO₂ nanoparticles were synthesized by pulsed-laser ablation of a titanium target immersed in an aqueous solution of surfactant sodium dodecyl sulfate (SDS) as well as in deionized water. The surfactant concentration dependence of TiO₂ nanocrystal formation was systematically characterized by X-ray diffraction, optical transmission spectroscopy, and transmission electron microscopy. The maximum amount of ultrafine anatase nanocrystalline particles (with mean size of 3 nm in diameter) was obtained in an aqueous solution of 0.01 M SDS. A probable formation process was proposed based on laser-induced reactive quenching at plasma-liquid interfaces and surfactant-mediated growth in a liquid solution. PACS 52.38.Mf; 52.50.Jm; 82.70.Uv; 81.07.Bc; 78.40.Fy     

Photothermally enhanced catalytic activity of partially aggregated gold nanoparticles

In the present study, a facile, rapid, and environmentally friendly method was used for the preparation of metal oxide nanoparticles in an ionic liquid medium. This technique involves mixing and heating the corresponding powder material (cadmium oxide, anatase, and hematite) and the selected ionic liquid (trihexyl(tetradecyl)phosphonium chloride, [P_6,6,6,14]Cl), without any other precursors or solvents. The confirmation of the existence of nanoparticles in the ionic liquid was carried out using UV?CVis absorption spectroscopy, and its concentration was determined by X-ray fluorescence. In order to analyze the shape and size distribution, transmission electron microscopy and a ZetaSizer (DLS technique) were used; finding out that the size of the hematite nanoparticles was 10?C55?nm. Nevertheless, for the cadmium oxide and the anatase nanoparticles, the size was between 2 and 15?nm. The composition of the prepared nanoparticles was studied by Raman spectroscopy. The structure of solids did not suffer any modification in their transformation to the nanoscale, as concluded from the X-ray powder diffraction analysis.     

Electron holography of gas-phase condensed Fe nanoparticles

Electron holography observations were performed on Fe nanoparticles with a mean size of about 50 nm synthesized by gas-phase condensation. Phase maps were obtained which represent the magnetic field both inside and around nanoparticle chains. The results suggest the presence of flux-closure magnetic configurations inside the particles, in agreement with recent micromagnetic calculations.     

Synthesis of magnetic nanoparticles: effects of polyelectrolyte concentration and pH

This study refers to the effect of sodium polyacrylate concentration (1 to 5 mass %) and pH (10 to 12) on the synthesis of magnetic nanoparticles (magnetite?Cmaghemite) and their characterization by Mössbauer spectroscopy. The magnetic particles were obtained by coprecipitation method using iron chloride (II) and iron chloride (III) as precursor reagents and sodium polyacrylate as stabilizing agent. All samples showed Mössbauer broad resonance lines in typical doublet and sextets patterns of magnetite or maghemite with corresponding wide particle size distributions. The stability of magnetic particles was carried out by measuring particle sizes with dynamic light scattering (DLS). The z-average values for magnetic particles were in the range 24 to 590 nm and no significant change in size was observed on aging by leaving this material in air for 20 days. X-ray diffraction patterns showed characteristic peaks of the spinel structure and have an increase in their broadening as the pH decreases, effect that is dominated by the decrease in crystallite sizes. The nanoparticles showed to be magnetic at pH 12 and at room temperature.     

A novel magnetic fluid based on starch-coated magnetite nanoparticles functionalized with homing peptide

Preparation and characterization in vitro and in vivo of a novel magnetic fluid based on starch-coated magnetite nanoparticles functionalized with homing peptide is reported in this paper. Precursory magnetic fluids stabilized with starch were prepared, in a polymeric starch matrix, by controlled chemical coprecipitation of magnetite phase from aqueous solutions. The average hydrodynamic diameter of starch-coated iron oxide nanoparticles (SIONs) was 46 nm. As a homing peptide, A54 is the most effective peptide specific to the human hepatocellular carcinoma cell line BEL-7402. Final magnetic fluids were obtained through chemical coupling of homing peptide labeled with 5-carboxyl-fluorescein (FAM-A54) and SIONs. Magnetic measurements showed the saturation magnetization value of SIONs amounted to 45 emu/g and the FAM-A54-coupled SIONs showed a good magnetic response in magnetic field. The results of experiments in vitro and in vivo showed that SIONs were endowed with specific affinity to corresponding tumor cells after coupling with FAM-A54 and the FAM-A54-coupled SIONs could be accumulated in the tumor tissue with more efficiency than individual magnetic targeting or biomolecular targeting. This novel magnetic fluid with dual function has great potential applications in diagnostics and therapeutics of human tumor such as drug targeting, magnetic hyperthermia, and magnetic resonance imaging.     

Evidence of a core–shell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanoparticles by neutron scattering

We report the evidence of a core?Cshell structure in the antiferromagnetic La_0.2Ce_0.8CrO₃ nanoparticles by using a combination of neutron diffraction, polarized neutron small angle scattering (SANSPOL), and dc magnetization techniques. The neutron diffraction study establishes that the present nanoparticles are antiferromagnetic in nature. The magnetic scattering in the SANSPOL study arises from the shell part of the nanoparticles due to the disordered surface spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean core diameter of 12.3±1.1?nm, and a shell thickness of 2.8±0.4?nm, giving a core?Cshell structure with an antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field.     

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. PACS 75.50.Mm; 61.46.Df; 68.37.Lp; 96.15.Pf; 75.75.+a     

External field-induced superferrimagnetism in magnetite nanoparticles

Film composites based on magnetite nanoparticles with a mean diameter of 4 nm in a polyvinyl alcohol matrix were studied by means of Mössbauer spectroscopy in a magnetic field of up to 3.4 kOe. The spectra were analyzed within the three-level relaxation model of the magnetic dynamics of an ensemble of single-domain particles, taking into account the precession and diffusion of the homogeneous magnetization of particles and their size distribution.