Definition
Friction modifiers (FMs) reduce friction between sliding surfaces operating in the boundary and mixed lubrication regimes. Unlike anti-wear additives, which prevent metal removal, friction modifiers primarily reduce energy loss and improve fuel efficiency.
Two main types:
- Organic friction modifiers (OFMs) — long-chain fatty acids, esters, and amides that adsorb onto metal surfaces to form low-shear monolayers (e.g., glycerol monooleate, oleamide)
- Organomolybdenum compounds (MoDTC, MoDTP) — form molybdenum disulfide (MoS₂) tribofilms under rubbing, providing very low friction coefficients
Friction modifiers are critical for achieving fuel economy targets in modern PCMO formulations (ILSAC GF-6, API SP) and automatic transmission fluids (ATF) where precise friction characteristics are specified by OEM friction requirements.