The influence of molecular structure on the frictional behaviour of lubricating fluids 2: Low coefficients of traction

Abstract

AbstractIn order to establish correlations between the chemical structure or constitution of fluid lubricants and their friction characteristics under elastohydrodynamic conditions, a number of model test fluids were tested in a twin‐disk machine. As test fluids, special saturated monobi‐, and tricyclic compounds, alkanes and polyethers were selected. The traction coefficients were shown to be strongly dependent on the chemical structure of the lubricants and on operational parameters. High coefficient values mostly arise from lubricant molecules that are shaped irregularly, with indentations and teeth as seen with Stuart‐Briegleb models, and allowing only heavily hampered rotational intramolecular motions along single bond axes. Low traction coefficients derive from lubricant molecules with a thread‐like shape and a minimum of structural subunits or functional groups involved in significant intermolecular interactions. In order to account for the results obtained, several paradigms and hypotheses are established and discussed in detail.