Vibrating-charge-driven water pump controlled by the deformation of the carbon nanotube.

The directed transport of water molecules in a single-walled carbon nanotube (SWNT) based on a ratchet effect is investigated by molecular dynamics simulations. The system is driven far away from thermal equilibrium by an additional deterministic perturbation of a vibrating charge, and the spatial inversion symmetry is broken by the continuous deformations of the SWNT. It is well-known that the water flux across a circular channel decreases when the channel is narrowed or deformed. However, our simulation results show that the water flux almost increases linearly within a deformation of 1.9 Å. There exists an optimized value of deformation at which the pumping capacity takes its maximum value. Moreover, the direction of transport even exhibits a change of sign with narrowing the carbon nanotube.