Friction modifier additives are often used in transmission fluids, power steering fluids and tractor hydraulic systems. They can help to reduce friction, prevent micro-pitting in gear lubricants and improve fuel efficiency.

There are two main types of friction modifiers. These include oil-soluble organomolybdenum compounds and functionalised polymers. Each type has its own unique properties.

Oil-soluble organomolybdenum friction modifiers are most effective in severe reciprocating sliding conditions. They form a thick boundary film, which helps to reduce rolling and sliding friction. The smooth film also helps to reduce friction between the metal surfaces.

In the past, organic friction modifiers were thought to work by forming adsorbed monolayers on solid surfaces. However, recent tribology experiments have revealed new insights into the behaviour of friction modifiers under boundary lubrication conditions.

Organic friction modifiers have been the subject of many studies. Initially, the majority of workers believed that the function of these modifiers was to adsorb on solid surfaces. Later, ultrathin film interferometry showed that the thickness of lubricant layers could be measured directly in rubbing contacts.

In recent years, interest has also been devoted to reducing carbon dioxide emissions. This is due to the global need for increased energy efficiency. A key factor in the development of lower viscosity lubricants is the development of robust friction modifiers.

Functionalised polymers are based on a block polymer structure. Typically, they are designed to adsorb on soot particles. Interestingly, the ability of the polymer molecules to adsorb on surfaces seems to be the determining factor of their effectiveness.