Droplets sliding over shearing surfaces studied by molecular dynamics

Abstract

in Wiley Online Library (wileyonlinelibrary.com) Through molecular dynamics, the sliding motion of a liquid drop embedded in another liquid over a substrate as a result of a shear flow is studied. The two immiscible Lennard-Jones liquids have the same density and viscosity. The system is isothermal. Viscosity, surface tension, and static contact angles follow from calibration simulations. Sliding speeds and drop deformations (in terms of dynamic contact angles) are determined as a function of the shear rate. The latter is nondimensionalized as a capillary number (Ca) that has been varied in the range 0.02-0.64. For Ca up to 0.32, sliding speeds are approximately linear in Ca. For larger Ca, very strong droplet deformations are observed.

Multiscale simulations of sliding droplets

“…The system as described above was the subject of MD simulations in [6] with 0.04 ≤ Ca ≤ 0.64 and 65 • ≤ θ ≤ 111 • . The fluids were Lennard-Jones (LJ) liquids with spherical molecules of mass m and diameter σ .…”

“…In a previous paper [6], we have investigated contact line motion from a molecular perspective (i.e., by using molecular dynamics, MD) for a relatively simple situation: a sessile drop of Fluid 1, immersed in Fluid 2 with the two immiscible fluids undergoing simple shear. The two fluids had the same density and viscosity; what separates them is their mutual surface tension.…”

“…Since molecular simulations can only handle nanoscopic systems, we want to generalize the results for sliding speeds obtained at the molecular level [6] to continuum models. The present paper focuses on options of how to deal with this generalization.…”

“…The present paper focuses on options of how to deal with this generalization. We have performed continuum simulations by means of the lattice Boltzmann method of the same systems as studied with MD [6]. The key choices that need to be made in the continuum simulations relate to the boundary conditions at the substrate.…”

“…The key choices that need to be made in the continuum simulations relate to the boundary conditions at the substrate. In making these choices, we were guided by the results from the MD simulations as obtained in [6].…”