The Chemical Principle Of Viscosity Index Modifier
Viscosity index modifier is usually an oil soluble macromolecule, in the form of rubber or solid at room temperature. For the ease of use, viscosity index modifier is usually diluted with 150SN or 100SN neutral oil to 5%~10% concentration. Multi-grade oil added with viscosity index modifier, compared with single grade oil with the same viscosity, it has a higher viscosity index and a flat viscosity-temperature curve.
For this kind of macromolecule to play such a role, the chemical principle is this: the polymers inside the viscosity index improver stretches at high temperature, and shrinks at low temperature. The change of this coil shape, makes the oil to have more frictions between the oil molecules at high temperature, and lower friction at low temperature, thus to improve the viscosity of lubricating oil performance.