Quite often, detergents and dispersants are grouped together mainly because their functions can complement each other. As noted above, the significant difference is that dispersants are ashless, while detergents are more metal-containing compounds.
However, some ashless dispersants also offer “cleaning” properties, so the two are not mutually exclusive.
A large oleophilic hydrocarbon tail and a polar hydrophilic head group can categorize detergents and dispersants. Typically, the tail solubilizes in the base fluid while the head is attracted to the contaminants in the lubricant.
Dispersant molecules envelop the solid contaminants to form micelles, and the non-polar tails prevent the adhesion of these particles onto the metal surfaces so that they agglomerate into larger particles and appear suspended.
Ashless dispersants are, by definition, those that do not contain metal and are typically derived from hydrocarbon polymers, with the most popular being polybutenes (PIBs).
For example, dispersants are typically required in concentrations of 2-6% in ATFs and are used to maintain cleanliness, disperse sludge, and reduce friction and wear3. These values in manual transmission fluids and axle lubricants vary from 1-4%.
