| WANG Chaoying,ZHANG Yile,XU Bing,YANG Huayong,CHEN Zhe.Effect of Alcohol Molecules Adsorption on Nanoscale Friction Behaviour of Graphite Basal Plane[J],53(21):1-5, 33 |
| Effect of Alcohol Molecules Adsorption on Nanoscale Friction Behaviour of Graphite Basal Plane |
| Received:October 21, 2024 Revised:November 05, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.21.001 |
| KeyWord:graphite alcohol molecules adsorption nanoscale friction tribochemical reactions atomic force microscopy |
| Author | Institution |
| WANG Chaoying |
State Key Laboratory of Fundamental Components of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou , China |
| ZHANG Yile |
State Key Laboratory of Fundamental Components of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou , China |
| XU Bing |
State Key Laboratory of Fundamental Components of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou , China |
| YANG Huayong |
State Key Laboratory of Fundamental Components of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou , China |
| CHEN Zhe |
State Key Laboratory of Fundamental Components of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou , China |
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| Abstract: |
| The work aims to investigate the nanoscale friction behaviour of graphite basal planes, as well as the mechanisms underlying its modulation. Highly oriented pyrolytic graphite (HOPG) crystals with freshly cleaved surfaces were immersed in high-purity alcohols for a controlled duration. After immersion, the crystals were dried with dry nitrogen gas to eliminate residual solvents for further analysis. The friction and adhesion forces on the graphite basal planes were then analyzed by atomic force microscopy (AFM). It was observed that both the friction and adhesion forces on the graphite surface notably changed following exposure to different alcohols. Specifically, the friction and adhesion forces decreased as the carbon chain length of the alcohol molecules increased. This result suggests a strong correlation between the molecular structure of alcohols and their ability to modulate the tribological properties of graphite basal planes. Under an applied load of 5 nN, the initially ultra-low friction on the graphite basal plane ((0.030±0.024) nN) was reduced by approximately 50% ((0.014±0.009) nN) after treatment in n-heptanol, a long-chain alcohol. In stark contrast, treatment with methanol, a short-chain alcohol, caused an eightfold increase in friction ((0.237±0.024) nN). This striking variation in friction behaviour highlights the significant effect of alcohol chain length on the performance of sliding interface. The underlying mechanism for this modulation lies in the interaction between the alcohol molecules and the contact interface. Alcohol molecules adsorbed at the sliding interface are able to regulate the contact quality. Long-chain alcohols, such as n-heptanol, possess higher conformational entropy, which facilitates easier interfacial sliding, thereby reducing friction. In contrast, short-chain alcohols like methanol induce less conformational entropy and thus hinder the sliding process, leading to increased frictional resistance. Another crucial aspect of this study is the role of friction-induced chemical reactions. The Si atoms in the SiO2 tip are highly susceptible to attack by the oxygen atoms in alcohol molecules, triggering nucleophilic substitution reactions, resulting in the formation of silica gel on the surface of the tip. The presence of this silica gel increases the contact area between the AFM tip and the graphite surface, which in turn contributes to higher friction and adhesion forces. Moreover, with the increase of the size of alcohol molecules, the nucleophilicity decreases, and the low carbon alcohol molecules are easier to approach silicon atoms in the process of nucleophilic substitution, and the tribochemical reaction rate is faster, which further affects the frictional behaviour. This study reveals a novel mechanism for regulating the frictional properties of graphite through the physical adsorption of alcohol molecules and friction-induced chemical reactions. The results demonstrate that the molecular structure of alcohols, particularly the length of their carbon chains, along with the rate of tribochemical reactions, play a critical role in determining the lubrication performance of graphite. These findings provide insights into the control and optimization of tribological properties of graphite, offering new opportunities for its application in nanoscale devices and lubrication systems. |
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