Reassessing fast water transport through carbon nanotubes

Pressure-driven water flow through carbon nanotubes (CNTs) with diameters ranging from 1.66 to 4.99 nm is examined using molecular dynamics simulation. The flow rate enhancement, defined as the ratio of the observed flow rate to that predicted from the no-slip Hagen-Poiseuille relation, is calculated for each CNT. The enhancement decreases with increasing CNT diameter and ranges from 433 to 47. By calculating the variation of water viscosity and slip length as a function of CNT diameter, it is found that the results can be fully explained in the context of continuum fluid mechanics. The enhancements are lower than previously reported experimental results, which range from 560 to 100 000, suggesting a miscalculation of the available flow area and/or the presence of an uncontrolled external driving force (such as an electric field) in the experiments. Introduction. The flow rates of pressure-driven water through membranes of 1.6 and 7 nm diameter carbon nanotubes (CNTs), as measured by Holt et al.1 and Majumder et al.,2 are two to five orders-of-magnitude greater than those predicted by the continuum-based no-slip Hagen-Poiseuill