Green-Kubo measurement of liquid-solid friction in finite-size systems

Abstract

To characterize liquid-solid friction using molecular dynamics simulations, Bocquet and Barrat (BB) [Phys. Rev. E 49, 3079-3092 (1994)] proposed to use the plateau value of a Green-Kubo (GK) integral of the friction force. The BB method is delicate to apply in finitesize simulations, where the GK integral vanishes at long times. Here, we derive an expression for the GK integral in finite-size systems, based on a Langevin description of a coarse-grained system effectively involving a certain thickness of liquid close to the wall. Fitting this expression to GK integrals obtained from simulations of a liquid slab provides the friction coefficient and the effective thickness of the coarse-grained system. We show that the coarse-grained system for a Lennard-Jones fluid between flat and smooth solid surfaces is 2-3 molecules thick, which provides a criterion for measuring the friction coefficient independently of confinement. As compared to nonequilibrium simulations, the new approach is more accurate and removes some ambiguities of nonequilibrium measurements. Overall, we hope that this new method can be used to characterize efficiently liquid-solid friction in a variety of systems of interest, e.g., for nanofluidic applications.

Fast increase of nanofluidic slip in supercooled water: the key role of dynamics

“…[22][23][24][25] On the modeling side, several efforts have been pursued in order to understand the molecular mechanisms that control friction, with special interest on the discussion of the relation between the friction coefficient and the time autocorrelation of the force exerted by the liquid on the wall. [26][27][28][29][30][31][32][33] Further work has been performed to study the impact on friction of different wall features such as wettability, 34,35 roughness, 36 crystallographic orientation, 37 electronic structure, [38][39][40] or electrostatic interactions. 41 Yet a large number of questions with regard to the interface properties, such as its viscoelastic or purely viscous nature [42][43][44] or the possible link with its interfacial thermal transport equivalents via wall's wetting properties, [45][46][47] remain open nowadays, limiting the perspectives for a rational search of optimal interfaces.…”

Full characterization of the hydrodynamic boundary condition at the atomic scale using an oscillating channel: Identification of the viscoelastic interfacial friction and the hydrodynamic boundary position

“…3 illustrate the difficulty to obtain the liquid-solid FC through the evaluation of the Green-Kubo integral of the friction force autocorrelation function [3,45] given by equilibrium MD simulations. In the evaluation of the Green-Kubo integral in systems of finite size, it is often assumed that the mass of the fluid involved in the liquid-solid friction is a finite constant [46][47][48], but the present results show that it is actually frequency dependent.…”

Tailoring nanocomposite interfaces with graphene to achieve high strength and toughness

“…where  is the friction coefficient and can be determined from the liquid-graphene interaction (96). S represents the surface area of the nanofiller.…”

“…The liquid/solid interface friction is described ( Fig. 6A ) as ( 95 ) where μ is the friction coefficient and can be determined from the liquid-graphene interaction ( 96 ). S represents the surface area of the nanofiller.…”