GOALI: Enabling Ultra-Low Viscosity Lubricants Through Fundamental Understanding of Additive Interactions and Tribofilm Growth Mechanisms: An In-Situ Study

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Automobile engine oils typically include several different performance additives, each of which serves a crucial role in improving fuel efficiency and engine reliability. One of the additive types that are routinely added to such lubricants are anti-wear additives, which are required to reduce wear and failure when metal-on-metal contact occurs between the various parts within automobile engines. One such additive, a molecule based on a combination of zinc, sulfur, phosphorous, oxygen, and hydrocarbons, is so effective at reducing wear while being inexpensive to produce that it is used in nearly every automotive engine oil. This molecule works by forming surface films at certain contact points within the engine. These films serve as a protective cushion for the underlying metal parts, protecting them from wear. Despite its widespread use, it remains unclear how this molecule generates these protective films. Increasingly, automotive lubricants are being formulated with lower viscosities which help improve fuel economy and reduce undesirable emissions. Unfortunately, the molecules used to formulate these lower viscosity oils can interfere with the anti-wear molecule?s ability to generate protective films and provide adequate wear protection. This Grant Opportunities for Academic Liaison with Industry (GOALI) research aims to contribute to solving this problem by using novel nanotechnology methods to improve our understanding of how the anti-wear protective films are formed and how their formation is affected by interactions with other types of additives. Findings of this research will inform the design of next-generation automotive lubricants and will thus have a direct impact on the U.S. economy through improved energy saving, reductions in maintenance-related costs, and reduction of undesirable emissions.In this research, a quantitative kinetic and thermodynamic understanding of anti-wear tribofilm formation mechanisms will be formulated using novel in-situ atomic force microscopy methods, recently developed at UPenn. In-situ atomic force microscopy enables the direct probe of nanoscale mechanochemistry of zinc dialkyldithiophosphate additives (known as ZDDP-based additives) which drives formation of tribofilms, as well as their interactions with novel basestock and co-additives including molybdenum-based friction modifiers and dispersants. Synergism or antagonism between anti-wear additives and co-additive chemistries will be identified and understood through measurement and interpretation of tribofilm growth kinetics. Together with ex-situ chemical and structural characterization techniques at UPenn, as well as lubricant expertise and component-scale testing at ExxonMobil, this research will help enable predictive design, development, and implementation of advanced formulations for next-generation lubricants. By identifying how co-additives affect the fundamental mechanisms of tribofilm growth, this research will in the longer-term help identify sulfur and phosphorous-free anti-wear additives. Sulfur and phosphorous are known to have deleterious impacts on automotive emissions, and thus developing alternatives to ZDDP additives is crucial for further reducing automotive emissions.