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The results of the study on the properties of carbon nanotubes-polymer nanocomposites have shown that the use of nanotubes (CNT) to fill the polymer matrices of different species significantly alter their physical properties compared to the original polymers. However, the influence of CNT on the properties of nanocomposites obtained at the molecular level has not been completely ascertained yet. Therefore, the purpose of this work was to examine the interaction of CNT with fragments of polymers with the same nature, but the different structure, for example, polyethylene and polypropylene using quantum chemistry. By method of density functional theory with the exchange-correlation functional B3LYP, the basis set 6-31G(d,p) and the Grimme dispersion correction, the energy values have been calculated of interaction between carbon nanotube fragments and oligomers of polyethylene and polypropylene, the most probable structures of their intermolecular complexes being optimized. A graphene-like plane of 40 carbon atoms and 16 atoms of hydrogen was chosen as a model for the outer surface of the multi-walled nanotubes (MWNT). In addition to the above described, two larger models were used, with the general formula C54H18 and C96H24 in order to take into account the dimensional effect of the surface of the nanotube fragment model on the interaction energy. It has been found that the interaction energy of a carbon nanotube fragment with an oligomer of polypropylene is greater, compared with polyethylene, which is consistent with the experimental data on melting temperatures of pure polymers and nanotube-polymer composites. The polymer with an outer surface of a carbon nanotube forms an intermolecular complex do not bound covalently and retained by intermolecular dispersion forces. Oligomers of polymeric matters and nanotube surfaces in nanocomposites formed are located closer to each other than separate polymeric links between them. [ABSTRACT FROM AUTHOR] more...

The production of stable dispersions of carbon nanotubes (CNTs), synthesized by CVD, in different liquids, is one of the methods of preparation of CNTs for introduction into polymeric matrix. The aim of this work is to produce composites of polyethylene (PE) - CNT, and the study of their structural characteristics, mechanical, thermodynamic, and kinetic properties as dependent on the concentration of multi-walled CNTs and the preliminary dispersion by several methods. Multi-walled CNTs were synthesized by catalytic pyrolysis (CCVD) using iron-containing catalyst in admixture with pyrogenic silica (grade A 300), which was prepared by coprecipitation of hydroxides of aluminum, magnesium and divalent iron. CNTs with a diameter of 10-20 nm were grown in a reactor with a volume of 24 dm3 with a smooth mixing of the catalyst layers due to rotation of the reactor. Deagglomeration of CNTs was carried out by processing in an ultrasonic dispergator or in a device that combines the cavitation mixing and shear deformation in aqueous solutions of different composition. Composite samples of the of PE–CNT with different concentration of the filler obtained by hot pressing at the temperature of 140 °C and the pressure of 5 MPa of polyethylene powders. Their surface was pre-deposited CNTs from stable aqueous dispersions. The structural characteristics of the CNTs and the composite of PE–CNTs is determined by the methods of transmission electron microscopy (JEM-100CXII), X-ray diffraction (DRON-3M, λСо = 0.179 nm). Structural and phase transitions and the processes of destruction of polymer composites in air are investigated by methods of DTA and DTG on a derivatograph Q 1500 D (Hungary). Electric conductivity at low frequencies (0.1, 1 and 10 kHz) was measured by double contact method with an immittancemeter E7-14. The frequency dependence of complex electric conductivity of the composites was evaluated from calculations of the impedance spectra in the frequency range 10-2-106 Hz obtained by an impedance spectrometer Solartron SI 1260. The carbon nanotubes (CNTS) introduction in a matrix of polyethylene in small amounts (up to 5 wt. %) leads to a nonmonotonic change of the degree of crystallinity of the matrix. Their electrophysical and thermodynamic properties were studied. The percolation threshold in systems PE–CNTs from certain experimental data on the electrical conductivity is in the range 0.0015-0.0020 in volume. The content CNT to 2 % increases the temperature of the thermal oxidative degradation of the polymer by almost 60 °C. Influence of CNTs on the structure and properties of the composite is the more significant, the greater the degree of CNTs deagglomeration. [ABSTRACT FROM AUTHOR] more...