Abstract
One of the requirements of engine lubricating oil is that it must have a low enough viscosity at low temperatures to assist in cold starting and a high enough viscosity at high temperatures to maintain its load-bearing characteristics. Viscosity Index (VI) is one approach used widely in the lubricating field to assess the variation of viscosity with temperature. The VI of both mineral and synthetic base oils can be improved by the addition of polymeric viscosity modifiers (VMs). VI improvement by VMs is widely attributed to the polymer coil size expanding with increasing temperature. However, there is very little physical data supporting this generally accepted mechanism. To address this issue, intrinsic viscosity measurements and Small-Angle Neutron Scattering (SANS) have been used to study the variation of polymer coil size with changing temperature and concentration in a selection of solvents. The results will show that coil size expansion with temperature is not necessary to achieve significant elevation of viscosity index.
Highlights
One of the essential requirements of engine lubricating oil is that it must have a low enough viscosity at low temperatures to assist in cold starting and a high enough viscosity at high temperatures to maintain its loadbearing characteristics
Consistent with previous studies by Muller, Gao and Rubin, the intrinsic viscosity of OCP2 slightly decreases with an increase in temperature, whereas [η] of both PMAs increases with temperature (Table 2)
It is common for base oils within a single family or series to be characterized by a power law model of KV40 vs. KV100 [33]
Summary
One of the essential requirements of engine lubricating oil is that it must have a low enough viscosity at low temperatures to assist in cold starting and a high enough viscosity at high temperatures to maintain its loadbearing characteristics. It is desirable to have a fluid whose viscosity-temperature dependence is small. There are many ways of expressing the variation of viscosity with temperature. One of the most widely used in the lubricating field is viscosity index (VI) [1]. The method involves comparing the kinematic viscosity of the fluid to that of two reference fluids at 40 ̊C and 100 ̊C. The higher the VI of a fluid, the smaller the viscosity-
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