Carbon nanostructures based on IR-pyrolyzed polyacrylonitrile

For the first time, it is shown that IR pyrolysis of a composite based on polyacrylonitrile and gadolinium chloride produces a metal-carbon nanocomposite where metal particles with a size of 4–11 nm form a fine dispersion in the structure of the carbon matrix. The carbon phase of the composite is a carbon-carbon nanocomposite with a structure in which carbon nanoparticles (bamboolike carbon nanotubes, carbon nanospheres, or octahedral carbon nanoparticles) are incorporated into the matrix graphite-like material.     

Water-soluble polyelectrolytes based on polyacrylonitrile for wastewater treatment

The possibility of modifying oxidized asphalt by performing polycondensation of maleic anhydride with aliphatic amines of various chemical structures in the dispersion medium was considered. The influence of the reactant structures and reaction conditions on the physicomechanical and structural-rheological properties of the polymer-modified asphalt was examined.     

Iron-containing nanocomposites based on mesoporous aluminosilicates

Here we report the synthesis and magnetic characterization of iron-containing nanocomposites based on mesoporous aluminosilicates (MAS). MAS with Al:Si ratio equal to 1:15 was synthesized by a two-step hydrothermal treatment. The chemical composition and structure of the matrix were determined by chemical analysis, TGA, SAXS and adsorption of nitrogen at 77 K. The intercalation of iron into the channels was performed either by cationic exchange or by soaking the initial matrix in Fe(CO)₅. Reduction/decomposition of the complex was carried out by thermal treatment in a hydrogen flow. The nanocomposites obtained were characterized by XRD, TEM, Mössbauer spectroscopy and magnetic measurements. It was shown that the first method does not give any magnetic phases at nanolevel. The second method results in the formation of magnetic iron-containing nanowires (with diameter <2 nm and length over 30 nm) in a mesoporous matrix, which possess blocking temperatures over 300 K and coercivity up to 31,000 A/m at room temperature.     

Tyrosine 89 accelerates Co-carbon bond homolysis in methylmalonyl-CoA mutase

The contribution of the active-site residue, Y89, to the trillion-fold acceleration of Co-carbon bond homolysis rate in the methylmalonyl-CoA mutase-catalyzed reaction has been evaluated by site-directed mutagenesis. Conversion of Y89 to phenylalanine or alanine results in a 10(3)-fold diminution of k(cat) and suppression of the overall kinetic isotope effect. The spectrum of the enzyme under steady-state conditions reveals the presence of AdoCbl but no cob(II)alamin. Together, these results are consistent with homolysis becoming completely rate determining in the forward direction in the two mutants and points to the role of Y89 as a molecular wedge in accelerating Co-carbon bond cleavage.     

Polymetalates based organic-inorganic nanocomposites

New nanocomposites materials have been synthesized. They present electrochemical and photochromic properties. They are based on a hybrid organic-inorganic network, in which tungsten heteropolyoxometalates (PW₁₂O ₄₀ ^3– , SiW₁₂O ₄₀ ^4– , W₁₀O ₃₂ ^4– , polymeric tungstate) are entrapped. High tungsten ratios could be reached and films or bulk materials have been obtained. The structure of these materials is described on the basis of multi-spectroscopic investigations (IR, EPR, NMR). Electrochemical redox reactions have been observed in thin films. Dark blue reversible coloration of the materials is obtained under UV irradiation. The photochromic mechanism has been investigated and shows the reversible formation of carbonyl group.     

Two-dimensional nanocomposites based on chemically modified graphene

The multiple functional groups and unique two-dimensional (2D) morphology make chemically modified graphene (CMG) an ideal template for the construction of 2D nanocomposites with various organic/inorganic components. Additionally, the recovered electrical conductivity of CMG may provide a fast-electron-transport channel and can thus promote the application of the resultant nanocomposites in optoelectronic and electrochemical devices. This Concept article summarizes the different strategies for the bottom-up fabrication of CMG-based 2D nanocomposites with small organic molecules, polymers, and inorganic nanoparticles, which represent the new directions in the development of graphene-based materials.     

Microstructure and properties of polyacrylonitrile based carbon fibers

The microstructure of polyacrylonitrile (PAN)-based carbon fibers with different mechanical properties was investigated. It was found that the tensile strength of the PAN-based carbon fibers generally decrease with the increase in the modulus. The properties of PAN-based carbon fiber are mainly controlled by the microstructure and microvoids. The increase in size and orientation of graphite crystallites follows the decrease in interlayer space of graphite sheets, which accompanies the increase in modulus and decrease in tensile strength of the carbon fibers. Simultaneously, the increase in the modulus of the carbon fibers accompanies the merging of the elliptical microvoids along the fiber axis and the turbostratic graphite in the carbon fibers transforms into 3D ordered graphite lamellar structure. This work provides useful information on tailoring the mechanical properties of carbon fibers by adjusting the microstructure.     

Synthesis and properties of an aminocarboxylic polyampholyte based on polyacrylonitrile fiber

Aminocarboxylic fibrous polyampholytes containing up to 2.5 mg-equiv g^?1 weakly acidic groups and up to 2.9 mg-equiv g^?1 weakly basic groups were prepared from Nitron commercial polyacrylonitrile fiber by its treatment with mixed aqueous solutions of diethylenetriamine and sodium silicate. The acid-base properties of the polyampholyte were studied.     

Methane sensor based on palladium/MWNT nanocomposites

Methane gas sensor was fabricated based on electrocatalytic properties of the Pd/MWNT nanocomposites on indium tin oxide (ITO)glass substrates.A linear response for methane was obtained in the range of 0-16%(v/v)with a detection limit of 0.167%(v/ v)and R.S.D.of 4.1%.After 100 times sensing or stable stored more than 12 months in atmosphere,unconspicuous measurable decrease was observed.The response time was less than 60s at room temperature and ambient pressure.Some common potential interferents in samp...     

Polystyrene nanocomposites based on quinolinium and pyridinium surfactants

In this paper pyridine and quinoline-containing salts were employed to modify montmorillonite. TGA analysis shows that the quinolinium modified clay has a higher thermal stability than the pyridinium modified clay. Polystyrene nanocomposites were prepared by in situ bulk polymerisation and direct melt blending using both clays. The X-ray diffraction and transmission electron microscopy results show the formation of intercalated structures. The 50% degradation temperature of the nanocomposites is increased and so is the amount of char from TGA analysis compared to the virgin polymer. Cone calorimetric results indicate that clay reduces the peak heat release rate and average mass loss rate and thus lowers the flammability of the polymer.     

Study on thermal properties of polyurethane nanocomposites based on organo-sepiolite

The effects of sepiolite modified with γ-aminopropyltriethoxylsilane (KH550-Sp) on thermal properties of polyurethane (PU) nanocomposites were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and tensile test. The DSC results showed that the glass transition temperature of hard segments in PU/KH550-Sp nanocomposite increased with the increase of KH550-Sp, because sepiolite restricted the formation of hydrogen bonding within hard segments of polyurethane. TG results revealed that the thermal stability of PU was improved by KH550-Sp, and the onset decomposition temperature for PU nanocomposites with a KH550-Sp content of 3 wt% was about 20 °C higher than that for pure PU. The tensile properties of pure PU and nanocomposites before and after ageing 120 °C for 72 h were determined, and it was observed that the percentage loss in tensile strength decreased with the addition of KH550-Sp because of an oxidation barrier of KH550-Sp confirmed by ATR-FTIR.     

A selective dopamine biosensor based on AgCl@polyaniline core-shell nanocomposites

Silver chloride@polyaniline (PANI) core-shell (AgCl@PANI) nanocomposites were synthesized in the presence of polyvinylpyrrolidone (PVP). The obtained AgCl@PANI nanocomposites could be easily dispersed in aqueous media, which overcame the processible issues of PANI. Moreover, the nanocomposites showed excellent electrochemical behavior at pH neutral environment, and had inhibitive effect on oxidation of ascorbic acid. Fourier transform infrared spectrophotometry (FTIR) confirmed the existence of PVP in the nanocomposites. The C=O group of PVP is easy to form hydrogen bonding with the hydroxyl group of ascorbic acid, which can prevent ascorbic acid from oxidization. A selective dopamine biosensor was constructed based on the particular characteristic of the AgCl@PANI nanocomposites by the simple drop-coating. The biosensor could detect dopamine at its very low concentration in the presence of 5000 time concentration of ascorbic acid at neutral environment.     

Structure and properties of organic-inorganic nanocomposites based on polyaryleneetherketone

Russian Chemical Bulletin - Polyaryleneetherketone (PAEK) based composites obtained by in situ filling method have been investigated. Ethyl silicate, tris-(methyldiethoxysiloxy)iron and...     

Ionic nanocomposites based on XNBR-OMg filled with layered nanoclays

Ionic elastomers based on carboxylated nitrile rubber (XNBR) crosslinked with magnesium oxide (OMg) and filled with layered nanoclays have been prepared. Two types of nanofillers were employed: a commercial one (Cloisite 15 A) and the other prepared in our laboratory (BCA-ODA). The properties of raw and vulcanized compounds have been studied in order to elucidate the effect of layered nanoclays. X-ray diffraction analysis shows that during compounding and crosslinking the macromolecular chains of rubber were intercalated in a commercial nanofiller, whilst our nanoclay was exfoliated. However, this fact does not affect the properties of compounds homogeneously. Vulcanization parameters, Mooney viscosity and decay and rheological properties were affected depending on the filler type. Mechanical properties were not significantly varied, but glass transition temperature and ionic transition temperature were shifted in comparison with those of the unfilled compound.     

Surface plasmon resonance biosensor based on water-soluble ZnO-Au nanocomposites

A wavelength modulation surface plasmon resonance biosensor based on ZnO-Au nanocomposites for the detection of human IgM was developed. Self-assembly technique has the advantages of flexibility, simplicity and the precise control of film component and was applied to the building of the sensor. The ZnO-Au nanocomposites are in a dumbbell-like shape and can be immobilized on the Au film through 1,6-hexanedithiol by covalent attachment. Meanwhile the activated ZnO nanocrystals can be used to connect protein. The biosensor based on ZnO-Au nanocomposites was used to detect human IgM. Some experimental conditions were examined and optimized. In the selected conditions, the modified biosensor exhibits a satisfactory response for human IgM in the concentration range of 0.30-20.00 μg mL⁻¹. However, the biosensor without ZnO-Au nanocomposites shows a response for human IgM in the concentration range of 1.25-20.00 μg mL⁻¹. Compared with the biosensor based on Au film, when the biosensor based on the ZnO-Au nanocomposites was applied, the sensitivity for determination of human IgM is significantly enhanced.     

Thermal properties of epoxy resin nanocomposites based on hydrotalcites

Epoxy resin nanocomposites containing home-made hydrotalcites (HTlc) have been prepared and their properties have been studied and compared with those of montmorillonite (MMT)-type layered silicates-based nanocomposites. Nanofiller dispersion in the polymer matrix has been evaluated by transmission (TEM) electron microscopy and wide angle X-ray diffraction (WAXD), while nanocomposite thermal properties have been studied in detail by thermogravimetric analysis (TGA/DTG) and cone calorimeter tests.The morphological studies have shown that the compatibilisation of the above two type of nanofillers allowed us to obtain nanostructured materials. As far as thermal properties are concerned, nanocomposites based on HTlc are found to decompose, both in air and nitrogen, following a trend similar to that of the neat polymer matrix, while in the case of the nanocomposite based on the organophilic MMT a slight improvement was found in air. Conversely, cone calorimetric tests have demonstrated that only the organophilic hydrotalcite was capable of decreasing the peak of the heat release rate in a relevant way.     

Multifunctional nanocomposites based on tetraethylenepentamine-modified graphene oxide/epoxy

Composites based on epoxy/graphene were investigated for thermal-mechanical performance. Initially, few-layer graphene oxide (GO) was modified with tetraethylenepentamine (GO-TEPA) in a reaction assisted by microwave radiation. GO and GO-TEPA samples were characterized for their structure and morphology. Composites containing 0.1, 0.3 and 0.5 wt.% of GO and GO-TEPA were prepared, and the effect of fillers on the morphology of cryofractured regions of epoxy matrix was observed through electron microscopy images. Dynamic mechanical thermal analysis (DMA) tests revealed increases of approximately 20 °C in glass transition. Moreover, when compared to neat polymer, composites containing 0.5 wt.% of GO-TEPA gained up to 103% in thermal conductivity (obtained by flash laser). Finally, nanoindentation analyses showed increases of 72% in Young's modulus and 143% in hardness for the same sample. The system is characterized as multifunctional nanocomposites because of the simultaneous gains in thermal and mechanical properties. The best results of the multifunctional composites were strongly associated with the chemical modification of the GO by TEPA.     

Physicochemical properties of hybrid guest-host nanocomposites based on polyaniline

The study concerns the influence of the method of preparation of hybrid guest-host nanocomposites based on polyaniline (a conducting polymer) on their structure, conductivity, electrochemical characteristics, electronic state, and redox activity__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 643–649, March, 2005.     

Preparation and investigation of polymer-polymer compositions based on polyacrylonitrile and aromatic polyamic acid

A modification of polyacrylonitrile (PAN) was carried out. As a result, a polymer compatible (in contrast to common PAN) with polyamic acid (PAA) was obtained. PAA, PAN and their mixtures in solution and in film were investigated by viscometry, massspectrometric thermal analysis (MTA), TG and electron microscopy. The physico-mechanical characteristics of the corresponding composite films were obtained.

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Zusammenfassung Polyacrylnitril (PAN) wurde modifiziert, das entstandene Polymer ist (im Gegensatz zu herkömmlichem PAN) ausreichend mischbar mit Polyamicsäure (PAA). PAA, PAN und ihre Gemische wurden in Lösung und als Film mittels Viskosimetrie, massenspektrometrischer Thermoanalyse (MTA), TG und Elektronenmikroskopie untersucht. Die physisch-mechanischen Charakteristika der entsprechenden Verbundstoffilme wurden ermittelt.

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The authors express their gratitude to Chalykh A. E. for technical aid and to Kuznetsov Yu. P. for the measurements of permeability of films to gases.