Highly Fluorinated Ionic Liquid Films as Nanometer-Thick Media Lubricants for Hard Disk Drives

Abstract

Ionic liquids (ILs) are promising candidates for the nextgeneration nanometer-thick lubricants in hard disc drives (HDDs) because of their excellent physiochemical properties and low monolayer (ML) thicknesses. However, the commercially available ILs have higher surface tension and higher friction than the state-of-the-art perfluoropolyether (PFPE) lubricant. In the current study, a fluorinated IL (FIL) lubricant, which contains cations with highly fluorinated alkyl chains, has been successfully synthesized. The surface tension of FIL is comparable to that of PFPE, which is ideal for enhancing the tribological performance of the FIL lubricant. The thermogravimetric analysis results showed that FIL has higher thermal stability than PFPE Ztetraol. Atomic force microscopy revealed that because of the intrinsically smaller molecular size of FIL, the ML thickness is only ∼50% of that of Ztetraol, which is expected to induce a lower lubricant thickness and higher areal density. Compared to the commercially available ILs, reduced friction of the nanometerthick FIL lubricant on carbon overcoat was also achieved because of its intrinsically lower surface tension. Our results demonstrate that FIL has great potential for application as the next-generation media lubricant in HDDs.

Effect of Solid Substrates on the Molecular Structure of Ionic Liquid Nanofilms

“…During the thin film fabrication processes, solid substrates were vertically dipped into and withdrawn from the dilute IL solutions at the speed of 1 mm/second. , As a common solvent in the hard disk drive industry, Vertrel XF evaporates instantly and completely after dipcoating. As the nanofilm thickness trends with the concentration of the dipcoating solution, various stages of the nanofilm growth were realized by fabricating the IL nanofilms independently using solutions with a sequential increase in concentration. ,, The thicknesses of IL nanofilms on silica and amorphous carbon were measured by ellipsometry using a J.A. Woollam alpha SE spectroscopic ellipsometer at the incident angle of 70°.…”

“…As the nanofilm thickness trends with the concentration of the dipcoating solution, various stages of the nanofilm growth were realized by fabricating the IL nanofilms independently using solutions with a sequential increase in concentration. 13,15,16 The thicknesses of IL nanofilms on silica and amorphous carbon were measured by ellipsometry using a J.A. Woollam alpha SE spectroscopic ellipsometer at the incident angle of 70°.…”

“…They are usually made of organic cations and organic or inorganic anions with bulky and asymmetric conformations. As a result, the electrostatic force and the lattice formation are dampened, leading to the low melting point. − Since the successful synthesis of air- and water-stable ILs, ILs have attracted a great deal of academic and industrial research interest due to their exceptional physiochemical properties, and ILs with a variety of chemical structures have been designed, synthesized, and studied. − Among all the booming applications of ILs, the IL/solid interface is particularly important to the revolution of many cutting-edge applications, e.g., media lubricants in the data storage industry, − additives for engine lubrication, − gas separation and carbon capture media, − green electrocatalysis, − and battery electrolytes. − Fundamental understanding of the interfacial molecular structure of ILs is critical to the performance of solid-confined ILs.…”

A functionalized ionic liquid as the next‐generation nano‐lubricant

“…Therefore, the ML thickness can be determined based on the change in the root mean square (RMS) surface roughness with the nanofilm thickness. 14,15 Figure 1e shows the atomic force microscopy (AFM) RMS surface roughness results for the HFIL-OH nanofilms with various thicknesses on COC, with the surface roughness results of PFPE Ztetraol as a control. The ML thickness of HFIL-OH has been determined to be ~0.75 nm.…”

“…The COC substrate is vertically submerged into and subsequently pulled out from the solutions at a speed of 1 mm/s using a KSV Instrument dipcoater. The thickness of the lubricant films is directly controlled by changing the solution concentration 14,15,42 …”