  Organic friction modifiers (OFMs) are important additives in the lubrication
of machines and especially of car engines where performance improvements are
constantly sought-after. Together with zinc dialkyldithiophosphates (ZDDPs)
antiwear additives, OFMs have a predominant impact on the tribological
behaviour of the lubricant. In the current study, the influence of OFMs on the
generation, tribological properties and chemistry of ZDDP tribofilms has been
investigated by combining tribological experiments (MTM) with in-situ film
thickness measurements through optical interference imaging (SLIM), Alicona
profilometry and X-ray photoelectron spectroscopy. OFMs and antiwear additives
have been found to competitively react/adsorb on the rubbing ferrous substrates
in a tribological contact. The formation and removal (through wear) of
tribofilms are dynamic processes which result from the simultaneous interaction
of these two additives with the surface of the wear track. By carefully
selecting the chemistry of OFMs, the formulator can achieve lubricants that
generate ZDDP antiwear films of optimum thickness, morphology and friction
according to the application-specific requirements.
