Slip length of water on graphene: Limitations of non-equilibrium molecular dynamics simulations

Abstract

Data for the flow rate of water in carbon nanopores is widely scattered, both in experiments and simulations. In this work, we aim at precisely quantifying the characteristic large slip length and flow rate of water flowing in a planar graphene nanochannel. First, we quantify the slip length using the intrinsic interfacial friction coefficient between water and graphene, which is found from equilibrium molecular dynamics (EMD) simulations. We then calculate the flow rate and the slip length from the streaming velocity profiles obtained using non-equilibrium molecular dynamics (NEMD) simulations and compare with the predictions from the EMD simulations. The slip length calculated from NEMD simulations is found to be extremely sensitive to the curvature of the velocity profile and it possesses large statistical errors. We therefore pose the question: Can a micrometer range slip length be reliably determined using velocity profiles obtained from NEMD simulations? Our answer is "not practical, if not impossible" based on the analysis given as the results. In the case of high slip systems such as water in carbon nanochannels, the EMD method results are more reliable, accurate, and computationally more efficient compared to the direct NEMD method for predicting the nanofluidic flow rate and hydrodynamic boundary condition.

Graphene Transistor as a Probe for Streaming Potential

“…We also argue that the contribution of other mechanisms, such as ion hopping 8 , phonon drag, 7, 8 and fluctuating asymmetric potentials, 2 to the induction of electrical currents in graphene is negligible. Indeed, for a pressure-driven microfluidic system, the slip length has been measured 30 and estimated numerically 31 to be on the order of tens of nanometers, which is negligible compared to our device size. Under these conditions, it would be reasonable to assume the liquid to be nearly static near the surface of graphene, rendering the above-mentioned mechanisms ineffective.…”

Rotation Motion of Designed Nano-Turbine

“…the dragging effect on the rotation motion. Besides, water exhibit considerable slippage at graphene surface3435363738, therefore, these water slippage also contribute to the much slower rotation motion. It should be noted that the slippage of water molecules can also be attributed to the hydrophobicity of graphene blade.…”

Non-Ewald methods: theory and applications to molecular systems

“…Here, we briefly review the Wolf method and its variants, for which the effectiveness in terms of the accuracy and computational cost have been demonstrated in many applications (Wolf et al 1999; Demontis et al 2001; Zahn et al 2002; Fennell and Gezelter 2006; Avendaño and Gil-Villegas 2006; Sepliarsky et al 2006; Ribeiro 2007; Desai 2007; Goto et al 2007; Mahadevan and Garofalini 2007; Nagata and Mukamel 2010; Chen et al 2010; Kuang and Gezelter 2010; Gdoutos et al 2010; Chevrot et al 2011; Kannam et al 2012; Méndez and Villegas 2012). …”