Fundamental understanding of the synthesis and tribological behavior of organic-inorganic nanoparticles

The objective of this doctoral research is to design, synthesize, and test an advanced lubricant additive using novel active nanostructures of inorganic layered solid lubricant particles (MoS2), integrated and encapsulated with organic molecules, namely triglycerides and phospholipids, respectively. It was hypothesized that this combination can uniquely respond under severe boundary lubrication conditions (where high frictional losses exist).Tribological studies using pin-on-disk and four-ball tests showed that this novel active material can significantly reduce friction and wear. The coefficient of friction was reduced in pin-on-disk from 0.15 to 0.04 when these nanoparticles were mixed with the base oil. Similarly, in four-ball tests, significant reduction in coefficient of friction (0.06-0.07) and wear (0.47 mm) reduction were observed. To understand the underlying mechanism of the improved tribological properties, tribo film analysis was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and atomic force microscopy (AFM). The results showed a patchy film of MoS2 sheets embedded in an amorphous phosphate matrix, approximately 200 nm thick and a cluster of 3 mum wide islands. The tribo films clearly showed traces of phosphorous delivered in the contact zone during deformation of MoS2 particles integrated with triglyceride and over coated with phospholipids molecules.The proposed active nanostructured inorganic-organic additive will potentially reduce/replace current additives, such as ZDDP, which pose severe environmental concerns. This project targets boundary lubrication, which is extremely important in a variety of applications including ball bearings, gears, transmissions etc., potentially saving hundreds of millions of dollars from fuel savings, reduced vehicle exhaust emissions and decreased down time, increasing the competitiveness of small and large US manufacturers. Even a modest 1.0% increase in efficiency will have a significant impact on the national economy . Innovations from this project should also benefit key application areas for organic-inorganic material complexes, for example pharmaceuticals, cosmetics and bio-fuels.Keywords/phrases. Advanced Lubricants, Solid Lubricant Nanoparticles, Top-Down Nanomanufacturing, Tribology, Tribo film, Energy Savings, Durability of systemsThese organic-inorganic nanoparticles were synthesized using a top-down nanomanufacturing process, commonly known as high-energy ball milling or mechanical milling. It was performed in the presence of ambient air followed by organic molecules (triglycerides) to produce nanoparticles with controlled morphologies and surface properties. SEM, particle size analysis, and XRD showed a particle size reduction up to 100 nm and a grain size of 6 nm. TEM showed that after air milling for 48 hrs, agglomerated clusters of quasi-spherical nanoparticles of MoS2 were formed. HRTEM shows that the inter-planar defects and milling assisted shearing between the platelets caused the resultant curling of the planes, forming these unique nanostructures. Further milling of these clusters for 48 hrs in an organic medium (triglycerides) produced mono-dispersed quasi-spherical nanoparticles (<100 nm size). Surface analysis showed the presence of hydrocarbons, COO- molecules on the deagglomerated nanoparticles indicating a chemisorbed capping layer. A capping layer was also confirmed by zeta potential analysis.