The role of sliding orientation on the tribological properties of polyethylene (PE) is investigated by using classical molecular dynamics simulations. Cross-linked PE surfaces slide against one another in two different directions: one that is perpendicular to and one that is parallel to the aligned direction of the polymer chains. The results indicate that sliding in the parallel direction occurs with a lower friction coefficient than sliding in the perpendicular direction. In both cases, gross level stick-slip motion is observed to be associated with the sliding of a restrained, corrugated molecular interface. In addition, the simulations demonstrate the way in which the system stores more shear strain energy during sliding in the perpendicular direction. The tribological behavior of these PE surfaces is compared to the behavior of similarly modeled polytetrafluoroethylene surfaces; the differences and similarities between the two systems are discussed.

The effect of thermostat configurations on the mechanical behavior of empty and butane (n-C4H10) filled (10, 10) carbon nanotubes (CNTs) is examined using classical, atomistic, molecular dynamics (MD) simulations. In particular, the influence of different types of thermostats, relative numbers of thermostat atoms, and rates of deformation are considered. The compressive forces on the atoms are calculated using the second generation reactive empirical bond-order potential. The results indicate that use of a Langevin thermostat leads to a substantial dependency of the results of CNT compression on the number of thermostat atoms and the rate of deformation. On the other hand, the Nosé-Hoover and the velocity rescaling thermostats exhibit consistent mechanical responses during CNT compression regardless of the relative number of thermostat atoms. However, the Nosé-Hoover thermostat fails to maintain the system temperature at a constant value during the compression process. Thus, this study indicates that the Langevin and velocity rescaling thermostats are more appropriate for use in classical MD simulations of CNT systems than the Nosé-Hoover thermostat, and reveals the conditions under which these thermostats should be used for optimal consistency.

No abstract

No abstract

No abstract