Committee Members Information

• Ph.D. Advisor: Professor Mani Sarathy, (Chemical Engineering KAUST)
• External Examiner: Professor Fabrice Dassenoy (Materials Science, Ecole Centrale de Lyon, 
  Laboratoire de Tribologie et Dynamique des Systèmes, FRANCE 
  
• Committee Chair: Professor Sanjay Rastogi (Chemistry, KAUST)
• 4th Committee Member: Professor James Turner (Mechanical Engineering, KAUST)

Abstract

The electrification of road transport has introduced lubrication challenges that conventional additive chemistries were not designed to meet. Electric vehicle (EV) drivetrains expose lubricants to higher speeds, elevated temperatures, and stray currents that cause electric discharge machining (EDM) damage, while the spread of diamond-like carbon (DLC) coatings has exposed the antagonistic behaviour of established friction modifiers such as molybdenum dialkyldithiocarbamate (MoDTC) on carbon surfaces. This thesis develops functionalized graphene quantum dots (GQDs), synthesised from petroleum asphaltenes, as a sustainable, multifunctional lubricant additive addressing both problems.

GQDs were produced by top-down oxidation of asphaltenes and rendered oil-dispersible through three functionalization routes: hexanol esterification (H-GQDs), polyethylenimine–oleate immobilisation (GQD-PEI-OL), and dodecanoic acid esterification (Dod-GQDs). Characterization by TEM, HRTEM, XRD, XPS, FTIR, and Raman spectroscopy confirmed that the graphitic core was preserved while the intended surface chemistry was grafted, and UV–Vis monitoring showed stable dispersions with under 11% change in relative absorbance over 22 days.

In a Group II mineral base oil, the functionalized GQDs reduced the coefficient of friction by up to 51% and wear scar volume by up to 50%, while raising electrical conductivity by up to two orders of magnitude—sufficient to dissipate charge yet within the safe dissipative window—offering a route to mitigate EDM damage through a protective graphitic tribofilm. In DLC-coated contacts, H-GQDs outperformed an MoDTC formulation that exhibited friction instability and elevated wear; XPS established that H-GQDs form a continuous, chemically anchored carbonaceous tribofilm, whereas MoDTC decomposition products react with the coating to form molybdenum carbide species that degrade its integrity.

Finally, in a McLaren IndyCar gearbox case study, Dod-GQDs at 1 wt% in Lucas L13 gear oil were identified as the optimum formulation, and a scale-up strategy developed with the Graphene Engineering Innovation Centre reduced projected batch production time from approximately 180 to 15 days.
Collectively, this thesis establishes asphaltene-derived functionalized GQDs as effective friction and anti-wear additives whose tailored surface chemistry simultaneously delivers electrical conductivity for EV protection and compatibility with advanced coatings, while valorising a residual petroleum stream.