| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Poster Session |
| Presenter: | Hiroki Murabayashi, Tohoku University, Japan |
| Authors: | H. Murabayashi, Tohoku University, Japan T. Tsuruda, Tohoku University, Japan Y. Wang, Tohoku University, Japan Y. Kobayashi, Tohoku University, Japan S. Bai, Tohoku University, Japan Y. Higuchi, Tohoku University, Japan N. Ozawa, Tohoku University, Japan K. Adachi, Tohoku University, Japan J.M. Martin, Ecole Centrale de Lyon, France M. Kubo, Tohoku University, Japan |
| Correspondent: | Click to Email |
In recent years, diamond-like carbon (DLC) is expected as a solid lubricant material for engines because of its excellent friction properties such as low friction and high wear resistance. DLC films are lubricated with oil in the engine. Furthermore, molybdenum dithiocarbamate (MoDTC) is used as friction modifier in oil. DLC coating with oil and MoDTC solution showed a low friction coefficient [1]. Moreover, the low friction of the DLC films with MoDTC was enhanced by a chemical reaction during friction, since the friction coefficient gradually decreased with increasing friction time. Understanding of the low friction mechanism of DLC with MoDTC is strongly required to decrease in the friction of the DLC films. Then, our purpose is to reveal the chemical reactions between the MoDTC and DLC films by our tight-binding quantum chemical molecular dynamics code [2].
To investigate chemical reaction between MoDTC and DLC film during friction, we perform the friction simulation of MoDTC sandwiched by the DLC surfaces. At first, we compress linkage isomer of MoDTC (LI-MoTC) by the DLC surfaces. Here, we use LI-MoDTC because it is isomerized in oil phase [3]. We apply a pressure of 1 GPa to the upper DLC film. After the compression, the C atom of the DLC surface binds with the S atom of LI-MoDTC and the C-S bond is generated between the DLC surface and LI-MoDTC. Next, to perform the friction simulation of DLC films with LI-MoDTC, we apply a pressure of 1 GPa to the DLC film and forcibly slide it with 100 m/s. The S-Mo bond in the adsorbed LI-MoDTC is elongated from 2.52 Å to 3.76 Å and the S-Mo bond is dissociated during the sliding. To reveal chemical reaction during the S-Mo bond dissociation in detail, we investigate electron transfer between LI-MoDTC and the DLC surface during the compression. The charge of S atom of LI-MoDTC changes from +0.45 to +0.82 before and after the generation of C-S bond. This indicates that electrons transfer from the sulfur atom of LI-MoDTC to the DLC films. We think that S-Mo bond is weakened due to the electron transfer between LI-MoDTC and DLC film. Thus, we suggest that the electron transfer from LI-MoDTC to DLC films during the LI-MoDTC adsorption on the DLC surface weakens the S-Mo bond and the mechanical force dissociates the weakened S-Mo bond during the friction.
[1] B. Vengudusamy et al., Tribology Intern., 54, 68-76 (2012).
[2] K. Hayashi, M. Kubo et al., J. Phys. Chem. C, 115, 22981-22986 (2011).
[3] T. Onodera, M. Kubo et al., Tribology Online, 3, 80-85 (2008).