Molecular Dynamics Simulations of the Chemical Modification of Polystyrene through C_xF_y⁺Beam Deposition

Abstract

The chemical modification of polystyrene through the deposition of a beam of polyatomic fluorocarbon ions (C 3 F 5 + and CF 3 + ) at experimental fluences is studied using classical molecular dynamics simulations with many-body empirical potentials. To facilitate these simulations, a new C-H-F potential is developed on the basis of the second-generation reactive empirical bond-order potential for hydrocarbons developed by Brenner. Lennard-Jones potentials are used to model long-range van der Waals interactions. The incident energy of the ion beam is 50 eV/ion, and it is deposited normal to the surface. The simulations illustrate the important differences in the chemical interactions of these polyatomic ions with the polystyrene. The CF 3 + ions are predicted to be more effective at fluorinating the polystyrene than C 3 F 5 + ions, and the dissociation of the C 3 F 5 + ions produce long-lived precursors to fluorocarbon thin film nucleation.

Effect of simulation conditions on friction in polytetrafluoroethylene (PTFE)

“…Short-range interatomic forces are calculated using the C-H-F reactive empirical bond order (REBO) potential [7] based on Brenner's second generation REBO potential for hydrocarbon systems [8]. Long-range van der Waals interactions are included in the form of a Lennard-Jones (LJ) potential to calculate interchain interaction [6].…”

Effect of Temperature on the Friction and Wear of PTFE by Atomic-Level Simulation

“…As in a number of previous studies of fluorocarbons, partial charges resulting from charge separation in the C-F bond are not explicitly accounted for using Columbic interaction but are implicitly treated by the short-ranged REBO potential [35] which is parameterized to capture the energetics and confirmations of fluorocarbons, in conjunction with the somewhat weaker, long-ranged van der Waals interactions. This implicit treatment of charge may lead to a slight overestimation of friction forces; nonetheless, the qualitative, overall trends of friction with respect to load and temperature should be adequately captured.…”

Temperature control in molecular dynamic simulations of non-equilibrium processes

“…Similar to the above examples, all system atoms are thermostated in [27,28] with an unspecified NVT thermostat, while in other studies either Berensden [29,30,31], velocity rescaling [32] or Langevin [33,34] thermostats are applied only to the border atoms of the cell.…”

“…Intuitively, a much more appealing method is the one where only boundary atoms of the system coming into contact with the environment (not treated explicitly in the simulations), are thermostated [22,29,30,31,32,33,34,39,40]. Indeed, the thermostated atoms in this method serve to mimic the "missing" environment of the entire system which, one may assume, is kept at thermodynamic equilibrium and is thus canonical.…”