G. Yu. Yurkov

Electrical and Magnetic Properties of Nanomaterials Containing Iron or Cobalt Nanoparticles

We have prepared nanocomposites consisting of narrowly sized metal-containing nanoparticles embedded in a polyethylene matrix and have established conditions for the fabrication of thick films and bulk materials from the synthesized polymer powders. Dielectric permittivity and resistivity measurements demonstrate that the electrical properties of the nanocomposites depend significantly on the nanoparticle size and content.The microwave absorption and permittivity of the materials are shown to vary little in a broad frequency range. The magnetization (including the remanent one) of the cobalt-containing nanomaterials is higher than that of the iron-containing samples.

PROSPECTS OF USING CARBONACEOUS NANOPARTICLES IN BINDERS FOR POLYMER COMPOSITES

Different aspects of using carbonaceous nanoparticles for the creation of polymer composites with improved physicomechanical and functional properties are considered. It is shown that functionalized car-bonaceous nanoparticles can be used as modifiers to control the process of curing and elastification of epoxy binders during the development of polymer composites for use in construction. The possibility of using nano-particle self-organization for conferring functional properties on composites and obtaining 3D-reinforced hybrid nanocomposites is investigated.

Synthesis and properties of CdS nanoparticles in a polyethylene matrix

Nanocomposites of cadmium sulfide and high-pressure polyethylene have been synthesized. The mechanism of the thermal decomposition of thiourea complexes during the synthesis of cadmium sulfide nanoparticles has been investigated. The nanoparticle size, composition, and structure of the nanocomposites have been determined by x-ray diffraction, transmission electron microscopy, IR spectroscopy, and EXAFS spectroscopy, and the thermal decomposition of the nanomaterials has been studied.

Optical properties of cadmium sulfide nanoparticles on the surface of polytetrafluoroethylene nanogranules

The spectral characteristics in the visible range of synthesized nanocomposites based on cadmium sulfide and ultradispersed polytetrafluoroethylene are investigated experimentally. Local perturbations are found in the long-wavelength regions of the reflection and absorption spectra, which are related to the optical transitions between the critical points of the valence and conduction bands of the nanocomposite. The dispersion relations for the refractive index and the absorption coefficient are obtained for undoped and managanesedoped nanocomposites. The following important parameters of the nanocomposites are obtained from the spectral measurements: the fundamental optical absorption edge (the band gap), the refractive index (ω → 0), and the absorption coefficient. It is shown that doping with managanese affects changes in these parameters.

Optical and photoluminescent properties of nanomaterials based on cadmium sulfide nanoparticles and polyethylene

The spectral characteristics of absorption and photoluminescence of synthetic composite materials based on cadmium sulfide nanoparticles and polyethylene are studied in the visible and near-IR wavelength ranges. It is shown that the quantum efficiency of a material with CdS nanoparticles about 6 nm in size in a matrix of high-pressure polyethylene is the highest. The estimation of the photoluminescence linewidth shows that the linewidth of this material is the smallest, amounting to 0.55 eV, which indicates that the structure of these nanoparticles is more perfect.

Nanometallization of Ultradispersed Polytetrafluoroethylene

The high reactivity of nanoparticles and their tendency toward spontaneous compaction accompanied by deterioration of basic physical properties make stabilization a major challenge in fabrication of materials based on metal nanoparticles. The best-developed method of stabilization is embedding nanoparticles in polymer matrices. The known “friability” of the structures of most partially crystalline carbon-chain polymers forms the basis for the method of introducing metal-containing nanoparticles into solution melts of polymers in hydrocarbon oils [5]. However, this method is inapplicable to “hard” polymer matrices, such as polytetrafluoroethylene. At the same time, creation of materials that combine opposite properties of the components at the nanolevel is one of the rapidly developing strategies of modern materials science. For example, it is expedient to augment the high thermal and chemical stability of polytetrafluoroethylene with electrical conductivity on a semiconductor scale, magnetization by means of introducing metal nanoparticles, or optoelectronic properties by introducing so-called quantum dots— nanoparticles of some metal sulfides and selenides. vents hinder the introduction of different nanoparticles into this matrix and their uniform distribution over its bulk. In searching for the solution to this problem, we have focused our attention on ultradispersed polytetrafluoroethylene (UPTFE). UPTFE was fabricated by a thermal gas dynamic method suitable for commercial production of UPTFE [6]. The essence of the method is in formation of a finely dispersed UPTFE powder upon the thermodestruction of the block polymer. The method of production and the trademark UPTFE-FORUM are covered by patents [6‐8].

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mössbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mössbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

Properties of three-dimensional composites based on opal matrices and magnetic nanoparticles

Three-dimensional nanocomposites consisting of an opal matrix and a metal have been prepared by the interaction of salts and oxides of different elements (Ni, Co, Fe, etc.) embedded in an opal matrix with isopropanol in the range of supercritical state parameters of the alcohol. According to X-ray powder diffraction analysis and transmission electron microscopy data, the composites consist of an X-ray amorphous opal matrix with pores filled by nanoparticles of Co (or CoOx), metallic Ni, or Fe3O4 with a magnetite structure of various morphology. The sizes of the nanoparticles do not exceed the diameter of the pores in the opal matrix. A complex investigation of the nanocomposites has been performed using the electron magnetic resonance and vibrating magnetometry methods. All the studied samples at room temperature exhibit a ferromagnetic behavior. The coercive force of the samples lies in the range from 150 Oe for iron-containing nanocomposites to 565 Oe for cobalt-containing nanocomposites.

Cobalt-Containing Core-Shell Nanoparticles on the Surface of Poly(tetrafluoroethylene) Microgranules

Cobalt-containing nanoparticles have been prepared via thermal decomposition of cobalt acetate on the surface of poly(tetrafluoroethylene) (PTFE) microgranules forming a fluidized bed over the surface of hot mineral oil. Using transmission electron microscopy, the average size of the cobalt-containing nanoparticles has been determined to be 3.6 nm. The composition and structure of the nanoparticles have been determined by x-ray diffraction, extended x-ray absorption fine structure spectroscopy, and electron paramagnetic resonance, and the magnetic properties of the synthesized nanomaterial have been studied. The results indicate that the nanoparticles have a core-shell structure, with a metallic cobalt core (≃10 vol%) and a shell consisting of three phases: Co3O4 (≃80%) and small amounts of CoO and CoF2 (≃10%). The fluoride phase results from the interaction of the nanoparticles with surface fluorine atoms of the PTFE microgranules.

Preparation of bismuth nanoparticles in opal matrices through reduction of bismuth compounds with supercritical isopropanol

Bismuth nanoparticles have been produced in pores of opal matrices by reducing bismuth salts and oxide compounds with supercritical isopropanol. According to transmission electron microscopy data, the diameter of the SiO2 spheres in the opal matrices is about 260 nm, and that of the bismuth nanoparticles does not exceed 80 nm.