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One of the decisive factors that determines the effectiveness of using carbon nanotubes (CNTs) for reinforcing polymer matrices is their uniform distribution in the matrix. It is shown that the percolation threshold in the polychlorotrifluoroethylene (PCTFE)–CNTs system, determined by electrical conductivity data, shifts to lower values with a more uniform distribution of CNTs, while the electrical conductivity increases and correlates with the structure and strength characteristics. Preliminary deagglomeration of CNTs was carried out using ultrasonic treatment in a dispersion of graphene nanoplatelets (GNPs). Three water systems with a CNTs content of 0.5, 0.25, and 0.125 wt.% were dispersed. The GNPs content was 0.1 mass fractions to 1 mass fractions of CNTs for all systems. The dependences of the real (εʹ) and imaginary (εʺ) components of the complex dielectric constant, electrical conductivity (σ) and relative bending strength limit on the volume content of CNTs (ϕ) were found, which have a percolation character. Percolation indices were determined for the dependences σ = f (ϕ), which for the specified concentrations were: flow thresholds (ϕc) − 0.0047, 0.0032, 0.00097 and critical indices (t) − 2.01, 1.78, 1.75, respectively. The most uniform distribution of CNTs, which was achieved at the minimum content of CNTs during dispersion (0.125 wt.% CNTs), corresponds to the maximum value of σ, the lowest percolation threshold, which correlates with the maximum bending strength limit. [ABSTRACT FROM AUTHOR]

The interaction of graphene with fragments of polychlorotrifluoroethylene (PCTFE) has been studied by quantum chemistry methods. Within the frameworks of the density functional theory with B3LYP exchangecorrelation functional, 6-31G(d,p) basis set and the Grimme dispersion correction, and the second order MøllerPlesset perturbation theory (MP2), the values of the interaction energy of graphene with polychlorotrifluoroethylene oligomers were calculated and the most probable structures of their intermolecular complexes were optimized. As a graphene model, graphene-like planes (GLP) of different sizes were chosen, namely: С40Н16, С54Н18 and С96Н24. Oligomers of polychlorotrifluoroethylene and graphene-like planes in the formed nanocomposites are located closer to each other than individual polymer links. When comparing the results of calculations by the B3LYP-D3/6-31G(d,p) and MP2/6-31G(d,p) methods, both in the case of interactions of polychlorotrifluoroethylene oligomers with each other and intermolecular complexes of polychlorotrifluoroethylene oligomers and graphene-like planes, it has been found that the second order MøllerPlesset method is characterized by a larger intermolecular distance and a lower energy of intermolecular interactions compared to the method of the density functional theory with the Grimme dispersion correction, which is explained by the fact that the MP2 method does not fully take into account the relatively small components of dispersion interactions. Analysis of the calculation results using quantum chemistry methods shows that the addition of graphene-like planes to the polychlorotrifluoroethylene polymer leads to an increase in the intermolecular interaction energy, regardless of the calculation method used and the sizes of polychlorotrifluoroethylene oligomers and graphene-like planes. This may indicate greater strength and thermal stability of the nanocomposite based on graphene-like planes with polychlorotrifluoroethylene oligomers. The zero value of the Gibbs free energy ΔGreact for the interaction of two dimers with each other is characteristic at 270 K, and the similar value of the interaction of the PCTFE dimer with GLP is at a much higher temperature (420 K). This fact reflects the growth in thermostability of nanocomposites as compared to the polymer itself. [ABSTRACT FROM AUTHOR]

The interaction of the epoxy component of fiberglass with the surface of a nanocarbon filler (multilayer carbon nanotubes) was investigated by experimental and quantum-chemical methods. It is shown that when the multilayer carbon nanotubes are introduced into the hardener of the epoxy composition to create fiberglass, the strength of this composite correlates with the degree of oxidation of the carbon atoms of their surface. Thus, the more oxygen-containing groups are on the surface of the nanocarbon filler, the smaller the strength of the eventual fiberglass is. To explain this effect, quantum-chemical calculations of the interaction of pure and oxidized surface models of a multilayer carbon nanotube (graphene-like planes) with a hardener molecule (triethylenetetramine) were performed by quantum chemistry methods. It is found that, regardless of the size of the graphene plane, the energy of the intermolecular interaction of triethylenetetramine with the model of the oxidized outer surface of multilayer carbon nanotubes is greater than the similar value for complexes with no oxidized outer surface. The oxidized surface of the multilayer carbon nanotube adsorbs the triethylenetetramine molecule exactly by amino groups, which are reactive centers when it is reacted with the outgoing resin. Thus, the oxidized multilayer carbon nanotubes impairs the interaction of the hardener with the epoxy. [ABSTRACT FROM AUTHOR]

Metal-containing nanocomposites containing nanoparticles of organic and inorganic materials, attract considerable attention of specialists in recent years due to a large number of possible applications. NiCo nanoparticles have been obtained on the surface of unoxidized and oxidized multiwall carbon nanotubes (MWCNT) by chemical precipitation of the corresponding carbonates from a solution of hydrazine hydrate at a temperature of 350 K. Oxidation of MWCNT was carried out in a solution of potassium dichromate and sulfuric acid. The purpose of this work is to synthesize composites of MWCNT/NiCo and to find differences in their electrophysical properties dependent on the nature of the MWCNT surface. The transmission electron microscopic and radiographic studies showed the presence of phases composites with the size of crystallites of 20–30 nm. The packing density of agglomerates of metal particles is higher in composites with unoxidized MWCNT. The metal particles are arranged on the surface of MWCNT more evenly and in shape more close to spherical in composites with oxidized MWCNT. The method of thermogravimetric analysis shows that the process of composites oxidation during heating for a composite containing oxidized MWCNT is more intense. It indicates a smaller particle size of metals. The real and imaginary components of the complex dielectric and magnetic permeabilities of the disperse composites was determined by the methods of ultrahigh-frequency interferometry. The corresponding values are somewhat higher for composites containing oxidized MWCNT in the ultrahigh-frequency range. The values of imaginary magnetic permeability are higher by 18 % for unoxidized MWCNT composites at low frequencies. The electrical conductivity at low frequencies is 2.9 and 1.6 Ohm–1·cm–1 for composites containing unoxidized and oxidized MWCNTs, respectively. [ABSTRACT FROM AUTHOR]

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To study the influence of graphene (GN) and the low-intensity electromagnetic radiation (LEMP) in the range of 39.5-48.0 GHz on the vital activity of the Saccharomyces cerevisiae yeast, an investigation of the rate of gassing power of yeast suspensions in the concentration of 0.03-0.12 wt. % by means of a volumetric method is reported. Three independent series of experiments were performed: the first one included the dependence of gassing power rates of yeast suspensions on the GN concentrations; the second and third ones were done to research the rates of gassing power in the presence GN and at various LEMR frequencies, where the irradiation procedure was different. It has to be noted that the yeast aqueous suspensions (alone and in the combination with GN) were irradiated in the second series while the yeast in anabiotic state were irradiated afterward the substrate with GN was added in the third series. The respiration intensity of the yeast suspensions was assessed comparing with the blank during each experiment. The vital processes of yeast suspensions are increased by 20-25 % compared to the blank in the presence of GN in the suspension, but no change of the gassing power rate behavior (as namely an acceleration or deceleration of lag phase, the change of the curve shape, etc.) in the presence of GN was observed in some cases. The presence of GN in suspensions containing dry yeast is a motivating factor. The initial stage is more sensitive to the presence of GN in the suspension. The activity of the yeast at the final stage is more stable, almost linear and independent on the GN content in the GN concentration range. The value of the relative gassing power rate of the yeast suspensions containing GN is higher than that of blank experiment (about 30 %). The mechanism of LEMR influence on microorganisms is under discussion for a long time, there is no common hypothesis concerning the reasons of this phenomenon, as the radiation wavelength significantly exceeds not only the size of the cell organelles, but also the size of the cell. Periodicity of the peaks in the case of yeast may indicate that the resonance phenomenon takes place not due to the actions of the first harmonics but as a result of its higher one. Namely, if the living organisms were exposure to the irradiation with monochromatic LEMR sources in the millimeter range, the resonance effect would not occur. It must be noted that the effect of resonance action can occur in the radio transparent atmosphere ( = 8-14, 50-100 microns) as radiation passes the waveguides filled with air and the filtration of the signal by the atmosphere components may occur. [ABSTRACT FROM AUTHOR]