Viscosity
Blends of liquids

As for pure liquids, the viscosity of a blend of liquids is difficult to predict from molecular principles. One method is to extend the molecular "cage" theory presented above for a pure liquid. This can be done with varying levels of sophistication. One expression resulting from such an analysis is the Lederer–Roegiers equation for a binary mixture:

where α {\displaystyle \alpha } is an empirical parameter, and x 1, 2 {\displaystyle x_{1,2}} and μ 1, 2 {\displaystyle \mu _{1,2}} are the respective mole fractions and viscosities of the component liquids.

Since blending is an important process in the lubricating and oil industries, a variety of empirical and proprietary equations exist for predicting the viscosity of a blend.
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