58th Annual Report on Research 2013 Under Sponsorship of the ACS Petroleum Research Fund

            The investigation of the effects of tribocharging and scale on mechanical properties of nano-objects, such as nanotubes, nanobuds and nanohorns from compounds such as molybdenum disulfide, tungsten disulfide and carbon and their incorporation into petroleum-based lubricants, is proposed in this research. Incorporating these known solid lubricants into petroleum-based oils may lead to enhanced lubricity. However, as sliding progresses over time, an increase in attractive electrostatic forces could lead to greater adhesion. Moreover, nano-objects have shown increased hardness and elastic modulus as compared to the bulk. During sliding, nano-object aggregation may occur, leading to changes in morphology of the adhered nano-objects and thus change in the mechanical properties. The use of atomic force microscopy (AFM) and electrostatic force microscopy (EFM) provides the mechanism for the characterization of morphology and charge density.

Initially, nanotubes, nanobuds and nanohorns will be deposited on metal and ceramic substrates either as dry nano-objects or as dispersions in petroleum-based oils. In the next phase, tribocharging studies will be performed using AFM and EFM to correlate adhesion and electrostatic attraction. Lastly mechanical properties will be evaluated using the Hysitron nanoindenter. Ball-on-flat tribometer studies will be performed on the macroscale along with phase two and three tests. This research will lead to an enhanced understanding of the properties of inorganic nanotube, nanobuds and nanohorns, and will lead to the creation of next generation petroleum-based oils with enhanced properties.

Objectives

1) Study of dry nano-objects

• Deposit dry nanotubes and nanobuds and nanohorns on metal and ceramic substrates.
• Perform tribocharging by sliding a glass sphere over nano-objects and measure adhesive force on the nanoscale.
• Use EFM to measure the charge density and correlate to change in adhesive force on the nanoscale.
• Perform indentation of single nano-objects and agglomerates to evaluate mechanical properties.
•  Determine the role of nano-object size and shape and ambient humidity on charge formation.

2) Study of nano-object and petroleum hybrid lubricants

• Produce stable dispersions of nanotubes, nanobuds and nanohorns on petroleum-based oil using sonication.
• Perform tribocharging by sliding a glass sphere over nano-objects and measure adhesive force on metals and ceramics coated with hybrid nano-object-petroleum lubricants as well as petroleum-based oil coated surfaces (without nano-objects) on the nanoscale.
• Use EFM to measure the charge density and correlate to the change in adhesive force on metals and ceramics coated with hybrid nano-object-petroleum lubricants as well as petroleum-based oil coated surfaces (without nano-objects) on the nanoscale.
• Perform adhesion studies of metals and ceramics coated with hybrid nano-object-petroleum lubricants at the macroscale with a ball-on-flat tribometer.
• Use surface DC voltmeter to measure the surface potential and correlate to change in adhesive force on metals and ceramics coated with hybrid nano-object-petroleum lubricants as well as petroleum-based oil coated surfaces (without nano-objects) on the macroscale.
• Determine the role of nano-object size and shape and ambient humidity on charge formation.

Progress to date

            Time was spent locating personnel with the necessary research background to perform the experiments outlined in the proposal. A new post-doc was recently hired and another researcher will be starting in fall, 2013. Significant progress is expected to be made in the coming year.