The results of Dereli and Süngü 17 indicate that the Young's modulus of (10, 10) nanotube decreases in the interval 0 K < T < 1000 K but increases at temperature higher than 1000 K.
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12 The Young's modulus values were calculated from the equation relating the modulus and standard deviation of the vibrational amplitude of the tube's free tip displacement. 17–19 Also, the temperature dependence of the stiffness of single-walled carbon nanotubes has been estimated by the molecular dynamics simulations of the intrinsic thermal vibrations of a single-walled carbon nanotube modelled as a clamped cantilever. 12,13,17 The temperature dependence of the Young's modulus, Y, for the nanotubes has been simulated using the determination of strain for a fixed stress 16,17 and the determination of stress for a fixed strain techniques. 18 The main approaches used in these works are the classical molecular dynamics with empirical potentials and semiempirical tight binding molecular dynamics. 6–11 Additional information on the behavior of TiO 2 nanostructures under mechanical loads at different temperatures can be obtained by theoretical modelling of the temperature dependence of the Young's modulus.Ī number of computer-aided studies has been performed to investigate the temperature dependence of the mechanical properties of the single-walled, double-walled carbon nanotubes 12–17 and carbon-based nanomaterials such as the fullerene and nanotube derivatives. 6Įxperimental measurements of the elastic properties of the nanostructures based on ZnO, TiO 2 and other inorganic compounds give strongly different results. 5 The mechanical characteristics of NWs are very important to understand the possibility of developing reliable photovoltaic and photocatalytic cells, and optical and electrical devices based on titania nanowires. Titania nanowires have exceptional photocatalytic and photovoltaic activity, and outstanding optical properties. The stability of the implant surface is determined by the elastic modulus of TiO 2 nanotubes and nanowires. 1 In medicine, the treatment of the surface of metallic titanium implants with TiO 2 nanotubes improves osteointegration of the implant and prevents dislocation and premature loosening. In particular, the strengthening of polystyrene films with small amounts of the TiO 2-based nanotubes enables the increase of the Young's modulus of the nanohybrid films by 18% and the tensile strength by 30%. Introduction The mechanical properties of TiO 2-based nanostructures (nanotubes, NTs, and nanowires, NWs) are important due to their practical applications.
This study reveals that the Poisson's ratios of the nanotubes and nanowires depend on the surface atoms chosen to measure the transverse dimensions of the nanostructures. Also, the temperature behavior of the Young's modulus, Poisson's ratio and period for the nanotubes and nanowires are considered. The present simulations demonstrate that the Young's modulus for the TiO 2-based nanowires decreases with the increase of the nanowire diameters, and approaches the modulus for the rutile bulk crystal from above. The Helmholtz free energy calculated for the set of fixed values of the nanoobject translational period allows obtaining the minimal Helmholtz free energy at specified temperatures in the range 0–1000 K. The Helmholtz free energy simulations were performed in the framework of quasi-harmonic approximation as a result of calculations of the potential energy and the harmonic phonon frequencies of the system under consideration. The temperature dependence of the Young's modulus was obtained through the calculation of the Helmholtz free energy of the system under isothermal thermodynamic conditions. In this work molecular mechanics simulations with the help of interatomic potentials were employed to predict the temperature dependence of the Young's modulus and Poisson's ratio of a number of TiO 2-based four-facetted nanotubes and nanowires.
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