Using a recently reported method for the statistical representation of gaseous diffusion within a cylindrical pore, we report here on an analysis of situations that describe fast diffusion within carbon nanotubes. It is proposed that if gaseous flow properties of the tube, in the highly rarefied situation, are due to there being only specular particle–wall reflections, then these particles can transit the tube via self-diffusion. On comparing this self-diffusive flux with Knudsen transport diffusion, our model predicts that enhanced diffusion is indeed possible in the carbon nanotube. Depending upon the statistical nature of the particle–wall scattering phenomenon, the enhancements are predicted be three to four times that of classical transport diffusion and, for certain conditions, the enhancement factor can be greater than 4.
Recently, molecular dynamics simulations have predicted that concentric layers of gaseous carbon dioxide particles will appear in carbon nanotubes. We show in this letter how this effect can be predicted analytically by considering the potential field generated by the pore wall. The layer potential expression thus derived can be used to reproduce the essential features of a particular MD study of gaseous carbon dioxide within a (40, 40) carbon nanotube and confirm, from an energetic point of view, that an outer gaseous layer will be stable. With a closed form expression for the layer potential known, we are able to derive formulas for quantities typically of interest in a Lennard-Jones analysis, such as minimum energy, equilibrium position and the location of zero potential.
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