Electrostatic-charge- and electric-field-induced smart gating for water transportation

Regulating and controlling the transport of water across nanochannels is of great importance in both fundamental research and practical applications because it is difficult to externally control water flow through nanochannels as in biological channels. To date, only a few hydrophobic nanochannels controlling the transport of water have been reported, all of which use exotic hydrophobic molecules. However, the effect of electrostatic charges, which plays an indispensable role in membrane proteins and dominates the energetics of water permeation across aquaporins, has not gained enough attention to control water transport through a solid-state nanochannel/nanopore. Here, we report electrostatic-charge-induced water gating of a single ion track-etched sub-10 nm channel. This system can directly realize the gating transition between an open, conductive state and a closed, nonconductive state by regulating the surface charge density through a process that involves alternating capillary evaporation and capillary condensation. Compared to the introduction of exotic hydrophobic molecules, water gating controlled by electrostatic charges is simple, convenient, and effective. Such a system anticipates potential applications including desalination, controllable valves, and drug delivery systems.