Tribo-surface charge and polar lubricant molecules on friction and lubrication under multiple 3D asperity contacts

Lubricant is usually a mixture of polar and non-polar molecules, and tribo-metal surfaces can be oxidised and have surface atoms with charges. A molecular dynamics simulation of bcc iron with additional charge as rough tribo-surface and polarisable PEO polymer as lubricant was proposed to investigate the tribo-surface charge and polar molecules on friction and lubrication during the compression and sliding. Tribo-surface roughness is crucial for asperity interaction because it affects real contact area, friction, wear and lubrication. Random Midpoint Displacement algorithm was introduced to generate 3D multiple asperities with irregular shape at upper and lower wall surfaces. The results show that compared to non-charged tribo-surfaces where the amount of lubricant and surface roughness determine the friction and lubrication, the charged tribo-surface attracts the polar PEO molecules to form a coated like layer; thereby resulting in a different tribology behaviour. The polar PEO polymers separate the positive charged sliding tribo-surfaces and reduce the direct asperity contact; hence significantly lowering the friction force.