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While ionic liquids (ILs) have attracted much attention as potential next-generation lubricant additives, their implementation in oil formulations has been hindered by their limited solubility in hydrocarbon fluids and corrosivity. Here, we encapsulate an oil-insoluble IL that has been studied in lubrication science, namely 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][TFSI]), within poly(ethylene glycol dimethacrylate-buytl methacrylate copolymer) (poly(EGDM-c-BMA)) microshells using a mini-emulsion polymerization process. The synthesized poly(EGDM-c-BMA)-encapsulated [HMIM][TFSI] microparticles are shown to be dispersible in a non-polar, synthetic oil (i.e., poly-α-olefin). Tribological experiments indicated that the microcapsules act as an additive reservoir that reduces friction by releasing the encapsulated IL at the sliding interface following the mechanical rupture of the polymer shell. X-ray photoelectron spectroscopy (XPS) measurements provided evidence that [HMIM][TFSI] does not tribochemically react on steel surfaces to create a reaction layer, thus suggesting that this IL reduces friction by generating a solid-like, layered structure upon nanoconfinement at sliding asperities, as proposed by previous nanoscale studies. The results of this work do not only provide new insights into the lubrication mechanism of ILs when used as additives in base oils in general, but also establish a new, broadly-applicable framework based on polymer encapsulation for utilizing ILs or other compounds with limited solubility as additives for oil formulations.
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A functionalized ionic liquid as the next‐generation nano‐lubricant
Abstract Ionic liquids (ILs) have attracted intensive research interest due to their outstanding physiochemical properties. However, comprehensive design is necessary for targeted applications and has rarely been conducted. As a result, the industry‐scale application of ILs is still very limited. In this academia–industry collaborative research among the University of Pittsburgh, Virginia Tech. University, and Seagate Technology LLC, we report the design, synthesis, molecular dynamics (MD) simulation, and characterization of a nanometer‐thick IL, which contains abundant fluorinated segments and a hydroxyl endgroup, as the next‐generation nano‐lubricant for hard disk drives (HDDs). The lab‐ and industry‐level testing results indicate that the IL lubricant performs significantly better than the state‐of‐the‐art lubricant, that is, perfluoropolyether (PFPE) that has been utilized for three decades in the HDD industry in two key functions: thermal stability and fly clearance. Meanwhile, the IL lubricant also shows excellent lubricity and durability. The outstanding performance of the IL has been attributed to its unique molecular structure on the solid substrate, which is supported by MD simulation results. Our work establishes the IL as a promising candidate among the next‐generation media lubricants in HDD industry. Meanwhile, the finding obtained here has important implications in many other applications involving nano‐lubricants.
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- Award ID(s):
- 1904486
- PAR ID:
- 10377996
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Droplet
- Volume:
- 1
- Issue:
- 2
- ISSN:
- 2731-4375
- Page Range / eLocation ID:
- p. 192-201
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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