Magnetic studies of iron oxide nanoparticles coated with oleic acid and Pluronic® block copolymer (original) (raw)
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We report the synthesis of phase pure, mono-dispersed Fe 3 O 4 nanoparticles of size ∼10 nm via chemical co-precipitation of ferrous and ferric ions, under controlled pH and temperature. The nanoparticles are oleic acid functionalized and hence dispersible in organic medium. The structure and morphology of nanoparticles are determined by analyzing XRD pattern and TEM micrographs, confirming the formation of phase pure Fe 3 O 4 nanoparticles. The magnetization studies reveal the superparamagnetic behaviour of the nanoparticles at room temperature. The changes in blocking temperatures (T B) of magnetic nanoparticles with applied magnetic fields (H ap), noted from the cusp of the zero-field-cooled magnetization, the indicate effects of dipole interactions. A decrease in blocking temperature from 95 K to 15 K has been observed on varying the magnetic field from 50 Oe to 5000 Oe. T B versus H relation follows the equation T B (H) = T o (1 − (H /H o)) m , i.e. the Néel–Brown model of magnetic relaxation in nanoparticles.
Magnetic properties of Fe[sub 3]O[sub 4] nanoparticles coated with oleic and dodecanoic acids
Journal of Applied Physics, 2010
Magnetic nanoparticles (NP) of magnetite (Fe 3 O 4 ) coated with oleic (OA) and dodecanoic acids (DA) were synthesized and investigated through Transmission Electron Microscopy (TEM), magnetization M , and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78, 76, and 65%) and the DA sample with 63% of Fe 3 O 4 . Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ∼ 5.5 nm. Magnetization measurements, performed in zero field cooled (ZFC) and field cooled (FC) processes under different external magnetic fields H, exhibited a maximum at a given temperature T B in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature T B decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase of T B . The observed behavior is related to the dipolar interaction (DI) between NP which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility χ ac measurements, where the temperature in which χ ′ peaks for different frequencies follows the Vogel-Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H vs. T B /T B (H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below T B , M vs. H curves show a coercive field (H C ) that increases monotonically with decreasing temperature. The saturation magnetization (M S ) follows the Bloch's law and values of M S at room temperature as high as 78 emu/g were estimated, a result corresponding to ∼ 80% of the bulk value. The overlap of M /M S vs. H/T curves for a given sample and the low H C at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M /M S vs. H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration.
Size dependent magnetic properties of iron oxide nanoparticles
Journal of Magnetism and Magnetic Materials, 2003
Uniform iron oxide nanoparticles in the size range from 10 to 24 nm and polydisperse 14 nm iron oxide particles were prepared by thermal decomposition of Fe(III) carboxylates in the presence of oleic acid and co-precipitation of Fe(II) and Fe(III) chlorides by ammonium hydroxide followed by oxidation, respectively. While the first method produced hydrophobic oleic acid coated particles, the second one formed hydrophilic, but uncoated, nanoparticles. To make the iron oxide particles water dispersible and colloidally stable, their surface was modified with poly(ethylene glycol) and sucrose, respectively. Size and size distribution of the nanoparticles was determined by transmission electron microscopy, dynamic light scattering and X-ray diffraction. Surface of the PEG-functionalized and sucrose-modified iron oxide particles was characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy and thermogravimetric analysis (TGA). Magnetic properties were measured by means of vibration sample magnetometry and specific absorption rate in alternating magnetic fields was determined calorimetrically. It was found, that larger ferrimagnetic particles showed higher heating performance than smaller superparamagnetic ones. In the transition range between superparamagnetism and ferrimagnetism, samples with a broader size distribution provided higher heating power than narrow size distributed particles of comparable mean size. Here presented particles showed promising properties for a possible application in magnetic hyperthermia.
Magnetic properties of fe3O4 nanoparticles coated with oleic and dodecanoicacids
Magnetic nanoparticles (NP) of magnetite (Fe 3 O 4 ) coated with oleic (OA) and dodecanoic acids (DA) were synthesized and investigated through Transmission Electron Microscopy (TEM), magnetization M , and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78, 76, and 65%) and the DA sample with 63% of Fe 3 O 4 . Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ∼ 5.5 nm. Magnetization measurements, performed in zero field cooled (ZFC) and field cooled (FC) processes under different external magnetic fields H, exhibited a maximum at a given temperature T B in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature T B decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase of T B . The observed behavior is related to the dipolar interaction (DI) between NP which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility χ ac measurements, where the temperature in which χ ′ peaks for different frequencies follows the Vogel-Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H vs. T B /T B (H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below T B , M vs. H curves show a coercive field (H C ) that increases monotonically with decreasing temperature. The saturation magnetization (M S ) follows the Bloch's law and values of M S at room temperature as high as 78 emu/g were estimated, a result corresponding to ∼ 80% of the bulk value. The overlap of M /M S vs. H/T curves for a given sample and the low H C at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M /M S vs. H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration.
Effect of Surface Modification on Magnetization of Iron Oxide Nanoparticle Colloids
Langmuir, 2012
Magnetic iron oxide nanoparticles have numerous applications in the biomedical field, some more mature, such as contrast agents in magnetic resonance imaging (MRI), and some emerging, such as heating agents in hyperthermia for cancer therapy. In all of these applications, the magnetic particles are coated with surfactants and polymers to enhance biocompatibility, prevent agglomeration, and add functionality. However, the coatings may interact with the surface atoms of the magnetic core and form a magnetically disordered layer, reducing the total amount of the magnetic phase, which is the key parameter in many applications. In the current study, amine and carboxyl functionalized and bare iron oxide nanoparticles, all suspended in water, were purchased and characterized. The presence of the coatings in commercial samples was verified with X-ray photoelectron spectroscopy (XPS). The class of iron oxide (magnetite) was verified via Raman spectroscopy and X-ray diffraction. In addition to these, inhouse prepared iron oxide nanoparticles coated with oleic acid and suspended in heptane and hexane were also investigated. The saturation magnetization obtained from vibrating sample magnetometry (VSM) measurements was used to determine the effective concentration of magnetic phase in all samples. The Tiron chelation test was then utilized to check the real concentration of the iron oxide in the suspension. The difference between the concentration results from VSM and the Tiron test confirmed the reduction of magnetic phase of magnetic core in the presence of coatings and different suspension media. For the biocompatible coatings, the largest reduction was experienced by amine particles, where the ratio of the effective weight of magnetic phase reported to the real weight was 0.5. Carboxyl-coated samples experienced smaller reduction with a ratio of 0.64. Uncoated sample also exhibits a reduction with a ratio of 0.6. Oleic acid covered samples show a solvent-depended reduction with a ratio of 0.5 in heptane and 0.4 in hexane. The corresponding effective thickness of the nonmagnetic layer between magnetic core and surface coating was calculated by fitting experimentally measured magnetization to the modified Langevin equation.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were encapsulated into poly(d,l-lactide-co-glycolide) (PLGA) particles using an oil-in-water-in-oil emulsion technique. The use of the oleic acid-coated SPIONs, and their suspension in the first oil phase led to well-dispersed nanoparticles in the PLGA matrix. Relative amounts of SPIONs encapsulated in PLGA could be varied by increasing the concentration of SPIONs in the first oil phase: doubling the amount in that phase doubled the amount of SPIONs in the PLGA. The saturation magnetization scaled proportionally with the amount of SPIONs in the PLGA and was significantly larger than other efforts to encapsulate magnetic nanoparticles in PLGA. Size of the composite particles, as determined by dynamic light scattering (DLS), could be varied from 280 to 160 nm by varying either power or time of sonication while the zeta potential remained near −20 mV for the composite, independent of SPION content. Transmission electron microscopy images showed SPIONs ranging in diameter from 5 to 15 nm embedded inside the polymer and indicated that they were uniformly dispersed within the PLGA particles. Small angle X-ray scattering (SAXS) showed that only the particles containing the largest amount of encapsulated SPIONs displayed a peak indicative of aggregation.
Surfactant Effects on the Structural and Magnetic Properties of Iron Oxide Nanoparticles
The Journal of Physical Chemistry C, 2014
Iron oxide nanoparticles were prepared using the simplest and most efficient chemical route, the coprecipitation, in the absence and the presence of three different and widely used surfactants. The purpose of this study is to investigate the possible influence of the different surfactants on the structure and therefore on the magnetic properties of the iron oxide nanoparticles. Thus, different techniques were employed in order to elucidate the composition and structure of the magnetic iron oxide nanoparticles. By combining transmission electron microscopy with X-ray powder diffraction and X-ray absorption fine structure measurements, we were able to determine and confirm the crystal structure of the constituent iron oxides. The magnetic properties were investigated by measuring the hysteresis loops where the surfactant influence on their collective magnetic behavior and subsequent AC magnetic hyperthermia response is apparent. The results indicate that the produced iron oxide nanoparticles may be considered as good candidates for biomedical applications in hyperthermia treatments because of their high heating capacity exhibited under an alternating magnetic field, which is sufficient to provoke damage to the cancer cells.
Journal of Magnetism and Magnetic Materials, 2009
Colloidal nanoparticles of Fe 3 O 4 (4 nm) were synthesized by high-temperature hydrolysis of chelated iron (II) and (III) diethylene glycol alkoxide complexes in a solution of the parent alcohol (H 2 DEG) without using capping ligands or surfactants: [Fe(DEG)Cl 2 ] 2-+ 2[Fe(DEG)Cl 3 ] 2-+ 2H 2 O + 2OH -→ Fe 3 O 4 + 3H 2 DEG + 8Cl -The obtained particles were reacted with different small-molecule polydentate ligands, and the resulting adducts were tested for aqueous colloid formation. Both the carboxyl and α-hydroxyl groups of the hydroxyacids are involved in coordination to the nanoparticles' surface. This coordination provides the major contribution to the stability of the ligandcoated nanoparticles against hydrolysis.