Magnetic Characteristics of Ferrimagnetic Microspheres Prepared by Dispersion Polymerization (original) (raw)
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Journal of Polymer Science Part A: Polymer Chemistry, 2004
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 Fe 3 O 4 is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2Ј-azobisisobutyronitrile (AIBN), 4,4Ј-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 m. 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.
Journal of Magnetism and Magnetic Materials, 2006
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 Fe 3 O 4 is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2Ј-azobisisobutyronitrile (AIBN), 4,4Ј-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 m. 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.
Chemistry of Materials, 2008
A novel method is described for the preparation of nearly monodispersed and highly magnetic responsive microspheres with magnetite nanocrystals formed in a polymeric matrix by hydrothermal reduction. The method is based on the formation of iron hydroxide/polymer composite microspheres by acid-catalyzed condensation polymerization of urea and formaldehyde in the presence of colloidal iron hydroxide. The iron hydroxide colloids entrapped in the polymer matrix are then in situ converted to magnetite nanocrystals by reaction with sodium borohydride under hydrothermal conditions. Characterization of the resulting microspheres with electron microscopy and vibrating sample magnetometry confirmed that these particles possessed a uniform spherical morphology, narrow particle size distribution, and high magnetic susceptibility. More interestingly, the magnetic nanoparticles embedded in the polymer matrix are of cubic shape and highly crystalline structure. While the growth of uniform composite microspheres is accounted for by the well-known LaMer model, the formation of the cubic magnetite nanocrystals appears to involve a dissolution-recrystallization process. After being coated with silica by the sol-gel approach, the magnetic particles were used as adsorbents for isolation of genomic DNA from biological samples, with results comparable to those obtained by magnetic silica microspheres. Incorporation of iron hydroxide colloids into polymer microspheres coupled with chemically induced phase transformation represents a new cost-effective approach to the preparation of uniform magnetic microspheres that is more controllable with respect to particle properties and more amenable to large-scale production.
Journal of Polymer Science Part A: Polymer Chemistry, 2000
Crosslinked poly(2-hydroxyethyl methacrylate)-based magnetic microspheres were prepared in a simple one-step procedure by dispersion polymerization in the presence of several kinds of iron oxides. Cellulose acetate butyrate and dibenzoyl peroxide were used as steric stabilizer and polymerization initiator, respectively, and ethylene dimethacrylate was a crosslinking agent. The resulting product was characterized in terms of particle size, particle size distribution, iron(III) content, and magnetic properties. In the presence of needle-like maghemite in the polymerization mixture and under suitable conditions, magnetic microspheres with relatively narrow size distribution were formed. An increase in the particle size and, at the same time, a decrease in molecular weight of uncrosslinked polymers resulted, as the continuous phase became richer in 2-methylpropan-1-ol. Coercive force of needle-like maghemitecontaining particles was higher than that of cubic magnetite-loaded microspheres. Coercive force increased with the decreasing iron content in the particles.
The preparation of magnetic nanoparticle assemblies for biomedical applications
The structure of magnetite 20 1.3.4 Magnetic properties of small nanoparticles: Single domain particles 22 1.3.5 Superparamagnetism 24 1.4 Stabilisation of magnetite nanoparticles in suspension 27 1.4.1 The stability of magnetic fluids 27 1.4.2 The surface chemistry of magnetite 28 1.4.3 Steric or entropie stabilisation 30 1.4.4 Stabilisation by long chain surfactants 1.4.5 Clustering and aggregation in aqueous suspension 1.5 Synthesis of magnetite nanoparticles 34 1.5.1 The synthesis of magnetic nanoparticles by alkaline coprecipitation 3 5 1.5.2 The synthesis of magnetic nanoparticles by other methods 39 1.6 Applications of magnetic fluids 42 1.6.1 Superparamagnetic nanoparticles in nanotechnology 42 1.6.2 Magnetic nanoparticles as mediators for magnetic hyperthermia 44 VI 1.6.3 Magnetic nanoparticles as contrast agents for MRI 1.6.4 The NMR relaxation mechanism in aqueous magnetic fluids 45 46 Chapter Two-Experimental Section 2.1 Introduction 2.2 Fast field cycling NMR 2.2.1 Historical development of the technique 55 2.2.2 The field cycling experiment 2.2.3 Practical considerations 2.3 Photon correlation spectroscopy 2.3.1 Principles of the technique 2.3.2 Practical considerations 65 2.4 Other analytical techniques 2.4.1 Atomic absorption spectroscopy 2.4.2 Redox distribution of iron in iron oxide samples 2.4.3 Fatty acid determination 2.4.4 Raman spectroscopy of iron oxide samples 71 2.4.5 Electron Microscopy 71 Chapter Three-Preparation and characterisation of aqueous magnetic fluids 3.1 Introduction 3.2 Experimental 3.2.1 Uncoated nanoparticles suspended in water 73 3.2.2 DNA stabilised magnetic suspensions 3.2.3 Surfactant coated nanoparticle suspensions in water 75 3.3 Results 3.3.1 Uncoated aqueous nanoparticle suspensions 3.3.2 DNA stabilised magnetic suspensions 3.3.3 Surfactant coated nanoparticle suspensions in water VII 3.4 Discussion 3.4.1 Uncoated aqueous nanoparticle suspensions 3.4.2 DNA stabilised magnetic suspensions 3.4.3 Coated nanoparticle suspensions in water 3.5 Conclusion Chapter Four 100-Alkaline coprecipitation o f surfactant stabilised magnetic nanoparticles and their characterisation in suspension 4.1 Introduction 4.2 Experimental 4.2.1 Ammonia coprecipitation of Fe(II) and Fe(III) salts 4.2.2 Sodium chloride assisted coprecipitation 103 4.2.3 Phase transfer from aqueous suspension into heptane 103 4.2.4 Effect of chain length on relaxivity in heptane suspension 4.2.5 Phase transfer from non-aqueous suspension into water 4.2.6 Uncoated nanoparticles in organic solvents 105 4.3 Results 4.3.1 Ammonia coprecipitation 105 4.3. 2 Effect of pH on the NMRD response 4.3.3 Effect of temperature on the NMRD response 4.3.4 Sodium chloride assisted coprecipitation 4.3.5 Effect of chain length on relaxivity in heptane suspension 4.4 Discussion 4.4.1 Sodium chloride assisted and non-assisted coprecipitation 111 4.4.2 Coprecipitated magnetite in heptane 4.4.3 Effect of chain length on relaxivity in heptane suspension 4.4.4 Non aqueous magnetite suspended in aqueous suspension 4.4.5 Uncoated magnetite in water and heptane 4.5 Conclusion VIII Chapter Five-The preparation and characterisation o f non-aqueous magnetic fluids 5.1 Introduction 5.2 Experimental 5.3 Results 5.3.1 General observations 5.3.2 The effect of temperature on the reaction 5.3.3 The effect of concentration on the PCS analysis 5.3.4 NMR relaxation rate measurements 5.3.5 The effect of concentration on the NMRD analysis 5.3.6 The relaxivity of the suspensions: 5.3.7 The effect of applying ultrasonic energy to the magnetic fluids: 5.3.8 Transmission electron microscopy results 5.3.9 Raman spectroscopic study of magnetite particles 5.3.10 Redox-distribution of iron in magnetite 5.4 Discussion 141 5.4.1 The synthesis of non-aqueous magnetic fluids 5.4.2 NMRD characterisation of the non-aqueous magnetic fluids 5.4.3 Consistency of the NMRD results with SPM theory 5.4.4 Interpretation of the NMRD results with SPM theory 5.5 Conclusions Chapter Six 153-The adsorption o f coated magnetite nanoparticles on silica 6.1
Journal of Applied Polymer Science, 2008
The study focuses on the characterization of the superparamagnetic microspheres of poly(methyl methacrylate) (PMMA) prepared by the modified suspension polymerization. The nano-sized oleic acid-coated magnetite particles (OMP) mixed with methyl methacrylate (MMA) monomers and divinylbenzene were employed to produce the nonporous superparamagnetic PMMA microspheres. The morphology, composition and magnetic properties of the magnetic PMMA microspheres were characterized with the scanning electron microscopy, particle size analyzer, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and superconductor quantum interference device. As a result, the obtained PMMA microspheres had the average particle size of 1.8-6.8 lm and magnetite content of 4.74-10.85 wt %. The corresponding saturation magnetization of the PMMA microspheres was in the range of 2.04-8.51 emu/g. The diameter of the PMMA microspheres showing the polydispersity significantly decreased with the higher weight ratio of OMP to MMA. On the contrary, the magnetite content and saturation magnetization of the PMMA microspheres would increase with the higher weight ratio of OMP to MMA. Furthermore, the distinct relationships between the characteristics of magnetic PMMA microspheres and the weight ratio of OMP to MMA have been proposed. The magnetic PMMA microspheres show the good stability in the solution with the pH region of 2.1-12.9.
Tailoring the magnetic behavior of polymeric particles for bioapplications
Journal of Polymer Engineering, 2000
In this study, magnetic polymeric nanoparticles were prepared use in for targeted drug delivery. First, iron oxide (Fe 3 O 4 ) magnetic nanoparticles (MNPs) were synthesized by coprecipitation with ferrous and ferric chloride salts. Then, to render the MNPs hydrophobic, the surfaces were covered with oleic acid. Finally, the hydrophobic MNPs (H-MNPs) were encapsulated with polymer. The emulsion evaporation technique was used for the preparation of polymer-coated H-MNP. Poly( dl -lactide-co-glycolide) (PLGA) and chitosan-modified PLGA were used as polymers. The polymeric nanoparticles were characterized and compared. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, size distribution, ζ potential, magnetic properties, and magnetite entrapment efficiency measurements were performed to investigate the properties of the nanoparticles. The XTT assay was performed to understand the biocompatibility (i.e., toxicity) of MNPs and magnetic polymeric nanoparticles to MCF-7 cells.
Polymer, 2006
Magnetic particles are very important systems with potential use in drug delivery systems, ferrofluids, and effluent treatment. In many situations, such as in biomedical applications, it is necessary to cover inorganic magnetic particles with an organic material, such as polymers. In this work, latices based on magnetite covered by poly(ethyl methacrylate-co-methacrylic acid) were obtained via miniemulsion polymerization. The resultant latices had particles in the nanometric range and presented a pronounced superparamagnetic behavior.
Preparation of biodegradable magnetic microspheres with poly(lactic acid)-coated magnetite
Journal of Magnetism and Magnetic Materials, 2009
Poly(lactic acid) (PLA)-coated magnetic nanoparticles were made using uncapped PLA with free carboxylate groups. The physical properties of these particles were compared to those of oleate-coated or oleate/sulphonate bilayer (W40) coated magnetic particles. Magnetic microspheres (MMS) with the matrix material poly(lactide-co-glycolide) (PLGA) or PLA were then formed by the emulsion solvent extraction method with encapsulation efficiencies of 40%, 83% and 96% for oleate, PLA and oleate/sulfonate-coated magnetic particles, respectively. MMS made from PLA-coated magnetite were hemocompatible and produced no hemolysis, whereas the other MMS were hemolytic above 0.3 mg/mL of blood.