A Nano-Syringe for the Transport of Thin Water Films Across Carbon Nanotube Membranes

The controlled flow of water molecules at the nanoscale is an initial step to many fluidic processes in nanotechnology. Here we show how thin films of water can be drawn through a nano-syringe built from a carbon nanotube membrane and a “plunger”. By increasing the speed of withdrawal of the plunger, we can obtain molecular transport through the membrane at flux rates exceeding 10²⁵ molecules cm^-2 s^-1. Above a threshold speed around 0.25 nm/ns, molecules cannot fill the chamber created by the plunger motion as fast as the chamber expands, and the resulting flux rate drops. By considering hydrophobic or hydrophilic plungers, we unexpectedly find that the nature of the water-plunger interactions does not affect the flux rate or the threshold plunger speed. While the water structure near the plunger surface differs significantly for different plunger interactions, the failure of the film away from the plunger surface is responsible for loss of transport. As a result, the surface interactions play a limited role in controlling the flux.