is a chemical compound whose molecules exhibit
electrically positive characteristics at one extremity and negative
characteristics at the other. Polar compounds are used as
additives in many
petroleum products. Polarity gives certain molecules a strong affinity
for solid surfaces; as lubricant additives (oiliness
agents), such molecules plate out to form a tenacious,
friction-reducing film. Some polar molecules are
oil-soluble at one end and water-soluble at the other end; in lubricants,
they act as emulsifiers, helping to form
stable oil-water emulsions. Such lubricants are said to have good
metal-wetting properties. Polar compounds with a strong attraction for solid
contaminants act as detergents in
engine oils by keeping contaminants finely
dispersed.