Wang, Bingchen
(2021)
Molecular Structure of Solid-Confined Ionic Liquids and Their Applications as Media Lubricants in Hard Disk Drives.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Media lubricants are critical to the reliability of hard disc drives (HDDs). Ionic liquids (ILs) are promising candidates as the next-generation media lubricants because of their excellent physiochemical properties. Both the fundamental understandings of the interfacial molecular structure at the IL/solid interfaces and the novel designs of the IL chemical structures are critical to the application of ILs as media lubricants.
First, we have investigated the molecular structure of mica-confined ILs. Experimental evidence from ATR-FTIR, contact angle measurement, and AFM shows that tuning relative humidity (RH) is an effective approach manipulating the molecular arrangement and macroscopic wettability of ILs on mica. More water adsorbs on mica at higher RH, which mobilizes the surface K+ and consequently initiates the layering of IL cations/anions. Additionally, unique quantized growths of mica-confined ILs with various cation alkyl chain lengths have been directly observed under AFM. The IL nanofilms initially cover more solid surface areas at the constant thickness of 2 monolayers (ML) until a quantized thickness increase by 2 ML. A double-layer building block of IL cations/anions is proposed. Time-dependent AFM results reveal the slower spreading of ILs with longer alkyl chains due to the stronger dispersive interactions.
Second, we have assessed the potential of nanometer-thick ILs as media lubricants. The TGA results indicate the commercially-available [Bmim][FAP] has higher thermal stability than the state-of-the-art perfluoropolyether (PFPE) lubricants. More importantly, AFM surface roughness results demonstrate that ILs have much lower ML thickness than PFPEs on carbon overcoat (COC) due to the smaller molecular sizes, which provides the opportunity to scale down the lubricant thickness and increase the areal density. Then a fluorinated IL (FIL) with a highly fluorinated cation alkyl chain has been synthesized to realize a reduced surface tension that is comparable to PFPEs. To enhance the bonding of ILs on COC and further reduce the surface tension, we have synthesized a novel IL, HFIL-OH, containing a hydroxyl endgroup and a fluorinated alkyl chain in the cation and a highly fluorinated anion. The successful development of the IL lubricants is a major step forward for ILs to be utilized as the next-generation media lubricants.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
18 June 2021 |
| Date Type: |
Publication |
| Defense Date: |
12 March 2021 |
| Approval Date: |
18 June 2021 |
| Submission Date: |
9 April 2021 |
| Access Restriction: |
2 year -- Restrict access to University of Pittsburgh for a period of 2 years. |
| Number of Pages: |
178 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Ionic liquids, molecular arrangement, layering, quantized growth, contact angle, wetting, media lubricants, nanometer-thick films, monolayer thickness |
| Date Deposited: |
18 Jun 2022 05:00 |
| Last Modified: |
18 Jun 2023 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/40591 |
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