The description of Double-wall carbon nanotubes

Double-wall carbon nanotubes form a special class of nanotubes because their morphology and properties are similar to those of SWNTs, but their chemical resistance is significantly improved. This is particularly important when the functionalization is required (this means grafting of chemical functions at the surface of the nanotubes) to add new properties to the CNT. In the case of SWNT, covalent functionalization will break some C = C double bonds, leaving "holes" in the structure of the nanotube and, therefore, to modify both its mechanical and electrical properties. In the case of DWNT, that the outer wall is changed. DWNT synthesis on gram scale was proposed in 2003 [6] by the CVD technique, the selective reduction of oxide solutions of methane and hydrogen.
The ability of telescopic movement of inner shells  and their unique mechanical properties [8] allow the use of multi-walled nanotubes as major arms movable in nanomechanical devices to come. The retraction force that occurs at a telescopic movement caused by the Lennard-Jones interaction between the shell and its value is about 1.5 nN.    
  The vibrational properties of Double-wall carbon nanotubes  is investigated by high-pressure resonance Raman scattering up to 30 GPa in two different pressure-transmitting media (PTM): paraffin oil and NaCl. The protection effect on the outer tube during compression is verified .The collapse of DWNTs is experimentally observed for the first time, showing to be two-step: the onset of the outer 1.56 nm diameter tube collapse at 21 GPa is followed by the collapse of the inner 0.86 nm diameter tube at a higher pressure of 25 GPa. This observation is supported by calculations.      
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