Molecular Modeling of Frictional Fracture Kinetics of Polymer Composites Using F4K20 as an Example

The influence of dispersed filler in the form of foundry coke on the wear resistance of polytetrafluoroethylene-based composite has been studied by the method of molecular dynamics. The application of this method made it possible to investigate the causes of increasing the wear resistance of the polymer composite at the molecular level. Two-layer molecular models of PTFE and its composite F4K20, consisting of 80 vol % PTFE + 20 vol % foundry coke were made. Computer simulation of wear product separation from two zones located in the tribocontact area has been performed. Differences in values of energy values of intermolecular interaction depending on the initial position of the separated molecules are shown. It was found that the energy value of intermolecular interaction determined by simulating the surface fracture of F4K20 is more than 30% higher than that determined for PTFE. The calculation of internal friction force in models of PTFE and F4K20 has been carried out. It was found that the internal friction force calculated at the molecular level in F4K20 is significantly higher than the same parameter calculated for PTFE. Visualization of the fracture process of the constructed models was carried out. It is noted that only PTFE molecules are observed when molecules are separated from the surface of both models. If the fracture process of F4K20 includes the near-surface region, the separation of foundry coke molecules is additionally initiated. As a result of the investigations a numerical estimation of change of characteristics of intermolecular interaction with the introduction of a filler into polymer resulting in more than two degrees increased wear resistance of PTFE-based composites is given, which is noted by many researchers. The research results can be used for the development of new composite materials including nanocomposites.