A Reactive Force Field Study on the Interaction of Lubricant with Diamond-Like Carbon Structures

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• 作者：Roghayyeh Lotfi ; ASM Jonayat ; Adri C. T. van Duin ; Mousumi M. Biswas ; Robert Hempstead
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 8, 2016
• 年：2016
• 卷：120
• 期：48
• 页码：27443-27451
• 全文大小：638K
• ISSN：1932-7455

文摘

We studied the degradation of a perfluoropolyether lubricant, i.e., D4OH, in the presence of different components present in hard disks including diamond-like carbon (DLC), using ReaxFF reactive force field based molecular dynamics simulations. To generate the DLC structure, a carbon-diamond structure was melted in an Ar-filled head space box at 7500 K, and was slowly cooled down to 3000 K. Then, a constant pressure (NPT) simulation was performed to adjust the sample volume and reduce the internal stress. Similarly, for growth of functionalized DLC, ethylene molecules were used as the carbon source and they were pyrolyzed in the presence of Ar atoms to make H-functionalized DLC (DLC:H). This DLC:H structure was subsequently heated in the presence of nitrogen molecules to make H/N functionalized DLC (DLC:H:N). The results indicate that, by controlling number of Ar atoms and N₂ molecules, it is possible to achieve the experimental H/N/C composition and sp²/sp³ ratio composition targets. Final DLC and DLC:H:N structures have an sp³:sp² ratio of 27.3, and 31.7%, respectively. Hydrogen and nitrogen contents of 17.9 and 13.7%, respectively, were obtained. After preparing the DLC structures, the spreading mechanism of lubricant droplet containing 9 D4OH strands was investigated over DLC and DLC:H:N structures. It was found that the speed of lubricant spreading over the nonfunctional structure (DLC) is higher than that for the functional structure (DLC:H:N). Moreover, our results indicated that the presence of both DLC and DLC:H:N affects the degradation chemistry of the lubricant.