Terahertz electric field induced melting and transport of monolayer water confined in double-walled carbon nanotubes

Abstract

Understanding the structures and dynamics of confined water in nanochannels holds great promise for various applications, ranging from membrane separation to blue energy collection. A setting of particular interest is the confined monolayer water within double-walled carbon nanotubes (DWCNTs), which demonstrates rich ice morphologies; however, the dynamics of this peculiar system are still unexplored. In this work, a series of molecular dynamics (MD) simulations reveal that the two-dimensional ice in DWCNTs can be effectively melted by terahertz electric fields but not by static electric fields, exhibiting an interesting ice to vapor-like transition along with extraordinary dynamical behaviors. Specifically, under appropriate field frequency, the water flow presents a sharp increase with the increase in field strength, indicating an excellent gating behavior. These remarkable findings are attributed to the resonance effect between the terahertz electric field and inherent vibration of water hydrogen bonds, causing the water molecules to change from the frozen to super permeation states. The amount of confined water exhibits a sudden reduction, confirming the breakdown of the hydrogen bond network. The distributions of density profiles, hydrogen bond number and dipole orientation demonstrate more details of the water structural change. Furthermore, under a certain field strength, the water flow shows a peculiar maximum behavior with the increase in field frequency, implying frequency optimization for water transport. These findings not only enhance our understanding of the phase transition behavior of water molecules confined within DWCNTs under the influence of a terahertz electric field but also provide a promising avenue for designing innovative nanofluidic devices.