Slip divergence of water flow in graphene nanochannels: the role of chirality

Abstract

Graphene has attracted considerable attention due to its characteristics as a 2D material and its fascinating properties, providing a potential building block for nanofabrication. In nanochannels the solid-liquid interface plays a non-negligible role in determining the fluid dynamics. Therefore, for an optimal design of nanofluidic devices, a comprehensive understanding of the slippage in a water flow confined between graphene walls is important. In nanoconfinement, experimental and computational studies have found the slip length to increase nonlinearly when the shear rate is larger than a critical value. Here, by conducting molecular dynamics simulations, we study the influence of the graphene crystallographic orientation on the slip boundary conditions inside a nanoslit channel. The flow in channels with heights of 2.0, 2.4 and 2.8 nm is driven parallel to the zig-zag and arm-chair crystallographic directions. We extract flow rates, velocity profiles, slip velocities and slip lengths. The slip velocity displays a linear relationship to the shear stress up to a critical value, which is not size dependent. Moreover, the slip length is found to be shear stress dependent above a critical shear stress value of 0.4 MPa. Furthermore, our results indicate that after this critical shear stress is reached, the flow rates are significantly influenced (up to 10%) by the particular orientation of the graphene topology.

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

“…The reported data about slip length are widely scattered, from less than a nanometer to several micrometers. [96] For the cases of water in CNTs, the numerical simulation gives 0.81-5.42 nm of slippage [98] while experimental values are 8-53 nm, [99] depending on the channel size. Slip lengths at the scale of micrometer are not unusual, especially in experimental works.…”

“…However, the slip lengths at the scale of nanometer are dominant in both numerical and experimental works. On graphene surface, the slip length for water is around 30-100 nm in molecular dynamics simulations [90,91,96] and 8 nm in experiments, [97] where the shear stress or even the chirality may make a difference. [96] For the cases of water in CNTs, the numerical simulation gives 0.81-5.42 nm of slippage [98] while experimental values are 8-53 nm, [99] depending on the channel size.…”

Effect of an external electric field on capillary filling of water in hydrophilic silica nanochannels

“…To elucidate the effect of externally applied electric fields in capillary filling of water in hydrophilic silica nanopores, we conduct a series of all-atom MD simulations using FAST-TUBE, a molecular dynamics simulation package which has widely been used to investigate fundamental fluid dynamics under nanoconfinement. 29,42,45,[63][64][65] Water molecules are described using the simple point charge SPC/E model 66 and the silica atoms by the TTAMm model developed by Guissani and Guillot 67 which is a modification of the original TTAM model. 68 Water-silica interactions are described using Coulomb and Buckingham potentials calibrated in our previous study 69 wherein the experimental value of the water contact angle reported by Thamdrup et al 70 in studies of capillary filling is used as criterion to calibrate the potential parameters.…”

“…68 Water-silica interactions are described using Coulomb and Buckingham potentials calibrated in our previous study 69 wherein the experimental value of the water contact angle reported by Thamdrup et al 70 in studies of capillary filling is used as criterion to calibrate the potential parameters. For further details of the potentials used here, we refer readers to Zambrano et al 69 We have chosen the SPC/E water model not only to be consistent with our previous works, 42,45,63,69 but also due to its simplicity and quantitative agreement with experiments to yield water reorientation and hydrogen bond dynamics. 44,51,[71][72][73] Moreover, studies have found that the value of the surface tension for the SPC/E model is in good agreement with experimental results.…”

Relation between boundary slip mechanisms and waterlike fluid behavior

“…For confined geometries the hydrodynamic equations are no longer valid, and in this case, the use of the no-slip boundary condition is at least questionable. Many experimental [1][2][3][4][5][6][7][8], theoretical, and computational [9][10][11][12][13][14][15] results report that there are several flow boundary conditions consistent with the fluid behavior and mobility [16][17][18][19] beyond the no-slip boundary condition. The amount of slip is usually measured through the magnitude of the slip length, defined as the ratio between the shear rate and the slip velocity [16][17][18][19].…”