Narrow Results

In the presented work, nanocomposites based on poly (vinylidene fluoride) (PVDF) and magnetite Fe₃O₄ nanoparticles were prepared. The structure and content of nanocomposite materials were studied by using scanning electron microscope (SEM), atomic-force microscope (AFM) and X-Ray diffraction (XRD). Magnetic properties of PVDF+Fe₃O₄ nanocomposites have been studied upon increasing nanoparticle content in polymer matrix upto 20%, revealing superparamagnetic behavior as Fe₃O₄ nanoparticles in polymer matrix act out like single-domain particles. It has also been observed that PVDF+Fe₃O₄-based nanocomposites can absorb the electromagnetic waves in the high frequency range 0.1–30 GHz. It has been shown that the absorption of high frequency radio waves by PVDF+Fe₃O₄ nanocomposites can be explained by the different molecular structures and also by the scattering of the radio waves at the boundary of nanoparticle-polymer matrix.

Sol–gel method has been employed to prepare Ni–Zn ferrite with chemical formula Ni${}_{1-x}$Zn_xFe₂O₄ where $x=$ 0, 0.1, 0.2, 0.3, 0.4 and 0.5. The structural Ni–Zn ferrite was studied via the X-ray diffractometer (XRD) pattern. X-ray analysis showed that there is a small shift in peaks towards shorter angles which increases with the concentration of zinc. Experimental values of lattice constant was varied from 8.34 of Ni ferrite to 8.397nm for Ni–Zn ferrite. The crystallite size of Ni ferrite was 83nm which is decreasing with substituted Zn to it and became 43nm at $4x=0.5$. Therefore, the superparamagnetic behavior appears with substitution of Zn to Ni ferrite. The saturation magnetization, remiensis, coersivity, magnetic moment and anisotropy constant were calculated according to hysteresis loop using the result of vibrating sample magnetometer (VSM). The effect of cation distribution appeared clearly through the saturation magnetization value which was 46.8emu/gm for nickel ferrite and increased to an optimum value (59.64emu/gm) at $x=0.3$.

Superparamagnetic (SP) crystalline cobalt ferrite (CoFe₂O₄) nanoparticles are synthesized by chemical co-precipitation method. Grown nanoparticles are annealed in air at various temperatures in the range 373 K to 1173 K to understand the variation in properties in nanoregion. Physical properties are analyzed for crystalline phase, crystallite size, particle size, shape, magnetization and relaxation behavior by using various characterization techniques viz. X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR). Annealing effect on various physical properties of particles are investigated. Particles are used in the development of stable ferrofluid.

High-quality hydrophobic or hydrophilic ferrofluid based on magnetite (Fe₃O₄) nanoparticles can be synthesized by one-pot direct synthesis which involves thermolysis of Iron(III) acetylacetonate, Fe(acac)₃ in hydrophobic or hydrophilic stabilizing agent, respectively. The structure of the nanoparticles dispersed in the ferrofluid was studied using XRD, FTIR, XPS, and TGA analysis, while morphology and size of the nanoparticles were determined by TEM. The magnetic properties of the samples were measured using VSM and SQUID measurement. The results show that oleylamine (OM) and tri(ethylene glycol) (TREG) coated Fe₃O₄ nanoparticles which are well stabilized in hydrophobic and hydrophilic ferrofluid, respectively, are relatively monodisperse, single crystalline and superparamagnetic in nature with the blocking temperature at around 100 K.

We report here a facile synthetic approach for preparing water-soluble Fe₃O₄ nanoparticle (NP) clusters with tunable size distribution and magnetic properties. The primary NP sizes were controlled by tuning the nucleation and growth rates with temperature and ligand concentration while the nanocluster sizes were manipulated by controlling interparticle interactions. We have investigated the size control of clusters as well as individual primary NPs via dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM). Superconducting quantum interference device (SQUID) was used to measure the magnetic properties of Fe₃O₄ NP for determining the effect of size distribution at room temperature. These water dispersible NP clusters can be utilized in various biomedical applications. In this study, we demonstrated the application of synthesized nanoclusters to enhance imaging contrast a novel ultrasound-based imaging modality, pulsed magneto-motive ultrasound (pMMUS) imaging. Our results indicated that by using the NP clusters with enhanced magnetic properties, the pMMUS signal increased significantly which is an essential requirement for further development of in vivo pMMUS imaging.

Monodispersed magnetite (Fe₃O₄) nanoparticles can be synthesized by thermal decomposition of iron(III) acetylacetonate, Fe(acac)₃. High saturation magnetization M_S of the magnetite particles is extremely important to realize the full potential of magnetite materials in biomedical application. In this work, we have studied the different effects (time, temperature and surfactant) on structure and magnetic properties of Fe₃O₄ nanoparticles. The M_S of the particles are enhanced after the synthesis at a higher reaction temperature and/or a longer reaction time. However, the increase in reaction temperature and/or reaction time resulted in particle size increase and the broadening of the particle size distribution. In this work, high M_S value of the magnetite particles has been achieved through adopting surfactant or modification of solvent to overcome the temperature and time effects, while the smaller size particles with an acceptable size distribution has been maintained. Size and morphology of the particles were studied by TEM while magnetic properties of the particles were measured using VSM. The saturation magnetization M_S of the particles can be increased at higher reaction temperature and/or longer reaction time, while narrow size distribution of the particles can be maintained either by the selective adsorption of oleic acid to the particle surface or by synthesizing them using solvent free thermal decomposition reaction.

Fulvic acid coated Fe₃O₄ superparamagnetic nanoparticles were synthesized by a coprecipitation technique with iron salts and a small molecule stabilizer-fulvic acid. The prepared nanoparticles were well dispersed in water with about 10 nm in size according to transmission electron microscopy (TEM) observations. Fourier transform infrared spectroscopy (FTIR) revealed that fulvic acid were successfully covalently bonded to Fe₃O₄ through the two adjacent phenolic hydroxyl groups and the carboxyl (-COOH) groups were functionalized to the surface. The vibrating sample magnetometer (VSM) result showed that the nanoparticles were superparamagnetic and the saturation magnetizations were 60 emu/g. Moreover, their efficacy of liver magnetic resonance imaging (MRI) contrast agent was investigated by using live rat and tumor-bearing rabbit models through conventional clinical 1.5T MRI.

Humic acid (HA)-coated Fe₃O₄ (Fe₃O₄/HA) superparamagnetic nanoparticles were synthesized by a chemical co-precipitation method with cheap and environmental friendly iron salts and HA. The as-synthesized samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The Fe₃O₄/HA nanoparticles showed faster adsorption rate and higher removal capacity of cationic organic dye Methylene blue (MB) in neutral water. Moreover, the MB desorption could be easily completed. And the reused performance of Fe₃O₄/HA nanoparticles was also excellent.

The hollow silica/cobalt ferrite (CoFe₂O₄) magnetic microsphere with amino-groups were successfully prepared via several steps, including preparing the chelating copolymer microparticles as template by soap-free emulsion polymerization, manufacturing the hollow cobalt ferrite magnetic microsphere by in-situ chemical co-precipitation following calcinations, and surface modifying of the hollow magnetic microsphere by 3-aminopropyltrime- thoxysilane via the sol-gel method. The average diameter of polymer microspheres was ca. 200 nm from transmission electron microscope (TEM) measurement. The structure of the hollow magnetic microsphere was characterized by using TEM and scanning electron microscope (SEM). The spinel-type lattice of CoFe₂O₄ shell layer was identified by using XRD measurement. The diameter of CoFe₂O₄ crystalline grains ranged from 54.1 nm to 8.5 nm which was estimated by Scherrer's equation. Additionally, the hollow silica/cobalt ferrite microsphere possesses superparamagnetic property after VSM measurement. The result of BET measurement reveals the hollow magnetic microsphere which has large surface areas (123.4m²/g). After glutaraldehyde modified, the maximum value of BSA immobilization capacity of the hollow magnetic microsphere was 33.8 mg/g at pH 5.0 buffer solution. For microwave absorption, when the hollow magnetic microsphere was compounded within epoxy resin, the maximum reflection loss of epoxy resins could reach -35dB at 5.4 GHz with 1.9 mm thickness.

Biomanipulation based on micro/nano structures is an attractive approach for biotechnology. To manipulate biological systems by magnetic forces, the magnetic labeling technology utilized magnetic nanoparticles (MNPs) as a common rule. Ferrofluid, well-dispersed MNPs, can be used for magnetic modification of the surface or as molds to form organized microstructures. For magnetic-based micro/nano structures, different methods to modulate magnetic field at the microscale have been developed. Specifically, this review focused on a new strategy which uses the concept of micromagnetism of patterned magnetic thin film with specific domain walls configurations to generate stable magnetic poles for cell patterning.