Air-stable Co-, Fe-, and Fe/Co-Nanoparticles and Ferrofluids

High performance magnetorheological fluids: very high magnetization FeCo-Fe3O4 nanoclusters in a ferrofluid carrier

High magnetization Fe₃O₄/OA-FeCo/Al₂O₃ nanocomposite magnetic clusters have been obtained using a modified oil-in-water miniemulsion method. These nanocomposite clusters dispersed in a ferrofluid carrier result in a magnetorheological fluid with improved characteristics. The magnetic clusters have a magnetic core consisting of a mixture of magnetite nanoparticles of about 6 nm average size, stabilized with oleic acid (Fe₃O₄/OA) and FeCo/Al₂O₃ particles of about 50 nm average size, compactly packed in the form of spherical clusters with a diameter distribution in the range 100-300 nm and a hydrophilic coating of sodium lauryl sulphate surfactant. The surface chemical composition of the Fe₃O₄/OA-FeCo/Al₂O₃ clusters investigated by XPS indicates the presence of the Co²⁺ and Co³⁺ oxidation states of cobalt and the components of Fe²⁺ and Fe³⁺ characteristic to both an enhanced oxidation state at the surface of the FeCo particles and to the presence of magnetic nanoparticles of spinel structure which are decorating the supporting FeCo. This specific decorating morphology is also indicated by TEM images. Advanced characterization of the Fe₃O₄/OA-FeCo/Al₂O₃ magnetic clusters has been performed using Mössbauer spectroscopy and magnetization measurements at various temperatures between 6 K and 200 K. The unexpected formation of Co ferrite decorating nanoparticles was supported by Mössbauer spectroscopy. The dispersion of magnetic clusters in the ferrofluid carrier highly influences the flow properties in the absence of the field (shear thinning for low and moderate shear rates) and especially in applied magnetic field, when significant magnetoviscous effect and shear thinning was observed for the whole range of shear rate values. Detailed analysis of the magnetorheological behavior of the nanocomposite magnetic clusters dispersed in a ferrofluid carrier evidence significantly higher normalized dynamic yield stress values in comparison with the magnetite nanocluster suspensions of the same mass concentration, a promising result for this new type of nanocomposite magnetorheological fluid.

Effect of Hydrothermal Reaction Time on Electrical, Structural and Magnetic Properties of Cobalt Ferrite

Cobalt ferrite was synthesized by hydrothermal route in order to investigate the effect of hydrothermal reaction time on structural, magnetic and dielectric properties. The synthesized cobalt ferrite was characterized by X-ray diffraction, Fourier transform infrared and Vibrating-Sample Magnetometer (VMS). XRD data analysis confirmed the formation of cubic inverse spinel ferrite for complete time series as the high intensity peak corresponds to cubic normal spinel structure. The ionic radii, cation distribution among tetrahedral and octahedral sites, lattice parameters, X-ray density, bond lengths were also investigated cobalt ferrite prepared at different hydrothermal reaction time. The crystallite size was found to be in the range of 11.79–32.78 nm. Tolerance factor was near unity that also confirms the formation of cubic ferrites. VSM studies revealed the magnetic nature of cobalt ferrite. The coercivity (1076.3Oe) was observed for a sample treated for 11 h. The squareness ratio was 0.56 that is close to 0.5 which shows uniaxial anisotropy in cobalt ferrite. Frequency dependent dielectric properties i.e. dielectric constant, AC conductivity, tangent loss and AC resistivity are calculated with the help of Impedance Analyzer. Intrinsic cation vibration of cubic spinel ferrites are confirmed from FTIR analysis in the range of 400–4000 cm−1. In view of enhanced properties, this technique could possibly be used for the synthesis of cobalt ferrite for different applications.

Doping of nematic cyanobiphenyl liquid crystals with mesogen-hybridized magnetic nanoparticles

Magnetic nanoparticles (MNPs) functionalized with (pro-)mesogenic ligands are implemented into a nematic liquid crystal (LC) and studied regarding both colloidal stability and magneto-optical behavior. In this study, the particle surface is specifically engineered to tune the MNP interactions with the LC host. For this purpose, four types of (pro-)mesogenic ligands (ML) are synthesized, which are composed of three structural parts, i.e., a rigid, LC motif (i.e., cyanobiphenyl) and a functional group for nanoparticle binding, both linked via a flexible spacer of different alkyl chain lengths. Electrostatically stabilized CoFe₂O₄ and γ-Fe₂O₃ nanoparticles with narrow size distribution and sizes below 3 nm are obtained via co-precipitation and subsequently functionalized to yield MNP@ML nanoparticles. Studies on the behaviour of the MNP@ML nanoparticles in the commercial LC host (i.e., 4-pentyl-4'-cyanobiphenyl (5CB)) in the bulk and in thin films in LC test cells, reveal the initial formation of some heterogeneities after transition from the isotropic to the nematic phase. Homogenous MNP@ML-5CB hybrids with long-term, colloidal stability, however, are obtained after magnetic separation of initially formed particle aggregates. In particular, MLs with carboxy groups and high structural flexibility (i.e., long linker lengths) are shown to be well suited to form stable MNP colloids, allowing for high MNP doping levels. As compared to undoped 5CB, the CoFe₂O₄@MLx-5CB hybrids show an increased sensitivity to the magnetic field, affecting the Fréedericksz transition. The strongest effect, however, is observed in magnetic and electric fields. The coupling of the ultrasmall, spherical MNPs with the LC director in the magnetic field suggests the formation of LC-induced, anisometric MNP clusters.

Ultrasmall inorganic nanoparticles: State-of-the-art and perspectives for biomedical applications

Ultrasmall nanoparticulate materials with core sizes in the 1-3nm range bridge the gap between single molecules and classical, larger-sized nanomaterials, not only in terms of spatial dimension, but also as regards physicochemical and pharmacokinetic properties. Due to these unique properties, ultrasmall nanoparticles appear to be promising materials for nanomedicinal applications. This review overviews the different synthetic methods of inorganic ultrasmall nanoparticles as well as their properties, characterization, surface modification and toxicity. We moreover summarize the current state of knowledge regarding pharmacokinetics, biodistribution and targeting of nanoscale materials. Aside from addressing the issue of biomolecular corona formation and elaborating on the interactions of ultrasmall nanoparticles with individual cells, we discuss the potential diagnostic, therapeutic and theranostic applications of ultrasmall nanoparticles in the emerging field of nanomedicine in the final part of this review.

KWS-1 high-resolution small-angle neutron scattering instrument at JCNS: current state

The KWS-1 small-angle neutron scattering (SANS) instrument operated by the Jülich Centre for Neutron Science (JCNS) at the research reactor FRM II of the Heinz Maier-Leibnitz Zentrum in Garching near Munich has been recently upgraded. The KWS-1 instrument was updated, from its active collimation apertures to the detector cabling. Most of the parts of the instrument were installed for the first time, including a broadband polarizer, a large-cross-section radio-frequency spin flipper, a chopper and neutron lenses. A custom-designed hexapod in the sample position allows heavy loads and precise sample positioning in the beam for conventional SANS experiments as well as for grazing-incidence SANS under applied magnetic field. With the foreseenin situpolarization analysis the main scientific topic of the instrument tends towards magnetism. The performance of the polarizer and flipper was checked with a polarized3He cell at the sample position. The results of these checks and a comparison of test measurements on a ferrofluid in a magnetic field with polarized and nonpolarized neutrons are presented.

Anisotropy of the magnetoviscous effect in ferrofluids containing nanoparticles exhibiting magnetic dipole interaction

The aim of this work has been the investigation of the anisotropy of the viscosity of a ferrofluid with magnetically interacting particles which are able to form structures in an applied magnetic field. The results of the experiments show a significant deviation from the case of a fluid without strong dipolar interactions. Furthermore, we have determined the dependence of the ratio of the viscosity coefficients on shear rate providing an insight into the microstructural reasons for the observed effects.

Magnetic nanomaterials for hyperthermia-based therapy and controlled drug delivery

Previous attempts to review the literature on magnetic nanomaterials for hyperthermia-based therapy focused primarily on magnetic fluid hyperthermia (MFH) using mono metallic/metal oxide nanoparticles. The term "hyperthermia" in the literature was also confined only to include use of heat for therapeutic applications. Recently, there have been a number of publications demonstrating magnetic nanoparticle-based hyperthermia to generate local heat resulting in the release of drugs either bound to the magnetic nanoparticle or encapsulated within polymeric matrices. In this review article, we present a case for broadening the meaning of the term "hyperthermia" by including thermotherapy as well as magnetically modulated controlled drug delivery. We provide a classification for controlled drug delivery using hyperthermia: Hyperthermia-based controlled drug delivery through bond breaking (DBB) and hyperthermia-based controlled drug delivery through enhanced permeability (DEP). The review also covers, for the first time, core-shell type magnetic nanomaterials, especially nanoshells prepared using layer-by-layer self-assembly, for the application of hyperthermia-based therapy and controlled drug delivery. The highlight of the review article is to portray potential opportunities for the combination of hyperthermia-based therapy and controlled drug release paradigms--towards successful application in personalized medicine.

Functionalized, biocompatible coating for superparamagnetic nanoparticles by controlled polymerization of a thioglycosidic monomer

It is demonstrated that water-soluble, glucosylated poly(pentafluorostyrene) derivatives revealed favorable coating material properties for magnetic iron oxide nanoparticles. To prepare the coating material in high reproducibility and purity as well as in sufficient amounts, a new route of synthesis is established. The preparation and characterization of the glucosylated, tetrafluorostyryl monomer, by thiol-para-fluorine "click" reaction, and its polymerization, via nitroxide-mediated radical process, is presented in detail. In addition, the coating material and the resulting particle properties are investigated by means of XPS, DLS, TGA, TEM, and cryo-TEM as well as flow cytometry. The glycopolymer acts as an appropriate stabilizing agent for the superparamagnetic nanoparticles by the formation of an approximately 10 nm thick shell, as shown by the XPS analysis. Furthermore, the application of FITC-labeled glycopolymer yielded fluorescent, superparamagnetic nanoparticles, which can be used for monitoring cell-carbohydrate interactions, because these particles show no cytotoxicity toward 3T3 fibroblasts.

Hydrothermal microemulsion synthesis of oxidatively stable cobalt nanocrystals encapsulated in surfactant/polymer complex shells

Air-stable magnetic cobalt nanocrystals have been conveniently prepared via a reverse micellar synthesis, followed by a hydrothermal treatment. The synthesis was carried out by first mixing an aqueous solution containing cobalt chloride and poly(sodium 4-styrenesulfonate) (PSS) with an organic mixture containing cetyltrimethylammonium bromide (CTAB) to form reverse micelles, followed by reducing cobalt ions with sodium borohydride. The resultant nanoparticles were then undergone a hydrothermal treatment at 165 degrees C for 8 h to generate well-dispersed CTAB/PSS-encapsulated cobalt nanocrystals with an average diameter of 3.5 +/- 0.5 nm. The nanoparticles were highly crystalline with a hexagonal close-packed crystal phase. The presence of CTAB/PSS complex coatings was identified by FT-IR and UV-vis spectroscopies as well as thermogravimetry analyses. The nanocrystals exhibited superparamagnetic property at room temperature with a saturation magnetization (M(s)) of 95 emu/g. The magnetization could be largely preserved after storage at room temperature for 4 months as the M(s) value only slightly decreased to 88 emu/g (measured at 300 K). Thus, the polymer encapsulation could not only improve thermal stability of the micelles for the growth and nucleation of Co atoms but also protect the resulting cobalt nanocrystals from oxidation through forming an oxygen impermeable sheath.