Molecular simulations of sliding on SDS surfactant films

Abstract

We use molecular dynamics simulations to study the frictional response of monolayers of the anionic surfactant sodium dodecyl sulfate and hemicylindrical aggregates physisorbed on gold. Our simulations of a sliding spherical asperity reveal the following two friction regimes: at low loads, the films show Amonton's friction with a friction force that rises linearly with normal load, and at high loads, the friction force is independent of the load as long as no direct solid–solid contact occurs. The transition between these two regimes happens when a single molecular layer is confined in the gap between the sliding bodies. The friction force at high loads on a monolayer rises monotonically with film density and drops slightly with the transition to hemicylindrical aggregates. This monotonous increase of friction force is compatible with a traditional plowing model of sliding friction. At low loads, the friction coefficient reaches a minimum at the intermediate surface concentrations. We attribute this behavior to a competition between adhesive forces, repulsion of the compressed film, and the onset of plowing.

dtool and dserver: A flexible ecosystem for findable data

“…For example, we have used dtool and dserver in combination with the workflow system FireWorks [ 27 ] to orchestrate parametric runs of molecular dynamics simulations (see Ref. [ 14 ]). Analysis and postprocessing of these simulations then occurs through Python scripts that query simulation results for specific sets of parameters.…”

“…This programmatic access asks researchers to bring along a certain willingness for working on a terminal, but in turn empowers them to transition more easily from manual data management to semi- and fully-automated workflows. Illustrative examples can be found in machine learning research [ 8 ], solid mechanics [ 9 – 11 ], multiscale simulations [ 12 , 13 ], and molecular dynamics simulations [ 14 ].…”