Preparation and colloidal stability of monodisperse magnetic polymer particles

A previously proposed method was examined for producing monodisperse, submicrometer-sized magnetic polymer particles. The method applies soap-free emulsion polymerization during which Fe3O4 magnetic nanoparticles are heterocoagulated onto precipitated polymer nuclei. To chemically fix the magnetic particles to the polymer nuclei, vinyl groups were introduced on the Fe3O4 particles in a preliminary surface modification reaction with methacryloxypropyltrimethoxysilane, and methacryloxypropyldimethoxysilane (MPDMS) was added to reaction systems of the soap-free emulsion polymerization. The colloidal dispersion stability of magnetic polymer particles was improved by the addition of an ionic monomer, sodium p-styrenesulfonate (NaSS), during the polymerization. The polymerizations were carried out with styrene monomer and potassium persulfate initiator in ranges of NaSS concentrations (0-2.4 x 10(-3) M), NaSS addition times (60-80 min), and monomer concentrations (0.3-0.6 M) at fixed concentrations of 1.6 x 10(-2) M initiator and 1.3 x 10(-2) M MPDMS for pH 4.5 adjusted with a buffer system of [CH3COOH]/[NaOH]. The addition of NaSS during the polymerization could maintain the dispersion stability of magnetic polymer particles during the polymerization. Selection of the reaction conditions enabled the preparation of colloidally stable, submicrometer-sized magnetic polymer particles that had coefficients of variation of distribution smaller than the standard criterion for monodispersity, 10%.     

Preparation of composite particles with magnetic silica core and fluorescent polymer shell

Dual functions of magnetic and fluorescent properties were created in composite particles that incorporated magnetite (Fe₃O₄) nanoparticles in particle cores of silica and fluorescent pyrene in particle shells of polystyrene. The Fe₃O₄ nanoparticles were prepared with a conventional homogeneous precipitation method and surface modified with a coupling agent of carboxyethylsilanetriol. The silica particles incorporating Fe₃O₄ nanoparticles were synthesized with a modified Stöber method in which the Fe₃O₄ nanoparticles were added to a system of tetraethylorthosilicate (TEOS)/ammonia/water/ethanol. Then, the magnetite/silica composite particles were coated with the pyrene/polystyrene shell in a soap-free emulsion polymerization, which was conducted in the presence of pyrene in a mixed solvent of water/ethanol. The composite particles prepared in the mixed solvent had both magnetic and fluorescent properties. The fluorescent spectrum of the particles with Fe₃O₄ was very similar to that without Fe₃O₄, indicating that the magnetic component within the core particles scarcely interfered with the fluorescent emission from the polymer shell.     

Preparation and characterization of conducting polyaniline layered magnetic nano composite polymer particles

Considering the application potentials of organic materials possessing both conducting and ferromagnetic functions in various electronic devices, an attempt was made to prepare conducting polyaniline (PANI) layered magnetic nano composite polymer particles. Two routes were used to modify magnetic Fe₃O₄ core particles. In one route, seeded emulsion polymerization of methyl methacrylate (MMA) was carried out in presence of nano‐sized Fe₃O₄ core particles. In another route, cross‐linker ethyleneglycol dimethacrylate (EGDM) was used in addition to MMA. The modified composite particles were named as Fe₃O₄/PMMA and Fe₃O₄/P(MMA‐EGDM), respectively. Finally, seeded chemical oxidative polymerization of aniline was carried out in the presence of Fe₃O₄/PMMA and Fe₃O₄/P(MMA‐EGDM) composite seed particles to obtain Fe₃O₄/PMMA/PANI and Fe₃O₄/P(MMA‐EGDM)/PANI composite polymer particles. The modification of Fe₃O₄ core particles was confirmed by electron micrographs, FTIR, UV–visible spectra, X‐ray photoelectron spectra, X‐ray diffraction pattern and thermogravimetric analyses. A comparative study showed that crosslinking of intermediate shell improved the magnetic susceptibility and electrical conductivity of PANI layered magnetic nano composite particles. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of Fe3O4/poly(styrene-co-N-isopropylacrylamide) magnetic particles with temperature sensitivity

 The average diameter, diameter distribution and surface morphology of Fe₃O₄/poly(styrene-co-N-isopropylacrylamide)[P(St-NIPAM)] particles were characterized by scanning electron microscopy. The copolymer structure was confirmed by IR spectroscopy, differential scanning calorimetry and elemental analysis. The content of Fe₃O₄ entrapped in the particles was determined by atomic absorption spectrometry. A coarse structure was observed on the surface of the Fe₃O₄/P(St-NIPAM) particles. The hydrodynamic diameter of the Fe₃O₄/P(St-NIPAM) particles was found to exhibit about a 15% decrease in diameter on changing the temperature from 25 to 40 °C. The results also showed that Fe₃O₄/P(St-NIPAM) an advantage of exploited magnetic separation. Received: 6 August 1999 Accepted in revised form: 16 November 1999     

Preparation of magnetic polymer colloids with Brownian magnetic relaxation

Magnetic polymer colloids (MPCs) consisting of CoFe₂O₄ nanoparticles (NPs) embedded in a poly(methyl methacrylate) (PMMA) matrix were synthesized by magnetic miniemulsion polymerization. CoFe₂O₄ NPs were modified with 3-trimethoxysilylpropylmethacrylate and directly emulsified with different concentrations of sodium dodecyl sulfate under ultrasonication for subsequent miniemulsion polymerization. The average diameter of the CoFe₂O₄/PMMA spheres (about 200 nm) was controlled by varying the amount of surfactant. Thermogravimetric analysis indicated that the magnetic content was in the range of 44 to 73 %. Magnetic properties of the dispersions were investigated by measuring equilibrium magnetization curves and the dynamic magnetic susceptibility as a function of frequency. The MPCs were found to follow the Debye model for the dynamic magnetic susceptibility, with a characteristic time given by the rotational hydrodynamic resistance and thermal energy through the Stokes-Einstein relation. This demonstrates that the MPCs respond to applied magnetic fields by rotating. Due to their uniform size and high magnetic loading, these colloids may be suitable in a variety of applications, including nanoscale mechanical probes and actuators in complex fluids and biological systems.     

基于MIL-100(Fe)的磁性纳米碳材料的制备及其在内源性肽富集中的应用

以Fe₃O₄为核，采用层层自组装的方法合成核壳型Fe₃O₄@MIL-100（Fe）磁性纳米材料，经高温煅烧得到具有较大孔径（17.78 nm）、高含碳量（6.79%）的磁性纳米材料Fe₃O₄@MC。将该材料用于多肽的富集，并通过基质辅助激光解吸电离飞行时间质谱仪（MALDI-TOF MS）进行鉴定。Fe₃O₄@MC材料从牛血清白蛋白（BSA）酶解液中富集得到33条肽段，且具有较高的选择性（BSA酶解液与BSA的质量比为1：400），用于人血清中内源性肽段的分离富集也取得了较好的效果。     

Electric conductivity of polymer films filled with magnetic nanoparticles

The conductivity of polymer composites with magnetic nanoparticles (MNP) containing magnetite and other MNP (Ni, Cu–Ni) in the layers and planar cells with Al electrodes is studied. For soluble polymers (polyvinylpyrrolidone and polyvinyl alcohol) containing 1–10 wt % of magnetite MNP, a substantial effect of MNP on surface conductivity is detected over a wide range (from 10^–10 to 10^–3 Ω^–1). It is shown that the addition of magnetite MNP not only results in a considerable change in cell conductivity, but also leads to its partially irreversible variation (by an order of magnitude or more) via minor modifications of the experimental conditions (temperature, electric field). For high-resistance samples with low probabilities of conducting chain formation, temperature current peaks are observed upon moderate heating (up to 350 K). These peaks are similar to the maxima observed upon polymer electret thermodischarges when the charges are captured by the deep centers associated with separate MNP or MNP aggregates. The type and position of the maxima are determined by the characteristics of the polymer matrix. For polyvinylpyrrolidone composites, the maxima are observed some time after heating (the echo effect). With composites based on solventborne polymers (polyalkanesterimides, soluble polyimide) and Ni, Cu–Ni MNP, no change in film conductivity measured electrophotographically is observed, due to the formation of a dielectric coating formed by polymer macromolecules adsorbed on the MNP surface. An explanation based on the possible formation of magnetic aggregates of magnetite MNP and conducting chains is proposed. Magnetic aggregation IPM is proposed as one way of controlling cell conductivity.     

Preparation and adsorption properties of monodisperse chitosan-bound Fe3O4 magnetic nanoparticles for removal of Cu(II) ions

Monodisperse chitosan-bound Fe(3)O(4) nanoparticles were developed as a novel magnetic nano-adsorbent for the removal of heavy metal ions. Chitosan was first carboxymethylated and then covalently bound on the surface of Fe(3)O(4) nanoparticles via carbodiimide activation. Transmission electron microscopy micrographs showed that the chitosan-bound Fe(3)O(4) nanoparticles were monodisperse and had a mean diameter of 13.5 nm. X-ray diffraction patterns indicated that the magnetic nanoparticles were pure Fe(3)O(4) with a spinel structure, and the binding of chitosan did not result in a phase change. The binding of chitosan was also demonstrated by the measurement of zeta potential, and the weight percentage of chitosan bound to Fe(3)O(4) nanoparticles was estimated to be about 4.92 wt%. The chitosan-bound Fe(3)O(4) nanoparticles were shown to be quite efficient for the removal of Cu(II) ions at pH>2. In particular, the adsorption rate was so fast that the equilibrium was achieved within 1 min due to the absence of internal diffusion resistance. The adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 21.5 mg g(-1) and a Langmuir adsorption equilibrium constant of 0.0165 L mg(-1). The pH and temperature effects revealed that the adsorption capacity increased significantly with increasing pH at pH 2-5, and the adsorption process was exothermic in nature with an enthalpy change of -6.14 kJ mol(-1) at 300-330 K.     

Preparation of ionic liquid-encapsulated polymer particles

Encapsulation of ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([Hmim][TFSA]), was carried out by microsuspension polymerization of ethylene glycol dimethacrylate (EGDM) utilizing the self-assembling of phase-separated polymer method, which had been proposed by us for the preparation of hollow polymer particles. After the optimization of the polymerization conditions, ionic liquid-encapsulated polymer particles, which have smooth surface morphology and a single hollow structure, were successfully prepared. Encapsulation efficiency of [Hmim][TFSA] was significantly improved from about 20–70 % by changing the shell polymer from polyEGDM homopolymer to poly(EGDM-butyl methacrylate) (50/50, w/w) copolymer, which was likely to have relatively low affinity for [Hmim][TFSA]. Additionally, ionic liquid-encapsulated polymer particles displaying ionic conductivity were successfully prepared using triethylene glycol dimethacrylate as divinyl monomer instead of EGDM.     

单分散双相可溶四氧化三铁纳米微粒的多醇法制备及磁性

以具有生物相容性的三嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯为表面活性剂,利用多醇合成法制备了Fe3O4纳米微粒;采用X射线粉末衍射仪、傅立叶变换红外光谱仪及透射电子显微镜分析了Fe3O4纳米微粒的晶体结构、化学结构及显微结构,采用振动样品磁强计测定了其磁性能.结果表明,所制得的Fe3O4磁性纳米微粒结晶度高,在室温下显示近似超顺磁性.采用Langevin方程对Fe3O4纳米微粒的磁滞回线进行拟合,结果显示其为磁性单畴.此外,Fe3O4磁性纳米微粒在无机和有机溶剂中均具有很好的分散性,显示出广阔的应用前景.     

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

Uranium(VI) was removed from aqueous solutions using carbon coated Fe₃O₄ nanoparticles (Fe₃O₄@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe₃O₄@C toward uranium(VI) was ∼120.20 mg g⁻¹ when the initial uranium(VI) concentration was 100 mg L⁻¹, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe₃O₄@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe₃O₄@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.     

Preparation of magnetic microspheres with thiol-containing polymer brushes and immobilization of gold nanoparticles in the brush layer

Narrow-disperse magnetic microspheres were prepared by alkaline coprecipitation of Fe²⁺ and Fe³⁺ ions within poly(acrylic acid–divinylbenzene) microspheres that were prepared by distillation–precipitation copolymerization. Magnetic microspheres with polymer brushes that contain epoxy groups were prepared by graft copolymerization of glycidyl methacrylate and glycerol monomethacrylate via atom transfer radical polymerization (ATRP) from the magnetic microsphere surfaces. Subsequently, magnetic microspheres with thiol-containing polymer brushes were prepared by treating the epoxy group-containing magnetic microspheres with sodium hydrosulfide. Gold nanoparticles were immobilized in the brush layer of the thiol-containing magnetic microspheres through Au–S coordination. The catalytic activity of the gold nanoparticle-immobilized magnetic microspheres was investigated using the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride as a model reaction. The catalyst could be reused for over 10 cycles without noticeable loss of catalytic activity.     

Preparation of micron-size monodisperse polymer particles by dispersion copolymerization of styrene with poly(2-oxazoline) macromonomer

This article describes the preparation of micron-size monodisperse polymer particles by dispersion copolymerization of styrene with a poly(2-oxazoline) macromonomer in an aqueous ethanol solution. The macromonomer acted as a comonomer as well as a stabilizer. The diameter of the particles increased as the concentration of the macromonomer decreased. The higher the molecular weight of the macromonomer, the smaller the particle size. The copolymerization in the solvent containing higher water content gave smaller polymer particles. Under the condition giving the monodisperse particles, the particles volume increased linearly with the yield of the particles. From ESCA analysis of the particle surface, poly(2-oxazoline) chains were enriched on the surface. © 1993 John Wiley & Sons, Inc.     

Soap-free synthesis of highly monodisperse magnetic polymer particles with amphoteric initiator

A method applying soap-free emulsion polymerization with an amphoteric initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-2-methyl-propionamidine], is proposed for synthesis of highly monodisperse particles composed of magnetic nanoparticles (Fe₃O₄/γ–Fe₂O₃) and polystyrene. The magnetic nanoparticles were pretreated by surface modification for introducing double bonds onto the particles. In the polymerization, magnetic nanoparticles were continuously supplied to the system for a certain period after the initiation of polymerization at various pH. Dissociation degrees of ionizable groups in the initiator molecules were controlled through pH by changing NH₃ concentrations at a constant NH₄Cl concentration. Selection of suitable pH in the polymerization could produce polymer particles that perfectly incorporated the supplied magnetic nanoparticles. The magnetic polymer particles had a coefficient of variation of size distribution as low as 4.3% with an average diameter of 515 nm and a saturation magnetization of 7.3 emu/g-sample. Electrophoresis measurements indicated that the magnetic polymer particles had an isoelectric point of pH 4.1.     

Polyaniline-coated Fe(3) O(4) nanoparticles: An anion exchange magnetic sorbent for solid-phase extraction

In this study, the capability of the prepared polyaniline-coated Fe(3) O(4) nanoparticles for magnetic solid-phase extraction of three parabens from environmental wastewater, cream, and toothpaste samples is presented. Synthesized Fe(3) O(4) nanoparticles were coated with sulfate-doped polyaniline via polymerization of aniline in the presence of Fe(3) O(4) nanoparticles and sulfuric acid. Here, polyaniline-coated Fe(3) O(4) nanoparticles are presented as anion exchange sorbent, which extract anionic form of parabens via anion exchange with dopant of polyaniline. The experimental conditions affecting extraction efficiency were further studied and optimized. The experimental results showed that maximum extraction efficiency can be obtained at 70 mL sample solution of pH 8, extraction and desorption times of 2 and 1 min, respectively, 100 μL of 3% (v/v) acetic acid in acetonitrile as eluent, and 100 mg of the adsorbent. Under these conditions, the linear dynamic ranges were 0.5-100 μg/L with good correlation coefficients (0.998-0.999). The detection limits were in the range of 0.3-0.4 μg/L and the relative standard deviations were less than 2.4 (n = 5) for the three parabens. Finally, this fast and efficient method was further employed for determination of target analytes in cream, toothpaste, and environmental wastewater samples and satisfactory results were obtained.     

Preparation and characterization of NiO(core)/Fe2O3(shell) composite particles

A novel hydrothermal coating process has been developed to deposit amorphous Ni(OH)₂·H₂O over octahedral α-Fe₂O₃ particles by treating aqueous dispersion of the preformed cores in Ni(NO₃)₂/CH₃COONa solution. NiO_(core)/Fe₂O_3(shell) composite particles were prepared by air sintering of the Ni(OH)₂·H₂O_(shell)/Fe₂O_3(core) particles at 200–500°C for 1–6 h. The changes of morphology, structure and weight of the hydrothermal and sintering products were studied by means of TEM, XRD, XPS, TG and IR analyzers. The nucleation and growth model was suggested for the non-isothermal decomposition of Ni(OH)₂·H₂O coatings and the kinetic equation was derived from the non-linear regression of the TG data. The activation in the thermal-decomposition process is 73.8 kJ mol⁻¹ and the pre-exponential factor is 1.95×10⁴ s⁻¹.     

Synthesis of raspberry-like monodisperse magnetic hollow hybrid nanospheres by coating polystyrene template with Fe(3)O(4)@SiO(2) particles

A new inorganic/organic hybrid material containing silsesquioxane was prepared by the reaction of caged octa (aminopropyl silsesquioxane) (POSS-NH(2)) with n-butyl glycidyl ether (nBGE) and 1,4-butanediol diglycidyl ether (BDGE). The copolymers of POSS, nBGE, and BDGE could be obtained with varied feed ratio of POSS-NH(2), nBGE, and BDGE in the preparation. The hybrid material was added into an epoxy resin (E51) for enhancing the toughening and thermal properties of the epoxy resin. The results showed that the toughening and the thermal properties of the cured epoxy resin were greatly improved by the addition of the hybrid. The enhancement was ascribed to nano-scale effect of the POSS structure and the formation of anchor structure in the cured network. The investigation of kinetics for the curing process of the hybrid-modified epoxy resin revealed that two kinds of curing reactions occurred in different temperature ranges. They were attributed to the reactions between amino groups of the curing agent with epoxy groups of E51 and with residue epoxy groups in the hybrid. The reacting activation energies were calculated based on Kissinger's and Flynn-Wall-Ozawa's methods, respectively.     

Preparation of spheroidal and ellipsoidal particles from spherical polymer particles by extension of polymer film

Generation of particles of various sizes and shapes can be of great interest to scientists and engineers. We have developed a new and robust apparatus which can generate oblate spheroids from spherical polymer particles. A sheet of film dispersed with spherical particles was held by an eight-jaw extensional apparatus. The jaws were positioned in the edges of a regular octagon and moved radially to induce biaxial extension in an oil bath above the glass transition temperatures of the film and particles. We have demonstrated that polystyrene particles dispersed in a polyvinyl alcohol film can be stretched to generate various shapes by this method. The microscopic studies show that the oblate spheroids obtained by this method are virtually exact spheroids without showing knife edges. Also depending on positions with regard to holders, ellipsoids and even prolate spheroids can be obtained. The method has been found to be robust in that the deformation is always reproducible regardless of film thickness and very small deformation can be applied for nearly spherical particles. We have confirmed that this method can be applied for particles of submicrons to 10?μm in diameter or even larger ones. It is expected that the spheroids and ellipsoids obtained by this method can be of help in many studies including colloids, suspension rheology, electrophoresis, printed electronics, and pharmaceutical science.     

Sorption of As(V) on aluminosilicates treated with Fe(II) nanoparticles

Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of Fe(II). Within this process the mineral surface has been laden with Fe(III) oxi(hydroxides) whose high affinity for the As(V) adsorption is well known. In all investigated systems the sorption capacity of Fe(II)-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and As(V)-saturated solids showed characteristic bands caused by Fe(III)SO(4), Fe(III)O, and AsO vibrations. In untreated As(V)-saturated solids no significant AsO vibrations were observed due to the negligible content of sorbed arsenate.     

Synthesis of microspherical cellulose particles and study of magnetic relaxation characteristics of their composites with Fe(III) ions

The possibility of preparing microspherical cellulose particles was examined.