Water Slippage on Graphitic and Metallic Surfaces: Impact of the Surface Packing Structure and Electron Density Tail

Abstract

While fluid flow at solid−liquid interfaces has been of great interest, studying its behavior is challenging because it requires a comprehensive understanding of the complex interactions that exist at various realistic solid−liquid interfaces. In particular, the slip phenomenon had been a debated subject for decades before the phenomenon was proven at a molecular level. Since the slip behavior is widely acknowledged, its fundamental relationships with other measurable physical properties have been studied intensively. Here, we present a first-principles-based multiscale simulation study on various solid−water interfacial systems to understand how the physical quantities influence the slip length. Based on the simulation results, we propose an extended quasi-universal relationship between the slip length and the work of adhesion by considering the surface packing density. Furthermore, we scrutinize the effects of the electron density tail from the solid wall on both the slip length and work of adhesion. We also investigate the relationship between the self-diffusivity of the fluid at the interface and the slip length. Our present study underlines the impact of atomic-level details of the solid−liquid interfaces, such as the surface packing structure and electrostatic interactions, on determining the hydrodynamic boundary conditions.

Liquid–Solid Interfaces under Dynamic Shear Flow: Recent Insights into the Interfacial Slip

“…On this basis, the interfacial electrical potential can be controlled through carefully designing the interfacial geometrical patterns and applying the flow fields (Figure C), thus controlling the interfacial slip length . In concert with the experimental investigation, the results of the MD simulation also explicitly demonstrated the impact of the surface charge and salt ions on the liquid–solid interfacial slip length. ,− The Couette flow simulation result has shown that the slip length decreased rapidly with an increase in the surface charge (Figure D), and considering a model interface between an aqueous sodium chloride solution and a solid wall for Poiseuille flow, the connection between the slip length and ion concentration can be built up with the viscous drag induced by counterions trapped on the solid surface (Figure E) …”

“…As the strongest intermolecular force, the inhibitory effect of the electrostatic interaction on the interfacial slip has been confirmed by fluorescence microscopy, SFG spectroscopy, and computational simulation. ,,,,, The slip length can thus be reduced by an increase in the the solid surface charge density or by adjusting the ion concentration in the solution. On the contrary, if the flow-induced interfacial slip is to be enhanced, only decreasing the charge distribution at the liquid–solid interface may not be enough, as X-ray and NR experiments have indicated that the interfacial neutral polymer systems might remain unchanged even at very high shear flow rates. ,, As discussed above, for the mineral/aqueous solution systems, the shear flow can change the dissolution of the mineral surface ion pairs, which may lead to only a reversible modification of the interfacial charge without inducing any detectable interfacial slip .…”

“…As the strongest intermolecular force, the inhibitory effect of the electrostatic interaction on the interfacial slip has been confirmed by fluorescence microscopy, SFG spectroscopy, and computational simulation. 30,31,33,34,58,96 The slip length can thus be reduced by an increase in the the solid surface charge density or by adjusting the ion concentration in the solution.…”

The application of QM/MM simulations in heterogeneous catalysis

“…When applied to a small test set of molecules, ∆G tot solv yielded a MAE of 5.51 kJ mol −1 with respect to experiment, which compared favourably to the MAE of the highly parameterised SM8 implicit solvent model (3.68 kJ mol −1 ) 131 . DFT-CES/2PT was then used to calculate the free energy of adhesion of water to a range of graphite and metallic facets 134,135 . Comparisons with experimentally derived values for the work of adhesion show the DFT-CES/2PT accurately determines the energetics of the interface (Gim et al 136 74.27 mJ m −2 vs. experiment 72.8 mJ m −2 137 ).…”

Density functional theory in classical explicit solvents: Mean‐field QM/MM method for simulating solid–liquid interfaces

“…44 We recently expanded our DFT-CES study to connect our molecular-level understanding of water-metal interfaces to hydrodynamic properties by properly choosing the Navier-Stokes boundary conditions. 45 Electrocatalytic CO 2 reduction at ionic liquidcatalyst interface…”