PFPE (or perfluoropolyether) is a long chain polymer which consists of carbon, oxygen and fluorine atoms. The molecular structure can be branched, linear, or a combination thereof depending on the desired physical properties. The diagram shows part of a linear PFPE molecule in simplified form:-
Bonding and Inertness
The fluorine and oxygen atoms are very strongly bonded to the carbon atoms, and as a result they reject electron interactions with surrounding atoms. As no part of the molecule is available for a reaction to take place, it is extremely inert. This inertness provides excellent high temperature performance and make PFPE extremely useful in the presence of highly reactive chemicals such as corrosives, acids and liquid oxygen.
Branching and Lubrication
The outer layer of non-reactive fluorine atoms means that adjacent molecules will easily slip by each other, allowing PFPE to form film layers across surfaces. This can be very useful in reducing friction and minimising wear.
When under heavy load these linear molecules slip across each other forming a very thin barrier between the surfaces, which is not beneficial for lubricant longevity. Heavily branched molecules cannot slip across each other as easily and will form thicker and longer-lasting barriers between surfaces.
This heavily branched structure does however bring disadvantages at lower temperature i.e. the more rigid structure results in a higher pour point.
To ensure both wide temperature range and good lubricity under heavy load, a partially branched molecule will provide the necessary balance of physical properties, hence the reason a partially branched molecular structure was selected for PFPE 501.