Theoretical and experimental study of the nanoparticle-driven blue phase stabilisation.

We have studied theoretically and experimentally the effects of various types of nanoparticles (NPs) on the temperature stability range [Formula: see text] T (BP) of liquid-crystalline (LC) blue phases. Using a mesoscopic Landau-de Gennes type approach we obtain that the defect core replacement (DCR) mechanism yields in the diluted regime [Formula: see text] T (BP)(x) [Formula: see text] 1/(1 - xb) , where x stands for the concentration of NPs and b is a constant. Our calculations suggest that the DCR mechanism is efficient if a local NP environment resembles the core structure of disclinations, which represent the characteristic property of BP structures. These predictions are in line with high-resolution ac calorimetry and optical polarising microscopy experiments using the CE8 LC and CdSe or aerosil NPs. In mixtures with CdSe NPs of 3.5nm diameter and hydrophobic coating the BPIII stability range has been extended up to 20K. On the contrary, the effect of aerosil silica nanoparticles of 7.0nm diameter and hydrophilic coating is very weak.

Synthesis and magnetic properties of Fe3O4 nanoparticles coated with biocompatible double hydrophilic block copolymer.

Fe3O4 nanoparticles coated with double hydrophilic biocompatible poly(sodium(2-sulfamate-3-carboxylate)isoprene)-b-poly(ethylene oxide) block copolymer were prepared by a one step precipitation method. The magnetic nanoparticles have 15 nm mean diameter (TEM), 68 nm hydrodynamic diameter, -30.10 mV zeta-potential and form very stable dispersion in aqueous media. Structural characterization using powder XRD and Mössbauer spectroscopy establish the magnetite phase, while thermogravimetric analysis and FT-IR spectroscopy confirm the presence of the block copolymer on the nanoparticles surface. The magnetic properties were determined using a vibrating sample magnetometer (VSM) at room temperature and reveal superparamagnetic behavior while the composite materials shows high saturation magnetization up to 67.7 emu/gr.

A general chemical route for the synthesis of capped nanocrystalline materials.

Noble metals, magnetic and semiconducting nanocrystalline materials have been synthesized via the thermolytic decomposition of inorganic metal salts, at high temperature, in commercial oleyl amine. The oleyl amine acts as high boiling point coordinating solvent, capping agent and, when required, as reducing agent. The crystal structure and morphology of the nanostructured materials have been studied with powder X-ray analysis (XRD) and transmission electron microscopy (TEM). The particles are well dispersed in non polar solvents such as hexane, toluene and chloroform and have uniform morphology.

One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites.

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240 °C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20 nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature Mössbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.

Large-scale synthesis, size control, and anisotropic growth of gamma-Fe2O3 nanoparticles: organosols and hydrosols.

Monodispersed, spherical gamma-Fe2O3 nanoparticles with controllable size in large-scale were prepared by thermolytic decomposition of FeCl3.6H2O in aliphatic amines. The nanoparticles gave very stable colloidal solution in organic solvents and can be easily converted to water-soluble by a very simple route. Their characterisation was based on TEM microscopy, XRD, Mössbauer, and magnetic measurements. Furthermore, a small amount of Pt can lead to the formation of anisotropic gamma-Fe2O3 nanostructures.

Synthesis and characterization of monodispersed rhodium nanoparticles organized in 3-D symmetrical structures soluble in organic media.

Monodispersed rhodium nanoparticles were synthesized through a flexible and very simple approach in a monosurfactant system by thermolysis of RhCl3, in which oleyl amine serves as capping, reducing agent, and high boiled solvent. The coated rhodium nanoparticles are monodispersed with 4 nm diameter and well characterised by TEM microscopy, UV-Vis spectroscopy, and X-ray diffraction measurements. The as prepared rhodium nanoparticles have the tendency to aggregate forming well-organized large symmetrical and spherical 3-D superstructures which generally have diameters between 40-60 nm as revealed by the characteristic TEM images. Due to the organic monolayer that encloses the nanoparticles are soluble in non-polar organic solvents.

The effect of Mn doping in FePt nanoparticles on the magnetic properties of the L1(0) phase.

FePtMn nanoparticles with a narrow size distribution and an average diameter of 3 nm were synthesized by the chemical reduction of Fe(acac)(3) and Pt(acac)(2) by NaBH(4) and the thermal decomposition of Mn(2)(CO)(10) in phenyl ether. The as-made nanoparticles have a disordered face-centred cubic (fcc) structure, which transformed after thermal treatment at 650 °C to an ordered face-centred tetragonal (fct) structure, possessing coercivity values up to 13.7 kOe at room temperature. The coercivity of the annealed samples depends on the amount of Mn added to the reaction mixture, with the coercive field increasing significantly with the partial substitution of Pt by Mn, while the partial substitution of Fe by Mn does not affect the magnetic properties strongly.

Catalytic reduction of N2O over Ag-Pd/Al2O3 bimetallic catalysts.

A study of the catalytic conversion of N2O to N2 over a bimetallic Ag-Pd catalyst is described in this article. Several Ag-Pd catalytic systems were prepared supported on Al2O3 with different ratios and their catalytic activity for the direct decomposition of N2O and their reduction with CO was measured. Based on the experimental results, it was observed that Ag-Pd bimetallic catalyst (5-0.5%) was the most active for both nitrous oxide reduction and direct decomposition. This high activity seems to be connected with a synergistic effect between Ag and Pd.