Fibrous Aggregation of Magnetite Nanoparticles Induced by a Time-Varied Magnetic Field (original) (raw)
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THE AGGREGATION OF IRON OXIDE NANOPARTICLES IN MAGNETIC FIELDS
The application of a magnetic field to a suspension of weakly magnetic nanoparticles should, based on previous work and theory, increase the aggregation between particles. This is due to the increase in the magnetic interaction in competition with repulsive forces due to the electric double layer. This hypothesis was tested using suspensions of magnetite and hematite nanoparticles. Magnetite particles were used to characterise the aggregation behaviour of strongly magnetic particles, which then served as a basis of comparison with hematite particles in a magnetic field. The expectation was that applying the magnetic field to the suspensions of weakly magnetic hematite particles would alter their aggregation behaviour to be more like that of the strongly magnetic magnetite particles. Experimental findings indicate this is not the case. No evidence was found indicating that the magnetic field altered particle interactions sufficiently to alter the aggregation. Aggregation behaviour was controlled by the chemical environment and shear forces. The magnetic field did influence the motion of the particles. In static experiments hematite particles were separated from suspension, the efficiency of which was related to the degree of aggregation and thus particle size. In stirred systems the balance between shear and Lorentz forces affected aggregate formation. As observed in previous work, small aggregation increases are possible but once aggregates reach a certain size the magnetic field affects the movement of particles and does not change interactions.
Magnetic properties of Fe-based nanoparticle assembly
Journal of Magnetism and Magnetic Materials, 2003
The magnetic properties of an assembly of very small Fe nanoparticles with an average diameter of the order of 3-5 nm are studied both experimentally and theoretically. The particles are dispersed in a polyethylene matrix with mass concentration 5%. The stray magnetic field of the samples with sizes 1 Â 1 Â 0.2 mm is measured by means of scanning SQUID microscope at 77 K as a function of external magnetic field. The presence of a weak remanent magnetization indicates a magnetic ordering in the samples studied at rather high temperatures. A distribution of the particle volumes or partial agglomeration of the particles within the assembly is suggested to be responsible for this unexpected behavior. r (S. Gudoshnikov). 0304-8853/03/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 0 2 ) 0 1 0 1 1 -9
On the magnetic aggregation of Fe3O4 nanoparticles
Computer Methods and Programs in Biomedicine, 2021
Background and objective In-vivo MRI-guided drug delivery concept is a personalized technique towards cancer treatment. A major bottleneck of this method, is the weak magnetic response of nanoparticles. A crucial improvement is the usage of paramagnetic nanoparticles aggregates since they can easier manipulated in human arteries than isolated particles. However its significance, not a comprehensive study to estimate the mean length and time to aggregate exists. Methods The present detailed numerical study includes all major discrete and continues forces and moments of the nanoscale in a global model. The effort is given in summarizing the effects of particle diameter and concentration, and magnetic field magnitude to comprehensive relations. Therefore, several cases with nanoparticles having various diameters and concentrations are simulated as magnetic field increases. Results It is found that aggregations with maximum length equal to 20 0 0 nm can be formed. In addition, the increase of the concentration leads to a decrease in the amount of the isolated particles. Consequently, 33% of the particles are isolated for the concentration of 2.25 mg / ml while 13% for the concentration of 10 mg / ml. Moreover, the increase of the permanent magnetic field and diameter of particles gives rise to an asymptotic behavior in the number of isolated particles. Furthermore, the mean length of aggregates scales linear with diameter and magnetic field, however, concentration increase results in a weaker effect. The larger aggregation that is formed is composed by 21 particles. Smaller time is needed for the completion of the aggregation process with larger particles. Additionally, the increase of the magnitude of the magnetic field leads to a decrease in the aggregation time process. Therefore, 8.5 ms are needed for the completion of the aggregation process for particles of 100 nm at B 0 = 0. 1 T while 7 ms at B 0 = 0. 9 T. Surprisedly, the mean time to aggregate is of the same order as in microparticles, although, with an opposite trend. Conclusions In this study, the evolution of the mean length of aggregations as well as the completion time of the aggregation process in the nano and micro range is evaluated. The present results could be useful to improve the magnetic nanoparticles assisted drug delivery method in order to minimize the side effects from the convectional cancer treatments like radiation and chemotherapy.
Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles
We have used low-field 1 H nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments of water protons, depending on the local strength of the field gradients. Hence, the spatial redistribution of the magnetic particles in the ferrofluid caused by the presence of an external magnetic field in a time scale of minutes can be monitored in real time, following the changes in the features of the NMR spectra during a period of about an hour. As previously reported [Heinrich et al., Phys. Rev. Lett., 2011, 106, 208301], in the homogeneous magnetic field of a NMR spectrometer, the aggregation of the particles of the IFF proceeds in two stages. The first stage corresponds to the gradual aggregation of monomers prior to and during the formation of chain-like structures. The second stage proceeds after the chains have reached a critical average length, favoring lateral association of the strings into hexagonal zipped-chain superstructures or bundles. In this work, we focus on the influence of a strongly inhomogeneous magnetic field on the aforementioned aggregation dynamics. The main observation is that, as the sample is immersed in a certain magnetic field gradient and kept there for a time t inh , magnetophoresis rapidly converts the ferrofluid into an aggregation state which finds its correspondence to a state on the evolution curve of the pristine sample in a homogeneous field. From the degree of aggregation reached at the time t inh , the IFF sample just evolves thereafter in the homogeneous field of the NMR spectrometer in exactly the same way as the pristine sample. The final equilibrium state always consists of a colloidal suspension of zipped-chain bundles with the chain axes aligned along the magnetic field direction.
Scientific Reports
Micro/nanostructures, which are assembled from various nanosized building blocks are of great scientific interests due to their combined features in the micro-and nanometer scale. This study for the first time demonstrates that ultrasmall superparamagnetic iron oxide nanoparticles can change the microstructure of their hydrocolloids under the action of external magnetic field. We aimed also at the establishment of the physiological temperature (39 °C) influence on the self-organization of silver and ultrasmall iron oxides nanoparticles (NPs) in hydrocolloids. Consequences of such induced changes were further investigated in terms of their potential effect on the biological activity in vitro. Physicochemical characterization included X-ray diffraction (XRD), optical microscopies (SEM, cryo-SEM, TEM, fluorescence), dynamic light scattering (DLS) techniques, energy dispersive (EDS), Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopies, zeta-potential and magnetic measurements. The results showed that magnetic field affected the hydrocolloids microstructure uniformity, fluorescence properties and photodynamic activity. Likewise, increased temperature caused changes in NPs hydrodynamic size distribution and in hydrocolloids microstructure. Magnetic field significantly improved photodynamic activity that was attributed to enhanced generation of reactive oxygen species due to reorganization of the microstructure.
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.
Journal of Nanoscience and Nanotechnology, 2012
The self-assembly of magnetic nanoparticles into higher-order organizations upon external magnetic stimulation has critical importance for the fabrication of discrete microstructures. In this study, the tuning of self-assembly behavior of magnetic Fe 3 O 4 nanoparticles (MNPs), with an average size of 6 nm, under the enhanced magnetic force upon changing the applied field strength and direction is explored. Upon evaporation of the solvent where the MNPs are suspended, formation of particular micrometer sized structures is achieved with a surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and MNPs. In this study, three different surfaces fabricated using sub-micrometer size magnetic beads in between the applied magnetic field and MNPs are used and the effect of the template pattern, applied field strength and direction are explored.
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.
Chemistry of Materials, 2013
This paper focuses on the magnetic properties of CoFe 2 O 4 nanoparticles, discussing the influence of nanoparticles arrangements obtained by different synthesis methods. Using high thermal decomposition (HTD) and direct micellar (DM) routes, three samples of CoFe 2 O 4 nanoparticles with equal primary particle size (∼5 nm) were prepared. The HTD method allows one to obtain highly crystalline primary nanoparticles coated by oleic acid organized in a self-assembling arrangement (ACoFe HTD). The DM method results to be appropriate to prepare either irregular arrangements (IACoFe DM) or spherical iso-oriented nanoporous assemblies (SACoFe DM) of primary CoFe 2 O 4 nanocrystals. Despite the same particle size, magnetization measurements of the HTD sample show a tendency toward cubic anisotropy (M r / M s ≈ 0.7), while in DM samples, a uniaxial anisotropy (M r /M s ≈ 0.4) is observed. The comparison between IACoFe DM and SACoFe DM samples indicates that the ordering of nanocrystals at the mesoscopic scale induces an increase of the coercive field (μ 0 H c ≈ 1.17 T → μ 0 H c ≈ 1.45 T) and of the reduced remanent magnetization (M r /M s ≈ 0.4 → M r /M s ≈ 0.5). The reason for these differences is discussed. In particular, a detailed study on interparticle interactions is carried out, highlighting the influence of the molecular coating and the formation of spherical iso-oriented assemblies.