Unraveling the interplay of load, substrate and molecular reactivity in tribological systems: a computational and experimental study

This thesis combines experimental and computational approaches to enhance the understanding of friction, wear, and mechanochemical reactions at sliding interfaces. The study addresses two main areas: the tribological behavior of Black Phosphorus (BP) as a standalone solid lubricant on various substrates, and the mechanochemical reactivity of confined molecules at metallic interfaces under applied loads. The experimental investigation of BP on different substrates reveals that applied load significantly influences its tribological properties. However, no universal trend was observed across all conditions, as performance is highly system-dependent, with substrate roughness playing a crucial role. Computational simulations using Density Functional Theory (DFT) further explored BP’s adhesion to different substrates, showing stronger adhesion for oxidized BP but weak correlation with the tribological performance, highlighting the critical role of substrate roughness in enhancing the lubricating effect. In a separate computational study, DFT simulations examined mechanochemical reactions of water and methane confined between metallic surfaces (interface) under increasing loads. The results showed that molecular dissociation occurs at lower activation energies and loads for the metallic interface compared to the single surface, indicating a higher catalytic effect. Furthermore, confinement-induced dissociation occurs once a threshold value of electron charge redistribution is reached, which is achieved at lower applied loads for interfaces compared to single surfaces. These findings contribute to the development of more efficient lubricants and coatings, highlighting the crucial role of substrate properties and mechanical forces in determining tribological performance. In addition, this work provides valuable insights into the mechanochemical reactions at the interface, deepening the understanding of the fundamental interactions in these scenarios.