Molecular dynamics of fluid flow at solid surfaces

Abstract

Molecular dynamics techniques are used to study the microscopic aspects of several slow viscous flows past a solid wall, where both fluid and wall have a molecular structure. Systems of several thousand molecules are found to exhibit reasonable continuum behavior, albeit with significant thermal fluctuations. In Couette and Poiseuille flow of liquids it is found that the no-slip boundary condition arises naturally as a consequence of molecular roughness, and that the velocity and stress fields agree with the solutions of the Stokes equations. At lower densities slip appears, which can be incorporated into a flow-independent slip-length boundary condition. The trajectories of individual molecules in Poiseuille flow are examined, and it is also found that their average behavior is given by Taylor–Aris hydrodynamic dispersion. An immiscible two-fluid system is simulated by a species-dependent intermolecular interaction. A static meniscus is observed whose contact angle agrees with simple estimates and, when motion occurs, velocity-dependent advancing and receding angles are observed. The local velocity field near a moving contact line shows a breakdown of the no-slip condition and, up to substantial statistical fluctuations, is consistent with earlier predictions of Dussan [AIChE J. 23, 131 (1977)].

Motion of grains, droplets, and bubbles in fluid-filled nanopores

“…For simplicity, we keep the pore wall atoms frozen at their crystalline positions. As is known from the MD studies of channel flows [28][29][30] occuring between two parallel plates, the walls may induce a layered structure in the density profile on the scale of several σ in the neighborhood of the walls. The magnitude of this effect depends on the strength of the interaction between the fluid and the wall and on the fluid density.…”

Molecular simulation and continuum mechanics study of simple fluids in non-isothermal planar couette flows

“…Koplik et al 16 found that the velocity profiles in molecular dynamics simulations of Poiseuille and Couette flow of Lennard-Jones fluids were similar to those predicted by continuum mechanics, even when the walls were atomistic ͑their wall atoms did not move during the simulation͒. Later, working with pseudo-crystalline solid walls, Thompson and Robbins 17 showed that for Lennard-Jones fluids, the wall-induced structure in the direction parallel to the walls did play an important role in determining the flow boundary conditions.…”

“…[11][12][13][14][15][16][17][18][19][20] These can be classified into two broad categories: homogeneous shear methods and boundary driven shear methods. Homogeneous shear methods 11 impart shear on a fluid by modifying the equations of motion and employing ''sliding brick'' periodic boundary conditions.…”

Wetting and particle adsorption in nanoflows

“…2 A paradigmatic example of this situation refers to the recurring question regarding the appropriate boundary conditions at the fluidsolid and fluid-fluid interfaces, a long standing problem that arises in the description of two immiscible fluids moving along a solid-surface. 3,4 In recent years, the sustained development of new microfluidic devices and their potential applications in a variety of fields, particularly those associated with the so called lab-on-a-chip 5 devices or µ-tas, 6,7 have led to a renewed interest in the problem of fluid flow under microscopic confinement. 8,9,10,11 Moreover, novel fabrication techniques are reaching resolutions in the nanometer scale 12,13 and nanofluidic devices are beginning to emerge as powerful tools in biotechnology and related areas.…”