Equilibrium measurement method of slip length based on fluctuating hydrodynamics

Abstract

We perform equilibrium molecular dynamics simulations for nanoscale fluids confined between two parallel walls and investigate how the autocorrelation function of force acting on one wall is related to the slip length. We demonstrate that for atomically smooth surfaces, the autocorrelation function is accurately described by linearized fluctuating hydrodynamics (LFH). Excellent agreement between the simulation and the LFH solution is found over a wide range of scales, specifically, from the time scale of fluid relaxation even to that of molecular motion. Fitting the simulation data yields a reasonable estimation of the slip length. Thus, LFH provides a starting point for examining the relationship between the slip length and the fluctuations of the force acting on the wall.

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.…”

Distinct Chemistries Explain Decoupling of Slip and Wettability in Atomically Smooth Aqueous Interfaces

“…The function C UU ( t ) ≡ ⟨ U ( t ) U (0)⟩ appearing in eq is the average velocity autocorrelation, and the time t N appearing in eqs and are taken long enough that the integrated correlation functions have plateaued but not so long that they have begun to decay to zero. This decay at long times is a reflection of the finite lateral extent of these systems, and evaluating the Green–Kubo relation at the plateau time is the standard procedure in such scenarios. ,,, …”

“…This decay at long times is a reflection of the finite lateral extent of these systems, and evaluating the Green−Kubo relation at the plateau time is the standard procedure in such scenarios. 16,19,41,42 Care must be taken in determining the fluid volume in which to apply the above Green−Kubo relations. In particular, since we will ultimately connect these results to a hydrodynamic model of the fluid flow, we must properly partition the fluid volume into three subregions: a hydrodynamic region where the bulk viscosity applies 43 and two contact regions in the vicinity of the walls.…”

Fast Increase of Nanofluidic Slip in Supercooled Water: the Key Role of Dynamics

“…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 [13][14][15][16][17][18][19]. Further work has been performed to study the impact on friction of different wall features such as wettability [20,21], roughness [22], crystallographic orientation [23], electronic structure [24], or electrostatic interactions [25].…”