Electrorheological and magnetorheological response of polypyrrole/magnetite nanocomposite particles

Magnetic nanoparticles of magnetite (Fe₃O₄) were synthesized within a conducting polypyrrole (PPY) matrix using a facile method, and employed as both electrorheological (ER) and magnetorheological (MR) materials to provide a well dispersed suspension of either ER or MR fluids. The PPY to Fe₃O₄ weight ratio was adjusted to 5 % to avoid possible deterioration of the magnetic properties of the Fe₃O₄ particles. Transmission electron microscopy and X-ray diffraction provided information on the structure and particle size of the PPY/Fe₃O₄. Both ER and MR performance of pure Fe₃O₄ and PPY/Fe₃O₄ nanocomposites were examined through rotational and oscillatory tests using a rotational rheometer under an applied electric and magnetic field, respectively, demonstrating typical ER and MR characteristics.     

One-pot synthesis of magnetic nanoparticles assembled on polysiloxane rod and their response to magnetic field

Rod-like assembled magnetite (Fe₃O₄) nanoparticles (NPs) were successfully synthesized in a one-pot process using a polysiloxane template derived from a dialkoxysilane. The assembly was constructed using the thiol-ene click reaction between thiol groups on the polysiloxane chain and allyl groups on Fe₃O₄ NPs. The thiol-containing polysiloxane chain and the allyl-containing Fe₃O₄ NPs were synthesized by the hydrolysis–condensation of 3-mercaptopropyl(dimethoxy)methylsilane and iron (III) allylacetylacetonate, respectively. Fe₃O₄ NPs of around 5 nm were uniformly dispersed on the siloxane rods and exhibited neither remanent magnetization nor coercivity. A fluid containing a dispersion of rod-like assembled Fe₃O₄ NPs showed yield stress even without the application of an external magnetic field, whereas spherical Fe₃O₄ NPs exhibited no yield stress. The rod-like assembled Fe₃O₄ NPs on anisotropic siloxane clearly exhibited typical magnetorheological behavior.     

Magnetic fluids’ stability improved by oleic acid bilayer-coated structure via one-pot synthesis

To improve the magnetic fluids’ stability and demonstrate the relationships between the bilayercoated structure and the stability, a simple method was proposed for preparingoleic acid bilayercoated Fe₃O₄ magnetic fluids. The hydrophilic Fe₃O₄ nanoparticles coated with the bilayer-oleic acid were synthesised by a one-pot process through the chemical co-precipitation under alkaline conditions. Next, the hydrophilic Fe₃O₄ particles were transformed to hydrophobic particles via carboxyl-protonated modification. Carboxyl-protonated modification was found to be a reversible process, i.e. the lipophilicity of the coated Fe₃O₄ nanoparticles could be controlled by protonating/ deprotonating the terminal carboxyl group. In addition, the space steric effect could be significantly enhanced by maximising the oleic acid adsorption and increasing the thickness of the coated layer, resulting in the oleic acid bilayer-coated Fe₃O₄ nanoparticles exhibiting better performance in the stability of the hexanemagnetic fluids than oleic acid monolayer-coated Fe₃O₄ nanoparticles.     

The Preparation of Light Magnetic Materials and it's Application on Magnetorheological Fluids

It is reported that preparation of magnetic material(nickel and cobalt) on the surface of light material. The density of the new material is low (Effective density of it is 2~3 g/cm3). The sedimental stability of the new magnetorheological fluid made by light magnetic material is similar to that of the MR fluid made by carbonyl nickel powders containing lots of anti-sedimental agent. The apparent viscosity of new MR fluids under magnetic field is dozens of times as high as the inital viscosity. Therefore the problem of settling of solid particles under gravity can be effectively prevented by manufacturing magnetorheological fluids using the new material.     

Stability, rheological, magnetorheological and volumetric characterizations of polymer based magnetic nanofluids

The Fe₃O₄ nanoparticles and Fe₃O₄ nanoparticles coated with oleic acid have been dispersed in base fluid of poly(ethylene glycol) (PEG). Stability and particle size distribution of these nanofluids have been studied by result analysis of UV–Vis spectroscopy, zeta potential and dynamic light scattering. Blue shift of UV–Vis spectra has been related to quantum effects such as band gap enlargement with particle size decreasing and also to effect of oleic acid on the ultraviolet wavelength. Flow behavior and suspension structure of Fe₃O₄ nanoparticles dispersed in PEG have been determined by rheological properties. Viscosity values of Fe₃O₄-PEG nanofluid as a function of temperature have also been investigated. The chain-like structure of Fe₃O₄ nanoparticles coated with oleic acid in base fluid of PEG has been verified by measuring the magnetorheological properties. The effect of temperature on magnetorheological properties of Fe₃O₄ nanoparticles coated with oleic acid has also been investigated in base fluid of PEG. The volumetric properties of Fe₃O₄-PEG and Fe₃O₄ coated with oleic acid–PEG nanofluids and PEG–oleic acid solution have also been measured at different temperatures to specify the suspension structure and also interactions of Fe₃O₄, PEG and oleic acid molecules.     

Dispersion of magnetic nanoparticles in a polymorphic liquid crystal

In order to enhance the phase stability of dispersions of magnetic nanoparticles (NPs) in a polymorphic liquid crystal, new ligands have been designed consisting of a terphenyl-based liquid crystalline core. The most stable dispersions were obtained with 7 nm super-paramagnetic Fe₃O₄ NPs decorated with the new ligands in place of 10 nm ferromagnetic CoFe₂O₄ spherical NPs.     

Copper(I)–creatine complex on magnetic nanoparticles as a green catalyst for N- and O-arylation in deep eutectic solvent

Immobilization of copper(I) ions on magnetic nanoparticles was performed using surface modification of Fe₃O₄ with creatine. Fe₃O₄@creatine-Cu(I) magnetic catalyst was synthesized and applied in C&bond;X cross-coupling reactions with aryl halides in a deep eutectic as a green solvent. The results indicate the Fe₃O₄@creatine-Cu(I) magnetic nanoparticles showed excellent activity and high stability. In addition, it was revealed that this catalyst can be recycled five times without significant loss in catalytic activity.     

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

In this study, magnesium ferrite (MgFe₂O₄) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe₂O₄ nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe₂O₄ nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe₂O₄ nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe₂O₄ nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.     

中空球状Fe3O4颗粒的合成及对刚果红溶液吸附-脱附能力的研究

通过简单的水热过程合成具有优良磁学性能的中空Fe3O4单晶颗粒。空心球状颗粒外部直径约500 nm,内径约200 nm,是由粒径为50 nm的颗粒团聚而成。随着反应时间的增加,相邻的Fe3O4纳米晶沿着(311)晶面取向团聚,经过奥斯瓦尔德熟化过程最终形成中空的球状颗粒。实验合成的Fe3O4粒子表现出特殊的磁学性能,具有相对较低的饱和磁化强度和较高的矫顽力。通过对刚果红溶液的吸附-脱附实验证明,中空结构Fe3O4颗粒对刚果红溶液有更高的吸附和脱附能力,在废水处理过程中,采用Fe3O4作为吸附剂,可以更高效的去除溶解的有机污染物,同时可以回收再利用,提高废水净化率,也进一步扩展了磁性材料的应用领域。     

Modification and application of Fe3O4 nanozymes in analytical chemistry: A review

In recent years, Fe₃O₄ nanomaterials have received much attention in analytical chemistry due to their excellent magnetic and peroxidase-like activity. As the catalytic characteristics of Fe₃O₄ nanomaterials is similar to those of horseradish peroxidase (HRP), Fe₃O₄ nanomaterials are also used as peroxidase mimics and have achieved a certain development in many fields based on latest research results. To improve the stability and catalytic ability of simple Fe₃O₄ nanomaterials, various modification strategies of Fe₃O₄ nanomaterials have been developed. The recent advances of these strategies have been presented and discussed. In addition, this paper introduces the application of Fe₃O₄ nanozymes in the detection of food and industrial pollutants, as well as in the field of biosafety.     

Magnetically tunable transparency for magnetorheological elastomer films consisting of polydimethylsiloxane and Fe3O4 nanoparticles

In this research, we demonstrate magnetically tunable transmittance for the magnetorheological elastomer films comprised of polydimethylsiloxane and Fe₃O₄ nanoparticles. The films bearing anisotropic and isotropic microtexture were prepared with and without magnetic field, respectively. The usage of toluene as diluent during the film preparation process leads to the increased tunable range of the magnetically induced transparency in comparison with our previous results. For the anisotropic film containing 1 wt% Fe₃O₄ nanoparticles, an increase of 23.01% in film transparency was observed at the wavelength of 600 nm with a magnetic field of B = ~ 80 mT applied, which is 2.67 times greater than the maximum change achieved in our previous research. The variation in transparency caused by the external magnetic field has been tentatively assigned to magnetostrictive effect. And the film microtexture might have a great influence upon the way an external magnetic field alters film transmittance.     

Decoration of Fe3O4 nanoparticles on the surface of poly(acrylic acid) functionalized multi‐walled carbon nanotubes by covalent bonding

Fe₃O₄ nanoparticles were indirectly implanted onto functionalized multi‐walled carbon nanotubes (MWCNTs) leading to a nanocomposite with stronger magnetic performance. Poly(acrylic acid) (PAA) oligomer was first reacted with hydroxyl‐functionalized MWCNTs (MWCNTs‐OH) forming PAA‐grafted MWCNTs (PAA‐g‐MWCNTs). Subsequently, Fe₃O₄ nanoparticles were attached onto the surface of PAA‐g‐MWCNTs through an amidation reaction between the amino groups on the surface of Fe₃O₄ nanoparticles and the carboxyl groups of PAA. Fourier transform infrared spectra confirmed that the Fe₃O₄ nanoparticles and PAA‐g‐MWCNTs were indeed chemically linked. The morphology of the nanocomposites was characterized using transmission electron microscope (TEM). The surface and bulk structure of the nanocomposites were examined using X‐ray diffraction, X‐ray photoelectron spectrometer (XPS), and thermogravimetric analysis (TGA). The magnetic performance was characterized by vibrating sample magnetometer (VSM) and the magnetic saturation value of the magnetic nanocomposites was 47 emu g^?1. The resulting products could be separated from deionized water under an external magnetic field within about 15 s. Finally, the magnetorheological (MR) performances of the synthesized magnetic nanocomposites and pure Fe₃O₄ nanoparticles were examined using a rotational rheometer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

The impact on the magnetic field growth of half-metallic Fe3O4 thin films

Half-metallic Fe₃O₄ films grown on a Si (100) substrate with a tantalum (Ta) buffer layer were prepared by DC magnetron reactive sputtering. Primary emphasis was placed on magnetic field growth of Fe₃O₄ thin film. The experiment's results showed that applying an external magnetic field to the samples during the growth was efficient to promote the polycrystalline Fe₃O₄ growth along certain directions. The magnetoresistance (MR) was also tested for comparison of the samples prepared with and without an external magnetic field, and showed that applying an external magnetic field can promote the MR values.     

Preparation of Fe3O4 magnetic fluid by one-step method with a microemulsion reactor

A W/O microemulsion was prepared with Span80-PS (petroleum sulfonate) as complex emulsifier, isopropanol as cosurfactant and kerosene as oil phase. The optimal constituents of microemulsion were found from pseudoternary phase diagrams: the mass ratio of Span80 to PS was 4:1 and complex surfactant to cosurfactant was 1:1. The Fe₃O₄ magnetic fluid was obtained by one-step method with the W/O microemulsion as microreactor to synthesize magnetic nanoparticles (reaction temperature was 30 °C and reaction time was 5 h) and kerosene as carrier liquid. The magnetic fluid was investigated by TEM, XRD and fluorescence microscope. The magnetism was determined by Gouy magnetic balance. The average particle size of Fe₃O₄ was 7.4 nm, and magnetic particles were well-dispersed. The stable Fe₃O₄ magnetic fluid with good magnetism may be produced by one-step method in the W/O microemulsion. Accordingly, the traditional preparation method of magnetic fluid can be simplified greatly. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22 (7) (in Chinese)     

Synthesis of Fe3O4/PAM superparamagnetic nano-hydrogels in water-in-oil emulsion

Abstract

In this study, the nano-sized water droplets (NWDs) in water-in-oil (W/O) emulsion were employed as mini-reactors, in which Fe₃O₄/PAM magnetic nano-hydrogels (MNHs) were obtained based on the coprecipitation and inverse emulsion polymerization. In addition, compound nonionic surfactant was used as the stabilizer of W/O emulsion. The test results showed that Fe₃O₄/PAM MNHs were quasi-sphere particles with a diameter of about 50–380?nm and had superparamagnetism. The percentage of PAM coating Fe₃O₄ was about 81%. The saturation magnetization of the Fe₃O₄/PAM MNHs was 21.6?emu/g (Fe₃O₄/AM (wt/wt)?=?16.63%). The W/O emulsion containing Fe₃O₄/PAM MNHs (E-2) changed from fluid to solidlike in an external magnetic field. As current intensified or shear rate increased, the shear stress of E-2 increased.     

Preparation and characterization of a novel DABCO-based ionic liquid supported on Fe3O4@TiO2 nanoparticles and investigation of its catalytic activity in the synthesis of quinazolinones

In this study, quinazolinone derivatives have been synthesized via a suitable and efficient procedure by one-potmulti-component reactions of 3-amino-1,2,4-triazole or 2-aminobenzimidazole, dimedone and aromatic aldehydes in the presence of Fe₃O₄@TiO₂-IL as nanocatalyst under solvent-free condition. The products were prepared in good to excellent yields using Fe₃O₄@TiO₂-IL magnetic nanocatalyst. The Fe₃O₄@TiO₂ magnetic nanoparticles (MNPs) were prepared using beet juice extract and functionalized with IL based on DABCO. Moreover, the core-shell structured magnetic Fe₃O₄@TiO₂-IL has been characterized by different techniques such as ¹H-NMR, FT-IR, VSM, XRD, SEM, TGA, TEM and EDX. To the best of our knowledge, the prepared ionic liquid displayed a good protective and activator agent for magnetic nanocatalyst.     

Designing of a magnetically separable Fe3O4@dopa@ML nano-catalyst for multiple organic transformations (epoxidation,reduction, and coupling) in aqueous medium

A copper(II) macrocyclic Schiff base complex (ML) was synthesized by condensation between 2,2-dimethylpropane-1,3-diammine and 2,6-diformyl-4-butylphenol with the aim to modify the surface of widely used magnetically separable nanocatalyst Fe₃O₄@dopa. ML was characterized by physicochemical techniques and single crystal X-ray diffraction. The newly synthesized heterogeneous catalyst Fe₃O₄@dopa@ML was characterized by SEM, TEM, PXRD, EDX, TGA, etc. ML showed stability in aqueous medium and utilizing this unique property, the heterogeneous catalyst Fe₃O₄@dopa@ML was used for catalyzing epoxidation, nitroarene reduction and C–C coupling (Henry reaction) in aqueous medium. The separation method of the prepared nano-catalyst is very easy and can be done with an external magnetic field. The experimental findings suggest that Fe₃O₄@dopa@ML is a versatile “green catalyst.”     

可循环磁性Pt/Fe3O4-MCNT催化剂上的肉桂醛选择性加氢反应

采用多步法依次将制备的Fe₃O₄纳米颗粒和Pt纳米颗粒负载到多壁碳纳米管(MCNT)上得到Pt/Fe₃O₄-MCNT磁性催化剂,以X射线衍射(XRD)、透射电镜(TEM)、超导量子干涉磁强计(SQUID)和热重-差热分析(TG-DTA)对Pt/Fe₃O₄-MCNT磁性催化剂的结构和磁性质进行了表征。研究发现预制备的Fe₃O₄纳米颗粒与Pt纳米颗粒均匀地分散于MCNT上,新制备以及多次使用后的Pt/Fe₃O₄-MCNT室温下都具有良好的超顺磁性。研究了Pt/Fe₃O₄-MCNT磁性催化剂上的肉桂醛选择性加氢反应,结果显示催化剂具有良好的C=O加氢活性,肉桂醛转化率在50%左右时,肉桂醇选择性可达96%以上。尺寸均一的Pt粒子均匀的分散在催化剂上可能是催化剂具有良好的C=O加氢选择性的重要原因。在外加磁场作用下催化剂可以高效地从液相反应体系中分离,经多次循环使用后仍具有良好的催化性能。     

Magnetite nanoparticles/chiral nematic liquid crystal composites with magnetically addressable and magnetically erasable characteristics

A magnetite (Fe₃O₄) nanoparticle/chiral nematic liquid crystal (N*-LC) composite was prepared and filled into a planar treated cell. The Fe₃O₄ nanoparticles had been modified by oleic acid so that they could be better dispersed in the composite. When a magnetic field was scanned on the outer surface of the cell locally, Fe₃O₄ nanoparticles moved towards the inner surface of the cell correspondingly, and the black expected information was displayed. When the magnet was applied to the opposite outer surface, the information was erased. After polymer network walls were prepared in the composite, the resolution of the information displayed increased. Then, through the formation of hydrogen bonds between the nanoparticles and chiral pyridine compound (CPC) doped in the composite, the pitch length of the N*-LC could be adjusted by altering the intensity of the applied magnetic field. The composite doped with CPC could potentially be used as a material for a type of reflective colour paper with magnetically controllable characteristics.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>composite particles

Using Fe₃O₄ nano-particles as seeds, a new type of Fe₃O₄/Au composite particles with core/shell structure and diameter of about 170 nm was prepared by reduction of Au³⁺ with hydroxylamine in an aqueous solution. Particle size analyzer and transmission electron microscope were used to analyze the size distribution and microstructure of the particles in different conditions. The result showed that the magnetically responsive property and suspension stability of Fe₃O₄ seeds as well as reduction conditions of Au³⁺to Au⁰are the main factors which are crucial for obtaining a colloid of the Fe₃O₄/Au composite particles with uniform particle dispersion, excellent stability, homogeneity in particle sizes, and effective response to an external magnet in aqueous suspension solutions. UV-Vis analysis revealed that there is a characteristic peak of Fe₃O₄/Au fluid. For particles with d(0.5)=168 nm, the λmax is 625 nm.