Calorimetric studies of carbon nanomaterials


Effects in the heat capacity (Cp) of carbon nanotubes (CNTs) that caused by low dimensions (1D, 2D), the unique structure and the geometry both pure and saturated with gases nanosystems are studied. The Cp of bundles of single-walled carbon nanotubes (SWNTs bundles) differs significantly from Cp of other carbon materials (graphene, graphite, diamond) at low temperatures. Cp of bundles of single-walled carbon nanotubes (SWNTs bundles) below 5 K is similar to that observed in 2D systems. At temperature above 100K the behavior of the Cp of the SWNTs bundles is identical to that of 1D system. Similar behavior was observed also for multiwalled carbon nanotubes (MWCNTs). Below 275 K with decreasing the temperature, the character of the temperature dependence of the Cp of MWCNT is changed from linear to quadratic and then to cubic. This is the result of the change of the behavior of Cp of MWCNTs from 1D, 2D and then to 3D.

The unique structure of SWNTs permits to obtain quasi-1D, -2D and -3D structures formed by adsorbates. The comparison of the experimental results of the Cp of 1D chains of gas adsorbetes with the theoretical models is presented. The questions about the processes of the decay of the dense chain into the shorter one, the features of the phonon spectrum and vibrational characteristics of the linear systems are discussed.

Heat capacity of fullerite C60 and the interstitial solid solution (CH4)0.4C60 have been investigated in the temperature interval 1.4 ‑ 120 K. The contribution of CH4 molecules to the heat capacity of solution has been separated. It was found that the contribution of the tunnel rotation of the CH4 molecules to the heat capacities is dominant below 8 K. The isotopic effect that caused by the difference between both the conversion rates and the rotational spectra of the nuclear spin species of CH4 and CD4 molecules are discussed.