Coils in Oils: Molecular-Scale Mechanisms of Viscosity Modifier Function
Ashlie Martini, Uma Shantini Ramasamy, Michelle Len
Viscosity modifiers, or viscosity index improvers, are additives that increase the viscosity of lubricating oils at elevated temperatures. These additives are high molecular weight polymers whose function is based on their thickening efficiency, viscosity-temperature relationship and shear stability. There are now many different additive chemistries available, all of which have advantages and disadvantages, and affect solution viscosity through different mechanisms. In this work, we use molecular dynamics simulations to explore these mechanisms for several additive molecules. The simulation-based approach enables us to isolate specific viscosity enhancing mechanisms and the findings show that the mechanism by which a viscosity modifier functions is related to the polymer itself. Understanding thickening mechanisms and how they impart additive function is critical to the development of new viscosity modifiers that enable lubricants to function efficiently over a wide range of temperatures; such developments are particularly relevant to enable current trends towards ultra-low viscosity oils for improved fuel efficiency.