Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

Silica–hematite (α-Fe₂O₃) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe²⁺), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.     

Polystyrene‐Core–Silica‐Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles

Polystyrene‐core–silica‐shell hybrid particles were synthesized by combining the self‐assembly of nanoparticles and the polymer with a silica coating strategy. The core–shell hybrid particles are composed of gold‐nanoparticle‐decorated polystyrene (PS‐AuNP) colloids as the core and silica particles as the shell. PS‐AuNP colloids were generated by the self‐assembly of the PS‐grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the “free” PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe₃O₄ nanoparticles were encapsulated in the core, which resulted in magnetic core–shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high‐temperature catalysis and as nanoreactors.     

Highly magnetic latexes from submicrometer oil in water ferrofluid emulsions

The synthesis of functionalized submicrometer magnetic latex particles is described as obtained from a preformed magnetic emulsion composed of organic ferrofluid droplets dispersed in water. Composite (polystyrene/γ‐Fe₂O₃) particles were prepared according to a two‐step procedure including the swelling of ferrofluid droplets with styrene and a crosslinking agent (divinyl benzene) followed by seeded emulsion polymerization with either an oil‐soluble [2,2′‐azobis(2‐isobutyronitrile)] or water‐soluble (potassium persulfate) initiator. Depending on the polymerization conditions, various particle morphologies were obtained, ranging from asymmetric structures, for which the polymer phase was separated from the inorganic magnetic phase, to regular core–shell morphologies showing a homogeneous encapsulation of the magnetic pigment by a crosslinked polymeric shell. The magnetic latexes were extensively characterized to determine their colloidal and magnetic properties. The desired core–shell structure was efficiently achieved with a given styrene/divinyl benzene ratio, potassium persulfate as the initiator, and an amphiphilic functional copolymer as the ferrofluid droplet stabilizer. Under these conditions, ferrofluid droplets were successfully turned into superparamagnetic polystyrene latex particles, about 200 nm in size, containing a large amount of iron oxide (60 wt %) and bearing carboxylic surface charges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2642–2656, 2006     

聚乙二醇包裹羰基铁核壳粒子的制备及水基磁流变液的性能

以羰基铁粉(CI)为原料用共溶胶-凝胶反应制备CI/聚乙二醇核壳复合粒子，并将其与水组成了磁流变液. 用SEM、TEM、FT-IR和VSM表征了核壳复合粒子的微观结构和静磁特性，并测试了水基磁流变液的性能. 结果表明，核壳复合粒子表面有SiO_x和聚乙二醇的包覆层，它有较好的亲水性和优良的软磁特性，用它组成的水基磁流变液具有抗沉降性优良、零场粘度低、磁流变效应显著等特点.     

Magnetic poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization in the presence of electrostatically stabilized ferrofluids

Fine magnetite nanoparticles, both electrostatically stabilized and nonstabilized, were synthesized in situ by precipitation of Fe(II) and Fe(III) salts in alkaline medium. Magnetic poly(glycidyl methacrylate) (PGMA) microspheres with core‐shell structure, where Fe₃O₄ is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2′‐azobisisobutyronitrile (AIBN), 4,4′‐azobis(4‐cyanovaleric acid) (ACVA), or ammonium persulfate (APS) in ethanol containing poly(vinylpyrrolidone) or ethylcellulose stabilizer in the presence of iron oxide ferrofluid. The average microsphere size ranged from 100 nm to 2 μm. The effects of the nature of ferrofluid, polymerization temperature, monomer, initiator, and stabilizer concentration on the PGMA particle size and polydispersity were studied. The particles contained 2–24 wt % of iron. AIBN produced larger microspheres than APS or ACVA. Polymers encapsulating electrostatically stabilized iron oxide particles contained lower amounts of oxirane groups compared with those obtained with untreated ferrofluid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5827–5837, 2004     

Preparation of Bowl-Like Polymer Particles via Multi-Step Emulsion Polymerization and Alkali Post-Treatment

Summary : Monodisperse P(BA-MMA-MAA-EGDMA)/P(St-MAA-DVB) core/shell latex particles were first synthesized by a four-step emulsion polymerization, and a new kind of latex particles with “bowl-like” morphology were obtained by post-treating the resultant core/shell particles under alkali condition. Results indicated that the feeding rates of the monomer mixture and initiator aqueous solution were the key parameters to obtain monodisperse core/shell latex particles in the emulsion polymerization process, and the latex particles with “bowl-like” morphology could be generated only when the treatment temperature was equal or higher than 70 °C.     

The effect of iron phosphate,alumina and silica coatings on the morphology of carbonyl iron particles

Carbonyl iron powders were coated with iron phosphate using phosphating method and boehmite (γ‐AlOOH) or silicon hydroxide (Si(OH)₄) nanoparticles derived from the hydrolysis of tri‐sec‐butoxide (Al(OC₄H₉)₃) or tetramethylsilane (Si(OCH₃)₄) using sol–gel method. The coated powders were dried and calcined at 400 °C for 3 h in air. Cross‐section morphology of coated carbonyl iron powders were investigated by scanning electron microscopy energy dispersive X‐ray analysis. Coated Fe micro‐particles were spherical in shape with ‘shell/core’ structures. The shells consisted of an amorphous layer with varying thickness (100–800 nm) and the core represented a carbonyl iron. Gelatinous morphology of dried FePO₄ coating composed from nanoparticles of iron oxyhydroxides and hydrated iron phosphate with a shell thickness of ～100 nm around iron particles was observed. In coatings based on alumina or silica xerogels with a thickness of ～100–150 nm or ～200–500 nm, the coatings were composed of iron oxyhydroxides and γ‐AlOOH or Si(OH)₄. The resulting XRD diffractograms revealed the hematite (α‐Fe₂O₃) and magnetite (Fe₃O₄) that were formed in phosphated and sol–gel coated iron powders. The X‐ray diffraction patterns did not verify the presence of phosphates, alumina or silica and indicate the amorphous or nanocrystalline structure of FePO₄, γ‐Al₂O₃ and SiO₂. Copyright © 2009 John Wiley & Sons, Ltd.     

碳纤维表面羰基铁的原位生长及吸波性能

以Fe(CO)5为前驱体,通过金属有机化学气相沉积(MOCVD),在碳纤维(CF)表面构筑厚度为纳米级的羰基铁(CI)壳层,通过改变沉积温度,调控核壳粉体的形貌结构和吸波性能。用X射线衍射仪、扫描电子显微镜和矢量网络分析仪对粉末的结构及电磁性能进行表征并对其吸波性能进行研究。结果表明:随着沉积温度升高(210~240℃),沉积到CF表面的羰基铁颗粒互相“吞并-融合”,此时CF-CI形成了完整的薄膜包覆型核壳结构;沉积温度太高时(270℃)会造成CF表面羰基铁壳层形貌的恶化。通过调节沉积温度,在纳米尺度上可以有效调控CI壳层的形貌,从而调节CF-CI核壳粒子的电磁性能。以核壳形貌及吸波性能为考察指标,最终确定最佳的沉积温度为240℃。以沉积温度为240℃时所获样品的电磁参数,模拟计算出涂层厚度为0.9 mm时,小于-10 dB的吸波带宽最大为4.6 GHz(13.4~18 GHz);涂层厚度为2.0 mm时,反射率达到最小值为-21.5 dB;厚度为0.9~3.9 mm时,在2~18 GHz均能实现吸波强度低于-10 dB。     

Studies on the Particle Morphology of Waterborne Cationic Polyurethane/Polyacrylate Microemulsions

Polyurethane containing tertiary nitrogen atoms was synthesized from polyol, diphenylmethane diisoccyanate (MDI) and N‐methyl diethanolamine. The polymer was converted into cationomers by quarternizing with methacrylic acid (MAA) and then dispersed in water. In this reaction, methyl methacrylate (MMA) was used to decrease viscosity; at the same time, it was the monomer in the later reaction. Finally the cationic polyurethane dispersions were further polymerized with an oil‐soluble initiator, azobisisobutyronitrile (AIBN), water‐soluble initiator, K₂S₂O₈ (KPS) and the mixture of AIBN and KPS. The different emulsion particles with shell‐core structure, “invert” shell‐core structure and “irregular” sandwich structure were obtained; the morphological structures were characterized by TEM observation, FT‐IR and particle size analysis.     

Ultrathin polydimethylsiloxane-coated carbonyl iron particles and their magnetorheological characteristics

An ultrathin polydimethylsiloxane (PDMS) layer with a mean thickness of 1 nm was coated on soft magnetic carbonyl iron (CI) particles by using a simple thermal evaporation process, and then their physical characteristics were examined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermal gravimetry analysis (TGA), and vibrating sample magnetometry (VSM). Magnetorheological (MR) fluid was prepared by using PDMS-coated CI powder, and its rheological behavior was investigated under different external magnetic field strengths using a rotational rheometer. The CI particles coated by a thin PDMS layer showed higher oxidation temperature than pristine CI particles and MR fluid consisting of PDMS-coated CI particles demonstrated better dispersion stability in a nonmagnetic carrier fluid.     

A new methodology for producing pyrocarbon composites containing zerovalent iron nanoparticles

A magnetic pyrocarbon composite containing nanoparticles with an overwhelming predominance of zerovalent iron has been synthesized. The nanocomposite has a core–shell–matrix structure in which Fe⁰ nanoparticles with an average size of 50 nm are located in the pyrocarbon matrix and coated with a ferrite shell preventing their aggregation and oxidation. The composite is distinguished for its high thermal stability, magnetic properties 59 G cm³/g, and electrical conductivity as high as that of graphite.     

Magnetite‐polylactic acid core–shell nanoparticles by ring‐opening polymerization under microwave irradiation

The synthesis of magnetic core–shell nanoparticles consisting of magnetite cores surface‐functionalized by glycolic acid covered by polylactic acid was performed by applying the “grafting‐from” strategy, where the polymerization is initiated from the particle surface. The surface initiated ring‐opening polymerization of D,L ‐lactide was initiated by tin (II) 2‐ethylhexanoate using microwave irradiation. Core–shell nanoparticles of high colloidal stability in water were obtained in this way. The morphology of the magnetic core–shell nanostructure was determined by transmission electron microscopy, and the chemical structure was elucidated by Fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy. Magnetic measurements revealed superparamagnetic behavior and high magnetization values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation and clinical application of immunomagnetic latex

Magnetic poly(methyl methacrylate) (PMMA)/poly(methyl methacrylate‐co‐methacrylic acid) [P(MMA–MAA)] composite polymer latices were synthesized by two‐stage soapless emulsion polymerization in the presence of magnetite (Fe₃O₄) ferrofluids. Different types and concentrations of fatty acids were reacted with the Fe₃O₄ particles, which were prepared by the coprecipitation of Fe(II) and Fe(III) salts to obtain stable Fe₃O₄ ferrofluids. The Fe₃O₄/polymer particles were monodisperse, and the composite polymer particle size was approximately 100 nm. The morphology of the magnetic composite polymer latex particles was a core–shell structure. The core was PMMA encapsulating Fe₃O₄ particles, and the shell was the P(MMA–MAA) copolymer. The carboxylic acid functional groups (COOH) of methacrylic acid (MAA) were mostly distributed on the surface of the composite polymer latex particles. Antibodies (anti‐human immunoglobulin G) were then chemically bound with COOH groups onto the surface of the magnetic core–shell composite latices through the medium of carbodiimide to form the antibody‐coated magnetic latices (magnetic immunolatices). The MAA shell composition of the composite latex could be adjusted to control the number of COOH groups and thus the number of antibody molecules on the magnetic composite latex particles. With a magnetic sorting device, the magnetic immunolatices derived from the magnetic PMMA/P(MMA–MAA) core–shell composite polymer latex performed well in cell‐separation experiments based on the antigen–antibody reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1342–1356, 2005     

<Superscript>68</Superscript>Ga-radiolabeled magnetic nanoparticles for PET–MRI imaging

In this study, magnetic multimodal nanoparticles with potential applications in magnetic- and nuclear-medicine imaging, magnetic resonance imaging, hyperthermia, and theranostic (therapeutic and diagnostic), applications were prepared by coating iron oxide nanoparticles with silica (core–shell), functionalizing with aminopropyltriethoxy silane and coupling with diethylenetriamine pentaacetic acid ligand (DTPA). Radiolabeling of core–shell–DTPA particles with ⁶⁸Ga radiometal was carried out through chelation of ⁶⁸Ga(III) ions by DTPA and was used for positron emission tomography. The biodistribution of the ⁶⁸Ga-radiolabeled magnetic nanoparticles compared to free ⁶⁸Ga(III) was checked in normal Balb/c mice up to 2 h.     

An emulsifier‐free core–shell polyacrylate/diacetone acrylamide emulsion with nano‐SiO2 for room temperature curable waterborne coatings

An emulsifier‐free core–shell polyacrylate emulsion, containing nano‐SiO₂ nanoparticles in the core and diacetone acrylamide (DAAM) in the shell, has been successfully prepared by emulsifier‐free seeded emulsion polymerization. The effects of reaction temperature, dropping time, nano‐SiO₂ and initiator contents, and variation of the composition of core monomers on the amount of coagulum, particle size, and monomer conversion have been investigated. The particle morphology and the distribution of emulsion particles have been measured by transmission electron microscopy (TEM) and dynamic light scattering. The keto‐carbonyl groups on the surface of the polyacrylate emulsion nanoparticles reacted with adipic dihydrazide (ADH) to form a film with a cross‐linked network structure at room temperature. Therefore, the emulsifier‐free core–shell emulsion could be used as a two‐component room temperature curable waterborne coating. It was also found that the properties of the coating were clearly superior after using the cross‐linker. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation of Hollow Polymeric Microspheres with Functionalized Surface on the Basis of Latex Particles with Multilayered Structure

Summary: Latices with “core-shell” particle morphology containing polar “core” and a shell on the basis of copolymer of styrene and functional vinyl monomer (allyl alcohol, vinyl acetate, methacrylic acid) has been obtained as a result of graft-copolymerization initiated from the surface of (meth)acrylate latex particles previously modified with functional polyperoxides. The processes of functional shell grafting as well as the processes of latex particle swelling with obtaining hollow microspheres due to neutralization of core carboxylic groups have been studied.     

Poly(p‐phenylenediamine)‐coated magnetic particles: Preparation and electrochemical properties

Magnetic particles are of great interest in various biomedical applications, such as, sample preparation, in vitro biomedical diagnosis, and therapy. For biosensing applications, the used functional magnetic particles should answer numerous criteria such as; submicron size in order to avoid rapid sedimentation, high magnetic content for fast separations under applied magnetic field, and finally, good colloidal stability. Therefore, the aim of this work was to prepare submicron magnetic core and conducting polymer shell particles. The polymer shell was induced using p‐phenylenediamine as key monomer. The obtained core–shell particles were characterized in terms of particle size, size distribution, magnetization properties, Fourier transform infrared (FTIR) analysis, surface morphology, chemical composition, cyclic voltammetry, and impedance spectroscopy. The best experimental condition was found using 40 mg of povidone (PVP—stabilizing agent) and 0.16 mmol of p‐phenylenediamine. Using such initial composition, the core‐shell magnetic nanoparticles shown a narrowed size distribution around 290 nm and high magnetic content (above 50%). The obtained amino containing submicron highly magnetic particles were found to be a conducting material and superparamagnetic in nature. These promising conducting magnetic particles can be used for both transport and lab‐on‐a‐chip detection.     

Enhancement of a magnetorheological PDMS elastomer with carbonyl iron particles

A magnetorheological elastomer based on silicone rubber with carbonyl iron micro-particles was developed. The influence of the different amount of iron particles was experimentally studied by means of XRD, SEM, FTIR, EDS, XPS, uniaxial tension and rheological and cyclic tests. Different contents of carbonyl iron particles (10–40 wt%) were used to obtain the ratio of magnetic particles/silicone rubber that could provide the best mechanical properties on the MRE material. It was found that the composite material can have an increase of about 95% in its tensile strength when adding 20% of carbonyl iron particles to the raw rubber material. SEM analysis indicates a good dispersion of the magnetic particles on the rubber matrix, and the FTIR and XPS techniques confirm, as expected, that there is no chemical interaction between the iron from the carbonyl iron particles and the silicone rubber matrix due to a proper coating of the particles with silicone oil used as coupling agent. The TGA results evidenced that the addition of coated carbonyl iron particles had an impact on the thermal stability of the MRE and on the formation of cross-linked structures. The viscoelastic behavior of the magnetorheological elastomer is described by running experimental test on a rheometer device. Furthermore, cyclic testing were performed on the material sample to characterize the Mullin's effect.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Synthesis and characterization of fillers of controlled structure based on polyhedral oligomeric silsesquioxane cages and their use in reinforcing siloxane elastomers

Four polyhedral oligomeric silsesquioxane (POSS) cages with vinyl groups were linked to a central siloxane core by hydrosilylation. The goal was to obtain filler particles of sizes between those of the POSS cages themselves and the much larger silica particles typically used to reinforce elastomers. The hydrosilylation reaction was monitored with Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the resulting structure was confirmed by mass spectrometry. Simply blending these POSS-based fillers into silanol-terminated poly(dimethylsiloxane) (PDMS) had little effect on the mechanical properties, but bonding them to PDMS provided considerable reinforcement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3314–3323, 2003