Structured elastomeric submillimeter films displaying magneto and piezo resistivity

Structured elastomer films (100–150 µm) presenting piezo and magneto resistance are described. The films are composites of filler particles, which are both electrically conductive and magnetic, dispersed in an elastomeric matrix. The particles consist of magnetite (6 nm) grouped in silver‐coated aggregates (Fe₃O₄@Ag). The matrix is styrene–butadiene rubber (SBR) in which diethylene glycol (DEG) is added. The particles, SBR and DEG, are dispersed in toluene and then placed between two rare earth magnets. Formation of pseudo‐chains (needles) of inorganic material aligned in the direction of the magnetic field is obtained after solvent evaporation. The addition of DEG is substantial to obtain an electrically conductive material. The electrical conductivity is anisotropic and increases when applying normal stresses and/or magnetic fields in the direction of the needles. The elastomers, particles, and needless were characterized by XRD, SEM, EDS, FTIR, DSC, TGA, VSM, profilometry, and stress–strain analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 574–586     

Experimental characterization and viscoelastic modeling of isotropic and anisotropic magnetorheological elastomers

The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone matrix filled by micro-sized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.     

Nanocomposite particles with core-shell morphology II. An investigation into the affecting parameters on preparation of Fe3O4-poly (butyl acrylate-styrene) particles via miniemulsion polymerization

The encapsulation of inorganic particles with polymers is desirable for many applications in order to improve the stability of the encapsulated products and disperse ability in different media. Colloidal particles with magnetic properties have become increasingly important both technologically and for fundamental studies. This is due to their tunable anisotropic. In the absence of an applied magnetic field, the particles have isotropic sphere dispersion, whereas in an external magnetic field the particles form anisotropic structures. Here, latexes containing nanocomposite particles of styrene-butyl acrylate/Fe₃O₄ with core-shell structure were prepared through miniemulsion polymerization technique. Magnetic composite nanospheres with high magnetic content were synthesized through miniemulsion polymerization using a new process based on a three-steps preparation route including two miniemulsion processes: (1) preparing a dispersion of oleic acid coated magnetite particles in water; (2) mixing of modified magnetite particles with styrene/butyl acrylate in the presence of sodium dodecyl sulfate (SDS), sorbitane mono oleate (Span 80), hexadecane (HD) and (3) miniemulsification of the modified Fe₃O₄ into the monomer droplets to reach to complete encapsulation. Subsequent polymerization generated magnetic nanocomposite spheres. Hence, the copolymerization reaction was performed on the surface of such particles in order to obtain core-shell morphology for these nanoparticles, which were characterized by several techniques such as TEM, SEM, DLS, TGA, VSM and FT-IR. The magnetic copolymer particles with diameter of 120-170 nm were obtained. The effect of several parameters such as magnetite, surfactants and hydrophobe amounts on the stability, particle size and magnetization were investigated and also optimized.     

Large-strain behaviour of Magneto-Rheological Elastomers tested under uniaxial compression and tension,and pure shear deformations

The large-strain behaviour of Magneto-Rheological Elastomers (MREs) is characterised experimentally under uniaxial compression, uniaxial tension and pure shear deformation, in the absence and in the presence of magnetic fields. MREs are ‘smart’ materials that can alter their properties instantaneously by the application of external stimuli. They hold great potential for use in adaptive stiffness devices. So far, the large-strain behaviour of MREs has not been well explored, and their behaviour under pure shear deformation has not been characterised. Tests on silicone rubber based isotropic and anisotropic MREs, with and without the application of an external magnetic field have been performed in this investigation. The MR effect, defined as the increase in tangent moduli, is studied versus large engineering strain. Strains were measured optically using a Digital Image Correlation (DIC) system. Relative MR effects up to 284% were found under uniaxial tension, when a magnetic field strength of 290 mT was applied with the loading direction parallel to the direction of particle alignment.     

Preparation and sedimentation behavior in magnetic fields of magnetite-covered clay particles

This work is devoted to the preparation of magnetite-covered clay particles in aqueous medium. For this purpose, magnetite nanoparticles were synthesized by a coprecipitation method. These magnetic particles are adhered to sodium montmorillonite (NaMt) particles in aqueous suspensions of both materials, by appropriate control of the electrolyte concentrations. The best condition to produce such heteroaggregation corresponds to acid pH and approximately 1 mol/L ionic strength, when the electrokinetic potentials (zeta-potential) of both NaMt and Fe3O4 particles have high enough and opposite sign, as demonstrated from electrophoresis measurements. When a layer of magnetite re-covers the clay particles, the application of an external magnetic field induces a magnetic moment in clay-magnetite particles parallel to the external magnetic flux density. The sedimentation behavior of such magnetic particles is studied in the absence or presence of an external magnetic field in a vertical direction. The whole sedimentation behavior is also strongly affected by the formation of big flocculi in the suspensions under the action of internal colloidal interactions. van der Waals and dipole-dipole magnetic attractions between magnetite-covered clay particles dominate the flocculation processes. The different relative orientation of the clay-magnetite particles (edge-to-edge, face-to-edge, and face-to-face) are discussed in order to predict the most favored flocculi configuration.     

Direct imaging of zero-field dipolar structures in colloidal dispersions of synthetic magnetite

Magnetite (Fe3O4) forms the basis of most dispersions studied in the field of magnetic fluids and magnetic colloids. Despite extensive theory and simulations on chain formation in dipolar fluids in zero field, such structures have not yet been imaged in laboratory-made magnetite dispersions. Here, we present the first direct observation of dipolar chain formation in zero field in a ferrofluid containing the largest synthetic single-domain magnetite particles studied so far. To our knowledge, this is the only ferrofluid system available at present that allows quantifying chain length and ring-size distributions of dipolar structures as a function of concentration and particle size.     

Electrochemical Sensing of Tryptophan and Tyrosine in Chronic Kidney Disease Patients Using Magnetic Core/Ag Nanoparticles Shell Nanocomposite Modified Electrode

Journal of Analytical Chemistry - This paper reports the production of a novel magnetic nanocomposite based on core-shell Fe3O4@Ag nanoparticles. Fe3O4@Ag nanoparticles were used to fabricate a...     

Systematic control of size,shape, structure,and magnetic properties of uniform magnetite and maghemite particles

As an application of the gel-sol method especially developed for the synthesis of general monodisperse particles in large quantities, uniform hematite (alpha-Fe2O3), magnetite (Fe3O4), and maghemite (gamma-Fe2O3) particles, precisely controlled in size, aspect ratio, and internal structure, have been prepared. For the synthesis of uniform ellipsoidal single-crystal particles of alpha-Fe2O3, a highly condensed suspension of fine beta-FeOOH particles doped with a prescribed amount of PO4(3-) ion in their interiors was aged at 140 degrees C for 24 h with seed particles of alpha-Fe2O3 in an acidic medium containing optimum concentrations of HCl and NaNO3. Systematic control of the aspect ratio and mean size was achieved by regulating the concentration of PO4(3-) ion incorporated into the beta-FeOOH particles and the number of seeds added. The resulting hematite particles were converted into magnetite by reduction in a H2 stream at 330 degrees C for 6 h; the magnetite was then oxidized to maghemite in an air stream at 240 degrees C for 2 h. Magnetite and maghemite thus prepared retained the original shape of the hematite. On the other hand, polycrystalline hematite particles of different sizes and aspect ratios were also prepared by aging a condensed Fe(OH)3 gel in the presence of different concentrations of SO4(2-) ion and seeds. The polycrystalline hematite particles were similarly converted into magnetite and then maghemite. The magnetic properties of these magnetite and maghemite particles were analyzed as a function of their mean particle volume, aspect ratio, and internal structure.     

External magnetic field-induced mesoscopic organization of Fe3O4 pyramids and carbon sheets

The current investigation is centered on the thermal decomposition of iron(II) acetyl acetonate, Fe(C5H7O2)2, in a closed cell at 700 degrees C, which is conducted under a magnetic field (MF) of 10 T. The product is compared with a similar reaction that was carried out without a MF. This article shows how the reaction without a MF produces spherical Fe3O4 particles coated with carbon. The same reaction in the presence of a 10 T MF causes the rejection of the carbon from the surface of pyramid-shaped Fe3O4 particles, increases the Fe3O4 particle diameter, forms separate carbon particles, and leads to the formation of an anisotropic (long cigarlike) orientation of Fe3O4 pyramids and C sheets. The macroscopic orientation of Fe3O4 pyramids+C sheets is stable even after the removal of an external MF. The suggested process can be used to fabricate large arrays of uniform wires comprised of some magnetic nanoparticles, and to improve the magnetic properties of nanoscale magnetic materials. The probable mechanism is developed for the growth and assembly behavior of magnetic Fe3O4 pyramids+C sheets under an external MF. The effect of an applied MF to synthesize morphologically different, but structurally the same, products with mesoscopic organization is the key theme of the present paper.     

Epoxidation of vinyl cyanides by lithium hypochlorite in the presence of Fe3O4@Ag-CTAB as a new eco-friendly catalyst in aqueous medium

Research on Chemical Intermediates - To cater to the requirement of environmental protection, cetyltrimethylammonium bromide (CTAB)-coated Fe3O4@Ag Nanoparticles as a new hybrid magnetic catalyst...     

Preparation of PMAA-coated Dysprosium Ferrite Ferrofluids and Study on the Superparamagnetism

IntroductionFerrofluids[1] consistof ultramicroscopic ferro-and ferrimagnetic particles coated with a monolayeror a bilayer of surfactant molecules,which are col-loidally dispersed in a carrier liquid.Under the in-fluence of an external magnetic field,such ferroflu-ids exhibit certain novel phenomena and severalphysical properties of theirs are modified.For ex-ample,ferrofluids are stable in the gravitationaland magnetic fields and behave not only as solidshaving a large saturation magnetizati…     

Porous Fe3O4 nanoparticles: synthesis and application in catalyzing epoxidation of styrene

A facile route was employed to synthesize porous magnetite via reaction of FeCl(3)·6H(2)O with N(2)H(4)·H(2)O in ethylene glycol without any structure-directing agent. The resultant Fe(3)O(4) particles were characterized by transmission electron microscopy, N(2) adsorption, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. It was demonstrated that the particle size varied in the range of 40-220 nm, and the pore size of particles was centered around 2 nm. The gases produced in the formation process of the particles played key role in the formation of the porous structure. The obtained porous magnetite was used as support to immobilize Au nanoparticles with size less than 2 nm with the assistance of L-cysteine. The as-prepared Fe(3)O(4) particles can effectively catalyze epoxidation of styrene, and the immobilization of Au nanoparticles on the Fe(3)O(4) support significantly improved the activity of the catalyst.     

Magnetically separable polyoxometalate catalyst for the oxidation of dibenzothiophene with H2O2

Two types of polyoxometalate-functionalized magnetic nanoparticles catalysts consisting of H(3)PW(12)O(40) supported on surface-modified Fe(3)O(4) magnetite nanoparticles were prepared using an easy synthetic route and successfully applied for the oxidation of dibenzothiophene. The magnetic catalysts showed a catalytic performance in the oxidation of dibenzothiophene in acetonitrile with hydrogen peroxide, and high conversions were obtained. The catalysts could be easily separated from the reaction solution by applying an external magnetic field and recycled several times.     

Delivery of nanogram payloads using magnetic porous silicon microcarriers

A transport and delivery system for nanogram quantities of molecular species that does not use microfluidic channels, pumps, or valves is described. Microparticles consisting of magnetic porous silicon are prepared, and loading and delivery of an enzymatic payload are demonstrated. The high porosity (60%) porous Si host particles are made magnetic by infusion of superparamagnetic iron oxide nanoparticles (30 nm-diameter magnetite, Fe(3)O(4)) under oxidative conditions. After magnetite incorporation, the porous microparticle is still empty enough to accommodate nanogram quantities of a molecular payload; the enzymes horseradish peroxidase or pronase E are used in the present work. The assembly can be transported to a microliter water droplet containing the enzyme substrate with the aid of an external magnetic field. The enzyme is released into the droplet upon contact. The particles can be transported through air or a hydrocarbon liquid without loss in enzymatic activity of the payload.     

Aqueous dispersions of magnetite nanoparticles complexed with copolyether dispersants: experiments and theory

Magnetite (Fe3O4) nanoparticles have been synthesized and complexed with carboxylate-functional block copolymers, and then aqueous dispersions of the complexes were investigated as functions of their chemical and morphological structures. The block copolymer dispersants had either poly(ethylene oxide), poly(ethylene oxide-co-propylene oxide), or poly(ethylene oxide-b-propylene oxide) outer blocks, and all of them had a polyurethane center block that contained pendent carboxylate groups. The complexes were formed through interactions of the carboxylates with the surfaces of the magnetite nanoparticles. The magnetite cores of the magnetite-copolymer complexes were near 10 nm in diameter, and the particles were superparamagnetic. Complexes with mass ratios of polymer to magnetite varying from 50:50 to 85:15 were studied. One of our objectives is to design complexes that form stable dispersions of discrete particles in water, yet that can be actuated (moved together) upon exposure to a uniform magnetic field. DLVO calculations that accounted for magnetic attractive interparticle forces, as well as van der Waals, steric, and electrostatic forces are presented. Compositions were identified wherein a shallow, attractive interparticle potential minimum appears once the magnetic term is applied. This suggests that it may be possible to tune the structures of superparamagnetic nanoparticle shells to allow discrete dispersions without a field, yet weak flocculation could be induced upon exposure to a field.     

反相微乳液合成30～100nm磁性聚合物纳米微球

利用反相微乳液一步法成功地制备了磁性聚合物纳米微球,微球粒径在30～100nm左右,均一性较好,研究表明,Fe(Ⅱ)浓度对微乳液和微胶乳的稳定性有很大影响,碱的种类、AOT和单体的含量能控制微球粒径,用振动探针式磁强仪(VSM)测定了不同比例的[Fe(Ⅱ)]/[Fe(Ⅲ)]所合成的聚合物微球的磁性,发现温度对合成高磁饱和强度和超顺磁性起关键作用,合成的磁性聚合物微胶乳透明且稳定性较好.     

Electrical impedance spectroscopy investigation of surfactant-magnetite-polypyrrole particles

We report an electrical impedance spectroscopy (EIS) characterization of composite systems formed by emulsion polymerization of polypyrrole (PPY) in concentrated aqueous solutions of sodium dodecyl sulfate (SDS) containing dispersed magnetite particles. SDS-(Fe3O4)-(conducting polymer) microaggregates with different iron contents were prepared by varying in a reciprocal manner the relative amounts of the metal oxide and PPY. We have measured the zeta-potential and the average size of the corresponding dispersed particles and examined their relative composition through energy dispersive X-ray (EDX) microanalysis and Fourier transform infrared (FTIR) spectroscopy. Important aspects of the charge transport in these composite particles can be identified by mapping the real and imaginary parts of their complex impedance as a function of the frequency of the applied external electric field. For instance, for binary composites SDS-(Fe3O4) polarization effects are dominant at the low-frequency regime, with a well-defined dielectric relaxation easily identifiable. On the other hand, when the relative amount of PPY is progressively increased in the ternary SDS-(Fe3O4)-PPY composites, a transition between different charge transport mechanisms is observed at higher frequencies. The EIS results suggest that in these ternary aggregates the PPY chains envelop the metal oxide clusters and effectively shield them from the external field, and that only in binary samples that do not contain PPY is that the surfactant molecules can directly enclose the magnetite particles. These results are consistent with the fact that the average size of the aggregates in the ternary composites is in general larger than those of either SDS-PPY or SDS-magnetite binary particles.     

Magnetic and Mössbauer Studies of Magnetite-Loaded Polyvinyl Alcohol Hydrogels

Materials producing strain in a magnetic field are known as magnetoelastic or magnetostrictive materials. A new type of material that is able to produce giant strain in a nonhomogeneous magnetic field has been developed. In these magnetic-field-sensitive gels (ferrogels) fine colloidal particles having superparamagnetic behavior are incorporated into a highly swollen elastic polymer network. Magnetic properties of ferrogels have been investigated using electron microscopy, static magnetization measurements, and M?ssbauer spectroscopy. Analysis of the data yielded information on the superparamagnetic behavior of ferrogels and made it possible to estimate the size distribution of the magnetic cores of magnetite particles made by chemical precipitation and built into a chemically cross-linked polyvinyl alcohol matrix. The results are interpreted on the basis of a core-shell model. Copyright 2000 Academic Press.     

Self-stabilized magnetic polymeric composite nanoparticles by emulsifier-free miniemulsion polymerization

Self-stabilized magnetic polymeric composite nanoparticles (SS-MPCPs) were prepared by emulsifier-free miniemulsion polymerization using styrene (St) as a monomer, sodium p-styrenesulfonate (NaSS) as an ionic comonomer, hexadecane (HD) as a hydrophobe, and 2,2'-azodiisobutyronitrile (AIBN) as an initiator in the presence of hydrophobic magnetite particles. The hydrophobic magnetite particles with an average size of about 10 nm were prepared by the acidification of the water-based magnetite ferrofluid, previously synthesized by a chemical coprecipitation method. Some colloidal features of the synthesized SS-MPCPs were analyzed. The morphology and the particle size distributions (PSDs) of the SS-MPCPs were observed and analyzed by transmission electron microscopy (TEM). The surface charge density was determined by conductometric titration. The surface hairy layer and the colloidal stability of SS-MPCPs against different electrolytes were determined by photon correlation spectroscopy (PCS). The average Fe3O4 content of SS-MPCPs was determined by thermogravimetric analysis (TGA). Vibrating sample magnetometry (VSM) was used to analyze the magnetic properties of the SS-MPCPs under dry conditions. The results show that the encapsulation of magnetite is successful and the distribution of magnetite particles inside SS-MPCPs is mainly in the core of the particles. The best SS-MPCPs prepared had a relatively narrow PSD, exhibited superparamagnetism, and possessed some magnetic response.     

MIL-101 (Fe) @Ag Rapid Synergistic Antimicrobial and Biosafety Evaluation of Nanomaterials

Metal-organic frameworks (MOFs), which have become popular in recent years as excellent carriers of drugs and biomimetic materials, have provided new research ideas for fighting pathogenic bacterial infections. Although various antimicrobial metal ions can be added to MOFs with physical methods, such as impregnation, to inhibit bacterial multiplication, this is inefficient and has many problems, such as an uneven distribution of antimicrobial ions in the MOF and the need for the simultaneous addition of large doses of metal ions. Here, we report on the use of MIL-101(Fe)@Ag with efficient metal-ion release and strong antimicrobial efficiency for co-sterilization. Fe-based MIL-101(Fe) was synthesized, and then Ag⁺ was uniformly introduced into the MOF by the substitution of Ag⁺ for Fe³⁺. Scanning electron microscopy, powder X-ray diffraction (PXRD) Fourier transform infrared spectroscopy, and thermogravimetric analysis were used to investigate the synthesized MIL-101(Fe)@Ag. The characteristic peaks of MIL-101(Fe) and silver ions could be clearly seen in the PXRD pattern. Comparing the diffraction peaks of the simulated PXRD patterns clearly showed that MIL-101(Fe) was successfully constructed and silver ions were successfully loaded into MIL-101(Fe) to synthesize an MOF with a bimetallic structure, that is, the target product MIL-101(Fe)@Ag. The antibacterial mechanism of the MOF material was also investigated. MIL-101(Fe)@Ag exhibited low cytotoxicity, so it has potential applications in the biological field. Overall, MIL-101(Fe)@Ag is an easily fabricated structurally engineered nanocomposite with broad-spectrum bactericidal activity.