Mechanism and Regulation of Spontaneous Water Transport in Graphene‐Based Nanoslits

Abstract

While nanometer-scale capillaries have long been theoretically and experimentally studied, their transport mechanisms have not yet been fully understood. Here, the flow control mechanism is theoretically clarified by molecular dynamics (MD) simulations of graphene-based nanoscale capillaries. The imbibition rate complies with a modified Lucas-Washburn equation. It changes non-monotonically with the slit width due to a compromise in competition of density and slip length. Secondly, the relative scale of imbibition and evaporation rate is length dependent. From short slits to long ones, the imbibition-evaporation process alters from evaporation controlled to imbibition controlled. Finally, hydrophilic modification is employed to enhance the rates. External modification can spread the water and accelerate the evaporation. Within the slit, the flow is accelerated by a positive hydrophilic gradient but detained by a negative one. These findings can be applied in a novel nanofluidic diode.

Structure and Transport Properties of Water and Hydrated Ions in Nano‐Confined Channels

“…[152] Therefore, the interaction between water molecules around hydrated ions and graphene membranes in the nanochannels could make the ions almost frictionless through the graphene layers. MD simulations have found that water can spontaneously and rapidly pass through graphene nanochannels.…”

“…MD simulations have found that water can spontaneously and rapidly pass through graphene nanochannels. [152] Therefore, the interaction between water molecules around hydrated ions and graphene membranes in the nanochannels could make the ions almost frictionless through the graphene layers. Early studies have found that the diffusion coefficients of ions and water confined in neutral channels are larger than those in bulk solution because of the incomplete solvation of ions and the low average water molecule density.…”