Electrostatic-Charge- and Electric-Field-Induced Smart Gating for Water Transportation

Abstract

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.

Wettability and Applications of Nanochannels

“…Generally, increasing the voltage can cause water wettability change from hydrophobic to hydrophilic state in the nanochannel. Jiang and co‐workers reported electrostatic charge inducing water wetting of a single sub‐10 nm poly(ethylene terephthalate) (PET) nanochannel (Figure b) . Such a system could directly achieve the gating transform from a wetting (conductive) state to a nonwetting (nonconductive) state through a process of vapor–liquid phase transitions by controlling the external electric field and surface charge density (Figure c).…”

“…e) At pH 7, the negatively charged nanochannel with a low density can be reversibly switched between hydrophobic and hydrophilic states by the voltage. a–e) Reproduced with permission . Copyright 2016, American Chemical Society.…”

“…These applications include liquid transport, confinements of metal, metal oxide, metal salt, polymer, and ionic liquid, all of which are based on the larger dimension of nanotubes. Moreover, the surface chemistry and structure of CNT nanochannels can be facilely modified for controlling liquid wettability and the interaction between liquid and the inside tube walls …”

“…Nanochannels for wettability investigation can be divided into 1D nanochannels, 2D nanochannels, and 3D nanochannels. The explorations of 1D nanochannels wettability include CNTs, boron nitride nanotubes (BNNTs), polymeric nanochannels, alumina nanochannels, and silicon nitride nanochannels . 2D nanochannels comprised of graphene, mica, gold, reduced graphene oxide (rGO), and graphene oxide are studied to understand the confined 2D nanochannels wettability.…”

Electric Field Induced Wetting of a Hydrophobic Gate in a Model Nanopore Based on the 5-HT3Receptor Channel

“…Importantly, this rectifying property would not only apply to ions, but also to water molecules. This not only extends the concept of the electric-field induced smart water gates 55 , but may also enable the creation of membrane systems that are semipermeable to water in a switchable fashion.…”