Modeling of lubricant additives using a molecularly-informed field theory

Lubricants are complex formulations that, in addition to a base oil, contain a variety of small molecule and polymer additives that can self-assemble into an array of structures and greatly influence the functional properties of the formulation. However, the large number of components these formulations contain leads to an extensive design space that makes it difficult to optimize their composition with traditional experimental iteration. While computational approaches seem attractive, many types of lubricant additives are high-molecular-weight polymers present at significant concentrations (~5 wt%), which makes them difficult to study using traditional molecular dynamics methods due to length and time scale limitations. To overcome this obstacle, we use small-scale, atomistic simulations to parameterize field-theoretic models to probe the behavior of lubricant additives of realistic sizes while maintaining a connection to the underlying chemistry. Here we validate this approach by making de novo predictions of the phase behavior of a acrylic diblock copolymer model system where the predicted behavior is in excellent agreement with small-angle X-ray scattering (SAXS) measurements. Moreover, we show the ability to predict properties in the dilute regime, such as critical micelle concentrations, that are more relevant to lubricant formulations. Furthermore, we show how our workflow can be extended to simulate lubricant-surface interfaces and study behavior in boundary lubrication regimes.