Kinetic Model of Gas Transport in Carbon Nanotube Channels

Carbon nanotubes represent a rare experimental realization of a nanofluidic channel, which has molecularly smooth walls and nanometer scale inner diameter. This unique combination of properties gives the carbon nanotube channel an ability to support enhanced transport of water and gases with flows often exceeding those of conventional channels by several orders of magnitude. Surprisingly, most of these transport enhancement phenomena can be explained using very simple mechanisms that hardly go beyond classical physics concepts. Here we present a simplified analytical model that uses classic kinetic theory formalism to describe gas transport in carbon nanotube channels and to highlight the role of surface defects and adsorbates in determining transport efficiency. We also extend this description to include the possibility of gas molecule diffusion along the nanotube walls. Our results show that in all cases the conditions at the nanotube channel walls play a critical role in determining the transport efficiency and that in some cases obtaining efficient transport has to involve optimization of flows from diffusion through the gas phase and along the nanotube surface.