What is a Lubricant Additive

No single description or definition adequately covers all lubricants or lubrication processes. For example, we have seen that a fluid can function as a lubricant by virtue of its viscosity as a liquid. We have also seen that a monomolecular film of stearic acid deposited on a metal surface acts as a lubricant and dramatically reduces the coefficient of friction. A polymeric substance such as polymethylmethacrylate when dissolved in an oil will increase its viscosity and improve its loadcarrying performance in the hydrodynamic lubrication process. Stearic acid dissolved in a carrier oil can effect a strong reduction in the coefficient of friction for metal rubbed against metal. 

We say that the polymethylmethacrylate or the stearic acid is a lubricant additive. In each case the substance is added to a carrier oil which by itself functions as a lubricant. Thus, if to an oil which has a 

On this basis viscosity improvers are excluded from consideration as lubricant additives in this discussion. It is true that viscous shear is 

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